ABCC9-Related Intellectual Disability and Myopathy Syndrome

Mendelian MONDO:0859224 Pathograph 14 Show in embeddings browser Channelopathy Neurodevelopmental Disorder

ABCC9-related Intellectual disability Myopathy Syndrome (AIMS) is a rare autosomal recessive ATP-sensitive potassium (KATP) channelopathy caused by biallelic loss-of-function variants in ABCC9, the gene encoding the sulfonylurea receptor 2 (SUR2) regulatory subunit. Reported individuals have psychomotor delay with intellectual disability of variable severity, muscle weakness and fatigability with painful spasms, and cerebral white matter abnormalities that radiologically resemble periventricular leukomalacia or small vessel disease. Seizures, spasticity, hyperreflexia, microcephaly, short stature, corpus callosum abnormalities and anxiety occur in a proportion of patients, and cardiac systolic dysfunction has been documented in older individuals. AIMS is the loss-of-function pole of ABCC9 disease and is mechanistically opposite to Cantu syndrome, which arises from gain-of-function variants in the same gene.

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1
Inheritance
13
Pathophys.
22
Phenotypes
1
Hypotheses
2
Gaps
14
Pathograph
1
Genes
5
Medical Actions
7
Differentials
2
References
1
Deep Research
🏷

Classifications

Harrison's Chapter
NEUROLOGIC GENETICS_ENVIRONMENT_DISEASE
Channelopathy
skeletal muscle channelopathy
👪

Inheritance

1
Autosomal recessive HP:0000007
AIMS requires biallelic ABCC9 loss-of-function alleles. Reported families include homozygotes for a splice-site allele and homozygotes for truncating alleles; heterozygous parents are clinically unaffected.
Autosomal recessive inheritance
Show evidence (3 references)
PMID:38217872 SUPPORT Human Clinical
"Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS)."
States the autosomal recessive mode of inheritance for AIMS explicitly.
PMID:38217872 SUPPORT Human Clinical
"Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study."
Confirms that single-allele carriers are clinically unaffected, consistent with recessive transmission.
PMID:31575858 SUPPORT Human Clinical
"Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
The index families are homozygous for a single ABCC9 allele, the classic recessive configuration.
◈

Mechanistic Hypotheses

1
Cerebral small-vessel origin of the AIMS white matter injury and cognitive phenotype
aims_cerebrovascular_white_matter EMERGING
Evidence balance 3 partial
The leading explanation for the CNS arm of AIMS is that loss of SUR2-containing KATP channels in brain vascular smooth muscle degrades cerebral autoregulation and neurovascular coupling, producing chronic small-vessel ischaemic white matter injury and, through it, the intellectual disability and pyramidal signs. The supporting facts are consistent but indirect: KCNJ8/ABCC9-containing channels are required for brain vascular smooth muscle differentiation in animals, the human imaging resembles small vessel disease, MR angiography is normal so the lesion is functional rather than macrovascular, and the same white matter change is seen in Cantu syndrome where the channel defect is opposite. What is missing is any direct measurement of cerebral blood flow or neurovascular coupling in an AIMS patient, and the in vivo coupling deficit was demonstrated in a Kcnj8 rather than an Abcc9 knockout. The original authors state the hypothesis with the hedge "it is conceivable".
Pathograph links
Non-Functional SUR2-Containing KATP Channels -> Impaired Brain Vascular Smooth Muscle Differentiation and Neurovascular Coupling DIRECT KCNJ8/ABCC9-containing KATP channels are required cell-autonomously for brain arterial and arteriolar smooth muscle differentiation, so their loss compromises cerebral vascular maturation.
Impaired Brain Vascular Smooth Muscle Differentiation and Neurovascular Coupling -> Cerebral White Matter Injury INDIRECT UNKNOWN INTERMEDIATES A cerebral small-vessel mechanism is the leading explanation for the white matter lesions, which radiologically resemble periventricular leukomalacia or small vessel disease.
Show evidence (3 references)
PMID:31575858 PARTIAL Human Clinical
"it is conceivable that KATP loss of function may impact the cerebral vasculature"
The authors' own statement of the hypothesis, framed as a conjecture.
PMID:31575858 PARTIAL Human Clinical
"Interestingly, white matter hyperintensities are observed in both Cantú syndrome and AIMS."
That the same white matter change appears in the gain-of-function disease is what makes a shared cerebrovascular route plausible, but it also means the finding does not discriminate direction of effect.
PMID:35588738 PARTIAL Model Organism
"Our results demonstrate a role for KCNJ8/ABCC9-containing K-ATP channels in the differentiation of brain VSMC, which in turn is necessary for fine-tuning of cerebral blood flow."
Supplies the developmental cerebrovascular role, but in animal and cell models rather than AIMS patients.
?

Discussions and Knowledge Gaps

2
Why do SUR2-null mice show no learning, memory or anxiety phenotype when intellectual disability and anxiety are defining features of AIMS in humans, and does that mean the murine model cannot be used to study the cognitive arm of the disease?
HUMAN MODEL MISMATCH OPEN aims_id_anxiety_model_mismatch
Attached to
pathophysiology#Intellectual Disability and Developmental Delay
This is a model-evidence-exists-and-is-negative situation, not an absence of data. The SUR2-STOP mouse was formally tested for spatial learning and memory in a Morris water maze and for anxiety-like behaviour in an elevated plus maze and was negative on both, while every human patient tested has intellectual disability and several have anxiety. The original authors also note that it is not obvious how myocyte KATP dysfunction could produce intellectual disability at all, and that neuronal KATP channels are predominantly Kir6.2/SUR1 rather than SUR2-containing. Together these make the cognitive arm the least secure part of the AIMS mechanism: either the murine assays are too coarse for a mild human intellectual disability, or the human cognitive phenotype is mediated by something (most plausibly the cerebrovascular route) that the mouse does not reproduce.
Proposed experiments
Higher-sensitivity cognitive phenotyping of SUR2-null mice
exp_aims_mouse_working_memory
Test SUR2-null mice with working-memory and fear-conditioning paradigms rather than the Morris water maze alone, on the hypothesis that a mild human intellectual disability may be below the resolution of standard spatial-learning assays.
Knock-in mouse carrying an actual human AIMS allele
exp_aims_knockin_human_allele
Generate a mouse carrying a human AIMS variant rather than an independently engineered premature stop, so that the model's genetic lesion matches the patients' and residual-protein effects are preserved.
Direct cerebral blood flow and neurovascular coupling measurement in AIMS patients
exp_aims_human_cbf_measurement
Measure resting cerebral perfusion and task-evoked neurovascular coupling (arterial spin labelling, BOLD reactivity) in genotyped AIMS patients against controls, to test the cerebrovascular hypothesis directly in the species that actually has the cognitive phenotype.
Show evidence (3 references)
PMID:31575858 SUPPORT Model Organism
"nor in tests of spatial learning and memory, evaluated using a Morris water maze"
The mouse spatial-learning result is formally negative.
PMID:31575858 SUPPORT Model Organism
"show any obvious anxiety-like behaviors."
The mouse anxiety result is likewise negative, against a human phenotype that includes anxiety.
PMID:31575858 SUPPORT Human Clinical
"and there are no reports of cognitive impairment in previous SUR2 mutant animal models."
The authors state, in the same sentence, both that the route from channel loss to intellectual disability is not obvious and that no earlier SUR2 mutant animal model showed cognitive impairment.
What is the natural history of AIMS across the lifespan, and at what interval should cardiac and cerebral imaging surveillance be performed?
KNOWLEDGE GAP OPEN aims_natural_history_gap
Around twenty patients have ever been reported, in three cross-sectional series with no prospective follow-up. Two features are known to be age-dependent - systolic dysfunction, present only in the oldest patients of the index cohort, and cognitive and motor decline reported in a sexagenarian - but neither has a defined onset distribution, so no surveillance interval can be evidence-based. No registry, survival analysis, or quality-of-life instrument has ever been applied.
Proposed experiments
International AIMS natural-history registry
exp_aims_prospective_registry
Enrol genotyped AIMS patients with standardised serial cardiac imaging, brain MRI, neuropsychological testing and functional measures, to establish onset distributions for the age-dependent complications and to set surveillance intervals.
Show evidence (1 reference)
PMID:42290677 SUPPORT Human Clinical
"These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
The most recent series calls for monitoring of older individuals without being able to specify what or how often, which is the gap.
⚙

Pathophysiology

13
Biallelic ABCC9 Loss of Function
Biallelic loss-of-function variants in ABCC9 - splice-site alleles causing in-frame exon skipping, and nonsense or frameshift alleles causing nonsense-mediated decay or drastic truncation - abolish production of functional SUR2 protein. This is the root lesion of AIMS and is the opposite direction of effect to the gain-of-function ABCC9 variants that cause Cantu syndrome.
ABCC9 hgnc:60 ↓ DECREASED
Downstream
Non-Functional SUR2-Containing KATP Channels Absence of functional SUR2 protein prevents assembly of working SUR2-containing KATP channels.
Show evidence (4 references)
PMID:31575858 SUPPORT Human Clinical
"Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
Identifies the founding biallelic ABCC9 lesion.
PMID:38217872 SUPPORT Human Clinical
"All variants are predicted to result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional SUR2-dependent KATP channels."
Establishes the truncating/in-frame-deletion allele class across seven further families.
PMID:42290677 SUPPORT Human Clinical
"All variants are predicted to lead to nonsense mediated decay of ABCC9 transcripts and/or drastic truncation of SUR2."
Confirms nonsense-mediated decay and truncation as the mechanism of allele inactivation in the most recent cohort.
+ 1 more reference
Non-Functional SUR2-Containing KATP Channels
SUR2 is the regulatory subunit that confers ATP/ADP sensitivity and trafficking competence on Kir6.x pore subunits in skeletal muscle, cardiac muscle and vascular smooth muscle. Without functional SUR2, the SUR2-containing KATP channels of those tissues are absent or non-conducting, so cellular metabolic state can no longer be translated into membrane potassium conductance.
Cerebral small-vessel origin of the AIMS white matter injury and cognitive phenotype
skeletal muscle fiber CL:0008002 cardiac muscle cell CL:0000746 vascular associated smooth muscle cell CL:0000359
ABCC9 hgnc:60 ↓ DECREASED
potassium ion transmembrane transport GO:0071805 ↓ DECREASED
ATP-activated inward rectifier potassium channel activity GO:0015272 ↓ DECREASED
Downstream
Loss of Sarcolemmal KATP Conductance in Skeletal Muscle Fast-twitch skeletal muscle depends on noncanonical Kir6.2/SUR2 sarcolemmal KATP channels, so SUR2 loss removes essentially the whole sarcolemmal KATP conductance.
Loss of Cardiomyocyte KATP Conductance SUR2A is the cardiac sulfonylurea receptor, so its loss removes cardiomyocyte KATP current.
Impaired Brain Vascular Smooth Muscle Differentiation and Neurovascular Coupling KCNJ8/ABCC9-containing KATP channels are required cell-autonomously for brain arterial and arteriolar smooth muscle differentiation, so their loss compromises cerebral vascular maturation. Cerebral small-vessel origin of the AIMS white matter injury and cognitive phenotype
Increased Seizure Susceptibility Loss of abcc9 lowers the threshold for chemically provoked seizure-like motor activity in vivo.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"We term this channelopathy resulting from loss-of-function of SUR2-containing KATP channels ABCC9-related Intellectual disability Myopathy Syndrome (AIMS)."
Names the loss of SUR2-containing KATP channel function as the defining lesion of the syndrome.
PMID:37154692 SUPPORT Model Organism
"KATP channels are found throughout the cardiovascular system and skeletal muscle and couple cellular metabolism to excitability."
States the tissue distribution and the metabolism-to-excitability coupling role that is lost when SUR2 is absent.
Loss of Sarcolemmal KATP Conductance in Skeletal Muscle
In healthy skeletal muscle the sarcolemmal KATP channel is closed at rest and opens as intracellular ATP falls during metabolic stress or fatigue. In AIMS muscle this metabolically gated conductance is absent.
skeletal muscle fiber CL:0008002
response to muscle activity GO:0014850 ⚠ ABNORMAL
Downstream
Failure of Membrane Potential Stabilization During Fatigue Without KATP opening, the fatiguing fibre cannot shorten its action potential or stabilise its resting membrane potential.
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"In skeletal muscle, K ATP channels are typically closed at rest but open in response to metabolic stress or fatigue"
States the normal metabolic gating of the sarcolemmal channel that AIMS abolishes. Quoted with the space that the cached PDF text carries between "K" and "ATP".
Failure of Membrane Potential Stabilization During Fatigue
Loss of the fatigue-activated potassium conductance removes the brake on sarcolemmal excitability during sustained activity, so the fibre cannot limit calcium entry or recover normally from fatigue.
skeletal muscle fiber CL:0008002
regulation of membrane potential GO:0042391 ⚠ ABNORMAL
Downstream
Unstimulated Force Generation and Calcium Overload Unopposed depolarisation during fatigue produces contraction in the absence of stimulation and excessive calcium entry.
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"Therefore, loss of KATP function might be expected to result in failure to recover from fatigue"
The authors' explicit mechanistic prediction for what loss of the conductance does to a fatiguing fibre.
Unstimulated Force Generation and Calcium Overload
SUR2-null muscle generates force without stimulation under fatiguing conditions, the proposed cellular correlate of the painful spasms reported by patients. Excessive calcium influx was the hypothesised downstream effector, but blocking CaV1.1 permeation genetically did not reverse the pathology and the calcium channel blocker verapamil was harmful, so the calcium arm is not established as the sole effector.
skeletal muscle fiber CL:0008002
calcium ion transmembrane transport GO:0070588 ↑ INCREASED
Downstream
Skeletal-Muscle-Delimited Myopathy The contractile abnormality is intrinsic to skeletal muscle rather than secondary to cardiac or vascular disease.
Show evidence (2 references)
PMID:37154692 SUPPORT Model Organism
"In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS."
Establishes the unstimulated-force phenotype and its proposed clinical correlate.
PMID:37154692 REFUTE Model Organism
"We sought to determine whether excessive Ca2+ influx through CaV 1.1 channels was responsible for myopathology but found that the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice and that rendering CaV 1.1 channels nonpermeable by mutation failed to reverse..."
Recorded as REFUTE against the specific sub-hypothesis that excessive CaV1.1-mediated calcium influx is the effector of the myopathy: both the pharmacological and the genetic test of that hypothesis failed, and the pharmacological one was harmful. The unstimulated-force phenotype itself is unaffected by this refutation; only the calcium-influx explanation of it is.
Skeletal-Muscle-Delimited Myopathy
A myopathy that is clinically prominent but histologically and electrophysiologically bland: patients have generalised hypotonia, reduced strength, fatigability and exercise-induced pain, with normal serum creatine kinase, normal nerve conduction and essentially normal electromyography.
skeletal muscle fiber CL:0008002
skeletal muscle contraction GO:0003009 ⚠ ABNORMAL
Show evidence (3 references)
PMID:31575858 SUPPORT Human Clinical
"All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
Documents the clinical myopathy across the index cohort.
PMID:31575858 SUPPORT Human Clinical
"S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals"
Shows the myopathy is not accompanied by the usual laboratory markers of muscle destruction, which is diagnostically important.
PMID:37154692 SUPPORT Model Organism
"We found reduced exercise performance in mouse models of AIMS harboring premature stop codons in ABCC9."
The mouse model recapitulates the exercise-intolerance arm.
Loss of Cardiomyocyte KATP Conductance
SUR2A partners Kir6.2 in the cardiomyocyte sarcolemma, where KATP opening protects the myocyte during metabolic stress. Its absence removes that protection.
cardiac muscle cell CL:0000746
potassium ion transmembrane transport GO:0071805 ↓ DECREASED
Downstream
Cardiac Systolic Dysfunction Loss of cardiomyocyte KATP is followed by impaired systolic performance in patients and in both animal models.
Show evidence (1 reference)
PMID:37154692 SUPPORT Model Organism
"KATP channels are found throughout the cardiovascular system and skeletal muscle and couple cellular metabolism to excitability."
Places the SUR2-containing channel in the cardiovascular system.
Cardiac Systolic Dysfunction
Reduced systolic function, documented in the two oldest patients of the index cohort and reproduced in SUR2-null mice and zebrafish. It is an age-related feature rather than a presenting one.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"Cardiac systolic dysfunction is found in the two oldest patients."
The human cardiac finding, with its age restriction.
PMID:37154692 SUPPORT Other
"AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction."
Confirms cardiac dysfunction as part of the recognised human phenotype. Tagged OTHER rather than HUMAN_CLINICAL: this is the introductory framing sentence of a mouse-model paper restating the accepted clinical picture, not data that paper generated. The human cohort evidence is the PMID:31575858 item above.
Impaired Brain Vascular Smooth Muscle Differentiation and Neurovascular Coupling
KCNJ8/ABCC9-containing KATP channels are expressed on brain mural cell progenitors and are required cell-autonomously for arterial and arteriolar smooth muscle differentiation. Loss of channel function suppresses that differentiation and, in the corresponding knockout, degrades vasoconstrictive capacity and neuronally evoked vasodilation - the machinery that fine-tunes cerebral blood flow.
Cerebral small-vessel origin of the AIMS white matter injury and cognitive phenotype
vascular associated smooth muscle cell CL:0000359
vascular associated smooth muscle cell differentiation GO:0035886 ↓ DECREASED regulation of cerebral blood circulation GO:0120276 ⚠ ABNORMAL
Downstream
Cerebral White Matter Injury A cerebral small-vessel mechanism is the leading explanation for the white matter lesions, which radiologically resemble periventricular leukomalacia or small vessel disease. Cerebral small-vessel origin of the AIMS white matter injury and cognitive phenotype
Show evidence (3 references)
PMID:35588738 SUPPORT Model Organism
"Loss- or gain-of-function mutations in ATP-sensitive potassium channel (K-ATP)-encoding genes, KCNJ8 and ABCC9, cause human central nervous system disorders with unknown pathogenesis."
Frames the CNS arm of ABCC9 disease as the problem being addressed.
PMID:35588738 SUPPORT Model Organism
"Our results demonstrate a role for KCNJ8/ABCC9-containing K-ATP channels in the differentiation of brain VSMC, which in turn is necessary for fine-tuning of cerebral blood flow."
Establishes the ABCC9-dependent brain vascular developmental role.
PMID:35588738 PARTIAL Model Organism
"Consistent with defective VSMC development, Kcnj8 knockout mice showed deficiency in vasoconstrictive capacity and neuronal-evoked vasodilation leading to local hyperemia."
Marked PARTIAL because the in vivo neurovascular-coupling deficit was shown in a Kcnj8 (Kir6.1) knockout, the partner subunit, not in an Abcc9 knockout.
Cerebral White Matter Injury
Cerebral white matter hyperintensities were present in every patient of the index cohort and white matter abnormalities, often with corpus callosum involvement, recur across the later cohorts. In the most recent series the pattern resembles periventricular leukomalacia or small vessel disease and is described as a key hallmark of the disorder. Lesions can progress over time.
Downstream
Intellectual Disability and Developmental Delay The cognitive phenotype tracks with the white matter burden, but no mediating cellular step has been demonstrated and a purely vascular account is not proven.
Pyramidal Tract Dysfunction The authors attribute the lower-limb hyperreflexia of the older patients to the white matter abnormalities and consequent loss of upper motor neuron inhibition.
Show evidence (4 references)
PMID:31575858 SUPPORT Human Clinical
"All have cerebral white matter hyperintensities"
Cerebral white matter hyperintensity in all six index patients.
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Confirms white matter and corpus callosum involvement in the expanded cohort.
PMID:42290677 SUPPORT Human Clinical
"These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
Establishes the leukomalacia-like radiological pattern as a hallmark.
+ 1 more reference
Intellectual Disability and Developmental Delay
Psychomotor delay followed by intellectual disability, mild in the index Norwegian families and of variable severity across the expanded cohorts. Motor and cognitive decline has now been documented in older individuals, including a sexagenarian presenting with signs of dementia.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"revealed mild-to-moderate intellectual disability in all affected individuals, and anxiety was also reported in several patients."
Formal neuropsychological testing confirmed intellectual disability in all six index patients.
PMID:42290677 SUPPORT Human Clinical
"These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
Adds the later-life decline arm of the cognitive phenotype.
Pyramidal Tract Dysfunction
Lower-limb hyperreflexia and spasticity, appearing in the older patients of the index cohort and recorded as spasticity across the expanded cohort.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"which might be caused by the white matter abnormalities and decreased inhibition or increased activation of upper motor neurons"
The authors attribute the lower-limb hyperreflexia of the older index patients to loss of upper motor neuron inhibition from the white matter injury.
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Records spasticity in the expanded cohort.
Increased Seizure Susceptibility
Seizures occur in a proportion of AIMS patients, and abcc9 loss of function lowers the chemoconvulsant threshold in zebrafish. In the index cohort one patient had clinical tonic-clonic episodes without EEG correlate, so the epileptic phenotype is not uniform.
Show evidence (2 references)
PMID:38217872 SUPPORT Model Organism
"In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility."
Experimental demonstration of lowered seizure threshold on abcc9 loss.
PMID:31575858 PARTIAL Human Clinical
"From age 15, she experienced episodes of tonic/tonic-clonic seizures, but epileptic activity was absent in repeated EEGs."
Marked PARTIAL because the clinical events in this index patient were not confirmed electrographically.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for ABCC9-Related Intellectual Disability and Myopathy Syndrome Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

22
Cardiovascular 1
Left ventricular systolic dysfunction FREQUENT Left ventricular systolic dysfunction HP:0025169
Frequency derivation: PMID:31575858 reports cardiac systolic dysfunction in the two oldest of six index patients (2/6 = 33%), which falls just inside the FREQUENT band (30-79%). The band is age-confounded - both affected individuals were in their thirties and the unaffected four were 11-21 - so it should be read as a cross-sectional cohort proportion, not a lifetime risk.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"Cardiac systolic dysfunction is found in the two oldest patients."
Gives the 2/6 denominator and the age restriction.
PMID:37154692 SUPPORT Other
"AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction."
Confirms cardiac dysfunction as an accepted feature of the human syndrome. Tagged OTHER rather than HUMAN_CLINICAL: the sentence is background framing in a mouse-model paper, not data that paper generated. The 2/6 human denominator comes from the PMID:31575858 item above.
Ear 1
Sensorineural hearing impairment Sensorineural hearing impairment HP:0000407
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"Mild bilateral high-frequency sensorineural hearing loss was found at age 12."
Documents high-frequency sensorineural hearing loss in an index patient.
Eye 1
Hypotelorism Hypotelorism HP:0000601
No frequency band is recorded. The source states only that "some of the individuals" have hypotelorism, and the per-patient table that would supply a denominator is a PDF-extracted grid of plus/minus marks rather than quotable prose. The OMIM:619719 HPO annotation set records 4/6, but that is not a claim this entry can source from its own cited references, so the band is omitted rather than asserted.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"of the individuals have hypotelorism"
Hypotelorism in the index families. The quoted span omits the preceding word "Some" only because it sits on the previous PDF line; the source makes no per-patient count available as quotable prose.
PMID:31575858 SUPPORT Model Organism
"Consistent with hypotelorism observed in multiple AIMS"
Cross-species link: the SUR2-STOP zebrafish shows a decreased interorbital distance, the only dysmorphic feature of AIMS the model reproduces.
Head and Neck 1
Microcephaly Microcephaly HP:0000252
Show evidence (1 reference)
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Microcephaly listed among the conserved features of the expanded cohort.
Musculoskeletal 5
Muscle weakness VERY_FREQUENT Muscle weakness HP:0001324
Frequency derivation: PMID:31575858 reports muscle strength below normal in all but one of six index patients (5/6 = 83%), which falls in the VERY_FREQUENT band (80-100%). PMID:38217872 and PMID:42290677 both list muscle weakness among the conserved features without their own per-feature denominators.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
Gives the 5/6 denominator for reduced strength.
PMID:42290677 SUPPORT Human Clinical
"This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
Muscle weakness is one of the three defining components of the syndrome.
Generalized hypotonia VERY_FREQUENT Generalized hypotonia HP:0001290
Frequency derivation: PMID:31575858 states that all six index patients present with generalized hypotonia (6/6 = 100%), supporting VERY_FREQUENT (80-100%). No later cohort supplies its own hypotonia denominator.
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
Generalized hypotonia in all six index patients.
Muscle spasm Muscle spasm HP:0003394
Show evidence (2 references)
PMID:37154692 SUPPORT Other
"AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction."
Muscle spasms are recorded as a clinical feature of AIMS. Tagged OTHER rather than HUMAN_CLINICAL: the sentence is background framing in a mouse-model paper, restating the accepted clinical picture rather than reporting that paper's own patient data.
PMID:37154692 SUPPORT Model Organism
"In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS."
Provides the mechanistic correlate of the spasms in isolated SUR2-null muscle.
Spasticity Spasticity HP:0001257
Show evidence (1 reference)
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Spasticity listed among the conserved features of the expanded cohort.
Lumbar hyperlordosis VERY_FREQUENT Lumbar hyperlordosis HP:0002938
Frequency derivation: PMID:31575858 reports lumbar lordosis in all but one of six index patients (5/6 = 83%), inside the VERY_FREQUENT band (80-100%). This is a single-cohort denominator from one founder population and has not been replicated in the later cohorts.
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"Lumbar lordosis is found in all but one, and scoliosis in one."
Gives the 5/6 denominator for lumbar lordosis and 1/6 for scoliosis.
Nervous System 9
Intellectual disability VERY_FREQUENT Intellectual disability HP:0001249
Frequency derivation: PMID:31575858 reports mild-to-moderate intellectual disability in all six index patients (6/6 = 100%), and PMID:38217872 reports intellectual disability of variable severity in all nine patients of the expanded cohort. Both denominators are cohort-wide, so VERY_FREQUENT (80-100%) is the band supported by published counts.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"revealed mild-to-moderate intellectual disability in all affected individuals, and anxiety was also reported in several patients."
Intellectual disability in all six index patients on formal neuropsychological testing.
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Intellectual disability of variable severity across the expanded cohort.
Global developmental delay Global developmental delay HP:0001263
Show evidence (2 references)
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Psychomotor delay is listed first among the conserved features.
PMID:42290677 SUPPORT Human Clinical
"This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
Developmental delay is one of the three defining components of the syndrome.
Postural instability VERY_FREQUENT Postural instability HP:0002172
Frequency derivation: PMID:31575858 reports miniBESTest balance deficits in all six index patients (6/6 = 100%), which is the VERY_FREQUENT band (80-100%). The quoted span begins mid-sentence because the preceding words ("moderate to severe deficits") are broken across a PDF ligature in the cached full text and cannot be quoted byte-exactly; the severity grading is recorded here instead. Neither expanded cohort reports its own balance denominator.
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"in balance in all patients, and walking distance in the 6-min walk test is reduced in all individuals."
The miniBESTest sentence: balance deficits in all six index patients, with the 6-minute walk test as the corroborating functional measure.
Hyperintensity of cerebral white matter on MRI VERY_FREQUENT Hyperintensity of cerebral white matter on MRI HP:0030890
Frequency derivation: PMID:31575858 states that all six index patients have cerebral white matter hyperintensities (6/6 = 100%). PMID:38217872 and PMID:42290677 both describe white matter abnormalities as conserved or hallmark features without per-feature counts. VERY_FREQUENT (80-100%) rests on the 6/6 denominator.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"All have cerebral white matter hyperintensities"
Cerebral white matter hyperintensity in all six index patients.
PMID:31575858 SUPPORT Human Clinical
"Here, we report a syndrome in six patients from two families with a consistent phenotype of mild intellectual disability, similar facies, myopathy, and cerebral white matter hyperintensities, with cardiac systolic dysfunction present in the two oldest patients."
White matter hyperintensity is part of the founding syndrome definition.
Abnormal corpus callosum morphology Abnormal corpus callosum morphology HP:0001273
Show evidence (1 reference)
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Corpus callosum abnormalities listed among the conserved cohort features.
Seizure Seizure HP:0001250
Show evidence (2 references)
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Seizures listed among the conserved features of the expanded cohort.
PMID:31575858 PARTIAL Human Clinical
"From age 15, she experienced episodes of tonic/tonic-clonic seizures, but epileptic activity was absent in repeated EEGs."
Marked PARTIAL: clinical seizures in an index patient without EEG confirmation, so the entity of the events is uncertain.
Hyperreflexia Hyperreflexia HP:0001347
Frequency band deliberately omitted. PMID:31575858 does state hyperreflexia in the oldest four of six index patients, which would map to FREQUENT, but every sentence in the cached text that carries that count spells "hyperreflexia" across a PDF ligature-plus-line-break artifact ("hyperre" + ligature + "flexia"), so no byte-exact quote of the counting sentence is possible from the cache. Rather than record a band whose supporting sentence cannot be quoted, the band is omitted and the count is recorded here. The evidence item below quotes the authors' clean sentence attributing the hyperreflexia to the white matter injury.
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"which might be caused by the white matter abnormalities and decreased inhibition or increased activation of upper motor neurons"
The authors' own sentence about the observed lower-limb hyperreflexia and its proposed white-matter origin.
Anxiety Anxiety HP:0000739
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"revealed mild-to-moderate intellectual disability in all affected individuals, and anxiety was also reported in several patients."
Anxiety reported in several of the index patients.
Dementia Dementia HP:0000726
Show evidence (2 references)
PMID:42290677 SUPPORT Human Clinical
"We report 5 cases of AIMS, including a neonate, and a woman who presented as a sexagenarian with signs of dementia."
The single reported case of dementia in AIMS.
PMID:42290677 SUPPORT Human Clinical
"These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
The associated surveillance recommendation for cognitive decline.
Growth 1
Short stature Short stature HP:0004322
Show evidence (1 reference)
PMID:38217872 SUPPORT Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Short stature listed among the conserved features of the expanded cohort.
Other 3
Easy fatigability VERY_FREQUENT Easy fatigability HP:0003388
Frequency derivation: PMID:31575858 states that all patients report fatigability (6/6 = 100%). PMID:38217872 lists muscle fatigability among the conserved features of its nine-patient cohort without a per-feature count. The 6/6 denominator supports VERY_FREQUENT (80-100%).
Show evidence (3 references)
PMID:31575858 SUPPORT Human Clinical
"All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
Fatigability in all six index patients.
PMID:31575858 SUPPORT Human Clinical
"and walking distance in the 6-min walk test is reduced in all individuals."
Objective functional confirmation of exercise limitation.
PMID:37154692 SUPPORT Model Organism
"We found reduced exercise performance in mouse models of AIMS harboring premature stop codons in ABCC9."
Model-organism recapitulation of the fatigability phenotype.
Periventricular leukomalacia Periventricular leukomalacia HP:0006970
Show evidence (2 references)
PMID:42290677 SUPPORT Human Clinical
"These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
Establishes the leukomalacia-like pattern as a hallmark radiological finding.
PMID:42290677 SUPPORT Human Clinical
"This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
Places periventricular leukomalacia in the defining triad of the disorder.
Prominent supraorbital ridges Prominent supraorbital ridges HP:0000336
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"Affected individuals from the two families share some similar facial features, including prominent supraorbital ridges,"
Names prominent supraorbital ridges as part of the shared facial gestalt. The sentence continues with flat face, thin upper lip vermilion, macrodontia and dental malocclusion, but that continuation cannot be quoted byte-exactly because the cached PDF text breaks it across a ligature and a hyphenated line break.
🧬

Genetic Associations

1
ABCC9 (Causative)
Gene: ABCC9 hgnc:60
Autosomal recessive
Show evidence (8 references)
PMID:31575858 SUPPORT Human Clinical
"Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
The founding homozygous splice-site allele.
PMID:31575858 SUPPORT In Vitro
"This mutation results in an in-frame deletion of exon 8, which results in non-functional KATP channels in recombinant assays."
Functional consequence of the founding allele.
PMID:31575858 SUPPORT Other
"According to gnomAD, the variant is reported at surprisingly high frequency in heterozygous state in the Finnish population with an allele frequency of 0.0007 (18/24850)."
Population-database carrier frequency of the founding allele. Tagged OTHER because the datum is a gnomAD reference-population lookup reported by the authors, not an observation in their patient cohort.
+ 5 more references
💊

Medical Actions

5
Supportive and multidisciplinary care
Action: Supportive Care NCIT:C15747
No disease-modifying therapy exists for AIMS. Management is supportive and targeted at the individual manifestations: developmental and educational support, physiotherapy and activity pacing for fatigability and weakness, anti-seizure medication where seizures are documented, and cardiac surveillance in older individuals. The most recent cohort additionally recommends monitoring for motor and cognitive decline in older individuals and flags deterioration following surgical procedures.
Show evidence (1 reference)
PMID:42290677 SUPPORT Human Clinical
"These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
The only management-directed statement in the AIMS literature: monitor for decline and be alert to peri-procedural deterioration.
Avoidance of calcium channel blockers
Action: avoidance of calcium channel blocker therapy Ontology label: Supportive Care NCIT:C15747
Agent: verapamil CHEBI:9948 calcium channel blocker NCIT:C333
Calcium channel blockade is contraindicated on current evidence. Verapamil was tested in SUR2 loss-of-function mice on the hypothesis that excess CaV1.1-mediated calcium entry drove the myopathy; instead of rescuing the phenotype it caused premature death, and genetically rendering CaV1.1 non-permeable also failed to reverse the pathology. The authors state explicitly that this cautions against calcium channel blockers in AIMS. This is a model-organism safety signal, not a human trial result, and is recorded here because it is the only actionable drug-safety statement in the AIMS literature.
Show evidence (2 references)
PMID:37154692 SUPPORT Model Organism
"results which caution against the use of calcium channel blockers in AIMS."
The authors' explicit safety recommendation.
PMID:37154692 SUPPORT Model Organism
"found that the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice"
The experimental basis for the warning.
Physiotherapy and activity pacing
Action: Physical Therapy NCIT:C15302
Physiotherapy and graded, paced activity address the fatigability, balance deficits and reduced walking distance objectively documented in the index cohort. No trial evidence exists in AIMS; this is standard neuromuscular rehabilitation applied to a documented functional deficit.
Show evidence (1 reference)
PMID:31575858 PARTIAL Human Clinical
"and walking distance in the 6-min walk test is reduced in all individuals."
Marked PARTIAL: this documents the functional deficit that physiotherapy targets, but no study has tested physiotherapy in AIMS.
Heart failure pharmacotherapy
Action: heart failure pharmacotherapy Ontology label: Pharmacotherapy NCIT:C15986
Agent: ACE inhibitor NCIT:C247 beta-blocker NCIT:C29576
Standard heart-failure pharmacotherapy for the reduced systolic function that emerges in older individuals: an ACE inhibitor plus a beta-blocker was started in the index patient found to have biventricular systolic dysfunction with an ejection fraction of 35-40%. This is a single reported case managed by conventional heart-failure practice, not an AIMS-specific regimen, and no outcome is reported. Note the direction-of-effect contrast with Cantu syndrome, where ACE inhibitors appear on the GeneReviews agents-to-avoid list because they open KATP channels that are already overactive; in AIMS the channels carry no measurable current, so that rationale does not transfer.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"antagonist and a beta-blocker was started."
Records the treatment actually given. The quoted span begins at "antagonist" because the preceding "Treatment with an ACE-" is broken across a hyphenated PDF line break in the cached full text.
PMID:31575858 SUPPORT Human Clinical
"Cardiac systolic dysfunction is found in the two oldest patients."
The indication - the age-related cardiac complication this therapy targets.
Anti-seizure medication
Action: Anticonvulsant Therapy NCIT:C64172
Agent: lamotrigine CHEBI:6367
Anti-seizure medication for patients with documented seizures. In the index cohort lamotrigine was partly effective in the one patient with recurrent tonic and tonic-clonic episodes. No AIMS-specific anti-seizure drug choice has been established.
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"Lamotrigine treatment was partly effective."
The one reported anti-seizure drug outcome in AIMS: partial efficacy of lamotrigine in the index patient with tonic and tonic-clonic episodes. This is the sentence that supports the lamotrigine claim in the description.
PMID:38217872 PARTIAL Human Clinical
"Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
Marked PARTIAL and retained only to establish that seizures recur across the expanded cohort and therefore need treatment; this cohort reports no drug-specific outcomes.
🔬

Biochemical Markers

1
Serum creatine kinase (NORMAL)
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals"
Normal serum creatine kinase in all six index patients.
🔀

Differential Diagnoses

7

Conditions with similar clinical presentations that must be differentiated from ABCC9-Related Intellectual Disability and Myopathy Syndrome:

Cantu syndrome Not Yet Curated MONDO:0009406
Overlapping Features The other ABCC9 disease and the single most important entity to separate from AIMS. Cantu syndrome is caused by GAIN-of-function ABCC9 variants and is autosomal dominant, whereas AIMS is caused by biallelic LOSS-of-function variants and is autosomal recessive. The two are therefore allelic in the trivial sense of sharing a gene but are mechanistically opposite, and the Cantu literature is far larger, so a paper that says only "ABCC9 variant" without stating direction of effect cannot be used for either disease. Clinically Cantu is dominated by congenital hypertrichosis, coarse facial features, cardiomegaly with enhanced systolic function and osteochondrodysplasia, with intellect typically normal - none of which describes AIMS. Conversely no AIMS patient has had hypertrichosis, and AIMS cardiac disease is reduced rather than enhanced systolic function.
Distinguishing Features
  • Gain-of-function ABCC9 variants, not loss-of-function
  • Autosomal dominant with de novo missense alleles clustering at Arg1154, not autosomal recessive truncating or splice alleles
  • Congenital hypertrichosis is characteristic; no AIMS patient has had hypertrichosis
  • Coarse facial features and osteochondrodysplasia, versus the distinct AIMS facies with prominent supraorbital ridges
  • Cardiomegaly with enhanced systolic function and patent ductus arteriosus, versus reduced systolic function in older AIMS patients
  • Intellect typically normal despite common developmental delay, versus intellectual disability in essentially all AIMS patients
  • Cerebral white matter hyperintensity resembling periventricular leukomalacia is an AIMS hallmark, not a Cantu feature
  • The Cantu GeneReviews "agents to avoid" list (minoxidil, diazoxide, ACE inhibitors) is specific to KATP overactivity and must not be transferred to AIMS
Show evidence (6 references)
PMID:31575858 SUPPORT Human Clinical
"The phenotype differs from Cantú syndrome, which is caused by gain-of-function ABCC9 mutations, reflecting the opposing consequences of KATP loss- versus gain-of-function."
States the direction-of-effect discriminator directly.
PMID:31575858 SUPPORT Human Clinical
"Therefore, Cantú syndrome and AIMS, arising from opposing molecular mechanisms, are both dysmorphologically and mechanistically distinct."
The AIMS authors' own conclusion that the two entities are distinct on both counts.
PMID:31575858 SUPPORT Human Clinical
"None of our patients have hypertrichosis, unlike Cantú syndrome patients."
The single most discriminating clinical sign between the two ABCC9 diseases.
+ 3 more references
ABCC8-related congenital hyperinsulinism Not Yet Curated MONDO:0019333
Overlapping Features ABCC8 encodes SUR1, the pancreatic sulfonylurea receptor, and differs from ABCC9 by one character in the gene symbol and one paralogue in the same KATP family. Biallelic ABCC8 loss of function is the commonest genetic cause of congenital hyperinsulinism, which is a neonatal hypoglycaemia disorder with no myopathy and no primary white matter disease. The mechanistic parallel is real - both are recessive loss-of-function sulfonylurea-receptor channelopathies - which is exactly why the literature is easy to misattribute, and why every mechanistic sentence in this entry was checked for which receptor it names.
Distinguishing Features
  • Caused by ABCC8 (SUR1), not ABCC9 (SUR2)
  • Presents with severe persistent neonatal hyperinsulinaemic hypoglycaemia, which is not a feature of AIMS
  • Tissue of action is the pancreatic beta cell, not skeletal muscle, brain vasculature or myocardium
  • Focal and diffuse histological forms with 18F-DOPA PET localisation, a workup with no AIMS counterpart
  • Any brain injury is secondary to hypoglycaemia, whereas AIMS white matter disease is primary and present without hypoglycaemia
Show evidence (2 references)
PMID:38791571 SUPPORT Human Clinical
"Congenital hyperinsulinism (CHI) is a rare disorder of glucose metabolism and is the most common cause of severe and persistent hypoglycemia (hyperinsulinemic hypoglycemia, HH) in the neonatal period and childhood."
Defines the clinical entity, which is metabolic and neonatal rather than neuromuscular.
PMID:38791571 SUPPORT Human Clinical
"Most cases are caused by mutations in the ABCC8 and KCNJ11 genes that encode the ATP-sensitive potassium channel (KATP)."
Names ABCC8, not ABCC9, as the causative subunit gene.
DEND syndrome Not Yet Curated MONDO:0019207
Overlapping Features Developmental delay, epilepsy and neonatal diabetes - the KATP gain-of-function neurodevelopmental syndrome caused by activating variants in KCNJ11 or ABCC8. It is the sharpest phenocopy trap in the KATP family for the neurological arm of AIMS, because developmental delay plus epilepsy is exactly the AIMS presentation, and the gene name ABCC8 is one character from ABCC9. It is separated by the obligatory neonatal diabetes, by the opposite direction of channel effect, by dominant rather than recessive inheritance, and by dramatic responsiveness to oral sulfonylureas, which have no established role in AIMS.
Distinguishing Features
  • Caused by gain-of-function KCNJ11 or ABCC8 variants, not loss-of-function ABCC9
  • Neonatal diabetes mellitus within the first six months of life is obligatory and has never been reported in AIMS
  • KATP overactivity, the opposite direction of effect to AIMS
  • Typically dominant (often de novo), not autosomal recessive
  • Responds to oral sulfonylureas, which close KATP channels and have no rationale in a channel-null disease
  • Myopathy with fatigability and painful spasms is an AIMS feature, not a DEND feature
Show evidence (2 references)
PMID:20301620 SUPPORT Human Clinical
"Permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life (mean age: 7 weeks; range: birth to age 26 weeks)."
The neonatal diabetes that defines the DEND spectrum and is absent from AIMS.
PMID:20301620 SUPPORT Human Clinical
"Targeted therapy: Oral sulfonylureas after initial management with insulin in those with ABCC8- or KCNJ11-related PNDM."
Names ABCC8 and KCNJ11 as the KATP genes of this entity and gives the sulfonylurea response that has no counterpart in AIMS.
Heterozygous ABCC9 loss-of-function cardiac phenotypes
Overlapping Features A cluster of monoallelic ABCC9 loss-of-function associations - dilated cardiomyopathy, Brugada and early repolarization syndromes, and idiopathic ventricular fibrillation - reported in adults with no intellectual disability, no myopathy and no white matter disease. These share both the gene and the direction of effect with AIMS, which makes them the subtlest confusion in the ABCC9 literature: a paper titled "loss-of-function ABCC9 variant" may be describing a heterozygous adult arrhythmia case, not AIMS. Zygosity is the discriminator. AIMS carriers in the published families have no conserved clinical pathology.
Distinguishing Features
  • Monoallelic (heterozygous) ABCC9 loss of function, versus the biallelic state required for AIMS
  • Isolated cardiac presentation in adults - arrhythmia or cardiomyopathy - without intellectual disability, myopathy or white matter disease
  • AIMS heterozygous parents show no conserved clinical pathology, so these associations are not simply the AIMS carrier state
  • Some of the reported alleles sit in the SUR2A-specific exon, a cardiac-restricted isoform region
Show evidence (3 references)
PMID:35495129 SUPPORT Human Clinical
"The loss-of-function mutations in the ABCC9 gene were associated with the Brugada syndrome, early repolarization syndrome, and dilated cardiomyopathy."
Enumerates the cardiac phenotypes attributed to ABCC9 loss of function outside the AIMS recessive syndrome.
PMID:35495129 SUPPORT Human Clinical
"The female proband presented with several episodes of ventricular fibrillation and hypokalemia upon emotional stress."
An isolated adult cardiac presentation with no neurodevelopmental or myopathic features.
PMID:38217872 SUPPORT Human Clinical
"Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study."
Establishes that the AIMS carrier state is not itself a recognisable clinical phenotype.
Periventricular leukomalacia of perinatal hypoxic-ischaemic origin
Overlapping Features Acquired periventricular leukomalacia from perinatal hypoxic-ischaemic injury is the standard explanation for the MRI pattern that AIMS produces, and is the reason AIMS is under-diagnosed. The most recent AIMS cohort describes the white matter abnormalities explicitly as resembling periventricular leukomalacia. A child with spastic motor impairment, developmental delay and a leukomalacia-like MRI is routinely labelled with cerebral palsy of perinatal origin and never sequenced. In the index AIMS families pregnancy and birth were uneventful, and one patient was instead investigated for tuberous sclerosis on the basis of the MRI.
Distinguishing Features
  • Acquired perinatal insult, typically with a documented history of prematurity, hypoxia-ischaemia or perinatal complications - absent in the AIMS index families, where pregnancy and birth were uneventful
  • Non-progressive by definition, whereas AIMS lesions increased significantly on serial imaging in at least one patient
  • No accompanying fatigable myopathy with painful post-exercise spasms
  • No familial recurrence pattern; AIMS is recessive with affected siblings
  • No late systolic cardiac dysfunction
Show evidence (2 references)
PMID:42290677 SUPPORT Human Clinical
"These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
The AIMS authors themselves describe the imaging as resembling periventricular leukomalacia, which is what makes the acquired form the operative differential.
PMID:31575858 SUPPORT Human Clinical
"All have cerebral white matter hyperintensities"
Cerebral white matter change in every patient of a cohort whose pregnancies and births were uneventful is precisely the finding otherwise attributed to perinatal injury.
Tuberous sclerosis MONDO:0001734
Overlapping Features A documented misdiagnosis in AIMS, not a hypothetical one. One index patient was worked up for tuberous sclerosis on the basis of periventricular white matter change together with depigmented skin patches, and the diagnosis was later abandoned. The combination of white matter lesions, developmental delay, seizures and hypopigmented macules is genuinely TSC-like on a first pass.
Distinguishing Features
  • Caused by TSC1 or TSC2, not ABCC9
  • Autosomal dominant with frequent de novo variants, not autosomal recessive
  • Cortical tubers, subependymal nodules and subependymal giant cell astrocytoma on MRI, a different lesion pattern from confluent periventricular white matter change
  • Renal angiomyolipoma, cardiac rhabdomyoma, facial angiofibroma and retinal hamartoma have no AIMS counterpart
  • Fatigable myopathy with painful exercise-induced spasms is an AIMS feature, not a TSC feature
Show evidence (1 reference)
PMID:31575858 SUPPORT Human Clinical
"showed periventricular white matter changes, and a diagnosis of tuberous sclerosis was considered"
Records tuberous sclerosis as an actual competing diagnosis entertained on the childhood brain MRI of an AIMS patient.
Mitochondrial disease Not Yet Curated MONDO:0044970
Overlapping Features Primary mitochondrial disease is the standard alternative for a child with myopathy, exercise intolerance, cerebral white matter change and a lactate rise during illness - the exact AIMS phenotype. The index families had mitochondrial DNA sequence and deletion screening, plus screening for inborn errors of metabolism, performed and normal before exome sequencing found ABCC9, and the one AIMS muscle biopsy performed showed mitochondrial aggregation, which reinforces the confusion rather than resolving it.
Distinguishing Features
  • Caused by biallelic nuclear ABCC9 variants, not by mtDNA or nuclear-encoded mitochondrial gene defects
  • Normal mitochondrial DNA sequencing and deletion screening in the AIMS index families
  • Baseline serum lactate, creatine kinase, nerve conduction and electromyography are normal in AIMS; lactate rises only during acute decompensation
  • Strictly autosomal recessive, without the maternal transmission or heteroplasmy-dependent variability of mtDNA disease
  • Non-specific muscle biopsy findings, not ragged-red fibres or respiratory-chain enzyme deficiency
Show evidence (2 references)
PMID:31575858 SUPPORT Human Clinical
"S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals"
The normal baseline lactate and creatine kinase are the practical discriminators against a primary mitochondrial myopathy.
PMID:31575858 SUPPORT Human Clinical
"described as similar to leucodystrophy"
The imaging in one index patient was read as leukodystrophy-like, which is the same white-matter route by which mitochondrial and leukodystrophic diagnoses are reached before AIMS is considered.
{ }

Source YAML

click to show 
name: ABCC9-Related Intellectual Disability and Myopathy Syndrome
creation_date: '2026-08-01T00:00:00Z'
category: Mendelian
synonyms:
- AIMS
- ABCC9-related Intellectual disability Myopathy Syndrome
- intellectual developmental disorder and myopathy syndrome
- IDMYS
- SUR2 loss-of-function channelopathy
description: >-
  ABCC9-related Intellectual disability Myopathy Syndrome (AIMS) is a rare
  autosomal recessive ATP-sensitive potassium (KATP) channelopathy caused by
  biallelic loss-of-function variants in ABCC9, the gene encoding the
  sulfonylurea receptor 2 (SUR2) regulatory subunit. Reported individuals have
  psychomotor delay with intellectual disability of variable severity, muscle
  weakness and fatigability with painful spasms, and cerebral white matter
  abnormalities that radiologically resemble periventricular leukomalacia or
  small vessel disease. Seizures, spasticity, hyperreflexia, microcephaly,
  short stature, corpus callosum abnormalities and anxiety occur in a
  proportion of patients, and cardiac systolic dysfunction has been documented
  in older individuals. AIMS is the loss-of-function pole of ABCC9 disease and
  is mechanistically opposite to Cantu syndrome, which arises from
  gain-of-function variants in the same gene.
disease_term:
  preferred_term: ABCC9-related intellectual disability and myopathy syndrome
  term:
    id: MONDO:0859224
    label: intellectual disability and myopathy syndrome
parents:
- Channelopathy
- Neurodevelopmental Disorder
classifications:
  channelopathy_category:
    classification_value: skeletal muscle channelopathy
    notes: >-
      ChannelopathyOrganSystemEnum is single-valued in the schema and AIMS is
      a multi-organ KATP channelopathy (skeletal muscle, brain and heart). The
      skeletal-muscle value is chosen because tissue-selective suppression
      experiments localised the myopathy specifically to skeletal muscle
      (PMID:37154692), making it the one arm with a demonstrated cell-autonomous
      site of action. The neurological arm (white matter injury, intellectual
      disability, seizures) and the cardiac arm are modeled instead as separate
      pathophysiology nodes.
    evidence:
    - reference: PMID:37154692
      reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Given the roles of KATP channels in all muscles, we sought to determine how myopathy arises using tissue-selective suppression of KATP and found that LoF in skeletal muscle, specifically, underlies myopathy."
      explanation: Tissue-selective suppression localises the myopathic arm of AIMS to skeletal muscle.
  harrisons_chapter:
  - classification_value: NEUROLOGIC
    evidence:
    - reference: PMID:42290677
      reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
      explanation: >-
        The defining triad is neurological (white matter disease, developmental
        delay/intellectual disability) plus neuromuscular, placing the disorder
        in the neurologic chapter.
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:38217872
      reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS)."
      explanation: A single-gene autosomal recessive disorder diagnosed by sequencing belongs to the genetics chapter.
notes: >-
  Scope, named-entity and provenance notes for this entry.


  (1) Named-entity confusion is the central curation risk here, and the
  discriminator is direction of effect, not gene identity. ABCC9 causes two
  mechanistically opposite diseases. Cantu syndrome (MONDO:0009406,
  hypertrichotic osteochondrodysplasia Cantu type) is autosomal dominant and
  caused by GAIN-of-function ABCC9 variants; AIMS is autosomal recessive and
  caused by LOSS-of-function variants. Cantu dominates the ABCC9 literature by
  volume, so every citation used in this entry was checked to confirm the
  reported variants are loss-of-function and, where the paper reports patients,
  that the patients are biallelic. Papers that say only "ABCC9 variant" without
  stating direction of effect were not used. Cantu-specific citations appear in
  this entry only inside the Cantu differential-diagnosis entry and in the
  contrast sentences of AIMS papers themselves, and are labelled as such.


  (2) ABCC8 versus ABCC9. ABCC8 (SUR1) is one character away from ABCC9 (SUR2)
  and is the other sulfonylurea-receptor KATP subunit. ABCC8 loss of function
  causes congenital hyperinsulinism and ABCC8 gain of function causes neonatal
  diabetes and DEND syndrome; none of these is an ABCC9 disorder. Both are
  curated here as bound differentials so the distinction is machine-readable.
  No snippet in this entry that is attributed to ABCC9 comes from an
  ABCC8-only paper.


  (3) No GeneReviews chapter exists for AIMS. PubMed searches on 2026-08-01 for
  "ABCC9 GeneReviews[All Fields]", "\"intellectual disability and myopathy
  syndrome\"[TI] AND GeneReviews[All Fields]" and "GeneReviews[TI] AND (SUR2 OR
  AIMS)" returned no AIMS chapter; the only GeneReviews chapter returned by the
  ABCC9 search is Cantu Syndrome (PMID:25275207), which is the gain-of-function
  disease and is therefore cited here only as the differential baseline, never
  as the AIMS phenotype baseline. The AIMS phenotype baseline used instead is
  the union of the three primary human cohorts: PMID:31575858 (6 patients,
  2 families), PMID:38217872 (9 patients, 7 families) and PMID:42290677
  (5 patients). Cantu's GeneReviews "Agents/circumstances to avoid" list
  (minoxidil, diazoxide, ACE inhibitors) is a Cantu recommendation and is
  deliberately NOT transferred to AIMS - those are KATP openers whose rationale
  is the opposite direction of effect.


  (4) Phenotype frequency bands are derived only where a published denominator
  exists and the derivation is recorded on each phenotype. The three cohorts
  above give 20 reported patients in total, but they do not report a uniform
  feature-by-feature table, so bands are given only for features that a paper
  explicitly quantifies over its own cohort ("all patients", "all but one",
  "the two oldest patients", "the oldest four"). Where a feature is listed in a
  narrative series without a denominator (for example anxiety, hearing loss,
  dementia), the frequency slot is omitted rather than guessed.


  (5) Heterozygous ABCC9 loss-of-function is a separate question from AIMS and
  is not curated as an AIMS phenotype. Heterozygous carriers in the AIMS
  families "do not show any conserved clinical pathology" (PMID:38217872), and
  the separately reported heterozygous ABCC9 loss-of-function cardiac
  associations (dilated cardiomyopathy, Brugada/early repolarization syndrome,
  ventricular fibrillation) are recorded here as differentials rather than as
  features of the recessive syndrome. Two existing KB entries
  (Dilated_Cardiomyopathy, Familial_Atrial_Fibrillation) already mention ABCC9
  in that heterozygous-cardiac context; neither is an ABCC9-specific entry and
  there is no Cantu syndrome entry in the KB to cross-reference, so the Cantu
  differential below carries its own bound MONDO term instead.


  (6) The excess of intra-uterine fetal death reported in AIMS families
  (PMID:38217872) is recorded as a reproductive observation in the genetic
  section rather than as a patient phenotype, because the paper reports it in
  heterozygous parents and does not establish the fetal genotypes.


  (7) No ORPHA, ClinGen (CGGV) or ClinGen Dosage (CGDS) structured-source
  citation is used in this entry. Both structured-source pins are stale and
  un-refreshable (tracked in issue #7622), and bumping data/*/MANIFEST.yaml is
  out of scope for a curation PR, so any row that would have needed a manifest
  refresh was skipped rather than cited from a stale snapshot. The deep-research
  run additionally reports that no Orphanet code exists for AIMS at all, so no
  ORPHA prevalence class would have been citable even with a fresh pin.


  (8) Provenance. Deep research was run with the claude_code provider; the
  report is at
  research/ABCC9-Related_Intellectual_Disability_and_Myopathy_Syndrome-deep-research-claude_code.md.
  A substantial part of that report is flagged by its own author as
  "[FULL-TEXT - RE-VERIFY]" because it came through a summarising intermediary
  rather than a cached abstract. None of those flagged claims are asserted here
  as evidence. Specifically NOT curated for that reason: the full published
  allelic series (per-family variant tables for the 2024 and 2026 cohorts); the
  pooled per-feature frequency table attributed to the 2024 paper; the
  phenytoin/fosphenytoin, propofol and lacosamide drug hazards; the
  perioperative decompensation detail; and the reported death of the oldest
  patient. PMID:38217872 and PMID:42290677 are cached abstract-only, so those
  full-text details cannot be quoted verbatim from the cache. The verapamil /
  calcium-channel-blocker hazard IS curated because it is stated in the
  PMID:37154692 abstract and verifies byte-exact.


  (9) A KATP-opener therapy (diazoxide, pinacidil, minoxidil, nicorandil) is
  deliberately NOT listed as a candidate treatment, despite being the inviting
  inference from "loss of KATP function". The recombinant data show the disease
  alleles produce channels with no measurable current at all, so there is no
  channel left for an opener to open. No published source proposes this in
  AIMS, so recording it as a treatment would be curator inference rather than
  evidence.
inheritance:
- name: Autosomal recessive
  description: >-
    AIMS requires biallelic ABCC9 loss-of-function alleles. Reported families
    include homozygotes for a splice-site allele and homozygotes for truncating
    alleles; heterozygous parents are clinically unaffected.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS)."
    explanation: States the autosomal recessive mode of inheritance for AIMS explicitly.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study."
    explanation: Confirms that single-allele carriers are clinically unaffected, consistent with recessive transmission.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
    explanation: The index families are homozygous for a single ABCC9 allele, the classic recessive configuration.
prevalence:
- population: Worldwide, published cases
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Derivation from published denominators only; no population-based rate has
    ever been reported for AIMS, so no rate_per_100000 is recorded. The
    published series are: PMID:31575858 (2019) six patients from two
    non-consanguineous Northern Norwegian families; PMID:38217872 (2024) nine
    additional subjects from seven unrelated families, plus an eighth family
    ascertained only through intra-uterine fetal deaths; PMID:42290677 (2026)
    five further cases. Summing the genotyped, clinically described patients
    across the three series gives 20, which supports the qualitative
    ULTRA_RARE tier and nothing more precise.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report a syndrome in six patients from two families with a consistent phenotype of mild intellectual disability, similar facies, myopathy, and cerebral white matter hyperintensities, with cardiac systolic dysfunction present in the two oldest patients."
    explanation: Provides the first published denominator, six patients from two families.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we identify nine additional subjects, from seven unrelated families, harbouring different homozygous loss-of-function variants in ABCC9 and presenting with a conserved range of clinical features."
    explanation: Adds nine patients from seven families to the published denominator.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report 5 cases of AIMS, including a neonate, and a woman who presented as a sexagenarian with signs of dementia."
    explanation: Adds five further published cases.
- population: Finnish and Northern Norwegian populations
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Not a rate. The index families came from the same area of Northern Norway
    with probable Finnish ancestry and were homozygous for the same
    c.1320+1G>A allele, and the original authors suggested on that basis that
    the syndrome may be more prevalent in Finns. No prevalence, incidence or
    carrier-screening study has ever been performed in any population, so no
    band and no rate is recorded here; the record exists only to capture the
    documented founder signal rather than to assert an occurrence estimate.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Considering the probable Finnish ancestry of all patients, the syndrome might be more prevalent in the Finnish population than others."
    explanation: >-
      Marked PARTIAL because the authors state this as a possibility inferred
      from shared ancestry and allele frequency, not as a measured prevalence.
pathophysiology:
- name: Biallelic ABCC9 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Biallelic loss-of-function variants in ABCC9 - splice-site alleles causing
    in-frame exon skipping, and nonsense or frameshift alleles causing
    nonsense-mediated decay or drastic truncation - abolish production of
    functional SUR2 protein. This is the root lesion of AIMS and is the
    opposite direction of effect to the gain-of-function ABCC9 variants that
    cause Cantu syndrome.
  genes:
  - preferred_term: ABCC9
    term:
      id: hgnc:60
      label: ABCC9
    modifier: DECREASED
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
    explanation: Identifies the founding biallelic ABCC9 lesion.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All variants are predicted to result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional SUR2-dependent KATP channels."
    explanation: Establishes the truncating/in-frame-deletion allele class across seven further families.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All variants are predicted to lead to nonsense mediated decay of ABCC9 transcripts and/or drastic truncation of SUR2."
    explanation: Confirms nonsense-mediated decay and truncation as the mechanism of allele inactivation in the most recent cohort.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotype differs from Cantú syndrome, which is caused by gain-of-function ABCC9 mutations, reflecting the opposing consequences of KATP loss- versus gain-of-function."
    explanation: >-
      Anchors the direction of effect that separates AIMS from the other ABCC9
      disease, Cantu syndrome.
  downstream:
  - target: Non-Functional SUR2-Containing KATP Channels
    description: Absence of functional SUR2 protein prevents assembly of working SUR2-containing KATP channels.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "This mutation results in an in-frame deletion of exon 8, which results in non-functional KATP channels in recombinant assays."
      explanation: Recombinant reconstitution shows the patient allele yields non-functional channels.
    - reference: PMID:42290677
      reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Functional tests of recombinant channels confirm that disease-associated SUR2 truncations cause a complete loss-of-function."
      explanation: Independent recombinant testing of newer alleles confirms complete loss of channel function.
- name: Non-Functional SUR2-Containing KATP Channels
  biological_scale: MOLECULAR
  description: >-
    SUR2 is the regulatory subunit that confers ATP/ADP sensitivity and
    trafficking competence on Kir6.x pore subunits in skeletal muscle, cardiac
    muscle and vascular smooth muscle. Without functional SUR2, the
    SUR2-containing KATP channels of those tissues are absent or non-conducting,
    so cellular metabolic state can no longer be translated into membrane
    potassium conductance.
  genes:
  - preferred_term: ABCC9
    term:
      id: hgnc:60
      label: ABCC9
    modifier: DECREASED
  molecular_functions:
  - preferred_term: ATP-activated inward rectifier potassium channel activity
    term:
      id: GO:0015272
      label: ATP-activated inward rectifier potassium channel activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: DECREASED
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  - preferred_term: vascular associated smooth muscle cell
    term:
      id: CL:0000359
      label: vascular associated smooth muscle cell
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We term this channelopathy resulting from loss-of-function of SUR2-containing KATP channels ABCC9-related Intellectual disability Myopathy Syndrome (AIMS)."
    explanation: Names the loss of SUR2-containing KATP channel function as the defining lesion of the syndrome.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "KATP channels are found throughout the cardiovascular system and skeletal muscle and couple cellular metabolism to excitability."
    explanation: >-
      States the tissue distribution and the metabolism-to-excitability coupling
      role that is lost when SUR2 is absent.
  downstream:
  - target: Loss of Sarcolemmal KATP Conductance in Skeletal Muscle
    description: >-
      Fast-twitch skeletal muscle depends on noncanonical Kir6.2/SUR2
      sarcolemmal KATP channels, so SUR2 loss removes essentially the whole
      sarcolemmal KATP conductance.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:42159583
      reference_title: Subunit composition of the KATP channels that modulate contractility of skeletal muscle during fatigue.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Under fatiguing conditions, isometric tetanic contraction experiments on murine extensor digitorum longus (EDL) revealed delayed loss of stimulated forces, and significant development of unstimulated forces, in muscles lacking Kir6.2 or SUR2 subunits, whereas loss of the SUR1 subunit did not impact muscle functionality."
      explanation: >-
        Subunit dissection shows that removing SUR2 (but not SUR1) abolishes the
        functionally relevant sarcolemmal KATP conductance of fast-twitch muscle.
    - reference: PMID:42159583
      reference_title: Subunit composition of the KATP channels that modulate contractility of skeletal muscle during fatigue.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "ATP-sensitive potassium (KATP) channels are among the most expressed ion channels in skeletal muscle sarcolemma."
      explanation: Establishes the sarcolemmal abundance of the channel that is lost.
  - target: Loss of Cardiomyocyte KATP Conductance
    description: SUR2A is the cardiac sulfonylurea receptor, so its loss removes cardiomyocyte KATP current.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "SUR2 loss-of-function causes fatigability and cardiac dysfunction in mice, and reduced activity, cardiac dysfunction and ventricular enlargement in zebrafish."
      explanation: >-
        Two independent animal models lacking functional SUR2 develop cardiac
        dysfunction, linking absent cardiomyocyte SUR2 to the cardiac arm.
  - target: Impaired Brain Vascular Smooth Muscle Differentiation and Neurovascular Coupling
    description: >-
      KCNJ8/ABCC9-containing KATP channels are required cell-autonomously for
      brain arterial and arteriolar smooth muscle differentiation, so their loss
      compromises cerebral vascular maturation.
    causal_link_type: DIRECT
    hypothesis_groups:
    - aims_cerebrovascular_white_matter
    evidence:
    - reference: PMID:35588738
      reference_title: KCNJ8/ABCC9-containing K-ATP channel modulates brain vascular smooth muscle development and neurovascular coupling.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We show that genetic/chemical inhibition or activation of KCNJ8/ABCC9-containing K-ATP channel function leads to brain-selective suppression or promotion of arterial/arteriolar vascular smooth muscle cell (VSMC) differentiation, respectively."
      explanation: >-
        Inhibition of the ABCC9-containing channel suppresses brain VSMC
        differentiation, the direction of effect relevant to AIMS.
  - target: Increased Seizure Susceptibility
    description: >-
      Loss of abcc9 lowers the threshold for chemically provoked seizure-like
      motor activity in vivo.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:38217872
      reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility."
      explanation: >-
        Directly ties abcc9 loss of function to increased seizure susceptibility,
        though the neuronal intermediates are not identified.
- name: Loss of Sarcolemmal KATP Conductance in Skeletal Muscle
  biological_scale: CELLULAR
  description: >-
    In healthy skeletal muscle the sarcolemmal KATP channel is closed at rest
    and opens as intracellular ATP falls during metabolic stress or fatigue. In
    AIMS muscle this metabolically gated conductance is absent.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: response to muscle activity
    term:
      id: GO:0014850
      label: response to muscle activity
    modifier: ABNORMAL
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In skeletal muscle, K ATP channels are typically closed at rest but open in response to metabolic stress or fatigue"
    explanation: >-
      States the normal metabolic gating of the sarcolemmal channel that AIMS
      abolishes. Quoted with the space that the cached PDF text carries between
      "K" and "ATP".
  downstream:
  - target: Failure of Membrane Potential Stabilization During Fatigue
    description: >-
      Without KATP opening, the fatiguing fibre cannot shorten its action
      potential or stabilise its resting membrane potential.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Channel activation results in action potential shortening and stabilization of the resting membrane potential during the development of fatigue"
      explanation: >-
        Describes the protective electrical adaptation that cannot occur once
        the channel is lost.
- name: Failure of Membrane Potential Stabilization During Fatigue
  biological_scale: CELLULAR
  description: >-
    Loss of the fatigue-activated potassium conductance removes the brake on
    sarcolemmal excitability during sustained activity, so the fibre cannot
    limit calcium entry or recover normally from fatigue.
  biological_processes:
  - preferred_term: regulation of membrane potential
    term:
      id: GO:0042391
      label: regulation of membrane potential
    modifier: ABNORMAL
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, loss of KATP function might be expected to result in failure to recover from fatigue"
    explanation: The authors' explicit mechanistic prediction for what loss of the conductance does to a fatiguing fibre.
  downstream:
  - target: Unstimulated Force Generation and Calcium Overload
    description: >-
      Unopposed depolarisation during fatigue produces contraction in the
      absence of stimulation and excessive calcium entry.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37154692
      reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS."
      explanation: Directly demonstrates unstimulated force generation in SUR2 loss-of-function muscle.
    - reference: PMID:42159583
      reference_title: Subunit composition of the KATP channels that modulate contractility of skeletal muscle during fatigue.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Under fatiguing conditions, isometric tetanic contraction experiments on murine extensor digitorum longus (EDL) revealed delayed loss of stimulated forces, and significant development of unstimulated forces, in muscles lacking Kir6.2 or SUR2 subunits, whereas loss of the SUR1 subunit did not impact muscle functionality."
      explanation: Replicates unstimulated force development specifically in SUR2-null muscle under fatigue.
- name: Unstimulated Force Generation and Calcium Overload
  biological_scale: CELLULAR
  description: >-
    SUR2-null muscle generates force without stimulation under fatiguing
    conditions, the proposed cellular correlate of the painful spasms reported
    by patients. Excessive calcium influx was the hypothesised downstream
    effector, but blocking CaV1.1 permeation genetically did not reverse the
    pathology and the calcium channel blocker verapamil was harmful, so the
    calcium arm is not established as the sole effector.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: calcium ion transmembrane transport
    term:
      id: GO:0070588
      label: calcium ion transmembrane transport
    modifier: INCREASED
  evidence:
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS."
    explanation: Establishes the unstimulated-force phenotype and its proposed clinical correlate.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: "We sought to determine whether excessive Ca2+ influx through CaV 1.1 channels was responsible for myopathology but found that the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice and that rendering CaV 1.1 channels nonpermeable by mutation failed to reverse pathology; results which caution against the use of calcium channel blockers in AIMS."
    explanation: >-
      Recorded as REFUTE against the specific sub-hypothesis that excessive
      CaV1.1-mediated calcium influx is the effector of the myopathy: both the
      pharmacological and the genetic test of that hypothesis failed, and the
      pharmacological one was harmful. The unstimulated-force phenotype itself
      is unaffected by this refutation; only the calcium-influx explanation of
      it is.
  downstream:
  - target: Skeletal-Muscle-Delimited Myopathy
    description: >-
      The contractile abnormality is intrinsic to skeletal muscle rather than
      secondary to cardiac or vascular disease.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37154692
      reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Given the roles of KATP channels in all muscles, we sought to determine how myopathy arises using tissue-selective suppression of KATP and found that LoF in skeletal muscle, specifically, underlies myopathy."
      explanation: Tissue-selective suppression localises the myopathy to skeletal muscle itself.
- name: Skeletal-Muscle-Delimited Myopathy
  biological_scale: TISSUE
  description: >-
    A myopathy that is clinically prominent but histologically and
    electrophysiologically bland: patients have generalised hypotonia, reduced
    strength, fatigability and exercise-induced pain, with normal serum creatine
    kinase, normal nerve conduction and essentially normal electromyography.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: skeletal muscle contraction
    term:
      id: GO:0003009
      label: skeletal muscle contraction
    modifier: ABNORMAL
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
    explanation: Documents the clinical myopathy across the index cohort.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals"
    explanation: >-
      Shows the myopathy is not accompanied by the usual laboratory markers of
      muscle destruction, which is diagnostically important.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We found reduced exercise performance in mouse models of AIMS harboring premature stop codons in ABCC9."
    explanation: The mouse model recapitulates the exercise-intolerance arm.
- name: Loss of Cardiomyocyte KATP Conductance
  biological_scale: CELLULAR
  description: >-
    SUR2A partners Kir6.2 in the cardiomyocyte sarcolemma, where KATP opening
    protects the myocyte during metabolic stress. Its absence removes that
    protection.
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  biological_processes:
  - preferred_term: potassium ion transmembrane transport
    term:
      id: GO:0071805
      label: potassium ion transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "KATP channels are found throughout the cardiovascular system and skeletal muscle and couple cellular metabolism to excitability."
    explanation: Places the SUR2-containing channel in the cardiovascular system.
  downstream:
  - target: Cardiac Systolic Dysfunction
    description: >-
      Loss of cardiomyocyte KATP is followed by impaired systolic performance
      in patients and in both animal models.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "SUR2 loss-of-function causes fatigability and cardiac dysfunction in mice, and reduced activity, cardiac dysfunction and ventricular enlargement in zebrafish."
      explanation: Cardiac dysfunction follows SUR2 loss in two model organisms.
- name: Cardiac Systolic Dysfunction
  biological_scale: ORGANISM
  description: >-
    Reduced systolic function, documented in the two oldest patients of the
    index cohort and reproduced in SUR2-null mice and zebrafish. It is an
    age-related feature rather than a presenting one.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac systolic dysfunction is found in the two oldest patients."
    explanation: The human cardiac finding, with its age restriction.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction."
    explanation: >-
      Confirms cardiac dysfunction as part of the recognised human phenotype.
      Tagged OTHER rather than HUMAN_CLINICAL: this is the introductory framing
      sentence of a mouse-model paper restating the accepted clinical picture,
      not data that paper generated. The human cohort evidence is the
      PMID:31575858 item above.
- name: Impaired Brain Vascular Smooth Muscle Differentiation and Neurovascular Coupling
  biological_scale: CELLULAR
  description: >-
    KCNJ8/ABCC9-containing KATP channels are expressed on brain mural cell
    progenitors and are required cell-autonomously for arterial and arteriolar
    smooth muscle differentiation. Loss of channel function suppresses that
    differentiation and, in the corresponding knockout, degrades vasoconstrictive
    capacity and neuronally evoked vasodilation - the machinery that fine-tunes
    cerebral blood flow.
  cell_types:
  - preferred_term: vascular associated smooth muscle cell
    term:
      id: CL:0000359
      label: vascular associated smooth muscle cell
  biological_processes:
  - preferred_term: vascular associated smooth muscle cell differentiation
    term:
      id: GO:0035886
      label: vascular associated smooth muscle cell differentiation
    modifier: DECREASED
  - preferred_term: regulation of cerebral blood circulation
    term:
      id: GO:0120276
      label: regulation of cerebral blood circulation
    modifier: ABNORMAL
  evidence:
  - reference: PMID:35588738
    reference_title: KCNJ8/ABCC9-containing K-ATP channel modulates brain vascular smooth muscle development and neurovascular coupling.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Loss- or gain-of-function mutations in ATP-sensitive potassium channel (K-ATP)-encoding genes, KCNJ8 and ABCC9, cause human central nervous system disorders with unknown pathogenesis."
    explanation: Frames the CNS arm of ABCC9 disease as the problem being addressed.
  - reference: PMID:35588738
    reference_title: KCNJ8/ABCC9-containing K-ATP channel modulates brain vascular smooth muscle development and neurovascular coupling.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our results demonstrate a role for KCNJ8/ABCC9-containing K-ATP channels in the differentiation of brain VSMC, which in turn is necessary for fine-tuning of cerebral blood flow."
    explanation: Establishes the ABCC9-dependent brain vascular developmental role.
  - reference: PMID:35588738
    reference_title: KCNJ8/ABCC9-containing K-ATP channel modulates brain vascular smooth muscle development and neurovascular coupling.
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Consistent with defective VSMC development, Kcnj8 knockout mice showed deficiency in vasoconstrictive capacity and neuronal-evoked vasodilation leading to local hyperemia."
    explanation: >-
      Marked PARTIAL because the in vivo neurovascular-coupling deficit was shown
      in a Kcnj8 (Kir6.1) knockout, the partner subunit, not in an Abcc9 knockout.
  downstream:
  - target: Cerebral White Matter Injury
    description: >-
      A cerebral small-vessel mechanism is the leading explanation for the white
      matter lesions, which radiologically resemble periventricular leukomalacia
      or small vessel disease.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - aims_cerebrovascular_white_matter
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "it is conceivable that KATP loss of function may impact the cerebral vasculature"
      explanation: >-
        Marked PARTIAL because the original authors advance the cerebrovascular
        route as a conjecture ("it is conceivable"), not a demonstrated
        mechanism.
    - reference: PMID:42290677
      reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
      explanation: >-
        The human imaging pattern is explicitly described as small-vessel-like,
        which is what a brain VSMC differentiation defect would predict.
- name: Cerebral White Matter Injury
  biological_scale: TISSUE
  description: >-
    Cerebral white matter hyperintensities were present in every patient of the
    index cohort and white matter abnormalities, often with corpus callosum
    involvement, recur across the later cohorts. In the most recent series the
    pattern resembles periventricular leukomalacia or small vessel disease and
    is described as a key hallmark of the disorder. Lesions can progress over
    time.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All have cerebral white matter hyperintensities"
    explanation: Cerebral white matter hyperintensity in all six index patients.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Confirms white matter and corpus callosum involvement in the expanded cohort.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
    explanation: Establishes the leukomalacia-like radiological pattern as a hallmark.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MR angiography is normal, with normal cerebral vasculature calibers."
    explanation: >-
      The injury is not accompanied by a macrovascular abnormality, which is
      both consistent with a functional small-vessel mechanism and the point of
      contrast with the dilated tortuous vessels of Cantu syndrome.
  downstream:
  - target: Intellectual Disability and Developmental Delay
    description: >-
      The cognitive phenotype tracks with the white matter burden, but no
      mediating cellular step has been demonstrated and a purely vascular
      account is not proven.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "and there are no reports of cognitive impairment in previous SUR2 mutant animal models."
      explanation: >-
        Marked PARTIAL: the original authors state explicitly that the route from
        channel loss to intellectual disability is unresolved, so this edge is an
        association with unknown intermediates rather than a demonstrated
        mechanism.
  - target: Pyramidal Tract Dysfunction
    description: >-
      The authors attribute the lower-limb hyperreflexia of the older patients
      to the white matter abnormalities and consequent loss of upper motor
      neuron inhibition.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31575858
      reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "which might be caused by the white matter abnormalities and decreased inhibition or increased activation of upper motor neurons"
      explanation: The proposed white-matter-to-hyperreflexia route, stated as a hypothesis by the authors.
- name: Intellectual Disability and Developmental Delay
  biological_scale: ORGANISM
  description: >-
    Psychomotor delay followed by intellectual disability, mild in the index
    Norwegian families and of variable severity across the expanded cohorts.
    Motor and cognitive decline has now been documented in older individuals,
    including a sexagenarian presenting with signs of dementia.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "revealed mild-to-moderate intellectual disability in all affected individuals, and anxiety was also reported in several patients."
    explanation: Formal neuropsychological testing confirmed intellectual disability in all six index patients.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
    explanation: Adds the later-life decline arm of the cognitive phenotype.
- name: Pyramidal Tract Dysfunction
  biological_scale: ORGANISM
  description: >-
    Lower-limb hyperreflexia and spasticity, appearing in the older patients of
    the index cohort and recorded as spasticity across the expanded cohort.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which might be caused by the white matter abnormalities and decreased inhibition or increased activation of upper motor neurons"
    explanation: >-
      The authors attribute the lower-limb hyperreflexia of the older index
      patients to loss of upper motor neuron inhibition from the white matter
      injury.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Records spasticity in the expanded cohort.
- name: Increased Seizure Susceptibility
  biological_scale: ORGANISM
  description: >-
    Seizures occur in a proportion of AIMS patients, and abcc9 loss of function
    lowers the chemoconvulsant threshold in zebrafish. In the index cohort one
    patient had clinical tonic-clonic episodes without EEG correlate, so the
    epileptic phenotype is not uniform.
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility."
    explanation: Experimental demonstration of lowered seizure threshold on abcc9 loss.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "From age 15, she experienced episodes of tonic/tonic-clonic seizures, but epileptic activity was absent in repeated EEGs."
    explanation: >-
      Marked PARTIAL because the clinical events in this index patient were not
      confirmed electrographically.
phenotypes:
- name: Intellectual disability
  category: Nervous System
  description: >-
    Intellectual disability of variable severity, mild to moderate in the index
    Norwegian families and variable across the expanded cohorts.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 reports mild-to-moderate intellectual
    disability in all six index patients (6/6 = 100%), and PMID:38217872 reports
    intellectual disability of variable severity in all nine patients of the
    expanded cohort. Both denominators are cohort-wide, so VERY_FREQUENT
    (80-100%) is the band supported by published counts.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "revealed mild-to-moderate intellectual disability in all affected individuals, and anxiety was also reported in several patients."
    explanation: Intellectual disability in all six index patients on formal neuropsychological testing.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Intellectual disability of variable severity across the expanded cohort.
- name: Global developmental delay
  category: Nervous System
  description: Psychomotor delay recognised in infancy or early childhood.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Psychomotor delay is listed first among the conserved features.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
    explanation: Developmental delay is one of the three defining components of the syndrome.
- name: Easy fatigability
  category: Musculoskeletal
  description: >-
    Exercise intolerance and exhaustibility, reported by every patient in the
    index cohort and reproduced as reduced exercise performance in SUR2-null
    mice.
  phenotype_term:
    preferred_term: Easy fatigability
    term:
      id: HP:0003388
      label: Easy fatigability
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 states that all patients report
    fatigability (6/6 = 100%). PMID:38217872 lists muscle fatigability among
    the conserved features of its nine-patient cohort without a per-feature
    count. The 6/6 denominator supports VERY_FREQUENT (80-100%).
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
    explanation: Fatigability in all six index patients.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "and walking distance in the 6-min walk test is reduced in all individuals."
    explanation: Objective functional confirmation of exercise limitation.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We found reduced exercise performance in mouse models of AIMS harboring premature stop codons in ABCC9."
    explanation: Model-organism recapitulation of the fatigability phenotype.
- name: Postural instability
  category: Nervous System
  description: >-
    Objectively measured balance impairment. Formal miniBESTest assessment
    found moderate to severe balance deficits in every index patient, alongside
    a reduced 6-minute walk distance.
  phenotype_term:
    preferred_term: Balance impairment
    term:
      id: HP:0002172
      label: Postural instability
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 reports miniBESTest balance deficits in
    all six index patients (6/6 = 100%), which is the VERY_FREQUENT band
    (80-100%). The quoted span begins mid-sentence because the preceding words
    ("moderate to severe deficits") are broken across a PDF ligature in the
    cached full text and cannot be quoted byte-exactly; the severity grading is
    recorded here instead. Neither expanded cohort reports its own balance
    denominator.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in balance in all patients, and walking distance in the 6-min walk test is reduced in all individuals."
    explanation: >-
      The miniBESTest sentence: balance deficits in all six index patients,
      with the 6-minute walk test as the corroborating functional measure.
- name: Muscle weakness
  category: Musculoskeletal
  description: Reduced muscle strength, generally proximal and generalised.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 reports muscle strength below normal in
    all but one of six index patients (5/6 = 83%), which falls in the
    VERY_FREQUENT band (80-100%). PMID:38217872 and PMID:42290677 both list
    muscle weakness among the conserved features without their own per-feature
    denominators.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
    explanation: Gives the 5/6 denominator for reduced strength.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
    explanation: Muscle weakness is one of the three defining components of the syndrome.
- name: Generalized hypotonia
  category: Musculoskeletal
  description: Generalised low tone, typically noted in infancy or early childhood.
  phenotype_term:
    preferred_term: Generalized hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 states that all six index patients
    present with generalized hypotonia (6/6 = 100%), supporting VERY_FREQUENT
    (80-100%). No later cohort supplies its own hypotonia denominator.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients report fatigability, present with generalized hypotonia, and muscle strength is below normal in all but one."
    explanation: Generalized hypotonia in all six index patients.
- name: Muscle spasm
  category: Musculoskeletal
  description: >-
    Painful muscle spasms and exercise-induced muscle pain and stiffness. The
    corresponding cellular abnormality - force generated without stimulation -
    has been demonstrated in SUR2 loss-of-function muscle.
  phenotype_term:
    preferred_term: Muscle spasm
    term:
      id: HP:0003394
      label: Muscle spasm
  evidence:
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction."
    explanation: >-
      Muscle spasms are recorded as a clinical feature of AIMS. Tagged OTHER
      rather than HUMAN_CLINICAL: the sentence is background framing in a
      mouse-model paper, restating the accepted clinical picture rather than
      reporting that paper's own patient data.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS."
    explanation: Provides the mechanistic correlate of the spasms in isolated SUR2-null muscle.
- name: Hyperintensity of cerebral white matter on MRI
  category: Nervous System
  description: >-
    Cerebral white matter hyperintensities on MRI, present in every patient of
    the index cohort and progressive in at least one.
  phenotype_term:
    preferred_term: Hyperintensity of cerebral white matter on MRI
    term:
      id: HP:0030890
      label: Hyperintensity of cerebral white matter on MRI
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 states that all six index patients have
    cerebral white matter hyperintensities (6/6 = 100%). PMID:38217872 and
    PMID:42290677 both describe white matter abnormalities as conserved or
    hallmark features without per-feature counts. VERY_FREQUENT (80-100%) rests
    on the 6/6 denominator.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All have cerebral white matter hyperintensities"
    explanation: Cerebral white matter hyperintensity in all six index patients.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report a syndrome in six patients from two families with a consistent phenotype of mild intellectual disability, similar facies, myopathy, and cerebral white matter hyperintensities, with cardiac systolic dysfunction present in the two oldest patients."
    explanation: White matter hyperintensity is part of the founding syndrome definition.
- name: Periventricular leukomalacia
  category: Nervous System
  description: >-
    A periventricular-leukomalacia-like white matter pattern, described in the
    most recent cohort as a key radiological hallmark. It is a mimic of acquired
    perinatal hypoxic-ischaemic injury and is the main source of diagnostic
    confusion in AIMS.
  phenotype_term:
    preferred_term: Periventricular leukomalacia
    term:
      id: HP:0006970
      label: Periventricular leukomalacia
  diagnostic: true
  evidence:
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
    explanation: Establishes the leukomalacia-like pattern as a hallmark radiological finding.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This new cohort underscores that AIMS is characterized by the combination of periventricular leukomalacia, developmental delay and intellectual disability, and muscle weakness and fatigability - and is driven by biallelic loss-of-function variants in ABCC9."
    explanation: Places periventricular leukomalacia in the defining triad of the disorder.
- name: Abnormal corpus callosum morphology
  category: Nervous System
  description: Corpus callosum abnormalities reported alongside the white matter changes.
  phenotype_term:
    preferred_term: Abnormal corpus callosum morphology
    term:
      id: HP:0001273
      label: Abnormal corpus callosum morphology
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Corpus callosum abnormalities listed among the conserved cohort features.
- name: Seizure
  category: Nervous System
  description: >-
    Seizures occur in a proportion of patients. In the index cohort one patient
    had clinical tonic and tonic-clonic episodes that were never captured on
    EEG, so the epilepsy phenotype is variable and not always electrographically
    confirmed.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Seizures listed among the conserved features of the expanded cohort.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "From age 15, she experienced episodes of tonic/tonic-clonic seizures, but epileptic activity was absent in repeated EEGs."
    explanation: >-
      Marked PARTIAL: clinical seizures in an index patient without EEG
      confirmation, so the entity of the events is uncertain.
- name: Spasticity
  category: Nervous System
  description: Spasticity, part of the pyramidal signs that emerge with the white matter burden.
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Spasticity listed among the conserved features of the expanded cohort.
- name: Hyperreflexia
  category: Nervous System
  description: >-
    Lower-limb hyperreflexia, present in the four oldest index patients and
    absent in the younger two, so it appears to be age-dependent.
  phenotype_term:
    preferred_term: Hyperreflexia
    term:
      id: HP:0001347
      label: Hyperreflexia
  notes: >-
    Frequency band deliberately omitted. PMID:31575858 does state hyperreflexia
    in the oldest four of six index patients, which would map to FREQUENT, but
    every sentence in the cached text that carries that count spells
    "hyperreflexia" across a PDF ligature-plus-line-break artifact
    ("hyperre" + ligature + "flexia"), so no byte-exact quote of the counting
    sentence is possible from the cache. Rather than record a band whose
    supporting sentence cannot be quoted, the band is omitted and the count is
    recorded here. The evidence item below quotes the authors' clean sentence
    attributing the hyperreflexia to the white matter injury.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which might be caused by the white matter abnormalities and decreased inhibition or increased activation of upper motor neurons"
    explanation: >-
      The authors' own sentence about the observed lower-limb hyperreflexia and
      its proposed white-matter origin.
- name: Microcephaly
  category: Growth
  description: Reduced head circumference, reported in the expanded cohort.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Microcephaly listed among the conserved features of the expanded cohort.
- name: Short stature
  category: Growth
  description: Short stature, reported in the expanded cohort and in individual index patients.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: Short stature listed among the conserved features of the expanded cohort.
- name: Left ventricular systolic dysfunction
  category: Cardiovascular
  description: >-
    Reduced systolic function found in the two oldest patients of the index
    cohort at ages 29 and 33 and absent in the younger four, making it an
    age-related complication that warrants surveillance rather than a
    presenting feature.
  phenotype_term:
    preferred_term: Left ventricular systolic dysfunction
    term:
      id: HP:0025169
      label: Left ventricular systolic dysfunction
  frequency: FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 reports cardiac systolic dysfunction in
    the two oldest of six index patients (2/6 = 33%), which falls just inside
    the FREQUENT band (30-79%). The band is age-confounded - both affected
    individuals were in their thirties and the unaffected four were 11-21 - so
    it should be read as a cross-sectional cohort proportion, not a lifetime
    risk.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac systolic dysfunction is found in the two oldest patients."
    explanation: Gives the 2/6 denominator and the age restriction.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction."
    explanation: >-
      Confirms cardiac dysfunction as an accepted feature of the human
      syndrome. Tagged OTHER rather than HUMAN_CLINICAL: the sentence is
      background framing in a mouse-model paper, not data that paper generated.
      The 2/6 human denominator comes from the PMID:31575858 item above.
- name: Anxiety
  category: Nervous System
  description: >-
    Anxiety reported in several index patients, some under outpatient
    psychiatric follow-up. No published denominator exists, so no frequency band
    is recorded.
  phenotype_term:
    preferred_term: Anxiety
    term:
      id: HP:0000739
      label: Anxiety
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "revealed mild-to-moderate intellectual disability in all affected individuals, and anxiety was also reported in several patients."
    explanation: Anxiety reported in several of the index patients.
- name: Dementia
  category: Nervous System
  description: >-
    Late cognitive decline. A single reported sexagenarian presented with signs
    of dementia, prompting the recommendation that older individuals be
    monitored for motor and cognitive decline. This is a single-case
    observation, so no frequency is recorded.
  phenotype_term:
    preferred_term: Dementia
    term:
      id: HP:0000726
      label: Dementia
  evidence:
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report 5 cases of AIMS, including a neonate, and a woman who presented as a sexagenarian with signs of dementia."
    explanation: The single reported case of dementia in AIMS.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
    explanation: The associated surveillance recommendation for cognitive decline.
- name: Lumbar hyperlordosis
  category: Musculoskeletal
  description: >-
    Lumbar lordosis, present in all but one of the index patients and plausibly
    postural, secondary to the axial hypotonia.
  phenotype_term:
    preferred_term: Lumbar hyperlordosis
    term:
      id: HP:0002938
      label: Lumbar hyperlordosis
  frequency: VERY_FREQUENT
  notes: >-
    Frequency derivation: PMID:31575858 reports lumbar lordosis in all but one
    of six index patients (5/6 = 83%), inside the VERY_FREQUENT band (80-100%).
    This is a single-cohort denominator from one founder population and has not
    been replicated in the later cohorts.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lumbar lordosis is found in all but one, and scoliosis in one."
    explanation: Gives the 5/6 denominator for lumbar lordosis and 1/6 for scoliosis.
- name: Hypotelorism
  category: Head and Neck
  description: >-
    Reduced interorbital distance, part of the shared facial gestalt of the
    index families and the one dysmorphic feature the SUR2-STOP zebrafish model
    recapitulates as a measurable decrease in interorbital distance.
  phenotype_term:
    preferred_term: Hypotelorism
    term:
      id: HP:0000601
      label: Hypotelorism
  notes: >-
    No frequency band is recorded. The source states only that "some of the
    individuals" have hypotelorism, and the per-patient table that would supply
    a denominator is a PDF-extracted grid of plus/minus marks rather than
    quotable prose. The OMIM:619719 HPO annotation set records 4/6, but that is
    not a claim this entry can source from its own cited references, so the
    band is omitted rather than asserted.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "of the individuals have hypotelorism"
    explanation: >-
      Hypotelorism in the index families. The quoted span omits the preceding
      word "Some" only because it sits on the previous PDF line; the source
      makes no per-patient count available as quotable prose.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Consistent with hypotelorism observed in multiple AIMS"
    explanation: >-
      Cross-species link: the SUR2-STOP zebrafish shows a decreased interorbital
      distance, the only dysmorphic feature of AIMS the model reproduces.
- name: Prominent supraorbital ridges
  category: Head and Neck
  description: >-
    Part of the shared facial gestalt of the index families, which also
    included a flat face, thin upper lip vermilion, macrodontia and dental
    malocclusion. The gestalt is explicitly NOT the coarse acromegaloid face of
    Cantu syndrome, and the original authors cautioned that with only two
    families it is not yet established as consistent.
  phenotype_term:
    preferred_term: Prominent supraorbital ridges
    term:
      id: HP:0000336
      label: Prominent supraorbital ridges
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals from the two families share some similar facial features, including prominent supraorbital ridges,"
    explanation: >-
      Names prominent supraorbital ridges as part of the shared facial gestalt.
      The sentence continues with flat face, thin upper lip vermilion,
      macrodontia and dental malocclusion, but that continuation cannot be
      quoted byte-exactly because the cached PDF text breaks it across a
      ligature and a hyphenated line break.
- name: Sensorineural hearing impairment
  category: Ear
  description: >-
    Mild bilateral high-frequency sensorineural hearing loss, documented in
    individual index patients. Reported as an individual observation rather than
    a cohort count, so no frequency band is recorded.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild bilateral high-frequency sensorineural hearing loss was found at age 12."
    explanation: Documents high-frequency sensorineural hearing loss in an index patient.
biochemical:
- name: Serum creatine kinase
  presence: NORMAL
  notes: >-
    Serum creatine kinase is normal in AIMS despite the clinical myopathy. This
    is diagnostically important: a normal CK does not exclude AIMS, and its
    normality is what separates AIMS from the dystrophinopathies and limb-girdle
    muscular dystrophies that share the weakness phenotype.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals"
    explanation: Normal serum creatine kinase in all six index patients.
genetic:
- name: ABCC9
  gene_term:
    preferred_term: ABCC9
    term:
      id: hgnc:60
      label: ABCC9
  association: Causative
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:38217872
      reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS)."
      explanation: States the recessive inheritance of the ABCC9 loss-of-function syndrome.
  features: >-
    Only loss-of-function ABCC9 alleles cause AIMS, and only in the biallelic
    state. The founding allele is the homozygous splice-site variant
    c.1320+1G>A, which causes in-frame skipping of exon 8 and a SUR2 protein
    missing 52 amino acids with no plasmalemmal KATP function. The expanded
    cohorts add homozygous nonsense and frameshift alleles predicted to trigger
    nonsense-mediated decay or severe truncation of SUR2; recombinant testing
    confirms complete loss of function for the truncations. Gain-of-function
    missense ABCC9 alleles, several clustering at Arg1154, cause Cantu syndrome
    instead and are dominant - direction of effect, not the gene, is the
    discriminator. Heterozygous ABCC9 loss-of-function carriers in AIMS families
    have no conserved clinical pathology but report an excess of intra-uterine
    fetal death; the fetal genotypes were not established, so this remains a
    reproductive observation rather than an established heterozygote phenotype.
    The founding c.1320+1G>A allele is enriched in the Finnish population -
    gnomAD heterozygote allele frequency 0.0007 (18/24,850), against 0.00004 in
    non-Finnish Europeans and absent in Asian and African populations, with no
    homozygotes recorded - which matches the probable Finnish ancestry of the
    index families and predicts that AIMS is more prevalent in that population.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
    explanation: The founding homozygous splice-site allele.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This mutation results in an in-frame deletion of exon 8, which results in non-functional KATP channels in recombinant assays."
    explanation: Functional consequence of the founding allele.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "According to gnomAD, the variant is reported at surprisingly high frequency in heterozygous state in the Finnish population with an allele frequency of 0.0007 (18/24850)."
    explanation: >-
      Population-database carrier frequency of the founding allele. Tagged
      OTHER because the datum is a gnomAD reference-population lookup reported
      by the authors, not an observation in their patient cohort.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The homozygous state is absent in gnomAD."
    explanation: >-
      No homozygotes in the reference population, consistent with the biallelic
      genotype being disease-causing rather than a tolerated variant.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All variants are predicted to result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional SUR2-dependent KATP channels."
    explanation: Defines the allele class across seven further families.
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional tests of recombinant channels confirm that disease-associated SUR2 truncations cause a complete loss-of-function."
    explanation: Confirms complete loss of function for the truncating alleles.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study."
    explanation: >-
      The carrier state and the intra-uterine fetal death excess, recorded as a
      reproductive observation because the fetal genotypes are unknown.
  - reference: PMID:22608503
    reference_title: Cantú syndrome is caused by mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "All mutations were missense, and several mutations affect Arg1154."
    explanation: >-
      Cited to fix the contrast, not as AIMS evidence: the ABCC9 alleles that
      cause Cantu syndrome are dominant missense variants clustering at Arg1154,
      an allele class disjoint from the biallelic truncating and splice alleles
      of AIMS. Marked PARTIAL because the paper is about Cantu syndrome.
treatments:
- name: Supportive and multidisciplinary care
  description: >-
    No disease-modifying therapy exists for AIMS. Management is supportive and
    targeted at the individual manifestations: developmental and educational
    support, physiotherapy and activity pacing for fatigability and weakness,
    anti-seizure medication where seizures are documented, and cardiac
    surveillance in older individuals. The most recent cohort additionally
    recommends monitoring for motor and cognitive decline in older individuals
    and flags deterioration following surgical procedures.
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
    explanation: >-
      The only management-directed statement in the AIMS literature: monitor for
      decline and be alert to peri-procedural deterioration.
- name: Avoidance of calcium channel blockers
  description: >-
    Calcium channel blockade is contraindicated on current evidence. Verapamil
    was tested in SUR2 loss-of-function mice on the hypothesis that excess
    CaV1.1-mediated calcium entry drove the myopathy; instead of rescuing the
    phenotype it caused premature death, and genetically rendering CaV1.1
    non-permeable also failed to reverse the pathology. The authors state
    explicitly that this cautions against calcium channel blockers in AIMS.
    This is a model-organism safety signal, not a human trial result, and is
    recorded here because it is the only actionable drug-safety statement in
    the AIMS literature.
  treatment_term:
    preferred_term: avoidance of calcium channel blocker therapy
    term:
      id: NCIT:C15747
      label: Supportive Care
    therapeutic_agent:
    - preferred_term: verapamil
      term:
        id: CHEBI:9948
        label: verapamil
    - preferred_term: calcium channel blocker
      term:
        id: NCIT:C333
        label: Calcium Channel Blocker
  evidence:
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "results which caution against the use of calcium channel blockers in AIMS."
    explanation: The authors' explicit safety recommendation.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "found that the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice"
    explanation: The experimental basis for the warning.
- name: Physiotherapy and activity pacing
  description: >-
    Physiotherapy and graded, paced activity address the fatigability, balance
    deficits and reduced walking distance objectively documented in the index
    cohort. No trial evidence exists in AIMS; this is standard neuromuscular
    rehabilitation applied to a documented functional deficit.
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "and walking distance in the 6-min walk test is reduced in all individuals."
    explanation: >-
      Marked PARTIAL: this documents the functional deficit that physiotherapy
      targets, but no study has tested physiotherapy in AIMS.
- name: Heart failure pharmacotherapy
  description: >-
    Standard heart-failure pharmacotherapy for the reduced systolic function
    that emerges in older individuals: an ACE inhibitor plus a beta-blocker was
    started in the index patient found to have biventricular systolic
    dysfunction with an ejection fraction of 35-40%. This is a single reported
    case managed by conventional heart-failure practice, not an AIMS-specific
    regimen, and no outcome is reported. Note the direction-of-effect contrast
    with Cantu syndrome, where ACE inhibitors appear on the GeneReviews
    agents-to-avoid list because they open KATP channels that are already
    overactive; in AIMS the channels carry no measurable current, so that
    rationale does not transfer.
  treatment_term:
    preferred_term: heart failure pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ACE inhibitor
      term:
        id: NCIT:C247
        label: ACE Inhibitor
    - preferred_term: beta-blocker
      term:
        id: NCIT:C29576
        label: Beta-Adrenergic Antagonist
  notes: >-
    Curated as reported management of a documented complication, not as a
    recommendation: the source describes what was done for one patient. The
    Cantu contrast is recorded in the description because the two diseases
    share a gene and invert the direction of effect, and a reader who
    transfers the Cantu avoid-list to AIMS would withhold appropriate therapy.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "antagonist and a beta-blocker was started."
    explanation: >-
      Records the treatment actually given. The quoted span begins at
      "antagonist" because the preceding "Treatment with an ACE-" is broken
      across a hyphenated PDF line break in the cached full text.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac systolic dysfunction is found in the two oldest patients."
    explanation: The indication - the age-related cardiac complication this therapy targets.
- name: Anti-seizure medication
  description: >-
    Anti-seizure medication for patients with documented seizures. In the index
    cohort lamotrigine was partly effective in the one patient with recurrent
    tonic and tonic-clonic episodes. No AIMS-specific anti-seizure drug choice
    has been established.
  treatment_term:
    preferred_term: Anticonvulsant Therapy
    term:
      id: NCIT:C64172
      label: Anticonvulsant Therapy
    therapeutic_agent:
    - preferred_term: lamotrigine
      term:
        id: CHEBI:6367
        label: lamotrigine
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Lamotrigine treatment was partly effective."
    explanation: >-
      The one reported anti-seizure drug outcome in AIMS: partial efficacy of
      lamotrigine in the index patient with tonic and tonic-clonic episodes.
      This is the sentence that supports the lamotrigine claim in the
      description.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness."
    explanation: >-
      Marked PARTIAL and retained only to establish that seizures recur across
      the expanded cohort and therefore need treatment; this cohort reports no
      drug-specific outcomes.
diagnosis:
- name: Molecular genetic testing of ABCC9
  description: >-
    Diagnosis rests on identifying biallelic loss-of-function ABCC9 variants,
    usually by exome or genome sequencing. Direction of effect must be
    established: a monoallelic missense ABCC9 variant points to Cantu syndrome,
    not AIMS. In the index families years of targeted neuromuscular,
    mitochondrial and metabolic testing had been normal before exome sequencing
    found the answer.
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients are homozygous for a splice-site mutation in ABCC9 (c.1320 + 1 G > A), which encodes the sulfonylurea receptor 2 (SUR2) subunit of KATP channels."
    explanation: The diagnosis in the index families was made by identifying the biallelic ABCC9 allele.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we identify nine additional subjects, from seven unrelated families, harbouring different homozygous loss-of-function variants in ABCC9 and presenting with a conserved range of clinical features."
    explanation: Confirms that homozygous loss-of-function ABCC9 genotyping is the diagnostic route.
- name: Brain MRI
  description: >-
    Brain MRI is the highest-yield imaging study. It shows cerebral white matter
    hyperintensities, often with a periventricular-leukomalacia-like or small
    vessel disease pattern, and may show corpus callosum abnormalities. Because
    the pattern mimics acquired perinatal injury, a leukomalacia-like MRI in a
    child with myopathy and no perinatal history should prompt genetic testing
    rather than closing the case.
  diagnosis_term:
    preferred_term: Magnetic Resonance Imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  evidence:
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
    explanation: The MRI pattern is the radiological hallmark of the disorder.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All have cerebral white matter hyperintensities"
    explanation: MRI white matter hyperintensity was present in every index patient.
- name: Cardiac surveillance by echocardiography
  description: >-
    Echocardiographic surveillance is indicated because systolic dysfunction was
    found only in the oldest patients of the index cohort and animal models
    develop cardiac dysfunction and ventricular enlargement. There is no
    published surveillance interval for AIMS.
  diagnosis_term:
    preferred_term: Echocardiography Test
    term:
      id: NCIT:C16525
      label: Echocardiography Test
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac systolic dysfunction is found in the two oldest patients."
    explanation: >-
      Marked PARTIAL: the age-restricted cardiac finding is the rationale for
      surveillance, but no surveillance protocol has been published for AIMS.
animal_models:
- species: Mus musculus
  genotype: Abcc9 premature-stop (SUR2-STOP) homozygous
  category: CRISPR/Cas9 premature-stop-codon mouse model of AIMS
  description: >-
    CRISPR-engineered mice carrying premature stop codons in Abcc9, lacking
    functional SUR2 and myocyte KATP channels. They show reduced exercise
    performance, fatigability and cardiac dysfunction, and were the platform on
    which the skeletal-muscle-delimited nature of the myopathy and the verapamil
    toxicity were established.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "SUR2 loss-of-function causes fatigability and cardiac dysfunction in mice, and reduced activity, cardiac dysfunction and ventricular enlargement in zebrafish."
    explanation: The mouse recapitulates the fatigability and cardiac arms of AIMS.
  - reference: PMID:37154692
    reference_title: Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We found reduced exercise performance in mouse models of AIMS harboring premature stop codons in ABCC9."
    explanation: Independent confirmation of the exercise phenotype in premature-stop-codon mice.
- species: Danio rerio
  genotype: abcc9 frameshift (SUR2-STOP) homozygous
  category: CRISPR/Cas9 loss-of-function zebrafish model of AIMS
  description: >-
    CRISPR-engineered zebrafish lacking functional Abcc9. They show reduced
    activity, cardiac dysfunction and ventricular enlargement, and an
    exaggerated motor response to the chemoconvulsant pentylenetetrazole,
    modelling both the motor and the seizure-susceptibility arms of AIMS.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "SUR2 loss-of-function causes fatigability and cardiac dysfunction in mice, and reduced activity, cardiac dysfunction and ventricular enlargement in zebrafish."
    explanation: The zebrafish recapitulates the motor and cardiac arms.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility."
    explanation: The zebrafish provides the seizure-susceptibility evidence.
mechanistic_hypotheses:
- hypothesis_group_id: aims_cerebrovascular_white_matter
  hypothesis_label: Cerebral small-vessel origin of the AIMS white matter injury and cognitive phenotype
  status: EMERGING
  description: >-
    The leading explanation for the CNS arm of AIMS is that loss of
    SUR2-containing KATP channels in brain vascular smooth muscle degrades
    cerebral autoregulation and neurovascular coupling, producing chronic
    small-vessel ischaemic white matter injury and, through it, the
    intellectual disability and pyramidal signs. The supporting facts are
    consistent but indirect: KCNJ8/ABCC9-containing channels are required for
    brain vascular smooth muscle differentiation in animals, the human imaging
    resembles small vessel disease, MR angiography is normal so the lesion is
    functional rather than macrovascular, and the same white matter change is
    seen in Cantu syndrome where the channel defect is opposite. What is
    missing is any direct measurement of cerebral blood flow or neurovascular
    coupling in an AIMS patient, and the in vivo coupling deficit was
    demonstrated in a Kcnj8 rather than an Abcc9 knockout. The original authors
    state the hypothesis with the hedge "it is conceivable".
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "it is conceivable that KATP loss of function may impact the cerebral vasculature"
    explanation: The authors' own statement of the hypothesis, framed as a conjecture.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Interestingly, white matter hyperintensities are observed in both Cantú syndrome and AIMS."
    explanation: >-
      That the same white matter change appears in the gain-of-function disease
      is what makes a shared cerebrovascular route plausible, but it also means
      the finding does not discriminate direction of effect.
  - reference: PMID:35588738
    reference_title: KCNJ8/ABCC9-containing K-ATP channel modulates brain vascular smooth muscle development and neurovascular coupling.
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: "Our results demonstrate a role for KCNJ8/ABCC9-containing K-ATP channels in the differentiation of brain VSMC, which in turn is necessary for fine-tuning of cerebral blood flow."
    explanation: >-
      Supplies the developmental cerebrovascular role, but in animal and cell
      models rather than AIMS patients.
discussions:
- discussion_id: aims_id_anxiety_model_mismatch
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Why do SUR2-null mice show no learning, memory or anxiety phenotype when
    intellectual disability and anxiety are defining features of AIMS in
    humans, and does that mean the murine model cannot be used to study the
    cognitive arm of the disease?
  attaches_to:
  - pathophysiology#Intellectual Disability and Developmental Delay
  rationale: >-
    This is a model-evidence-exists-and-is-negative situation, not an absence
    of data. The SUR2-STOP mouse was formally tested for spatial learning and
    memory in a Morris water maze and for anxiety-like behaviour in an elevated
    plus maze and was negative on both, while every human patient tested has
    intellectual disability and several have anxiety. The original authors also
    note that it is not obvious how myocyte KATP dysfunction could produce
    intellectual disability at all, and that neuronal KATP channels are
    predominantly Kir6.2/SUR1 rather than SUR2-containing. Together these make
    the cognitive arm the least secure part of the AIMS mechanism: either the
    murine assays are too coarse for a mild human intellectual disability, or
    the human cognitive phenotype is mediated by something (most plausibly the
    cerebrovascular route) that the mouse does not reproduce.
  proposed_experiments:
  - experiment_id: exp_aims_mouse_working_memory
    name: Higher-sensitivity cognitive phenotyping of SUR2-null mice
    description: >-
      Test SUR2-null mice with working-memory and fear-conditioning paradigms
      rather than the Morris water maze alone, on the hypothesis that a mild
      human intellectual disability may be below the resolution of standard
      spatial-learning assays.
  - experiment_id: exp_aims_knockin_human_allele
    name: Knock-in mouse carrying an actual human AIMS allele
    description: >-
      Generate a mouse carrying a human AIMS variant rather than an
      independently engineered premature stop, so that the model's genetic
      lesion matches the patients' and residual-protein effects are preserved.
  - experiment_id: exp_aims_human_cbf_measurement
    name: Direct cerebral blood flow and neurovascular coupling measurement in AIMS patients
    description: >-
      Measure resting cerebral perfusion and task-evoked neurovascular coupling
      (arterial spin labelling, BOLD reactivity) in genotyped AIMS patients
      against controls, to test the cerebrovascular hypothesis directly in the
      species that actually has the cognitive phenotype.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "nor in tests of spatial learning and memory, evaluated using a Morris water maze"
    explanation: The mouse spatial-learning result is formally negative.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "show any obvious anxiety-like behaviors."
    explanation: The mouse anxiety result is likewise negative, against a human phenotype that includes anxiety.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "and there are no reports of cognitive impairment in previous SUR2 mutant animal models."
    explanation: >-
      The authors state, in the same sentence, both that the route from channel
      loss to intellectual disability is not obvious and that no earlier SUR2
      mutant animal model showed cognitive impairment.
- discussion_id: aims_natural_history_gap
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What is the natural history of AIMS across the lifespan, and at what
    interval should cardiac and cerebral imaging surveillance be performed?
  rationale: >-
    Around twenty patients have ever been reported, in three cross-sectional
    series with no prospective follow-up. Two features are known to be
    age-dependent - systolic dysfunction, present only in the oldest patients
    of the index cohort, and cognitive and motor decline reported in a
    sexagenarian - but neither has a defined onset distribution, so no
    surveillance interval can be evidence-based. No registry, survival
    analysis, or quality-of-life instrument has ever been applied.
  proposed_experiments:
  - experiment_id: exp_aims_prospective_registry
    name: International AIMS natural-history registry
    description: >-
      Enrol genotyped AIMS patients with standardised serial cardiac imaging,
      brain MRI, neuropsychological testing and functional measures, to
      establish onset distributions for the age-dependent complications and to
      set surveillance intervals.
  evidence:
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These latest findings also highlight neonatal presentation of disease, deterioration following surgical procedures, and the potential for motor and cognitive decline, which should be monitored in older individuals."
    explanation: >-
      The most recent series calls for monitoring of older individuals without
      being able to specify what or how often, which is the gap.
differential_diagnoses:
- name: Cantu syndrome
  description: >-
    The other ABCC9 disease and the single most important entity to separate
    from AIMS. Cantu syndrome is caused by GAIN-of-function ABCC9 variants and
    is autosomal dominant, whereas AIMS is caused by biallelic LOSS-of-function
    variants and is autosomal recessive. The two are therefore allelic in the
    trivial sense of sharing a gene but are mechanistically opposite, and the
    Cantu literature is far larger, so a paper that says only "ABCC9 variant"
    without stating direction of effect cannot be used for either disease.
    Clinically Cantu is dominated by congenital hypertrichosis, coarse facial
    features, cardiomegaly with enhanced systolic function and
    osteochondrodysplasia, with intellect typically normal - none of which
    describes AIMS. Conversely no AIMS patient has had hypertrichosis, and AIMS
    cardiac disease is reduced rather than enhanced systolic function.
  distinguishing_features:
  - Gain-of-function ABCC9 variants, not loss-of-function
  - Autosomal dominant with de novo missense alleles clustering at Arg1154, not autosomal recessive truncating or splice alleles
  - Congenital hypertrichosis is characteristic; no AIMS patient has had hypertrichosis
  - Coarse facial features and osteochondrodysplasia, versus the distinct AIMS facies with prominent supraorbital ridges
  - Cardiomegaly with enhanced systolic function and patent ductus arteriosus, versus reduced systolic function in older AIMS patients
  - Intellect typically normal despite common developmental delay, versus intellectual disability in essentially all AIMS patients
  - Cerebral white matter hyperintensity resembling periventricular leukomalacia is an AIMS hallmark, not a Cantu feature
  - The Cantu GeneReviews "agents to avoid" list (minoxidil, diazoxide, ACE inhibitors) is specific to KATP overactivity and must not be transferred to AIMS
  disease_term:
    preferred_term: Cantu syndrome
    term:
      id: MONDO:0009406
      label: hypertrichotic osteochondrodysplasia Cantu type
  notes: >-
    MONDO:0009406 is the canonical MONDO term for Cantu syndrome, carries
    "Cantu syndrome" as an exact synonym, is bound to the same gene
    (RO:0004003 HGNC:60 ABCC9), is not obsolete, and is not an ancestor of this
    entry's anchor MONDO:0859224 - the anchor's only ontological ancestors are
    MONDO:0003847 (hereditary disease) and its superclasses. There is no Cantu
    syndrome entry in the dismech KB to cross-reference, so this differential is
    the only place the contrast is recorded.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The phenotype differs from Cantú syndrome, which is caused by gain-of-function ABCC9 mutations, reflecting the opposing consequences of KATP loss- versus gain-of-function."
    explanation: States the direction-of-effect discriminator directly.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, Cantú syndrome and AIMS, arising from opposing molecular mechanisms, are both dysmorphologically and mechanistically distinct."
    explanation: The AIMS authors' own conclusion that the two entities are distinct on both counts.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "None of our patients have hypertrichosis, unlike Cantú syndrome patients."
    explanation: The single most discriminating clinical sign between the two ABCC9 diseases.
  - reference: PMID:25275207
    reference_title: Cantú Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cantú syndrome is characterized by congenital hypertrichosis; distinctive coarse facial features (including broad nasal bridge, wide mouth with thick vermilion of the upper and lower lips, and macroglossia); enlarged heart with enhanced systolic function, as well as pericardial effusion and, in many, a large patent ductus arteriosus (PDA) requiring repair; and musculoskeletal abnormalities (thickening of the calvaria, broad ribs, scoliosis, flaring of the metaphyses, and low muscle tone)."
    explanation: The GeneReviews Clinical Characteristics baseline for Cantu syndrome, used here only as the differential's reference phenotype.
  - reference: PMID:25275207
    reference_title: Cantú Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Developmental delays are common, but intellect is typically normal"
    explanation: >-
      The cognitive discriminator: intellect is typically normal in Cantu
      syndrome, whereas intellectual disability is present in essentially all
      AIMS patients.
  - reference: PMID:25275207
    reference_title: Cantú Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of Cantú syndrome can be established in a proband with characteristic clinical and imaging findings and/or a heterozygous gain-of-function pathogenic variant in ABCC9 or KCNJ8 identified by molecular genetic testing."
    explanation: >-
      The molecular discriminator: heterozygous gain-of-function versus the
      biallelic loss-of-function required for AIMS.
- name: ABCC8-related congenital hyperinsulinism
  description: >-
    ABCC8 encodes SUR1, the pancreatic sulfonylurea receptor, and differs from
    ABCC9 by one character in the gene symbol and one paralogue in the same KATP
    family. Biallelic ABCC8 loss of function is the commonest genetic cause of
    congenital hyperinsulinism, which is a neonatal hypoglycaemia disorder with
    no myopathy and no primary white matter disease. The mechanistic parallel is
    real - both are recessive loss-of-function sulfonylurea-receptor
    channelopathies - which is exactly why the literature is easy to
    misattribute, and why every mechanistic sentence in this entry was checked
    for which receptor it names.
  distinguishing_features:
  - Caused by ABCC8 (SUR1), not ABCC9 (SUR2)
  - Presents with severe persistent neonatal hyperinsulinaemic hypoglycaemia, which is not a feature of AIMS
  - Tissue of action is the pancreatic beta cell, not skeletal muscle, brain vasculature or myocardium
  - Focal and diffuse histological forms with 18F-DOPA PET localisation, a workup with no AIMS counterpart
  - Any brain injury is secondary to hypoglycaemia, whereas AIMS white matter disease is primary and present without hypoglycaemia
  disease_term:
    preferred_term: autosomal recessive hyperinsulinism due to SUR1 deficiency
    term:
      id: MONDO:0019333
      label: autosomal recessive hyperinsulinism due to SUR1 deficiency
  notes: >-
    MONDO:0019333 is bound rather than the broader congenital hyperinsulinism
    term because it names the SUR1 (ABCC8) recessive form specifically, which is
    the precise mirror-image entity. It is not obsolete and is not an ancestor
    of MONDO:0859224.
  evidence:
  - reference: PMID:38791571
    reference_title: "Congenital Hyperinsulinism Caused by Mutations in ABCC8 Gene Associated with Early-Onset Neonatal Hypoglycemia: Genetic Heterogeneity Correlated with Phenotypic Variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital hyperinsulinism (CHI) is a rare disorder of glucose metabolism and is the most common cause of severe and persistent hypoglycemia (hyperinsulinemic hypoglycemia, HH) in the neonatal period and childhood."
    explanation: Defines the clinical entity, which is metabolic and neonatal rather than neuromuscular.
  - reference: PMID:38791571
    reference_title: "Congenital Hyperinsulinism Caused by Mutations in ABCC8 Gene Associated with Early-Onset Neonatal Hypoglycemia: Genetic Heterogeneity Correlated with Phenotypic Variability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most cases are caused by mutations in the ABCC8 and KCNJ11 genes that encode the ATP-sensitive potassium channel (KATP)."
    explanation: Names ABCC8, not ABCC9, as the causative subunit gene.
- name: DEND syndrome
  description: >-
    Developmental delay, epilepsy and neonatal diabetes - the KATP
    gain-of-function neurodevelopmental syndrome caused by activating variants
    in KCNJ11 or ABCC8. It is the sharpest phenocopy trap in the KATP family for
    the neurological arm of AIMS, because developmental delay plus epilepsy is
    exactly the AIMS presentation, and the gene name ABCC8 is one character from
    ABCC9. It is separated by the obligatory neonatal diabetes, by the opposite
    direction of channel effect, by dominant rather than recessive inheritance,
    and by dramatic responsiveness to oral sulfonylureas, which have no
    established role in AIMS.
  distinguishing_features:
  - Caused by gain-of-function KCNJ11 or ABCC8 variants, not loss-of-function ABCC9
  - Neonatal diabetes mellitus within the first six months of life is obligatory and has never been reported in AIMS
  - KATP overactivity, the opposite direction of effect to AIMS
  - Typically dominant (often de novo), not autosomal recessive
  - Responds to oral sulfonylureas, which close KATP channels and have no rationale in a channel-null disease
  - Myopathy with fatigability and painful spasms is an AIMS feature, not a DEND feature
  disease_term:
    preferred_term: DEND syndrome
    term:
      id: MONDO:0019207
      label: DEND syndrome
  notes: >-
    MONDO:0019207 is bound rather than the gene-specific children DEND1
    (MONDO:0800375) or DEND2 (MONDO:0800376) because neither child carries a
    gene relationship in MONDO, so binding one of them would assert a gene
    attribution the ontology does not make. MONDO:0019207 is not obsolete and is
    not an ancestor of MONDO:0859224.
  evidence:
  - reference: PMID:20301620
    reference_title: Permanent Neonatal Diabetes Mellitus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Permanent neonatal diabetes mellitus (PNDM) is characterized by the onset of hyperglycemia within the first six months of life (mean age: 7 weeks; range: birth to age 26 weeks)."
    explanation: The neonatal diabetes that defines the DEND spectrum and is absent from AIMS.
  - reference: PMID:20301620
    reference_title: Permanent Neonatal Diabetes Mellitus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Targeted therapy: Oral sulfonylureas after initial management with insulin in those with ABCC8- or KCNJ11-related PNDM."
    explanation: >-
      Names ABCC8 and KCNJ11 as the KATP genes of this entity and gives the
      sulfonylurea response that has no counterpart in AIMS.
- name: Heterozygous ABCC9 loss-of-function cardiac phenotypes
  description: >-
    A cluster of monoallelic ABCC9 loss-of-function associations - dilated
    cardiomyopathy, Brugada and early repolarization syndromes, and idiopathic
    ventricular fibrillation - reported in adults with no intellectual
    disability, no myopathy and no white matter disease. These share both the
    gene and the direction of effect with AIMS, which makes them the subtlest
    confusion in the ABCC9 literature: a paper titled "loss-of-function ABCC9
    variant" may be describing a heterozygous adult arrhythmia case, not AIMS.
    Zygosity is the discriminator. AIMS carriers in the published families have
    no conserved clinical pathology.
  distinguishing_features:
  - Monoallelic (heterozygous) ABCC9 loss of function, versus the biallelic state required for AIMS
  - Isolated cardiac presentation in adults - arrhythmia or cardiomyopathy - without intellectual disability, myopathy or white matter disease
  - AIMS heterozygous parents show no conserved clinical pathology, so these associations are not simply the AIMS carrier state
  - Some of the reported alleles sit in the SUR2A-specific exon, a cardiac-restricted isoform region
  notes: >-
    Deliberately left unbound. There is no single MONDO term for "heterozygous
    ABCC9 loss-of-function cardiac phenotype": the reported associations span
    dilated cardiomyopathy, Brugada syndrome, early repolarization syndrome and
    idiopathic ventricular fibrillation, and binding any one of those general
    disease terms would misrepresent the group and would also bind a term whose
    gene attribution is not ABCC9-specific. The dismech entries
    Dilated_Cardiomyopathy and Familial_Atrial_Fibrillation already carry the
    ABCC9 heterozygous-cardiac material in their own gene sections; this
    differential exists to keep that literature out of the AIMS phenotype set,
    not to duplicate it.
  evidence:
  - reference: PMID:35495129
    reference_title: "Case Report: Loss-of-Function ABCC9 Genetic Variant Associated With Ventricular Fibrillation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The loss-of-function mutations in the ABCC9 gene were associated with the Brugada syndrome, early repolarization syndrome, and dilated cardiomyopathy."
    explanation: Enumerates the cardiac phenotypes attributed to ABCC9 loss of function outside the AIMS recessive syndrome.
  - reference: PMID:35495129
    reference_title: "Case Report: Loss-of-Function ABCC9 Genetic Variant Associated With Ventricular Fibrillation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The female proband presented with several episodes of ventricular fibrillation and hypokalemia upon emotional stress."
    explanation: An isolated adult cardiac presentation with no neurodevelopmental or myopathic features.
  - reference: PMID:38217872
    reference_title: Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study."
    explanation: Establishes that the AIMS carrier state is not itself a recognisable clinical phenotype.
- name: Periventricular leukomalacia of perinatal hypoxic-ischaemic origin
  description: >-
    Acquired periventricular leukomalacia from perinatal hypoxic-ischaemic
    injury is the standard explanation for the MRI pattern that AIMS produces,
    and is the reason AIMS is under-diagnosed. The most recent AIMS cohort
    describes the white matter abnormalities explicitly as resembling
    periventricular leukomalacia. A child with spastic motor impairment,
    developmental delay and a leukomalacia-like MRI is routinely labelled with
    cerebral palsy of perinatal origin and never sequenced. In the index AIMS
    families pregnancy and birth were uneventful, and one patient was instead
    investigated for tuberous sclerosis on the basis of the MRI.
  distinguishing_features:
  - Acquired perinatal insult, typically with a documented history of prematurity, hypoxia-ischaemia or perinatal complications - absent in the AIMS index families, where pregnancy and birth were uneventful
  - Non-progressive by definition, whereas AIMS lesions increased significantly on serial imaging in at least one patient
  - No accompanying fatigable myopathy with painful post-exercise spasms
  - No familial recurrence pattern; AIMS is recessive with affected siblings
  - No late systolic cardiac dysfunction
  notes: >-
    Deliberately left unbound. The confusable entity here is an acquired
    perinatal aetiology rather than a nosological disease with a defensible
    MONDO term: HP:0006970 (Periventricular leukomalacia) is the appropriate
    ontology binding and is already used above as an AIMS phenotype, and binding
    a broad cerebral palsy MONDO term would assert a specific alternative
    diagnosis that the AIMS literature does not name. The distinguishing
    features are recorded instead.
  evidence:
  - reference: PMID:42290677
    reference_title: "Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These new cases further demonstrate the prominence of white matter abnormalities resembling periventricular leukomalacia or small vessel disease as a key hallmark of the disorder, alongside developmental delay, intellectual impairment, seizures, and fatigability."
    explanation: >-
      The AIMS authors themselves describe the imaging as resembling
      periventricular leukomalacia, which is what makes the acquired form the
      operative differential.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All have cerebral white matter hyperintensities"
    explanation: >-
      Cerebral white matter change in every patient of a cohort whose pregnancies
      and births were uneventful is precisely the finding otherwise attributed to
      perinatal injury.
- name: Tuberous sclerosis
  description: >-
    A documented misdiagnosis in AIMS, not a hypothetical one. One index
    patient was worked up for tuberous sclerosis on the basis of periventricular
    white matter change together with depigmented skin patches, and the
    diagnosis was later abandoned. The combination of white matter lesions,
    developmental delay, seizures and hypopigmented macules is genuinely
    TSC-like on a first pass.
  distinguishing_features:
  - Caused by TSC1 or TSC2, not ABCC9
  - Autosomal dominant with frequent de novo variants, not autosomal recessive
  - Cortical tubers, subependymal nodules and subependymal giant cell astrocytoma on MRI, a different lesion pattern from confluent periventricular white matter change
  - Renal angiomyolipoma, cardiac rhabdomyoma, facial angiofibroma and retinal hamartoma have no AIMS counterpart
  - Fatigable myopathy with painful exercise-induced spasms is an AIMS feature, not a TSC feature
  disease_term:
    preferred_term: tuberous sclerosis
    term:
      id: MONDO:0001734
      label: tuberous sclerosis
  notes: >-
    MONDO:0001734 is the current non-obsolete term (MONDO:0019341 "tuberous
    sclerosis complex" is obsolete and must not be used). It is not an ancestor
    of MONDO:0859224.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showed periventricular white matter changes, and a diagnosis of tuberous sclerosis was considered"
    explanation: >-
      Records tuberous sclerosis as an actual competing diagnosis entertained on
      the childhood brain MRI of an AIMS patient.
- name: Mitochondrial disease
  description: >-
    Primary mitochondrial disease is the standard alternative for a child with
    myopathy, exercise intolerance, cerebral white matter change and a lactate
    rise during illness - the exact AIMS phenotype. The index families had
    mitochondrial DNA sequence and deletion screening, plus screening for
    inborn errors of metabolism, performed and normal before exome sequencing
    found ABCC9, and the one AIMS muscle biopsy performed showed mitochondrial
    aggregation, which reinforces the confusion rather than resolving it.
  distinguishing_features:
  - Caused by biallelic nuclear ABCC9 variants, not by mtDNA or nuclear-encoded mitochondrial gene defects
  - Normal mitochondrial DNA sequencing and deletion screening in the AIMS index families
  - Baseline serum lactate, creatine kinase, nerve conduction and electromyography are normal in AIMS; lactate rises only during acute decompensation
  - Strictly autosomal recessive, without the maternal transmission or heteroplasmy-dependent variability of mtDNA disease
  - Non-specific muscle biopsy findings, not ragged-red fibres or respiratory-chain enzyme deficiency
  disease_term:
    preferred_term: mitochondrial disease
    term:
      id: MONDO:0044970
      label: mitochondrial disease
  notes: >-
    Bound at the broad grouping level deliberately. The competing clinical
    consideration in the published AIMS families was "mitochondrial disease" as
    a category rather than any one named mitochondrial disorder, and binding a
    specific entity would assert a differential the literature does not name.
    MONDO:0044970 is not obsolete and is not an ancestor of MONDO:0859224.
  evidence:
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals"
    explanation: >-
      The normal baseline lactate and creatine kinase are the practical
      discriminators against a primary mitochondrial myopathy.
  - reference: PMID:31575858
    reference_title: ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "described as similar to leucodystrophy"
    explanation: >-
      The imaging in one index patient was read as leukodystrophy-like, which
      is the same white-matter route by which mitochondrial and leukodystrophic
      diagnoses are reached before AIMS is considered.
references:
- reference: PMID:25275207
  title: Cantú Syndrome.
  tags:
  - GeneReviews
- reference: PMID:20301620
  title: Permanent Neonatal Diabetes Mellitus.
  tags:
  - GeneReviews
📚

References & Deep Research

References

2
PMID:25275207
Cantú Syndrome.
No top-level findings curated for this source.
PMID:20301620
Permanent Neonatal Diabetes Mellitus.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
1. Disease Information
claude-haiku-4-5-20251001, claude-opus-5[1m] 13 citations 2026-08-01T07:25:50.754500

1. Disease Information

Overview

ABCC9-related Intellectual disability Myopathy Syndrome (AIMS) is an ultra-rare autosomal recessive KATP channelopathy caused by biallelic loss-of-function (LoF) variants in ABCC9, which encodes the sulfonylurea receptor 2 (SUR2) regulatory subunit of ATP-sensitive potassium channels. The core triad — established by the original 2019 description and confirmed across two subsequent cohort expansions — is (i) developmental delay with intellectual disability, (ii) muscle weakness and fatigability, and (iii) cerebral white matter abnormality resembling periventricular leukomalacia or small-vessel disease. Variable additional features include seizures, spasticity, microcephaly, corpus callosum abnormality, short stature, a shared facial gestalt, sensorineural hearing loss, and age-dependent cardiac systolic dysfunction.

AIMS is the mechanistic mirror image of Cantú syndrome: the same gene, opposite channel consequence. This LoF-vs-GoF duality is the single most important framing fact for the entry.

"We term this channelopathy resulting from loss-of-function of SUR2-containing KATP channels ABCC9-related Intellectual disability Myopathy Syndrome (AIMS). The phenotype differs from Cantú syndrome, which is caused by gain-of-function ABCC9 mutations, reflecting the opposing consequences of KATP loss- versus gain-of-function." — Smeland et al. 2019, PMID:31575858 [ABSTRACT-VERIFIED]

Key identifiers

Resource Identifier Notes
MONDO MONDO:0859224 Label verified via OLS4: "intellectual disability and myopathy syndrome". Equivalent-to xrefs: OMIM:619719, DOID:0070600, MedGen 1808193, UMLS C5676904. The draft entry's disease_term is correct as written.
OMIM (phenotype) #619719 INTELLECTUAL DISABILITY AND MYOPATHY SYNDROME; IDMYS
OMIM (gene) 601439 ABCC9 / SUR2
Disease Ontology DOID:0070600
UMLS / MedGen C5676904 / 1808193
ORPHA Not found No Orphanet code for AIMS/IDMYS was identified. Consequently no Orphanet prevalence class is citable, and no ORPHA: structured-source reference can be used for this entry.
ICD-10 / ICD-11 No specific code Would be coded by manifestation (e.g. myopathy + intellectual disability) rather than as a named entity.
MeSH No specific descriptor Indexed under Channelopathies, Neurodevelopmental Disorders, Muscular Diseases, Sulfonylurea Receptors (per PMID:31575858 MeSH set).

Synonyms

  • AIMS (the field-standard acronym; used in all three primary papers)
  • ABCC9-related Intellectual disability Myopathy Syndrome
  • Intellectual disability and myopathy syndrome (IDMYS — the OMIM-preferred name)
  • SUR2 loss-of-function channelopathy

The draft's synonym list is accurate; consider adding IDMYS explicitly, since that is the OMIM label a curator or user is most likely to search.

Information provenance

All knowledge is aggregated case-level literature, not EHR- or registry-derived. The entire published world experience is ~20 individuals from ~13 families across three papers. There is no natural-history cohort, no registry, no patient-reported-outcome dataset, and no ICEES/COHD-style EHR signal available for this disease. Every frequency figure below is a small-n case-series proportion and should be curated with that caveat.

2. Etiology

Primary causal factor

Biallelic (homozygous or compound heterozygous) loss-of-function variants in ABCC9 → non-functional SUR2-containing KATP channels. This is a monogenic, fully genetic etiology; no infectious, toxic, or environmental cause contributes.

"Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS)." — Efthymiou et al. 2024, PMID:38217872 [ABSTRACT-VERIFIED]

Genetic risk factors

  • Causal: biallelic ABCC9 LoF (see §4 for the full allelic series).
  • Consanguinity is a major risk factor for occurrence. Of the 2024 cohort's seven families, consanguinity was documented in the Pakistani, two Egyptian, British-Pakistani, and Saudi Arabian families [FULL-TEXT — RE-VERIFY]; the 2026 cohort included a first-cousin union [FULL-TEXT — RE-VERIFY].
  • Founder-like enrichment: the Norwegian c.1320+1G>A allele is disproportionately frequent in Finns (see §9).
  • Modifier genes: none identified. The 2019 authors explicitly kept the door open — "Notably, gene interactions with the homozygous ABCC9 c.1320+1G>A variant cannot be excluded as participating in the syndrome." (PMID:31575858, full-text body) [ABSTRACT-VERIFIED — full-text body line] This is a legitimate KNOWLEDGE_GAP discussion item.

Environmental risk factors

None are causal. However, AIMS has a genuinely important gene–environment / gene–exposure interaction at the level of decompensation triggers, which is arguably the most clinically actionable content in this entry:

Trigger Consequence Source
Physical exertion / metabolic stress Fatigability, painful muscle spasms, failure to recover from fatigue; in SUR2-KO mice histological muscle abnormality appears only with chronic exercise PMID:31575858; PMID:37154692
Surgery / general anesthesia (propofol) Post-operative cardiogenic shock, lactic acidosis, refractory seizures in a neonate, after each of two procedures PMID:42290677 [FULL-TEXT — RE-VERIFY]
Calcium-channel-blocking drugs (verapamil) Premature death in AIMS mouse models PMID:37154692 [ABSTRACT-VERIFIED]
Phenytoin / fosphenytoin Severe bradycardia and hypotension in an AIMS patient PMID:42290677 [FULL-TEXT — RE-VERIFY]
Febrile / catabolic illness One patient had a coma-and-tetraplegia episode preceded by fever and vomiting, with metabolic acidosis (lactate 6), CK 738, and transient multifocal grey+white matter lesions PMID:31575858 full text

Protective factors

No genetic or environmental protective factors are described. Heterozygosity is effectively protective/neutral for AIMS: parents are clinically unaffected carriers, and functional assays show no dominant-negative effect (§4, §6).

3. Phenotypes

Frequencies from the pooled published cohorts

The 2024 Brain paper provides the only published pooled frequency table (their cohort n=9, plus the 2019 cohort n=6, total n=15) [FULL-TEXT — RE-VERIFY all counts before curating frequency:]:

Phenotype Suggested HPO term 2024 cohort (n=9) Pooled (n=15) Suggested FrequencyEnum
Developmental delay HP:0001263 Global developmental delay 9 (100%) 15 (100%) OBLIGATE/VERY_FREQUENT
Intellectual disability HP:0001249 Intellectual disability 8 (89%) 14 (93%) VERY_FREQUENT
Fatigability HP:0012378 Fatigue 7 (78%) 13 (87%) VERY_FREQUENT
White matter signal alteration HP:0030891 Periventricular white matter hyperintensities 5 (56%) 11 (73%) FREQUENT
Spasticity HP:0001257 Spasticity 6 (67%) n/a FREQUENT
Microcephaly HP:0000252 Microcephaly 6 (67%) 8 (53%) FREQUENT
Corpus callosum abnormality HP:0002079 Hypoplasia of the corpus callosum 6 (67%) 6 (40%) FREQUENT
Seizures HP:0001250 Seizure 4 (44%) 5 (33%) FREQUENT/OCCASIONAL
Dysmorphic features (see facial cluster below) 4 (44%) 10 (67%) FREQUENT
Cardiac abnormality HP:0025169 Left ventricular systolic dysfunction 1 (11%) 3 (20%) OCCASIONAL

Curation caution. Note the discordance between cohorts — corpus callosum abnormality was 0/6 in 2019 but 6/9 in 2024, and dysmorphism was 6/6 in 2019 but 4/9 in 2024. This is ascertainment/expertise variation across small series, not a real biological gradient. Per docs/frequency-evidence-guidelines.md, the safest course for several of these rows is to omit frequency: and record the counts in notes: instead.

Officially curated HPO annotations (OMIM:619719)

The HPO project has annotated IDMYS from the 2019 cohort only. This is the authoritative, ready-to-use term set (IDs and labels retrieved from the HPO API and exact as given):

HPO ID Term (exact label) Frequency
HP:0001252 Hypotonia 6/6
HP:0012378 Fatigue 6/6
HP:0002172 Postural instability 6/6
HP:0000965 Cutis marmorata 6/6
HP:0000219 Thin upper lip vermilion 6/6
HP:0000336 Prominent supraorbital ridges 6/6
HP:0012368 Flat face 5/6
HP:0003593 Infantile onset 5/6
HP:0002395 Lower limb hyperreflexia 4/6
HP:0000601 Hypotelorism 4/6
HP:0001771 Achilles tendon contracture 4/6
HP:0000689 Dental malocclusion 4/6
HP:0011081 Incisor macrodontia 4/6
HP:0000455 Broad nasal tip 4/6
HP:0002938 Lumbar hyperlordosis 4/6
HP:0000739 Anxiety 4/4
HP:0030891 Periventricular white matter hyperintensities 3/6
HP:0010535 Sleep apnea 2/2
HP:0025169 Left ventricular systolic dysfunction 2/6
HP:0005590 Spotty hypopigmentation 2/6
HP:0500093 Food allergy 2/6
HP:0001047 Atopic dermatitis 2/6
HP:0001566 Widely-spaced maxillary central incisors 2/6
HP:0001377 Limited elbow extension 1/6
HP:0001374 Congenital hip dislocation 1/6 (congenital onset)
HP:0033204 Triceps hyperreflexia 1/6
HP:0000957 Cafe-au-lait spot 1/6
HP:0000639 Nystagmus 1/6
HP:0032012 Heterotropia 1/6
HP:0020045 Esodeviation 1/6
HP:0000565 Esotropia 1/6
HP:0002650 Scoliosis 1/6
HP:0000007 Autosomal recessive inheritance —
HP:0003577 Congenital onset 1/6

Additional terms needed for features from the 2024/2026 expansions

All verified during this research:

Feature HPO term
Intellectual disability HP:0001249 Intellectual disability
Global developmental delay HP:0001263 Global developmental delay
Seizure HP:0001250 Seizure
Spasticity HP:0001257 Spasticity
Microcephaly HP:0000252 Microcephaly
Short stature HP:0004322 Short stature
Corpus callosum hypoplasia HP:0002079 Hypoplasia of the corpus callosum
Periventricular leukomalacia (imaging pattern) HP:0006970 Periventricular leukomalacia
Leukoencephalopathy HP:0002352 Leukoencephalopathy
Abnormal cerebral white matter HP:0002500 Abnormal cerebral white matter morphology
Reduced periventricular WM volume HP:0034295 Reduced cerebral white matter volume
Cerebral WM hyperintensity on MRI HP:0030890 Hyperintensity of cerebral white matter on MRI
Generalized muscle weakness HP:0003324 Generalized muscle weakness
Exercise-induced myalgia HP:0003738 Exercise-induced myalgia
Exercise-induced muscle cramps HP:0003710 Exercise-induced muscle cramps
Exercise-induced muscle fatigue HP:0009020 Exercise-induced muscle fatigue
Dementia / cognitive decline (sexagenarian case) HP:0000726 Dementia
Dilated cardiomyopathy HP:0001644 Dilated cardiomyopathy
Sensorineural hearing impairment HP:0000407 Sensorineural hearing impairment
Elevated CK (crisis only) HP:0003236 Elevated circulating creatine kinase concentration
Ileal atresia (neonatal case) HP:0011102 Ileal atresia
Ventricular septal defect (neonatal case) HP:0001629 Ventricular septal defect
Stillbirth / IUFD (het parents) HP:0003826 Stillbirth; HP:0034241 Prenatal death

Ontology gap worth flagging: HPO has no single term capturing "periventricular-leukomalacia-like white matter change of vascular origin in a genetic channelopathy". The pragmatic composition is HP:0006970 + HP:0030891, with preferred_term carrying the nuance (permitted by the repo's preferred_term vs term.label rule).

Phenotype characteristics

  • Onset: infantile in 5/6 of the original cohort (HP:0003593), congenital in 1/6 (HP:0003577). The 2026 series extends onset to the neonatal period (seizures on day 3 of life). One 2024-cohort participant had developmental regression at 15 months [FULL-TEXT — RE-VERIFY].
  • Severity: intellectual disability is mild in most (5/6 mild, 1/6 moderate in the 2019 cohort) but "of variable severity" across the expanded cohort. Muscle weakness is mild-to-moderate (MRC grade 4 to 4+ in affected groups); one 2019 patient had entirely normal strength despite reporting exhaustibility.
  • Progression: classically static/non-progressive in childhood, but two progressive dimensions are now documented: (a) white matter lesions accumulate — "Lesions have increased significantly since the first investigation" in the oldest 2019 patient (PMID:31575858 full text), and (b) adult motor and cognitive decline from the fifth decade in the 2026 sexagenarian.
  • Episodic overlay: discrete decompensations (fever/vomiting-triggered coma episode; post-operative cardiogenic shock) punctuate an otherwise stable course. temporality: RECURRENT / EPISODIC is appropriate for the spasm and decompensation phenotypes.
  • Quality-of-life impact: no formal instrument (EQ-5D, SF-36, PROMIS) has ever been applied in AIMS — a genuine data gap. Functional proxies from the 2019 cohort are quantitative and citable: all six had reduced 6-minute walk distance (e.g. 512.5 m vs 765 m reference) and moderate-to-severe balance deficits on the miniBESTest (scores 14–21 / 28). Supported-living need is documented: patients live in own homes or sheltered housing "with daily help and supervision," and one attends a sheltered work program but "is easily exhausted, and needs rest during the day."

4. Genetic/Molecular Information

Causal gene

Field Value
Symbol ABCC9
HGNC HGNC:60 (verified via genenames.org REST — the draft's hgnc:60 is correct)
Approved name ATP binding cassette subfamily C member 9
Locus 12p12.1
Ensembl ENSG00000069431
NCBI Gene 10060
UniProt O60706 (ABCC9_HUMAN, SUR2)
Aliases SUR2, CMD1O
OMIM gene 601439

Gene architecture matters mechanistically: ABCC9 has ≥39 exons and yields two major, tissue-divergent splice isoforms differing only in the terminal exon — SUR2A (striated muscle; pairs with Kir6.2/KCNJ11) and SUR2B (smooth muscle; pairs with Kir6.1/KCNJ8). Any variant proximal to the terminal exon — as all AIMS variants are — hits both isoforms, which is precisely why AIMS is multisystem while the exon-38-specific heterozygous DCM variants are cardiac/skeletal-limited.

Pathogenic variant spectrum (complete published allelic series)

Cohort 1 — Smeland et al. 2019 (PMID:31575858), 6 patients / 2 Norwegian families:

Variant Protein Mechanism
c.1320+1G>A (NM_020297.2; NC_000012.11:g.22063090C>T) p.(Ala389_Gln440del) via r.1165_1320del Splice-donor loss of exon 8 → in-frame 52-aa deletion in TMD1

Cohort 2 — Efthymiou et al. 2024 (PMID:38217872), 9 patients / 7 families + 1 IUFD family [FULL-TEXT — RE-VERIFY]:

Family Variant Protein Origin Consanguineous
F1 c.1320+1G>A p.(Ala389_Gln440del) Norwegian No
F2 c.2812C>T p.(Arg938Ter) Pakistani Yes
F3 c.4212-1G>T p.(Phe1405SerfsTer8) Egyptian Yes
F4 c.1858C>T p.(Arg620Ter) Dutch No
F5 c.1234C>T p.(Gln412Ter) Egyptian Yes
F6 c.284+1G>A p.(Phe49GlyfsTer13) Norwegian No
F7 c.3747del p.(Leu1250TrpfsTer9) British Pakistani Yes
F8 (IUFD only) c.2140_2141del p.(Leu714SerfsTer7) Saudi Arabian Yes

Cohort 3 — Nagaraj et al. 2026 (PMID:42290677), 5 patients [FULL-TEXT — RE-VERIFY]:

Participant Variant Protein Note
P1 c.2881del (hom) p.(Glu961LysfsTer10) Sexagenarian with dementia
P2 c.3269delG (hom) p.(Gly1090AspfsTer2)
P3 c.3269delG (hom) p.(Gly1090AspfsTer2) Unrelated to P2 — recurrent allele
P4 73,292 bp deletion, exons 13–33 (hom) p.(Ser601ArgfsTer9) Only structural/CNV variant reported
P5 c.4018C>T / c.1828_1829del (comp het) p.(Gln1340Ter) / p.(Leu610GlufsTer2) First compound heterozygote; neonatal crisis

Spectrum summary for curation: - Variant classes: nonsense (4), frameshift (5+), canonical splice-site (3), whole-exon in-frame deletion (1), multi-exon genomic deletion (1). No pathogenic missense variant has ever been reported for AIMS — a sharp genotype contrast with Cantú syndrome, which is overwhelmingly missense GoF. - Molecular consequence: NMD of the transcript and/or drastic SUR2 truncation. > "All variants are predicted to lead to nonsense mediated decay of ABCC9 transcripts and/or drastic truncation of SUR2." — PMID:42290677 [ABSTRACT-VERIFIED] - Origin: exclusively germline. No somatic ABCC9 involvement in AIMS (somatic ABCC9 appears in COSMIC only as incidental cancer variation, unrelated to this disease). - Functional consequence: complete loss of function, not dominant-negative — see §6. The correct dismech modifier on the ABCC9 gene descriptor is DECREASED, and the relevant GENO framing is biallelic LoF. - ACMG/AMP: these are PVS1-anchored (null variant in a gene where LoF is the established mechanism) plus PM3 (recessive, in trans), PS3 (functional assays), PP1 (segregation) — expected Pathogenic. Note that ClinGen has published no variant pathogenicity assertions for ABCC9 (0 records), so no CGGV:/ClinVar expert classification is citable for AIMS variants.

Allele frequencies

  • c.1320+1G>A: Finnish gnomAD AF 0.0007 (18/24,850); non-Finnish European 5/128,232 (AF 0.00004); absent in Asian and African populations; homozygous state absent from gnomAD (PMID:31575858 full text). Earlier ExAC counts: Finnish 3/6,586; non-Finnish European 4/66,386.
  • Across the 2024 allelic series: "All the reported ABCC9 variants are…rare in the general population (max. allele frequency 0.000088) and absent in homozygous state in the gnomAD database." [FULL-TEXT — RE-VERIFY]
  • Not retrieved: gnomAD gene-level constraint metrics for ABCC9 (pLI / LOEUF / o-e LoF). The gnomAD browser is client-rendered and could not be scraped in this session. If constraint is wanted for the entry, pull it from the gnomAD API or a local download rather than asserting a value.

Allelic series — other ABCC9 diseases (essential differential context)

Disease Mechanism Inheritance ClinGen validity (verified 2026)
AIMS / IDMYS (this entry) Biallelic LoF AR No ClinGen curation — gap
Cantú syndrome (hypertrichotic osteochondrodysplasia; MONDO:0009406, OMIM #239850) Heterozygous GoF (mostly missense) AD Definitive (Syndromic Disorders GCEP, 2025-02-21)
Dilated cardiomyopathy 1O (OMIM #608569) Heterozygous LoF missense in exon 38 (SUR2A-specific) AD Limited (DCM GCEP, 2026-03-04)
Atrial fibrillation, familial, 12 (OMIM #614050) Missense in the same SUR2A-specific exon; single 53-year-old patient AD —
Brugada syndrome — AD Disputed (Hereditary Cardiovascular Disease GCEP, 2025-10-28)

The paralogous pancreatic/neuronal pair ABCC8/KCNJ11 completes the family logic: GoF → neonatal diabetes; LoF → congenital hyperinsulinism.

Modifier genes, epigenetics, chromosomal abnormalities

  • Modifiers: none identified. The 2024 paper's observation that two unrelated families share c.3269delG with differing severity (P2 had seizures and regression; P3 had isolated ID with a normal MRI) is direct evidence of modifier or stochastic effects and is an excellent KNOWLEDGE_GAP/mechanistic_hypotheses candidate.
  • Epigenetics: no data. No methylation episignature, no DiseaseMeth/ENCODE-based analysis exists for AIMS. Do not populate this section.
  • Chromosomal abnormalities: none causal. Notably, karyotype/G-banding, high-resolution SNP array, FMR1 CGG repeat analysis, DMPK PCR, mtDNA screening, and metabolic screening were all normal in the 2019 patients before exome analysis — clinically useful negative information for the diagnostics section. The one exception is P4's 73.3 kb intragenic deletion of exons 13–33, which is a CNV detectable by array/CNV-aware sequencing.

5. Environmental Information

  • Environmental factors: none contributory to causation. CTD/TOXNET yield no AIMS-relevant exposure.
  • Lifestyle factors: none causal. Exercise is a symptom trigger (spasms, myalgia, fatigability), not a risk factor. Two 2019 patients became overweight (>97.5th percentile) in adulthood after early failure-to-thrive, and obesity contributed to obstructive sleep apnea in one — a modifiable comorbidity, not an etiologic factor.
  • Infectious agents: not applicable. One febrile illness preceded a coma episode, but as a decompensation trigger rather than a pathogen-mediated cause.

The substantive content for this section is iatrogenic exposure (§12 drugs-to-avoid), which is where the real "environmental" risk in AIMS lies.

6. Mechanism / Pathophysiology

Molecular foundation

KATP channels are octameric complexes of four pore-forming Kir6.x subunits and four regulatory SURx subunits that couple cellular metabolic state to membrane excitability. ATP binding to Kir6.x inhibits the channel; Mg-ADP/Mg-ATP binding to the SURx nucleotide-binding domains stimulates it. SUR2 is therefore the metabolic sensor arm of the channel — losing it does not merely reduce current, it abolishes the metabolism-to-excitability coupling entirely in SUR2-dependent tissues.

Tissue pairing (PMID:31575858 full text): "Pancreatic and neuronal KATP channels are predominantly formed by Kir6.2 and SUR1, smooth muscle KATP channels are comprised of Kir6.1 and SUR2B, and the predominant combination in striated muscle is Kir6.2 and SUR2A."

Proximal molecular defect

The exon-8 in-frame deletion removes SUR2 residues Ala389–Gln440, disrupting multiple transmembrane helices in TMD1. Consequences measured in Cosm6 cells:

  1. ~50% reduction in SUR2 protein on Western blot.
  2. Complete abolition of ⁸⁶Rb⁺ efflux — "cells expressing Kir6.2/SUR2AΔ8 showed no rubidium efflux above the background levels observed in GFP-transfected cells."
  3. Complete absence of KATP current in inside-out patch clamp.
  4. Same result for SUR2BΔ8 — so both isoforms are dead.
  5. No dominant-negative effect: a 1:1 WT:Δ8 co-expression gave WT-like efflux rates and unchanged ATP IC₅₀ / pinacidil activation — "in the heterozygous context, the c.1320+1G>A mutation is without significant effect." This is the molecular explanation for healthy carrier parents.

The 2026 paper reproduced complete LoF for three further truncating variants (p.Glu961LysfsTer10, p.Gly1090AspfsTer2, p.Ser601ArgfsTer9) using a landing-pad HEK293 / FLIPR membrane-potential assay (no oligomycin-A-induced hyperpolarization) plus patch clamp, again with no major dominant-negative effect [FULL-TEXT — RE-VERIFY].

"Functional tests of recombinant channels confirm that disease-associated SUR2 truncations cause a complete loss-of-function." — PMID:42290677 [ABSTRACT-VERIFIED]

Causal chains — three mechanistically distinct downstream arms

The pathophysiology graph should be modeled as one molecular trigger fanning into three tissue-specific arms, because the arms have genuinely different intermediate biology.

Arm A — Skeletal muscle (myopathy). This arm is causally proven to be muscle-intrinsic.

ABCC9 biallelic LoF (MOLECULAR)
  → loss of SUR2A/Kir6.2 KATP in skeletal myocytes (CELLULAR)
  → failure of fatigue-induced action-potential shortening and
    resting-membrane-potential stabilization (CELLULAR)
  → excessive Ca2+ entry, elevated resting tension,
    abnormal unstimulated force generation (CELLULAR)
  → myofiber stress/degeneration, impaired fatigue recovery (TISSUE)
  → fatigability, muscle weakness, painful exercise-induced spasms (ORGANISM)

The 2019 mechanistic rationale, verbatim from the full text: "In skeletal muscle, KATP channels are typically closed at rest but open in response to metabolic stress or fatigue. Channel activation results in action potential shortening and stabilization of the resting membrane potential during the development of fatigue, which serves to reduce intracellular calcium, decrease resting tension and protect myocytes from damage. Therefore, loss of KATP function might be expected to result in failure to recover from fatigue, myofiber degeneration, and excessive calcium influx."

McClenaghan et al. 2023 then localized this arm by tissue-selective knockdown and, importantly, falsified the obvious Ca²⁺-influx hypothesis:

"Given the roles of KATP channels in all muscles, we sought to determine how myopathy arises using tissue-selective suppression of KATP and found that LoF in skeletal muscle, specifically, underlies myopathy. In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS. We sought to determine whether excessive Ca2+ influx through CaV 1.1 channels was responsible for myopathology but found that the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice and that rendering CaV 1.1 channels nonpermeable by mutation failed to reverse pathology; results which caution against the use of calcium channel blockers in AIMS." — PMID:37154692 [ABSTRACT-VERIFIED]

That negative result is scientifically important and should be curated as a supports: REFUTE evidence item against a CaV1.1-influx sub-hypothesis — it is exactly the kind of falsified mechanism dismech is designed to record rather than discard.

Arm B — Cerebral vasculature → white matter injury (the leading explanation for the CNS phenotype).

ABCC9 biallelic LoF (MOLECULAR)
  → loss of SUR2B/Kir6.1 KATP in vascular smooth muscle (CELLULAR)
  → increased vascular tone / hypertension; loss of metabolic
    vasodilatory reserve (TISSUE)
  → impaired dynamic coupling of cerebral blood flow to
    neuronal metabolic demand; chronic hypoperfusion (TISSUE)
  → ischemic periventricular white matter injury, small-vessel
    disease, lacunar-like cavitation, mineral deposition (TISSUE)
  → intellectual disability, spasticity, hyperreflexia,
    seizures, later cognitive decline (ORGANISM)

The 2019 authors' framing: "recent data demonstrate that SUR2-containing KATP channels play a critical role in regulation of cerebral vascular architecture… Since KATP channel GoF results in chronic vasodilation and altered neuro–vascular coupling, it is conceivable that KATP loss of function may impact the cerebral vasculature in a way that results in impaired dynamic coupling of blood flow to match neuronal metabolic demand." They add that the white matter hyperintensities seen in both Cantú syndrome and AIMS "could result from ischemic events due to dysregulated cerebral blood flow, although the cognitive phenotype seems to be more definite in AIMS than in Cantú syndrome."

Supporting evidence: hypertension was significantly increased in SUR2-STOP mice; cardinal vein red-cell velocity was increased in SUR2-STOP zebrafish; and the 2026 sexagenarian's imaging evolved into frank severe vascular leukoencephalopathy with perivascular space dilation and lacunar-like cavitations [FULL-TEXT — RE-VERIFY]. Note also that MR angiography was normal with normal cerebral vessel calibers in the 2019 patients — so this is a functional microvascular/autoregulatory defect, not a macrovascular malformation. That distinction is a genuine contrast with Cantú syndrome (dilated, tortuous vessels) and should be stated explicitly.

Mark this arm as status: EMERGING in mechanistic_hypotheses — the 2019 authors themselves say "it is conceivable," and no direct human CBF/neurovascular-coupling measurement in AIMS exists.

Arm C — Cardiac (age-dependent).

ABCC9 biallelic LoF (MOLECULAR)
  → loss of SUR2A/Kir6.2 KATP in cardiomyocytes; loss of
    metabolic stress protection (CELLULAR)
  → reduced contractile reserve, cardiomyocyte apoptosis
    (TUNEL+ in zebrafish) (CELLULAR/TISSUE)
  → biventricular systolic dysfunction, LV dilation (TISSUE)
  → early-stage dilated cardiomyopathy, heart failure;
    acute cardiogenic shock under stress (ORGANISM)

Human anchor: the two oldest 2019 patients had biventricular systolic dysfunction (EF 35–40% and 48%), raised NT-proBNP, and cardiac-MRI LV dilation "compatible with early-stage dilated cardiomyopathy," while a teenage echocardiogram in the same patient had been normal — establishing age-dependent emergence. The authors compare with the heterozygous exon-38 DCM patients who were older with far worse EFs (15–23%) and conclude: "This may suggest a progressive cardiomyopathy which will require longitudinal analysis in AIMS."

Notably, zebrafish hearts showed no fibrosis (AFOG) and normal myofiber/tropomyosin structure despite marked ventricular enlargement — so this is a functional/apoptotic remodeling process rather than a primary fibrotic cardiomyopathy. That argues against naive conformance to fibrotic_response and for conformance to cardiomyopathy_maladaptive_remodeling.

Unexplained: the intellectual disability itself

The 2019 authors are admirably candid, and this should be curated as a first-class knowledge gap:

"It is not obvious how myocyte KATP dysfunction could explain the intellectual disability or anxiety, and there are no reports of cognitive impairment in previous SUR2 mutant animal models." Neuronal KATP is predominantly Kir6.2/SUR1, though SUR2 transcripts are reported in central and peripheral neurons and implicated in hippocampal sclerosis of aging and ALS.

This is a textbook HUMAN_MODEL_MISMATCH case per the repo's CLAUDE.md guidance, not a plain KNOWLEDGE_GAP: the SUR2-STOP mouse was formally tested for cognition and anxiety and was negative on all of it (locomotor activity, sensorimotor battery, Morris water maze spatial learning, elevated plus maze), while the defining human feature is intellectual disability plus anxiety in 4/4 assessed. The authors' own caveat — "mild cognitive impairment, as seen in humans, can be difficult to recognize in animals" — plus their suggestion of working-memory/fear-conditioning testing maps directly onto proposed_experiments.

Cellular processes, cell types, and compartments

Ontology Term Verified label
GO CC GO:0008282 "inward rectifying potassium channel" — ⚠️ the canonical GO label is not "ATP-sensitive potassium channel complex"; that is a synonym. Use the canonical label in term.label and put "ATP-sensitive potassium channel complex (KATP)" in preferred_term. Its definition explicitly describes the four Kir6.x + four SURx architecture.
GO MF GO:0015272 "ATP-activated inward rectifier potassium channel activity" — the precise molecular function lost
GO MF GO:0017098 "sulfonylurea receptor binding"
GO BP GO:0071805 "potassium ion transmembrane transport"
GO BP GO:1901379 "regulation of potassium ion transmembrane transport"
GO BP GO:0042391 regulation of membrane potential (commonly used; verify with OAK before committing)
CL CL:0008002 "skeletal muscle fiber" — primary myopathy cell type
CL CL:0000192 "smooth muscle cell" — vascular arm
CL CL:0000746 cardiac muscle cell (verify with OAK)
CL CL:0000128 oligodendrocyte — plausible white-matter target, but no direct AIMS evidence; omit unless supported
UBERON UBERON:0002437 "cerebral hemisphere white matter"
UBERON UBERON:0008967 "centrum semiovale" — explicitly named in two patients' MRI reports
CHEBI CHEBI:9948 verapamil (the contraindicated agent)

Metabolic, immune, biochemical, and profiling data

  • Biochemical abnormality: the defect is an ion channel defect. Routine biochemistry is characteristically normal: "S-CK, B-lactate, nerve conduction velocities, and electromyography, including repetitive nerve stimulation, are normal in all individuals, except for discrete myopathic discharges in patient 2–2." Abnormal values appear only during crises (lactate 6, CK 738) or incidentally (hyperprolactinemia 720 mIU/L in one patient, with normal pituitary MRI).
  • Metabolic changes: no primary metabolic derangement; inborn-errors-of-metabolism screening was normal. Mouse SUR2 nulls show lower serum glucose and enhanced insulin action (MGI) — an interesting, unexplored translational thread with no human counterpart reported.
  • Immune involvement: none mechanistically. Atopic dermatitis (2/6), food allergies with anaphylaxis, and cyclosporine treatment in one patient are recorded features whose relationship to SUR2 is entirely unexplained — curate as associations, not mechanism.
  • Transcriptomics / proteomics / metabolomics / lipidomics / single-cell / spatial / multi-omics / CRISPR screens: no AIMS-specific datasets exist. The only quantitative expression data is zebrafish qPCR showing ~4-fold reduced abcc9 mRNA in SUR2-STOP larvae, consistent with NMD. Leave these subsections empty rather than importing generic ABCC9 GTEx data as if it were disease data.

Suggested dismech module conformance

AIMS is a strong multi-module conformer candidate: - cardiomyopathy_maladaptive_remodeling → Arm C (#Ventricular Remodeling). Good fit; note the absence of fibrosis in the fish model. - epilepsy_excitation_inhibition_imbalance → the seizure phenotype (#Excitation-Inhibition Imbalance), with the zebrafish PTZ hypersensitivity as supporting MODEL_ORGANISM evidence. - A new KATP channelopathy grouping is the more valuable structural contribution: AIMS + Cantú syndrome + DCM1O + neonatal diabetes + congenital hyperinsulinism form a textbook GoF/LoF antagonistic pair set across two paralogous gene pairs. This parallels the existing cellular_senescence / senescence_tumor_suppression two-module treatment of opposing arms, and would fit kb/groupings/ with grouping_basis: [SHARED_MECHANISM, SHARED_GENE_FAMILY].

7. Anatomical Structures Affected

Primary organs / systems

System Structures UBERON
Central nervous system Cerebral white matter (periventricular, juxtacortical, frontal/parietal), centrum semiovale, corpus callosum, basal ganglia, pons, brainstem, cerebellum UBERON:0002437 cerebral hemisphere white matter; UBERON:0008967 centrum semiovale; UBERON:0002336 corpus callosum; UBERON:0002420 basal ganglion; UBERON:0000988 pons*
Skeletal muscle Generalized, with proximal and truncal predominance UBERON:0001134 skeletal muscle tissue*
Heart Both ventricles (biventricular systolic dysfunction); LV dilation UBERON:0002084 heart left ventricle; UBERON:0002080 heart right ventricle
Vasculature Cerebral microvasculature (functional, not structural); systemic arteries (hypertension) UBERON:0001637 artery; UBERON:0001981 blood vessel

* commonly-used IDs stated from knowledge; verify with just validate-terms / OAK before committing. Only UBERON:0002437 and UBERON:0008967 were verified live in this session.

Secondary involvement: skeleton (lumbar hyperlordosis, scoliosis, congenital hip dislocation, Achilles contractures), eye/oculomotor (nystagmus, strabismus/esotropia, heterotropia), inner ear (bilateral high-frequency sensorineural hearing loss), skin (cutis marmorata in 6/6, spotty hypopigmentation, café-au-lait macule, atopic dermatitis, facial telangiectasia), craniofacial/dental (macrodontia, malocclusion, widely spaced incisors), GI (feeding difficulties, ileal atresia in the neonate), upper airway (obstructive sleep apnea).

Tissue and cell level: striated muscle fibers (CL:0008002), cardiac myocytes (CL:0000746), vascular smooth muscle cells (CL:0000192). Muscle histology is strikingly bland — a single biopsy showed only "unspecific changes of mitochondrial aggregation and muscle fiber caliber variation" — consistent with mouse data showing histological abnormality only after chronic exercise.

Subcellular level: the plasma membrane KATP complex (GO:0008282) is the site of the defect; the 2019 paper specifically frames the loss as of "plasmalemmal KATP function." A mitochondrial angle exists in the literature (a prior mouse allele retains a "mitochondria-limited short form" of SUR2, and one patient's biopsy showed mitochondrial aggregation) but mitochondrial SUR2 is not established as an AIMS mechanism — do not assert it.

Lateralization: predominantly bilateral and symmetric (white matter changes, hearing loss, hyperreflexia, ventricular dysfunction). Documented asymmetric exceptions: unilateral left lower-extremity weakness with limping in one patient, unilateral Achilles contracture in another, and a single left-anterior-horn periventricular lesion.

8. Temporal Development

Onset - Neonatal: recurrent emesis, feeding difficulty, ileal atresia, multifocal seizures on day 3 (2026 case) — the earliest documented presentation. - Infantile: HP:0003593 in 5/6 of the original cohort — hypotonia, delayed psychomotor development, feeding difficulty, low weight, typically noticed in toddler years. - Congenital: HP:0003577 in 1/6 (congenital hip dislocation). - Prenatal / lethal extreme: recurrent intrauterine fetal death in heterozygous couples, including two IUFDs of fetuses confirmed homozygous for p.(Arg620Ter) [FULL-TEXT — RE-VERIFY]. - Pattern: insidious and chronic, with superimposed acute episodes.

Progression / stages — a useful three-stage model emerges from the pooled natural history: 1. Early (infancy–childhood): hypotonia, developmental delay, feeding difficulty, failure to thrive, toe-walking/in-toeing, lumbar lordosis. Cardiac and cognitive testing may be normal. 2. Intermediate (adolescence–early adulthood): mild-to-moderate ID confirmed on neuropsychological testing, fatigability, exercise-induced myalgia/spasms, hyperreflexia, balance impairment, accumulating white matter lesions, anxiety; weight often shifts from low to overweight. 3. Late (fourth decade onward): biventricular systolic dysfunction/early DCM; progression of leukoencephalopathy toward vascular small-vessel disease with cavitation and calcification; motor and cognitive decline with global muscle atrophy and dementia-like presentation (2026 sexagenarian, died in her early sixties of aspiration-related asphyxiation) [FULL-TEXT — RE-VERIFY].

Rate: slow. Static-appearing through childhood, which is why AIMS was long mistaken for a static encephalopathy — but explicitly not static on imaging ("Lesions have increased significantly since the first investigation") or in late adulthood.

Course: chronic, lifelong, progressive with an episodic overlay. Not relapsing-remitting.

Remission: none. The only documented reversibility is imaging: the fever-triggered multifocal lesions in patient 1–4 "were normalized a few weeks later, except for a white matter lesion," and he "regained the same psychomotor level as before" — evidence that acute decompensations can be survivable and partly reversible.

Critical periods / windows for intervention - Perioperative period — the highest-acuity documented window (two post-operative decompensations in one neonate). - Antiseizure and anesthetic drug selection at any age. - Adulthood cardiac surveillance — the 2019 patient had a normal teenage echocardiogram and dysfunction by age 33, so a single normal childhood echo does not discharge the risk. - Early developmental years for habilitation, feeding, and educational support.

9. Inheritance and Population

Epidemiology. No prevalence or incidence estimate has ever been published, and there is no Orphanet prevalence class (no ORPHA code exists). The literature total is ~20 individuals from ~13 families (2019: 6; 2024: 9 + IUFDs; 2026: 5). For dismech Prevalence, the honest structured record is:

prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Approximately 20 affected individuals from ~13 families reported across
    three publications (2019-2026). No prevalence or incidence estimate has
    been published; no Orphanet epidemiology record exists.

Do not derive a rate_per_100000 from carrier frequency — that inference is not in the literature.

Inheritance pattern. Autosomal recessive (HP:0000007). Verified by homozygosity in all affected individuals with heterozygous unaffected parents and one heterozygous unaffected sibling, plus one compound heterozygote with variants confirmed in trans (paternal/maternal).

Penetrance. Appears complete for the core triad in biallelic carriers, though the very small n and the 2026 participant with isolated ID and a normal MRI show variable expressivity of individual features. Heterozygotes have no AIMS phenotype: "Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death" (PMID:38217872) [ABSTRACT-VERIFIED].

Expressivity. Variable — most sharply demonstrated by the two unrelated homozygotes for the identical c.3269delG allele with markedly different severity (regression + seizures vs. IQ 69 with normal imaging). Cardiac involvement is age-dependent rather than variant-dependent.

Genetic anticipation. Not applicable (no repeat expansion).

Germline mosaicism. Not reported.

Founder effect. Strongly suggested for c.1320+1G>A: both 2019 families came from the same area of Northern Norway with probable Finnish ancestry, yet whole-genome kinship analysis excluded relatedness (kinship coefficient 0.0403, versus ~0.05 expected for unrelated samples), and the allele sits in a shared 3.8 Mb homozygous block (chr12:18,326,590–22,176,010, hg19). Combined with the Finnish gnomAD AF of 0.0007, the authors concluded: "Considering the probable Finnish ancestry of all patients, the syndrome might be more prevalent in the Finnish population than others." A second Norwegian allele (c.284+1G>A) appeared in the 2024 cohort.

Consanguinity. A major contributor outside Northern Europe — documented in Pakistani, Egyptian (×2), Saudi Arabian, and British-Pakistani families, and in the 2026 first-cousin family.

Carrier frequency. Best estimate is the Finnish c.1320+1G>A allele frequency of 0.0007 (≈1 in 690 carriers for that single allele in Finns) — but note this is a per-allele figure, not a pan-allelic carrier rate, and no carrier-screening study exists.

Population demographics. Reported ancestries: Norwegian (with probable Finnish ancestry), Dutch, Pakistani, British Pakistani, Egyptian, Saudi Arabian, Brazilian and Italian contributions via the 2026 author network. Absent from gnomAD Asian and African populations for the founder allele. Geographic distribution reflects where exome sequencing and expert networks are concentrated, not true disease distribution — this is ascertainment bias and should be stated as such.

Sex ratio. Roughly balanced with no evidence of sex bias: 2019 cohort 2F/4M; 2026 cohort 4F/1M. Consistent with autosomal inheritance. (Note: the PMID:31575858 MeSH set anomalously includes Genetic Diseases, X-Linked and Intellectual Disability/parasitology — clear MEDLINE indexing artifacts, not claims about the disease. Do not propagate these.)

Age distribution of reported individuals. Newborn to early sixties; the 2019 cohort spanned 11–33 years at report.

10. Diagnostics

The diagnostic gestalt

The 2026 authors give the single most useful practical recommendation: the constellation of periventricular leukomalacia + developmental delay/intellectual disability + muscle weakness and fatigability should prompt investigation for an ABCC9-related disorder [FULL-TEXT — RE-VERIFY]. This matters because the imaging pattern mimics acquired perinatal hypoxic-ischemic injury, so AIMS is easily dismissed as non-genetic.

Laboratory tests — mostly normal, which is itself diagnostic information

  • Creatine kinase: normal in all 2019 patients and in the 2026 participant tested; elevated (738) only during acute crisis. A normal CK does not exclude AIMS — a critical negative, since it steers clinicians away from a myopathy workup. LOINC: CK 2157-6.
  • Lactate: normal at baseline; elevated in crisis (6 mmol/L). LOINC 2524-7.
  • Prolactin: hyperprolactinemia in one patient with normal pituitary MRI (incidental). NT-proBNP: raised in the patient with heart failure, normal in his sister with milder dysfunction.
  • Normal: metabolic/IEM screening, mtDNA sequence and deletion screening.

Biomarkers: there is no diagnostic or prognostic biomarker for AIMS. NT-proBNP serves only as a generic heart-failure marker. This is a real gap worth recording.

Imaging — the highest-yield test

Brain MRI is the cornerstone. Findings: periventricular and juxtacortical white matter T2/FLAIR hyperintensities (centrum semiovale, frontal and parietal, anterior temporal lobes, external capsules); reduced periventricular white matter volume; corpus callosum hypoplasia/agenesis; punctate lesions in basal ganglia, pons, brainstem and cerebellum suggesting mineral deposition/calcification; in advanced disease, dilated perivascular spaces and lacunar-infarct-like cavitations. MR angiography is normal with normal vessel calibers — a key discriminator from Cantú syndrome. MRS was normal in the one patient tested. Serial imaging is recommended, since lesions accumulate.

Cardiac imaging: echocardiography ± cardiac MRI. Cardiac MRI detected LV dilation that echo missed (LV diameter was within normal range on echo in the same patient) — so echo alone may under-call early cardiomyopathy.

Electrophysiology — characteristically normal

EMG, nerve conduction velocity, repetitive nerve stimulation, and EEG were normal in all 2019 patients (bar discrete myopathic discharges in one). Notably, one patient with clinical tonic–clonic episodes had repeatedly normal EEGs — clinically important, because normal EEG does not exclude the paroxysmal events, and it feeds the hypothesis that some episodes are circulatory rather than epileptic.

Biopsy / pathology

Muscle biopsy is low-yield and non-specific: "caliber changes, mitochondrial aggregations." Not recommended as a diagnostic route; its main value is exclusionary.

Genetic testing — the definitive route

  • Recommended first-line: exome or genome sequencing (trio-based where possible). Both cohorts were solved this way, and the 2019 patients had already had extensive normal targeted testing (G-banding, high-resolution SNP array, FMR1 CGG, DMPK PCR, multiple neuromuscular gene panels, mtDNA, IEM screening) before ES/GS succeeded.
  • Gene panels: ABCC9 is included in large neurodevelopmental/neuromuscular panels (the 2019 study used a >4,800-gene panel). No AIMS-specific panel exists.
  • WGS adds value for excluding alternatives, resolving relatedness (kinship coefficient), and for CNV detection — essential given the 73.3 kb exon 13–33 deletion in the 2026 cohort. A sequencing pipeline blind to intragenic CNVs can miss AIMS.
  • Single-gene testing is reasonable only for targeted familial testing or in a Finnish/Northern Norwegian patient with the classic triad (founder allele).
  • CMA/karyotype/FISH: normal in AIMS; CMA would only detect the large intragenic deletion if probe coverage is adequate.
  • mtDNA testing: normal — but frequently performed, because the phenotype (myopathy + white matter disease + lactate rise in crisis) mimics mitochondrial disease.
  • Repeat expansion testing: not applicable.
  • RNA/functional confirmation: cDNA analysis from fibroblasts confirmed exon 8 skipping in the 2019 family — a good template for splice-variant validation. Recombinant channel assays (⁸⁶Rb⁺ efflux, patch clamp, landing-pad/FLIPR membrane potential) are research-grade PS3 evidence, not clinical tests.
  • Omics diagnostics (proteomics/metabolomics/epigenomics/liquid biopsy): no role established.

Clinical criteria and differential diagnosis

There are no formal consensus diagnostic criteria — diagnosis is molecular plus phenotype fit.

Differential, with discriminators (several of these are documented misdiagnoses in the published families, which makes them high-value KB content):

Alternative How to distinguish
Cantú syndrome (ABCC9 GoF, MONDO:0009406) Hypertrichosis and coarse facies present; cardiomegaly with high cardiac output; dilated tortuous vessels on MRA; intellect typically normal. AIMS: no hypertrichosis, normal MRA, definite ID, reduced systolic function.
Tuberous sclerosis Actually diagnosed and later abandoned in Family 2 because of depigmented patches + white matter lesions. TSC has cortical tubers/SEGA and a different MRI pattern.
Acute disseminated encephalomyelitis Actually considered for patient 1–4's coma episode; re-read as "inflammatory perivascular reaction," lesions resolved.
Perinatal hypoxic-ischemic periventricular leukomalacia Radiologically near-identical; distinguished by absent perinatal risk history, progression over time, and the muscle/ID/cardiac triad.
Leukodystrophies Patient 2–1's MRI was described as "similar to leucodystrophy"; distinguished by genotype and by the myopathy/cardiac phenotype.
Mitochondrial disease Overlapping myopathy + WM disease + crisis lactate; excluded by normal mtDNA/IEM screening.
Congenital muscular dystrophy / congenital myopathy Normal-to-mildly-abnormal CK, normal EMG, non-specific biopsy in AIMS.
Genetic cerebral small-vessel disease (e.g. CADASIL) Later onset, no ID/myopathy, different genotype.
Thanatophoric dysplasia Suspected in a terminated Family 1 fetus with micromelia and narrow thorax; the 2019 authors flagged it as a probable unrelated finding — worth curating as an explicit non-attribution so future readers don't add skeletal dysplasia to the AIMS phenotype.

Screening

  • Newborn screening: not included in any program; no biochemical marker exists to enable it.
  • Carrier screening: not offered. Mechanistically justifiable in Finnish/Northern Norwegian populations for c.1320+1G>A given AF 0.0007, but no such program or recommendation is published — flag as inference, not practice.
  • Cascade testing: appropriate for at-risk relatives once a familial variant is known; ACMG-standard.
  • Prenatal/PGT: technically available for known familial variants (§13).

11. Outcome / Prognosis

Survival and mortality. No survival statistics, life-expectancy estimate, or mortality rate exists — n is far too small. Documented outcomes at the extremes: recurrent intrauterine fetal death in homozygous fetuses (the most severe reported outcome), and death in the early sixties from aspiration-related asphyxiation in the oldest reported patient after progressive motor/cognitive decline [FULL-TEXT — RE-VERIFY]. Most reported individuals were alive at report, aged 11–33. Preliminary read: survival into at least the sixth decade is possible, with heart failure, aspiration, perioperative decompensation, and refractory neonatal seizures as the identified threats.

Morbidity and function. Lifelong disability across motor, cognitive, and stamina domains. Concrete functional data: reduced 6-minute walk distance in 6/6; miniBESTest balance scores 14–21/28 in 6/6; supported or sheltered living with daily supervision in the adults; sheltered employment limited by exhaustion. Global proximal muscle atrophy with inability to walk in the advanced case.

Quality-of-life measures. None applied. No EQ-5D, SF-36, PROMIS, or disease-specific instrument has been used in AIMS. Explicit gap.

Complications. Heart failure / early dilated cardiomyopathy; refractory seizures including infantile spasms; obstructive sleep apnea; scoliosis and contractures; aspiration; feeding failure requiring gastrostomy; anxiety requiring pharmacotherapy; perioperative cardiogenic shock; progressive vascular leukoencephalopathy; sensorineural hearing loss.

Recovery potential. No recovery of the neurodevelopmental deficit. Acute decompensations can resolve substantially — the coma/tetraplegia episode resolved with return to baseline psychomotor level and near-complete lesion resolution, and the neonate's cardiac function normalized with VSD closure by 2 months.

Prognostic factors. Provisional, low-confidence given n: older age (cardiac dysfunction and cognitive decline both age-associated); surgical/anesthetic exposure; neonatal presentation (the most acutely unstable course); presence of seizures. No molecular genotype–phenotype correlation is established — the two unrelated c.3269delG homozygotes with divergent severity argue directly against simple variant-based prognostication, and all variants tested are complete LoF regardless of position.

Prognostic biomarkers. None. NT-proBNP tracks heart failure only.

12. Treatment

There is no disease-specific, curative, or channel-directed therapy for AIMS. Management is entirely supportive and surveillance-based. The most valuable content in this section is the drugs-to-avoid list, which is unusually well-evidenced for a 20-patient disease.

Contraindicated / high-caution agents — the actionable core

Agent / class Evidence Strength
Verapamil / calcium channel blockers (CHEBI:9948) "the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice… results which caution against the use of calcium channel blockers in AIMS" — PMID:37154692 [ABSTRACT-VERIFIED] MODEL_ORGANISM, strong and explicit
Phenytoin / fosphenytoin Caused severe bradycardia and hypotension in an AIMS patient (patient 1–1, age 17); calcium-channel-blocking activity HUMAN_CLINICAL, single case [FULL-TEXT — RE-VERIFY]
Propofol Two post-operative decompensations (cardiogenic shock, lactic acidosis) in a neonate; inhibits cardiac L-type Ca²⁺ channels, associated with bradycardia HUMAN_CLINICAL, single case [FULL-TEXT — RE-VERIFY]
Lacosamide (maintenance) Discontinued for bradycardia risk (used acutely with benefit) HUMAN_CLINICAL [FULL-TEXT — RE-VERIFY]

Reported general principle: loss of SUR2-dependent KATP channels is expected to alter cardiac resilience to stressors and may have complex, unpredictable effects on cardiac-acting drugs [FULL-TEXT — RE-VERIFY]. The 2026 authors call for systematic screening of antiseizure drugs for cardiovascular toxicity in SUR2-deficient animal models.

Contrast worth curating explicitly. Cantú syndrome's GeneReviews "agents to avoid" list is minoxidil, diazoxide, and ACE inhibitors — i.e. KATP openers (PMID:25275207) [ABSTRACT-VERIFIED]. AIMS' avoid-list is calcium channel blockers and Ca-channel-blocking anesthetics/antiseizure drugs. The two diseases have opposite pharmacological hazards, exactly as their opposite channel defects predict. This is a compelling, non-obvious pairing for the KB.

Supportive and symptomatic management, with NCIT terms

Intervention NCIT treatment_term therapeutic_modality Notes
Antiseizure therapy — levetiracetam preferred NCIT:C15986 Pharmacotherapy SMALL_MOLECULE Preferred because its mechanism (synaptic vesicle protein) avoids cardiac channel blockade. Lamotrigine was "partly effective" in patient 1–1. ACTH used for infantile spasms.
Heart failure therapy — ACE inhibitor + beta-blocker NCIT:C15986 Pharmacotherapy SMALL_MOLECULE Started in patient 2–1 (EF 35–40%). Note ACE inhibitors are avoided in Cantú but used in AIMS — the inverse logic again.
Anxiolytic therapy — SSRI NCIT:C15986 Pharmacotherapy SMALL_MOLECULE Used in patient 2–1 for anxiety (4/4 assessed patients had anxiety).
Physical therapy / habilitation NCIT:C15302 Physical Therapy BEHAVIORAL Core management; two 2019 authors were from a physiotherapy/pediatric-rehabilitation service.
Rehabilitation NCIT:C15315 Rehabilitation BEHAVIORAL
Developmental and educational support NCIT:C181743 Behavioral Counseling (verify) BEHAVIORAL Adapted schooling documented.
Nutritional support / gastrostomy NCIT:C15433 Nutritional Support — ⚠️ Per CLAUDE.md, do not auto-tag as BEHAVIORAL; assess the actual intervention.
Orthopedic / scoliosis and contracture management NCIT:C16186 Orthopedic Surgical Procedure SURGERY Congenital hip dysplasia treated; contractures and scoliosis managed.
OSA surgery NCIT:C15329 Surgical Procedure SURGERY Operative treatment recommended for OSA in patient 1–4.
Genetic counseling NCIT:C15240 Genetic Counseling — See §13.
Supportive care NCIT:C15747 Supportive Care —

Also documented: cyclosporine for severe atopic eczema (one patient), steroids given during the ADEM-like episode, and hearing aids implied by bilateral high-frequency SNHL (note: there is no reliable NCIT clinical-action term for hearing-aid use, per CLAUDE.md).

Advanced therapeutics

  • Gene therapy, gene editing, cell therapy, RNA therapy, targeted therapy, immunotherapy: none developed, none in trial. Conceptually, an autosomal-recessive LoF channelopathy is a rational gene-replacement target, but ABCC9 is a large gene, the relevant tissues (skeletal muscle, vascular smooth muscle, brain vasculature, heart) are broadly distributed, and no preclinical program is published.
  • Pharmacogenomics: no PharmGKB/CPIC entry for ABCC9 in AIMS. The clinically relevant pharmacology is the mechanism-based hazard above, not metabolizer status. (Incidentally, the 2026 neonate also had G6PD deficiency, which carries its own independent drug-avoidance list — a confounder in that case, not an AIMS feature.)

Clinical trials

No clinical trial has ever been registered for AIMS. A ClinicalTrials.gov search yields no AIMS/IDMYS interventional or observational study. Leave clinical_trials: empty.

A mechanistic caution for curators

It is tempting to reason that if AIMS is loss of KATP function, a KATP opener (diazoxide, pinacidil, minoxidil, nicorandil) should help. The functional data argue this cannot work: SUR2Δ8 and the truncating variants produce channels with no measurable current at all, and pinacidil activation was tested and required WT SUR2 to be present. A pharmacological opener needs a functional channel to open. I state this explicitly because it is an inviting inference that the literature does not support — it should not be curated as a candidate therapy, and if recorded at all it belongs in a discussions KNOWLEDGE_GAP entry, clearly labeled as unsupported reasoning rather than as a treatment.

13. Prevention

Primary prevention. Not possible for the genotype. Prevention is reproductive, via genetic counseling, carrier testing of at-risk relatives, prenatal diagnosis, and preimplantation genetic testing for known familial variants. The recurrent IUFDs in heterozygous couples make reproductive counseling unusually consequential here — couples may present with pregnancy loss before any living affected child is diagnosed.

Secondary prevention (early detection). No newborn or population screening exists. Realistic secondary prevention is early molecular diagnosis via exome/genome sequencing in a child with the triad, which unlocks the drug-avoidance list and cardiac surveillance before harm occurs.

Tertiary prevention (preventing complications) — the most actionable level, and where the entry should concentrate: 1. Perioperative planning — anesthetic and antiseizure drug review before any procedure; avoid propofol; monitor cardiac function and lactate post-operatively. 2. Avoid calcium channel blockers and Ca-channel-blocking antiseizure drugs; prefer levetiracetam. 3. Longitudinal cardiac surveillance — periodic echocardiography (consider cardiac MRI, which detected dilation echo missed) with NT-proBNP, continuing into adulthood even after normal childhood studies. 4. Serial brain MRI to track lesion accumulation. 5. Audiological monitoring for progressive high-frequency SNHL. 6. Orthopedic surveillance for scoliosis and contractures; physiotherapy to preserve function. 7. Weight management — the low-weight-to-overweight trajectory contributed to OSA. 8. Aspiration risk assessment in advanced disease (cause of death in the oldest patient). 9. Activity pacing — exertion triggers spasms and myalgia; graded rather than maximal exercise (note the mouse data showing muscle histopathology emerges specifically with chronic heavy exercise).

Immunization, public health, environmental, and prophylactic interventions: not applicable — no infectious, environmental, or population-level dimension to this disease.

14. Other Species / Natural Disease

Taxonomy of species with relevant ABCC9 biology:

Species NCBI Taxon Gene Identifier
Homo sapiens NCBITaxon:9606 ABCC9 HGNC:60; NCBI Gene 10060
Mus musculus NCBITaxon:10090 Abcc9 MGI:1352630; NCBI Gene 20928 (verified)
Danio rerio NCBITaxon:7955 abcc9 ZFIN gene abcc9 — ZFIN ID not retrieved (site required interactive verification); look it up before curating
Canis lupus familiaris NCBITaxon:9615 ABCC9 see natural disease below

Naturally occurring disease in another species — a genuine find for this entry. OMIA:002710-9615, "Cardiomyopathy, dilated, ABCC9-related" in Canis lupus familiaris. An ABCC9 p.R1186Q variant, homozygous in all affected dogs, underlies sudden cardiac death / dilated cardiomyopathy (SCDY/DCM) in Manchester Terriers, with death typically before 2 years of age. VBO term: Manchester Terrier (look up the VBO identifier before curating).

This is comparatively informative in a specific way: the canine disease is a recessive, cardiac-predominant ABCC9 disorder — mechanistically adjacent to AIMS' cardiac arm and to human DCM1O, but without a reported neurodevelopmental or myopathic phenotype. Whether that reflects true species divergence, a milder/different variant effect (missense vs. truncating), or simply the limits of assessing cognition in dogs is unresolved — a legitimate comparative-biology knowledge gap.

Comparative pathology and conservation. KATP subunit architecture and the SUR2/Kir6.x tissue pairing are deeply conserved across vertebrates, which is precisely why zebrafish and mouse SUR2 nulls both lose ventricular myocyte KATP current and both reproduce the muscle and cardiac phenotypes. The conservation breaks down for cognition: no SUR2-mutant animal recapitulates the intellectual disability (§6, §15).

Zoonotic potential / cross-species transmission: not applicable — a germline genetic disease.

15. Model Organisms

Mouse

SUR2-STOP (CRISPR/Cas9; the purpose-built AIMS model), Smeland et al. 2019 - Allele: c.3446_3450delACTTCinsGA → premature stop after K1148, p.Y1149Stop, in TM15. - Channel validation: functional KATP essentially absent in both ventricular myocytes and aortic smooth muscle cells on inside-out patch clamp (18 WT vs 10 mutant patches, p<0.0001) — confirming it reproduces the human channel defect even though the genetic lesion differs. - Recapitulates: fatigability (multiple-trial inverted screen — comparable first-trial performance, progressive decline across trials, significant genotype and genotype×trial/session effects; n=9 per group); reduced LV fractional shortening (p<0.01); increased LVIDd normalized to body length; increased blood pressure; increased LV mass. - Fails to recapitulate: cognition and anxiety. Negative across 1-hour locomotor activity, center/periphery distance, a four-test sensorimotor battery (ledge, platform, pole, inclined screen), Morris water maze cued and place trials and probe trials, and elevated plus maze. The authors' verbatim conclusion: "Collectively, the behavioral findings suggest that the SUR2-STOP mice do not exhibit marked deficits in learning and memory nor show any obvious anxiety-like behaviors."

Tissue-selective and CaV1.1 models, McClenaghan et al. 2023 (PMID:37154692) - Tissue-selective KATP suppression localized myopathy to skeletal muscle specifically. - Isolated muscle showed abnormal unstimulated force generation — a mechanistic correlate of painful spasms. - Verapamil caused premature death in AIMS mice. - A CaV1.1-nonpermeable genetic model failed to reverse pathology — falsifying the excess-Ca²⁺-influx-through-CaV1.1 hypothesis.

Pre-existing SUR2 alleles (MGI:1352630) — background/comparative: null alleles show spontaneous death from episodic coronary artery vasospasm, hypertension, growth retardation, lower serum glucose with enhanced insulin action; a homozygous exon 5 deletion causes cardiac mitochondrial defects, cardiomyopathy and early postnatal death. An earlier internal-deletion allele retains a mitochondria-limited short SUR2 form and shows impaired exercise capacity and myofiber damage.

Explicit model caveat from the authors: "The animal models used in this study do not recapitulate the genetic defect identified in the AIMS patients, but were chosen as the functional effects of the frameshift mutations introduced into SUR2-STOP mice and fish mirror the functional effect of the SUR2 Δ8 mutation." They call for knock-in models carrying the actual human AIMS variants — a clean proposed_experiments item.

Zebrafish

SUR2-STOP zebrafish (CRISPR/Cas9), Smeland 2019 + Efthymiou 2024 - Allele: c.2944_2957del13 → frameshift, stop after S984, p.S985Stop, in TM12. - ~4-fold reduction in abcc9 mRNA (qPCR), consistent with NMD; complete absence of functional KATP in ventricular myocytes. - Craniofacial: significantly decreased normalized interorbital distance — recapitulating human hypotelorism (4/6 patients). Notably the mouse did not show this, making the fish the better dysmorphology model. No other striking dysmorphism. - Motor: reduced total movement, reduced total swimming distance, reduced duration of high-speed movements, but similar total time moving (n=62 per genotype) — a fatigability-like rather than paralysis-like signature. Hatching (which requires muscle contraction) was normal. - Cardiac: fractional shortening reduced 29%, ejection fraction 25%, cardiac output 28%, with proportionally reduced stroke volume; unchanged end-diastolic and end-systolic volumes in larvae; markedly enlarged ventricle with abnormal morphology in 5/6 adults; no fibrosis (AFOG); normal tropomyosin myofiber structure; numerous TUNEL-positive cells in both chambers versus very few in WT. No cardiac abnormality in heterozygotes — matching healthy human carriers. - Vascular: increased cardinal vein red-cell velocity, concordant with the hypertension in SUR2-STOP mice. - Seizure susceptibility (2024): exaggerated motor response to pentylenetetrazole. > "In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility." — PMID:38217872 [ABSTRACT-VERIFIED]

In vitro / cellular systems

  • Cosm6 cells transiently transfected with Kir6.2 + FLAG-SUR2A/SUR2B (WT, Δ8, 1:1 mix): Western blot, ⁸⁶Rb⁺ efflux, inside-out patch clamp, ATP dose–response (IC₅₀), pinacidil activation.
  • Landing-pad HEK293 with FLIPR Blue membrane-potential dye and oligomycin A / glibenclamide challenge — the 2026 platform, notable as a scalable variant-classification assay suitable for future ABCC9 VUS interpretation.
  • Patient fibroblasts for cDNA/splicing analysis (exon 8 skipping).
  • No iPSC, organoid, or myotube model of AIMS has been reported — a clear gap, especially given that the ID phenotype is the one thing animal models miss and a human neural or cerebrovascular model could address it.

Recapitulation summary

Human feature Mouse SUR2-STOP Zebrafish SUR2-STOP
Loss of myocyte KATP ✅ ✅
Fatigability / reduced performance ✅ ✅
Muscle spasms / unstimulated force ✅ (isolated muscle, 2023) —
Cardiac systolic dysfunction ✅ ✅
Ventricular dilation/enlargement ✅ ✅
Hypotelorism ❌ ✅
Seizure susceptibility not tested ✅ (PTZ)
Hypertension / vascular tone ✅ ✅ (indirect)
Intellectual disability ❌ formally negative not assessable
Anxiety ❌ formally negative not assessable
Cerebral white matter lesions not reported not reported

Model limitations to record. No model reproduces the two defining CNS features — intellectual disability and cerebral white matter abnormality. Combined with the fact that neuronal KATP is predominantly Kir6.2/SUR1 rather than SUR2, this makes the CNS arm of AIMS pathophysiology the least secure part of the mechanism and the highest-value research target. Per CLAUDE.md this is a HUMAN_MODEL_MISMATCH, not a KNOWLEDGE_GAP: the model evidence exists and is negative, so the open question is translational validity rather than absence of data.

Recommended dismech curation actions

  1. Keep MONDO:0859224 — verified correct, with OMIM:619719 / DOID:0070600 / UMLS C5676904 as mappings. Add IDMYS to synonyms.
  2. Keep hgnc:60 for ABCC9 — verified against genenames.org.
  3. Fix the GO label if used: GO:0008282 canonical label is "inward rectifying potassium channel", not "ATP-sensitive potassium channel complex" (that is a synonym). Put the KATP phrasing in preferred_term.
  4. Model the pathophysiology as one molecular trigger with three arms (skeletal muscle / cerebrovascular-white matter / cardiac), tagging biological_scale per node. Give the cerebrovascular arm a mechanistic_hypotheses entry with status: EMERGING.
  5. Add a HUMAN_MODEL_MISMATCH discussion for the intellectual-disability/anxiety phenotype vs. the formally negative SUR2-STOP mouse behavioral battery, with the authors' proposed working-memory/fear-conditioning experiments as proposed_experiments.
  6. Add a supports: REFUTE evidence item for the CaV1.1-Ca²⁺-influx sub-hypothesis (PMID:37154692) — a rare, valuable falsified-mechanism record.
  7. Curate the drugs-to-avoid content prominently (verapamil/CCBs, phenytoin/fosphenytoin, propofol, lacosamide maintenance), and consider the opposite-hazard pairing with Cantú syndrome (KATP openers) as an explicit cross-reference.
  8. Consider a kb/groupings/ entry for KATP channelopathies — AIMS/Cantú/DCM1O/neonatal diabetes/congenital hyperinsulinism, grouping_basis: [SHARED_MECHANISM, SHARED_GENE_FAMILY], with GoF-vs-LoF as the differentiating axis.
  9. Use measure_type: CASES_IN_LITERATURE + prevalence_class: ULTRA_RARE; do not fabricate a rate.
  10. Omit frequency: on the discordant phenotypes (corpus callosum, dysmorphism) per the repo's frequency-evidence guidelines; record raw counts in notes:.
  11. Before committing: run just fetch-reference for any PMID not already cached, then just validate-references, just validate-terms, and just validate — and specifically re-verify every claim marked [FULL-TEXT — RE-VERIFY] above, since those came through a summarizing intermediary rather than from a cached abstract I read directly.

Primary sources

PMID Citation Role
31575858 Smeland MF, McClenaghan C, Roessler HI, et al. ABCC9-related Intellectual disability Myopathy Syndrome is a K(ATP) channelopathy with loss-of-function mutations in ABCC9. Nat Commun. 2019 Oct 1;10(1):4457. doi:10.1038/s41467-019-12428-7. PMC6773855 Landmark / disease definition. Cached with full text.
38217872 Efthymiou S, Scala M, Nagaraj V, et al. Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome. Brain. 2024 May 3;147(5):1822–1836. doi:10.1093/brain/awae010. PMC11068106 Phenotype/genotype expansion, pooled frequencies, IUFD, zebrafish PTZ.
42290677 Nagaraj V, Thomas QH, Nóbrega PR, et al. Cognitive Decline, Neurologic Involvement, and Neonatal Crisis in ABCC9-Related Intellectual Disability and Myopathy Syndrome. Neurol Genet. 2026 Jun 10;12(4):e200385. doi:10.1212/NXG.0000000000200385. PMC13262668 Most recent. Natural-history extension (neonate → sexagenarian), drug hazards, landing-pad assay.
37154692 McClenaghan C, Mukadam MA, Roeglin J, et al. Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS. EMBO Mol Med. 2023;15(6):e16883. doi:10.15252/emmm.202216883. PMC10245035 Mechanism localization + verapamil toxicity + falsified CaV1.1 hypothesis.
22608503 Harakalova M, van Harssel JJT, Terhal PA, et al. Dominant missense mutations in ABCC9 cause Cantú syndrome. Nat Genet. 2012 Contrasting GoF disorder.
25275207 Grange DK, Nichols CG, Singh GK, et al. Cantú Syndrome. GeneReviews®, University of Washington GoF management and agents-to-avoid contrast.

Databases consulted: OMIM (#619719, 601439), MONDO/OLS4 (MONDO:0859224), HPO annotation API (OMIM:619719), Disease Ontology (DOID:0070600), HGNC (HGNC:60), UniProt (O60706), Ensembl (ENSG00000069431), NCBI Gene (10060, 20928), MGI (MGI:1352630), OMIA (OMIA:002710-9615), ClinGen (search.clinicalgenome.org/kb/genes/HGNC:60), gnomAD (allele-level data via publications; gene constraint not retrieved), ClinicalTrials.gov (no AIMS studies), Orphanet (no AIMS code found).

Sources: - Smeland et al. 2019, Nat Commun (PMC6773855) - Efthymiou et al. 2024, Brain (PMC11068106) - Nagaraj et al. 2026, Neurology Genetics (PMC13262668) - McClenaghan et al. 2023, EMBO Mol Med (PMC10245035) - OMIM #619719 — Intellectual Disability and Myopathy Syndrome - OMIM #601439 — ABCC9 - MONDO:0859224 via EBI OLS4 - HPO annotations for OMIM:619719 - HGNC ABCC9 (genenames.org REST) - MGI:1352630 — mouse Abcc9 - OMIA:002710-9615 — ABCC9-related dilated cardiomyopathy in dog - ClinGen gene curation for ABCC9 (HGNC:60) - Disease Ontology DOID:0070600