Sorbitol Dehydrogenase Deficiency

Genetic MONDO:0030055 Pathograph 21 Show in embeddings browser distal hereditary motor neuropathy axonal Charcot-Marie-Tooth disease

Sorbitol dehydrogenase (SORD) deficiency - also called SORD deficiency with peripheral neuropathy (SORDD), CMT-SORD, or distal hereditary motor neuronopathy autosomal recessive 8 (HMNR8) - is an autosomal recessive, adolescent-onset, length-dependent axonal peripheral neuropathy caused by biallelic loss-of-function variants in SORD. It was defined as a disease entity only in 2020 and is now recognised as one of the most frequent recessive causes of axonal Charcot-Marie-Tooth disease type 2 (CMT2) and distal hereditary motor neuropathy (dHMN). The mechanism is an enzyme block in the two-step polyol pathway. Aldose reductase reduces glucose to sorbitol; SORD then oxidises sorbitol to fructose. When SORD is absent, sorbitol - a poorly membrane-permeant polyol - accumulates in cells, serum, CSF and peripheral nerve, and a motor-predominant axonal degeneration follows. This is the same pathway invoked in diabetic neuropathy, but here it is driven by a germline enzyme deficiency at normal blood glucose, which is why the disease is repeatedly described as a genetic window onto polyol-pathway neurotoxicity. Two features make the entry unusual among inherited neuropathies. First, it has a directly measurable biochemical readout: fasting serum sorbitol is roughly two orders of magnitude above control, and urine sorbitol plus xylitol, or a red-cell SORD activity assay, can be used for case finding - which matters because the SORD2P pseudogene makes short-read molecular diagnosis unreliable and hides a recurrent SORD/SORD2P inversion allele. Second, the enzyme block is therapeutically approachable from upstream: inhibiting aldose reductase reduces the flux into sorbitol rather than replacing the missing enzyme, the rationale for the govorestat (AT-007) programme. The entry deliberately spans the CMT2/dHMN boundary rather than choosing one label. Roughly two-thirds of patients are classified as CMT2 and one-third as dHMN in the largest cohort, on one genotype and one mechanism, so the split is a clinical description of the same disease rather than two entities.

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1
Inheritance
8
Pathophys.
12
Phenotypes
3
Hypotheses
3
Gaps
21
Pathograph
1
Genes
4
Variants
3
Medical Actions
1
Trials
5
Models
4
References
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Deep Research
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Classifications

Harrison's Part
NEUROLOGIC
👪

Inheritance

1
Autosomal recessive HP:0000007
Disease requires biallelic SORD loss-of-function variants - homozygosity for the recurrent c.757delG frameshift allele, compound heterozygosity for that allele with a second variant, or (increasingly recognised) a SORD/SORD2P inversion in trans. Heterozygous carriers have reduced SORD protein but are unaffected. Just over half of probands are sporadic with neither a family history nor reported consanguinity, but consanguinity is not negligible: 18% of the largest cohort had consanguineous parents.
Autosomal recessive inheritance
Show evidence (4 references)
PMID:32367058 SUPPORT Human Clinical
"We identified 45 individuals from 38 families across multiple ancestries carrying the nonsense c.757delG (p.Ala253GlnfsTer27) variant in SORD, in either a homozygous or compound heterozygous state."
Establishes the biallelic (homozygous or compound heterozygous) requirement across unrelated families and ancestries.
PMID:32367058 SUPPORT In Vitro
"SORD protein was absent in all patients and the SORD levels were reduced in unaffected carriers compared to controls"
Shows the gene-dosage basis of recessiveness - carriers retain partial protein and are unaffected, while biallelic patients have none.
PMID:39938083 SUPPORT Human Clinical
"Thus, in 79 (55%) individuals the disease was sporadic, without report of family history of neuropathy or consanguinity."
Quantifies the sporadic majority, which is a bare majority rather than the overwhelming one a looser phrasing would imply.
+ 1 more reference
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Mechanistic Hypotheses

3
Osmotic injury to Schwann cells and myelin
osmotic_myelin_injury_model CANONICAL
Sorbitol is a polar polyol that crosses membranes poorly, so trapping it raises intracellular osmolarity and draws water in. On this model the primary target is the myelinating Schwann cell, and the observable signature is the enlarged "ballooned" myelin sheath that the Sord-null rat shows around otherwise intact axons, with axonal degeneration following secondarily. It is marked CANONICAL as the leading proposal in the mammalian literature - it is the only candidate with a matching structural lesion, and the same abnormality appears in galactosemic neuropathy, another polyol disorder - but leading is not the same as established: no study has measured water content or osmolyte composition in SORD-deficient nerve.
Pathograph links
Polyol Pathway Block with Sorbitol Accumulation -> Osmotic Stress in Schwann Cells and Myelinated Axons INDIRECT UNKNOWN INTERMEDIATES The osmotic arm: a trapped, poorly permeant polyol raises intracellular osmolarity. Curated as a competing model rather than a settled step.
Osmotic Stress in Schwann Cells and Myelinated Axons -> Distal Motor Axonal Degeneration and Demyelination INDIRECT UNKNOWN INTERMEDIATES On this model the Schwann cell is injured first and axonal degeneration is secondary, which is what the rat morphology - swollen sheaths around initially intact axons - suggests.
Bioenergetic failure and oxidative stress
mitochondrial_oxidative_model ALTERNATIVE
Sorbitol accumulation is followed by falling ATP production and rising reactive oxygen species, and axons - the longest and most energy-hungry compartment - fail first. This is the best-evidenced arm in the sense of having direct measurements behind it, but the measurements are in Drosophila brain and muscle and in human skeletal muscle proteomics, neither of which is peripheral nerve, and none of them shows the deficit causing axonal loss.
Pathograph links
Polyol Pathway Block with Sorbitol Accumulation -> Mitochondrial Dysfunction and Oxidative Stress INDIRECT UNKNOWN INTERMEDIATES The oxidative arm: bioenergetic failure and ROS accumulation follow the accumulation, but the steps linking the two are not established.
Mitochondrial Dysfunction and Oxidative Stress -> Distal Motor Axonal Degeneration and Demyelination INDIRECT UNKNOWN INTERMEDIATES Bioenergetic failure and oxidative stress are the amplifying arm shared with other length-dependent axonopathies.
NADPH and NAD+ cofactor imbalance
redox_cofactor_imbalance_model EMERGING
Evidence balance 1 support
Flux through the polyol pathway consumes NADPH at the aldose reductase step and regenerates NAD+ at the SORD step. Losing SORD leaves the reductive step running without its oxidative partner, depleting NADPH - and with it the glutathione-based antioxidant capacity - while NAD+ is not regenerated. This is a well-developed idea in the diabetic-neuropathy literature, but in SORD deficiency it is named as a plausible candidate rather than measured, which is why it is EMERGING and carries no node of its own.
Show evidence (1 reference)
PMID:32367058 SUPPORT Other
"one or more of the known effects of decreased SORD activity, including increased sorbitol level, cellular osmolarity, oxidative stress and decreased NADPH levels, are plausible"
The discovery authors list cofactor depletion among the candidate routes. PARTIAL because it is named as plausible, not demonstrated.
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Discussions and Knowledge Gaps

3
By what route does trapped intracellular sorbitol kill long motor axons - osmotic stress, oxidative stress, NADPH/NAD+ cofactor imbalance, or some combination - and why are motor axons affected while sensory axons are largely spared?
KNOWLEDGE GAP OPEN gap_sorbitol_to_axon_mechanism
Attached to
pathophysiology#Polyol Pathway Block with Sorbitol Accumulation pathophysiology#Osmotic Stress in Schwann Cells and Myelinated Axons pathophysiology#Mitochondrial Dysfunction and Oxidative Stress pathophysiology#Distal Motor Axonal Degeneration and Demyelination
The genotype-to-metabolite half of the mechanism is settled, and the metabolite-to-axon half is not. The candidates are curated as competing mechanistic_hypotheses rather than argued in prose here: osmotic_myelin_injury_model (CANONICAL), mitochondrial_oxidative_model (ALTERNATIVE) and redox_cofactor_imbalance_model (EMERGING), with the first two carried on tagged causal edges out of the accumulation node. This discussion records what would settle between them. The discovery authors listed osmotic stress, oxidative stress and reduced NADPH as plausible and did not choose between them, and the govorestat study restated that the mechanisms of sorbitol-induced degeneration are not fully elucidated. The gap matters therapeutically as well as descriptively: substrate reduction works upstream of whichever route is correct, so it can succeed without settling the question, but any attempt to protect the axon downstream needs the answer. The motor-over-sensory selectivity is a second, related unknown - sorbitol accumulates systemically, yet the lesion is selective, and the ballooned myelin seen in the rat points at Schwann cells as at least a co-target.
Proposed experiments
Compartment-resolved osmotic versus oxidative dissection in Sord-null rat nerve
exp_osmotic_vs_oxidative_rat_nerve
In Sord-/- rat sciatic and tibial nerve, measure Schwann cell and axonal water content and organic-osmolyte composition alongside oxidative-damage markers and NADPH/NADP+ and NAD+/NADH ratios, at ages before and after the onset of conduction slowing, and test whether an antioxidant that does not lower sorbitol prevents the lesion. A dissociation between sorbitol lowering and antioxidant protection would separate the osmotic and oxidative arms.
Motor versus sensory neuron comparison in isogenic human cultures
exp_motor_vs_sensory_isogenic_ipsc
Differentiate isogenic patient and gene-corrected iPSC lines into motor and sensory neurons in microfluidic axon-compartment devices, and compare sorbitol handling, axonal transport, bioenergetics and axon survival between the two lineages under matched glucose. This tests whether the selectivity is cell-intrinsic or requires the Schwann cell.
Show evidence (2 references)
PMID:32367058 SUPPORT Other
"Our findings do not fully elucidate yet the mechanism of axonal damage caused by SORD deficiency: one or more of the known effects of decreased SORD activity, including increased sorbitol level, cellular osmolarity, oxidative stress and decreased NADPH levels, are plausible"
The discovery authors state the gap and enumerate the candidate routes.
PMID:37014713 SUPPORT Other
"The underlying mechanisms of sorbitol-induced degeneration have not been fully elucidated"
Restates the gap three years later, confirming it remains open.
Why does a mouse with markedly reduced SORD protein develop no neuropathy and no conduction slowing, when biallelic SORD loss reliably causes neuropathy in humans and a motor-predominant neuropathy in the rat?
HUMAN MODEL MISMATCH OPEN mismatch_mouse_sord_no_neuropathy
Attached to
pathophysiology#Distal Motor Axonal Degeneration and Demyelination
This is a mismatch rather than an absence of evidence: the C57BL/LiA mouse has been studied and is negative. The explanation offered - that standard mouse chow is low in sugar relative to human and Drosophila diets, so polyol flux never reaches the level needed to accumulate toxic sorbitol - is attractive because it predicts the disease is flux-dependent rather than purely genotype-dependent, and because SORD deficiency does aggravate neuropathy in diabetic rodents. It is also untested. The alternative, that the hypomorphic allele leaves enough residual enzyme, is not excluded. The distinction matters for interpreting every negative rodent result in this disease and for whether dietary sugar should be treated as a modifier in patients.
Proposed experiments
High-sugar diet and ageing challenge in the hypomorphic mouse
exp_high_sugar_diet_hypomorphic_mouse
Maintain C57BL/LiA and control mice on standard versus high-sugar diets to old age, with serial motor nerve conduction, nerve histology and nerve sorbitol. Emergence of the lesion on the high-sugar arm alone would confirm flux dependence; its absence under both would point instead at residual enzyme activity or a species difference.
Null versus hypomorph comparison
exp_null_vs_hypomorph_mouse
Phenotype a true Sord-null mouse alongside C57BL/LiA under identical husbandry, measuring residual enzyme activity, nerve sorbitol and conduction. This separates allele strength from diet as the explanation.
Show evidence (2 references)
PMID:32367058 SUPPORT Model Organism
"Mice that have significantly reduced levels of SORD protein due to an intronic splicing mutation (C57BL/LiA mice), bred and fed according to the standard laboratory conditions, do not develop neuropathy or even slowed nerve conduction velocities"
Establishes the negative mouse result that constitutes the mismatch.
PMID:38538210 SUPPORT Model Organism
"In summary, Sord-/- rats develop a motor-predominant neuropathy that closely resembles the human phenotype."
The contrasting positive rodent result that makes the mouse finding a mismatch rather than a rule about rodents.
Should SORD deficiency be curated as one disease spanning CMT2 and dHMN, as it is here, or split along the clinical labels its patients receive?
INTERPRETATION OPEN interpretation_cmt2_dhmn_split
Attached to
pathophysiology#Motor-Predominant Hereditary Neuropathy Spanning CMT2 and dHMN
Cohorts assign the same genotype to different labels in different proportions - roughly two-thirds CMT2 in the largest multicentre series, but a dHMN majority in the French and Swiss cohort - and a third label, intermediate CMT, is used for patients whose conduction velocities fall in between. The labels track how much sensory involvement was found and how velocities were interpreted, not genotype, mechanism, or the allele carried. Splitting would therefore produce entries that differ in ascertainment rather than in biology. MONDO indexes the disease under the dHMN branch (MONDO:0030055, is_a neuronopathy, distal hereditary motor, autosomal recessive), which this entry follows for its disease_term while recording the CMT2 presentation as the same disease.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Two-thirds of cases were diagnosed with CMT2 while one-third had distal hereditary motor neuropathy."
The CMT2-majority split in the largest cohort.
PMID:36943151 SUPPORT Human Clinical
"Eighteen had dHMN, nine had CMT2, and three had intermediate CMT."
The opposite split in an independent cohort, which is the argument against splitting the entry on these labels.
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Pathophysiology

8
Biallelic SORD Loss-of-Function Variants
Two loss-of-function SORD alleles. The recurrent frameshift c.757delG (p.Ala253GlnfsTer27) dominates the allele spectrum worldwide and is found homozygously in most patients; c.458C>A (p.Ala153Asp) is the commonest second allele. A third allele class - inversion between SORD and its highly homologous pseudogene SORD2P - is invisible to short-read sequencing and accounts for a further tranche of cases. Missense alleles act by destabilising the enzyme rather than by any dominant-negative or neomorphic route: c.404A>G produces insoluble SORD aggregates in vitro, and a splice allele c.908+1G>C disrupts the transcript.
SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this genetic context concerns this gene This genetic context concerns SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee. allele_type: frameshift, missense, splice-site, and gene-pseudogene inversion variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: LOSS_OF_FUNCTION
Homozygous in most patients and compound heterozygous in the remainder; all characterised alleles converge on absent or non-functional enzyme.
Downstream
Loss of Sorbitol Dehydrogenase Activity Absent or unstable protein leaves the cell with no functional sorbitol dehydrogenase.
Show evidence (2 references)
PMID:32367058 SUPPORT Human Clinical
"We identified 45 individuals from 38 families across multiple ancestries carrying the nonsense c.757delG (p.Ala253GlnfsTer27) variant in SORD, in either a homozygous or compound heterozygous state."
The discovery cohort establishing c.757delG as the dominant recurrent allele across ancestries.
PMID:33397963 SUPPORT In Vitro
"In vitro cell functional studies showed that c.404 A > G variant resulted in aggregate formation of SORD and low protein solubility, confirming the pathogenicity of SORD variants."
Functional demonstration that a missense allele destroys the enzyme by destabilising it, supporting a loss-of-function rather than dominant-negative reading.
Loss of Sorbitol Dehydrogenase Activity
Sorbitol dehydrogenase (EC 1.1.1.14), the NAD+-dependent second enzyme of the polyol pathway, is absent from patient cells. Protein is undetectable by western blot in fibroblasts homozygous for c.757delG, and red-cell enzyme activity is significantly reduced against run controls - a difference large enough that a screening assay has been built on it. The 30% figure quoted in the biochemical record is that assay's proposed cutoff, not a measured residual activity of the disease.
sorbitol dehydrogenase activity GO:0003939 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves absent sorbitol dehydrogenase activity, annotated with L-iditol 2-dehydrogenase (NAD+) activity (GO:0003939). GO:0003939 is a molecular function from the Gene Ontology. ∅ ABSENT
Experimental models
Patient-derived skin fibroblasts (SORD c.757delG homozygous) PRIMARY CELL CULTURE Human cells carrying the patient genotype, with complete absence of the enzyme protein.
Downstream
Polyol Pathway Block with Sorbitol Accumulation With the oxidative step gone, sorbitol produced by aldose reductase has no exit and is trapped.
Show evidence (2 references)
PMID:32367058 SUPPORT In Vitro
"SORD protein was absent in all patients and the SORD levels were reduced in unaffected carriers compared to controls"
Direct demonstration of absent enzyme protein in patient-derived cells.
PMID:42021567 SUPPORT Human Clinical
"RBC SORD activity was significantly reduced in individuals diagnosed with SORD deficiency when compared to within-run controls"
Confirms the enzymatic (not merely protein-level) deficit directly in patient material.
Polyol Pathway Block with Sorbitol Accumulation
Aldose reductase continues to reduce glucose to sorbitol, but the second step is blocked, so sorbitol - a polar, poorly membrane-permeant polyol - accumulates. Intracellular sorbitol is more than ten-fold elevated in patient fibroblasts and fasting serum sorbitol is roughly two orders of magnitude above control. In the Sord-null rat the accumulation is documented in the compartment that matters: serum, CSF and peripheral nerve. This is the metabolic insult that the conserved peripheral-axonal-degeneration module describes generically; here it is the whole trigger, with no toxic, inflammatory or hyperglycaemic component.
Bioenergetic failure and oxidative stress Osmotic injury to Schwann cells and myelin
sorbitol catabolism GO:0006062 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased sorbitol catabolism, annotated with D-sorbitol catabolic process (GO:0006062). GO:0006062 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Patient iPSC-derived motor neurons IPSC DERIVED MODEL Provides the sorbitol readout in a human motor neuron rather than in a fibroblast or fly.
Animal models
Sord knockout Sprague Dawley rat Rat recapitulates Establishes that sorbitol accumulates in the nervous-system compartments that patient serum measurements cannot reach.
Drosophila Sodh2 loss-of-function Drosophila melanogaster rescues Aldose reductase inhibitor feeding normalised sorbitol and rescued motor and eye phenotypes, which is the pharmacological proof that the metabolite and not some other consequence of the genotype drives degeneration.
Downstream
Osmotic Stress in Schwann Cells and Myelinated Axons The osmotic arm: a trapped, poorly permeant polyol raises intracellular osmolarity. Curated as a competing model rather than a settled step. Osmotic injury to Schwann cells and myelin
Mitochondrial Dysfunction and Oxidative Stress The oxidative arm: bioenergetic failure and ROS accumulation follow the accumulation, but the steps linking the two are not established. Bioenergetic failure and oxidative stress
Distal Motor Axonal Degeneration and Demyelination Deliberately retained alongside the two hypothesis-tagged arms above: the accumulation-to-axon link is evidenced pharmacologically (removing the metabolite prevents degeneration) without any of the candidate routes being established, so this edge carries the part of the claim that survives whichever model turns out to be right. See the gap_sorbitol_to_axon_mechanism discussion.
Show evidence (3 references)
PMID:32367058 SUPPORT Other
"SORD is an enzyme that converts sorbitol into fructose in the two-step polyol pathway previously implicated in diabetic neuropathy."
States the enzymatic step whose loss produces the block. Evidence source is OTHER because this is a definitional background statement, not a clinical observation.
PMID:32367058 SUPPORT In Vitro
"intracellular sorbitol concentrations were over 10 times higher in patient fibroblasts compared to controls"
Quantifies the intracellular accumulation in human patient cells.
PMID:38538210 SUPPORT Model Organism
"Sord-/- rats had remarkably increased levels of sorbitol in serum, CSF and peripheral nerve."
Shows the accumulation reaches the peripheral nerve compartment, which patient serum measurements cannot establish.
Osmotic Stress in Schwann Cells and Myelinated Axons
The osmotic candidate for how a trapped metabolite injures nerve. Sorbitol crosses membranes poorly, so an unclearable intracellular pool should draw water in, and the structural finding that fits is the enlarged "ballooned" myelin sheath seen around otherwise intact axons in the Sord-null rat - an abnormality also described in galactosemic neuropathy, where a different polyol accumulates. The node is HYPOTHETICAL by design: the lesion is consistent with osmotic swelling and is the reason this is the leading model, but nobody has measured water content, osmolyte composition or volume regulation in SORD-deficient nerve, so the inference runs from morphology to mechanism rather than the other way round.
Osmotic injury to Schwann cells and myelin
Schwann cell CL:0002573 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Schwann cell (CL:0002573). CL:0002573 is a cell type from the Cell Ontology.
response to osmotic stress GO:0006970 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased response to osmotic stress (GO:0006970). GO:0006970 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Distal Motor Axonal Degeneration and Demyelination On this model the Schwann cell is injured first and axonal degeneration is secondary, which is what the rat morphology - swollen sheaths around initially intact axons - suggests. Osmotic injury to Schwann cells and myelin
Show evidence (1 reference)
PMID:38538210 SUPPORT Model Organism
"Light and electron microscopy of the peripheral nervous system revealed degenerating myelinated axons, de- and remyelinated axons, and a likely pathognomonic finding-enlarged 'ballooned' myelin sheaths."
The myelin abnormality that motivates the osmotic reading. PARTIAL because ballooned myelin is consistent with osmotic swelling but is not a measurement of it, and the authors call it pathognomonic of the disease rather than of a mechanism.
Mitochondrial Dysfunction and Oxidative Stress
Sord-deficient Drosophila show reduced brain ATP production and reactive oxygen species accumulation in CNS and muscle, and both are corrected by aldose reductase inhibition, which ties them to sorbitol rather than to the genotype in general. Independent human support comes from proteomic analysis of patient skeletal muscle, where respiratory complex I deficiency dominated and the malate/oxaloacetate ratio was raised. The node is marked PROVISIONAL because the animal evidence is invertebrate and the human evidence is muscle proteomics rather than nerve.
Bioenergetic failure and oxidative stress
response to oxidative stress GO:0006979 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased response to oxidative stress (GO:0006979). GO:0006979 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
Drosophila Sodh2 loss-of-function Drosophila melanogaster recapitulates Supplies the bioenergetic and oxidative-stress evidence for this node.
Downstream
Distal Motor Axonal Degeneration and Demyelination Bioenergetic failure and oxidative stress are the amplifying arm shared with other length-dependent axonopathies. Bioenergetic failure and oxidative stress
Show evidence (2 references)
PMID:37014713 SUPPORT Model Organism
"In addition, we found reduced ATP production in the brain and ROS accumulation in the CNS and muscle, indicating mitochondrial dysfunction."
Bioenergetic and oxidative readouts in the Drosophila model of SORD loss.
PMID:40580554 SUPPORT Human Clinical
"Complex I deficiency was dominant in the proteomic analysis and the malic acid/oxaloacetic acid ratio was significantly higher in the patients than in controls."
Human corroboration of a mitochondrial abnormality, but measured in skeletal muscle rather than in peripheral nerve, hence PARTIAL.
Distal Motor Axonal Degeneration and Demyelination
Degeneration falls on myelinated motor axons and largely spares myelinated sensory axons - the structural counterpart of the motor-predominant clinical picture. Rat nerve shows degenerating myelinated axons, de- and remyelinated axons, and enlarged "ballooned" myelin sheaths that the authors propose as a pathognomonic feature. Human sural nerve, sampled in a sensory nerve in a motor-predominant disease, shows correspondingly mild change: modest loss of large myelinated fibres with a few thinly myelinated fibres.
motor neuron CL:0000100 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves motor neuron (CL:0000100). CL:0000100 is a cell type from the Cell Ontology. Schwann cell CL:0002573 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Schwann cell (CL:0002573). CL:0002573 is a cell type from the Cell Ontology. sensory neuron CL:0000101 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves sensory neuron (CL:0000101). CL:0000101 is a cell type from the Cell Ontology.
peripheral nerve UBERON:0001021 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in peripheral nerve, annotated with nerve (UBERON:0001021). UBERON:0001021 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
Sord knockout Sprague Dawley rat Rat recapitulates Reproduces the motor-over-sensory selectivity of the human lesion at the level of nerve pathology and conduction.
C57BL/LiA mouse with reduced SORD Mouse fails to recapitulate Reduced SORD protein in this strain does not produce the human lesion, so the model cannot be used to test the axonal-degeneration arm.
Downstream
Length-Dependent Motor-Predominant Nerve Fiber Dysfunction
Show evidence (3 references)
PMID:38538210 SUPPORT Model Organism
"Light and electron microscopy of the peripheral nervous system revealed degenerating myelinated axons, de- and remyelinated axons, and a likely pathognomonic finding-enlarged 'ballooned' myelin sheaths."
Primary structural description of the lesion, including the myelin abnormality that suggests an osmotic component.
PMID:38538210 SUPPORT Model Organism
"These findings mainly affected myelinated motor axons; myelinated sensory axons were largely spared."
Establishes the motor-over-sensory selectivity at the level of nerve pathology.
PMID:40580554 SUPPORT Human Clinical
"Sural nerve biopsies showed mild loss of large, myelinated fibers, and a few thin myelinated fibers."
Human nerve histology; mild because the sural nerve is sensory and this is a motor-predominant disease.
Length-Dependent Motor-Predominant Nerve Fiber Dysfunction
Nerve conduction shows a motor-predominant axonal neuropathy, with conduction velocities reduced into the intermediate range in a minority - which is why some patients are labelled intermediate CMT. Sensory conduction is affected in a pattern that is not simply length-dependent: upper-limb sensory responses are abnormal more often than lower-limb ones, an inversion of the usual gradient that is itself a diagnostic clue. Conformance to the module's length-dependent node is therefore declared for the motor arm only; the sensory pattern curated here is the exception to it, not an instance of it.
Downstream
Motor-Predominant Hereditary Neuropathy Spanning CMT2 and dHMN
Show evidence (2 references)
PMID:32367058 SUPPORT Human Clinical
"Detailed nerve conduction studies were available in 42 patients and invariably showed a motor axonal neuropathy"
Establishes the electrophysiological signature as invariant across the discovery cohort.
PMID:39938083 SUPPORT Human Clinical
"Sensory conductions in the upper limbs appeared more frequently affected than in the lower limbs."
Records the non-length-dependent sensory pattern in the largest cohort.
Motor-Predominant Hereditary Neuropathy Spanning CMT2 and dHMN
The clinical endpoint is a slowly progressive distal weakness and amyotrophy with foot deformity, beginning in the second decade. Whether an individual is labelled CMT2 or dHMN depends on how much sensory involvement is found, not on genotype: about two-thirds are classified as CMT2 and one-third as dHMN on the same allele spectrum.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Two-thirds of cases were diagnosed with CMT2 while one-third had distal hereditary motor neuropathy."
Documents that one genotype produces both clinical labels.
PMID:36943151 SUPPORT Human Clinical
"Eighteen had dHMN, nine had CMT2, and three had intermediate CMT."
Independent cohort showing the same spread of clinical labels, here with dHMN in the majority.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Sorbitol Dehydrogenase Deficiency 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

12
Metabolism 1
Elevated Serum Creatine Kinase Elevated circulating creatine kinase concentration HP:0003236 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating creatine kinase concentration (HP:0003236). HP:0003236 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38406380 SUPPORT Human Clinical
"Since creatine phosphokinase (CPK) values were persistently raised (1.5fold increased) and a Next-Generation Sequencing CMT-associated panel failed in identifying pathogenic variants, a muscle biopsy was performed"
Documents raised CK and the diagnostic detour it caused. No frequency is asserted: the source describes itself as an isolated report and states that no association between SORD variants and muscle involvement had been described before it, so there is no cohort denominator to band.
Musculoskeletal 1
Mild Scoliosis OCCASIONAL HP:0002650 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Scoliosis (HP:0002650), qualified as severity mild. HP:0002650 is a phenotype from the Human Phenotype Ontology.
Severity: MILD
Show evidence (1 reference)
PMID:32367058 SUPPORT Human Clinical
"Seven patients had upper limb tremor, four had mild scoliosis and two had mild hearing loss."
Four of the 45 patients in the discovery cohort is 8.9%, which is the OCCASIONAL band (5-29%), not VERY_RARE.
Nervous System 2
Retained or Brisk Upper Limb and Patellar Reflexes Hyperreflexia HP:0001347 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperreflexia (HP:0001347). HP:0001347 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Deep tendon reflexes in the upper limbs and knees were frequently retained or even increased, while ankle reflexes were more typically reduced or absent."
Establishes the dissociation: preserved or increased above the ankle, reduced or absent at it.
PMID:39938083 SUPPORT Human Clinical
"Upper limb and patellar reflexes may be retained or even brisk, suggesting the presence of a possible subclinical involvement of the CNS, as also observed in other axonal CMT subtypes"
Repeats the observation and offers the subclinical-CNS reading. PARTIAL because the CNS involvement is proposed, not shown - the same paper reports no relevant imaging change.
Upper Limb Tremor OCCASIONAL HP:0001337 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tremor (HP:0001337). HP:0001337 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32367058 SUPPORT Human Clinical
"Seven patients had upper limb tremor, four had mild scoliosis and two had mild hearing loss."
Seven of 45 patients gives an OCCASIONAL frequency.
Other 8
Distal Lower Limb Muscle Weakness VERY_FREQUENT HP:0009053 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Distal lower limb muscle weakness (HP:0009053), qualified as course progressive. HP:0009053 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (2 references)
PMID:32367058 SUPPORT Human Clinical
"All individuals had limb weakness, but only one-half had sensory impairment."
Limb weakness in every patient of the discovery cohort supports the VERY_FREQUENT band.
PMID:39938083 SUPPORT Human Clinical
"Although foot dorsiflexion was the most affected muscle group, dorsal and plantar flexion had a similar degree of weakness in most cases"
Localises the weakness to the distal lower limb in the largest cohort.
Foot Dorsiflexor Weakness HP:0009027 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Foot dorsiflexor weakness (HP:0009027), qualified as course progressive. HP:0009027 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (1 reference)
PMID:39938083 SUPPORT Human Clinical
"Foot dorsiflexion and plantar flexion decreased significantly with age."
Identifies dorsiflexion as an affected and progressively declining muscle group.
Foot Deformity FREQUENT Abnormal foot morphology HP:0001760 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Foot deformity, annotated with Abnormal foot morphology (HP:0001760). HP:0001760 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:39938083 SUPPORT Human Clinical
"Disease onset was usually in the second decade of life, however, 79% of patients reported foot deformities and 46% described poor performance in sport activities at school, suggesting an earlier onset of disease."
79% in the largest cohort supports the FREQUENT band, and the same sentence carries the inference that disease begins before the presenting complaint.
PMID:32367058 SUPPORT Human Clinical
"two thirds of the patients reported foot deformities, indicating that the neuropathy probably started earlier in life"
Gives the frequency band and the inference about subclinical onset.
PMID:36943151 SUPPORT Human Clinical
"Thirty patients had SORD peripheral neuropathy associating LL weakness with muscular atrophy, foot deformities (87%), and sometimes proximal LL weakness (20%) or distal upper limb weakness (50%)."
Independent cohort reporting foot deformity in 87%.
Distal Amyotrophy VERY_FREQUENT HP:0003693 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Distal amyotrophy (HP:0003693), qualified as course progressive. HP:0003693 is a phenotype from the Human Phenotype Ontology.
Course: PROGRESSIVE
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Distal atrophy was observed in 98% of cases."
Direct quantitative support for the VERY_FREQUENT band (80-100%).
PMID:36943151 SUPPORT Human Clinical
"Thirty patients had SORD peripheral neuropathy associating LL weakness with muscular atrophy, foot deformities (87%), and sometimes proximal LL weakness (20%) or distal upper limb weakness (50%)."
Muscular atrophy accompanying lower-limb weakness in all 30 patients of an independent cohort.
Distal Upper Limb Weakness FREQUENT Distal upper limb muscle weakness HP:0008959 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Distal upper limb muscle weakness (HP:0008959). HP:0008959 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Half of the patients had reduced strength of intrinsic hand muscles, while most patients had reduced strength of distal lower limb muscles."
Half of the largest cohort places this in the FREQUENT band (30-79%), and the same sentence records that the lower limb is affected more often.
PMID:36943151 SUPPORT Human Clinical
"sometimes proximal LL weakness (20%) or distal upper limb weakness (50%)"
Independent cohort giving the same 50% figure.
Distal Sensory Impairment FREQUENT HP:0002936 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Distal sensory impairment (HP:0002936). HP:0002936 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:32367058 SUPPORT Human Clinical
"All individuals had limb weakness, but only one-half had sensory impairment."
Direct frequency statement placing sensory impairment in the FREQUENT band and subordinate to the motor deficit.
PMID:39938083 SUPPORT Human Clinical
"SNAP amplitude or slower conduction velocities were observed in up to 76% of cases in the upper limbs but only 27% in the lower limbs, thus confirming the observation of a previous smaller case series."
Quantifies the inverted upper-limb-over-lower-limb sensory gradient that the description asserts, which would otherwise be an uncited claim.
Reduced or Absent Ankle Reflexes FREQUENT Reduced tendon reflexes HP:0001315 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Reduced tendon reflexes (HP:0001315). HP:0001315 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Deep tendon reflexes in the upper limbs and knees were frequently retained or even increased, while ankle reflexes were more typically reduced or absent."
"More typically reduced or absent" is a qualitative majority statement, which maps to the FREQUENT band; no cohort denominator is given, so no narrower band is asserted.
PMID:34819907 SUPPORT Human Clinical
"They shared a common phenotype, with motor-predominant distal muscle weakness and atrophy of the lower limb and decreased or absent deep tendon reflex and foot deformities."
Independent cohort reporting decreased or absent reflexes as part of the shared phenotype.
Motor Axonal Neuropathy on Nerve Conduction Studies VERY_FREQUENT HP:0007002 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Motor axonal neuropathy (HP:0007002). HP:0007002 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:32367058 SUPPORT Human Clinical
"Detailed nerve conduction studies were available in 42 patients and invariably showed a motor axonal neuropathy"
Nerve conduction was abnormal in the same motor axonal pattern in all 42 studied patients of the discovery cohort, which supports the VERY_FREQUENT band.
PMID:39938083 SUPPORT Human Clinical
"Nerve conduction studies were suggestive of a motor predominant axonal neuropathy, with reduced conduction velocities in the intermediate range in a quarter of the cases."
Confirms the pattern and quantifies the intermediate-velocity subset.
🧬

Genetic Associations

1
SORD (SORD (15q21.1) encodes the 357-residue cytosolic NAD+-dependent sorbitol dehydrogenase. Biallelic loss-of-function is necessary and sufficient for disease. Molecular diagnosis is complicated by SORD2P, a highly homologous non-functional pseudogene in which the recurrent c.757delG position is fixed on most control chromosomes, so short-read data mismap and biallelic status is hard to phase; long-read sequencing resolves both problems, and a recurrent SORD/SORD2P inversion is only detectable that way.)
Gene: SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Autosomal recessive
Show evidence (3 references)
PMID:32367058 SUPPORT Human Clinical
"SORD has a non-functional highly homologous paralogue, the pseudogene SORD2P, which is thought to have arisen from the duplication of SORD within a 0.5 Mb region on chromosome 15"
Describes the pseudogene that makes standard molecular diagnosis unreliable.
PMID:35224818 SUPPORT Human Clinical
"Subsequent Oxford Nanopore Tech (ONT) long-read sequencing was used to successfully differentiate SORD from the highly homologous non-functional SORD2P pseudogene and confirmed that the mutations were biallelic through haplotype-resolved analysis."
Demonstrates the technical solution to the pseudogene and phasing problems.
PMID:41282915 SUPPORT Human Clinical
"we identified novel and recurrent inversions between SORD and its pseudogene SORD2P in 13 out of 151 patients (9%) affected by SORD-related Charcot-Marie-Tooth (CMT) neuropathy, including 6 out of 8 (75%) of SORD-CMT cases where only one pathogenic variant was identified on short read..."
Establishes gene-pseudogene inversion as a third recurrent allele class and explains apparently monoallelic cases.
🔬

Variants

4
SORD c.757delG (p.Ala253GlnfsTer27) Pathogenic
Gene: SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee. frameshift
Recurrent single-nucleotide deletion in SORD exon 7 producing a frameshift and premature termination. It is by far the commonest pathogenic allele, present homozygously in most reported patients and on one allele in most of the rest, and it recurs across European, Middle Eastern and East Asian ancestries rather than tracking a single founder haplotype.
Show evidence (2 references)
PMID:36943151 SUPPORT Human Clinical
"Sixteen carried a homozygous c.757delG (p.Ala253Glnfs*27) variant, and 11 carried compound heterozygous variants"
Shows the allele dominating a 30-patient European cohort in both homozygous and compound heterozygous form.
PMID:39938083 SUPPORT Human Clinical
"We confirmed c.757delG (p.Ala253GlnfsTer27) as the most common pathogenic allele, followed by c.458C>A (p.Ala153Asp), while other variants were identified, mostly in single cases."
Confirms the allele hierarchy in the largest multicentre cohort.
SORD c.458C>A (p.Ala153Asp) Pathogenic
Gene: SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee. missense
Missense allele, the second commonest after c.757delG and the one most often found in trans with it. Curated as a variant record because the allele spectrum of this disease is short and top-heavy: two alleles account for most of it, and the rest are largely private.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"We confirmed c.757delG (p.Ala253GlnfsTer27) as the most common pathogenic allele, followed by c.458C>A (p.Ala153Asp), while other variants were identified, mostly in single cases."
Places this allele second in the spectrum, in the largest cohort.
PMID:38975976 SUPPORT Human Clinical
"One additional case carried this variant on one allele only and an additional pathogenic missense variant c.458C > A (p.Ala153Asp) on the other allele."
Independent report of the allele in trans with c.757delG, the usual compound heterozygous configuration.
SORD/SORD2P gene-pseudogene inversion Pathogenic
Gene: SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee. inversion
A structural rearrangement between SORD and its pseudogene, and the third commonest pathogenic allele class. It is curated as a variant in its own right rather than left in the diagnostic discussion because it changes what a negative result means: short-read sequencing cannot see it, so it is concentrated precisely among the cases that look monoallelic and therefore unsolved.
Show evidence (1 reference)
PMID:41282915 SUPPORT Human Clinical
"we identified novel and recurrent inversions between SORD and its pseudogene SORD2P in 13 out of 151 patients (9%) affected by SORD-related Charcot-Marie-Tooth (CMT) neuropathy, including 6 out of 8 (75%) of SORD-CMT cases where only one pathogenic variant was identified on short read..."
Establishes both the allele's rank in the spectrum and its concentration in apparently single-variant cases.
SORD c.908+1G>C Pathogenic
Gene: SORD hgnc:11184 HUGO Gene Nomenclature Committee (hgnc) Relation: this variant is in this gene This variant is in SORD (hgnc:11184). hgnc:11184 is a gene from the HUGO Gene Nomenclature Committee. splice site
Splice-donor variant shown by ex vivo cDNA analysis to impair splicing of the SORD transcript - one of the few SORD alleles with direct transcript-level functional evidence.
Show evidence (1 reference)
PMID:33397963 SUPPORT In Vitro
"Ex vivo cDNA polymerase chain reaction confirmed that c.908 + 1 G > C variant was associated with impaired splicing of the SORD transcript."
Transcript-level demonstration of the splicing defect.
🗃️

External Assertions

2
OMIM HMNR8 (SORD)
OMIM disease record OMIM:618912
OMIM phenotype entry for neuronopathy, distal hereditary motor, autosomal recessive 8, the SORD-related recessive neuropathy.
Orphanet sorbitol dehydrogenase deficiency
Orphanet disease record ORPHA:700508
Orphanet disorder record for sorbitol dehydrogenase deficiency, cross-referenced from MONDO:0030055.
💊

Medical Actions

3
Aldose Reductase Inhibition (Investigational)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: epalrestat CHEBI:31539 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses epalrestat (CHEBI:31539). CHEBI:31539 is a therapeutic agent from Chemical Entities of Biological Interest. govorestat (AT-007) Relation: this treatment uses this therapeutic agent This treatment uses govorestat (AT-007).
Substrate reduction rather than enzyme replacement: inhibiting aldose reductase, the enzyme upstream of the block, reduces flux of glucose into sorbitol and so lowers sorbitol despite the missing SORD. Epalrestat and ranirestat established the principle in patient fibroblasts and in Drosophila; the CNS-penetrant next-generation inhibitor govorestat (AT-007) carried it into the clinic, lowering sorbitol in patient fibroblasts, iPSC-derived motor neurons and fly brain and rescuing synaptic, locomotor and mitochondrial phenotypes in flies. No aldose reductase inhibitor is approved for this indication, and this entry records no clinical efficacy claim: the evidence curated here is preclinical, and the clinical trial is listed separately under clinical_trials.
Mechanism Target:
INHIBITS Polyol Pathway Block with Sorbitol Accumulation — The drug acts one step upstream of the genetic lesion, cutting production of the metabolite that accumulates rather than restoring the missing enzyme.
Show evidence (1 reference)
PMID:32367058 SUPPORT In Vitro
"In patient fibroblasts both Epalrestat and Ranirestat significantly reduced sorbitol levels"
Target engagement in human patient cells: inhibiting the upstream enzyme lowers the metabolite that accumulates. Quoted from the fibroblast experiment alone so the evidence source is unambiguously in vitro.
Show evidence (2 references)
PMID:37014713 SUPPORT In Vitro
"AT-007 significantly reduced sorbitol levels in patient-derived fibroblasts, induced pluripotent stem cell-derived (iPSC-derived) motor neurons, and Drosophila brains."
Target engagement for govorestat in human patient-derived cells including motor neurons. The quoted sentence also reports fly brain; the item is tagged IN_VITRO for the human-cell measurements it is cited for, and the Drosophila arm is carried separately by the MODEL_ORGANISM item below.
PMID:37014713 SUPPORT Model Organism
"AT-007 feeding in Sord-deficient Drosophila mitigated synaptic degeneration and significantly improved synaptic transduction, locomotor activity, and mitochondrial function."
Phenotypic rescue in vivo, but in an invertebrate model - the basis for the trial, not evidence of clinical benefit.
Ankle-Foot Orthoses and Rehabilitation
Action: physical therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is physical therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. Ontology label: Physical Therapy NCIT:C15302
The current standard of care is supportive: ankle-foot orthoses for foot drop, plus physiotherapy for gait and strength maintenance. About a quarter of patients take up orthoses, usually in their thirties.
Target Phenotypes: Foot dorsiflexor weakness HP:0009027 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Foot dorsiflexor weakness (HP:0009027). HP:0009027 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:39938083 SUPPORT Human Clinical
"One-fourth of patients used ankle foot orthoses, usually in their 30s, but most patients maintained independent ambulation later in life."
Documents orthotic use and its timing in the largest cohort.
Genetic Counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Autosomal recessive recurrence counselling for families, with the practical caveat that carrier and biallelic status cannot be read reliably off short-read sequencing because of SORD2P; serum sorbitol or long-read sequencing may be needed to settle a genotype.
🔬

Biochemical Markers

3
Elevated Fasting Serum Sorbitol (INCREASED)
Context: The defining biochemical abnormality and the practical diagnostic test. Fasting serum sorbitol is roughly two orders of magnitude above control and separates patients from both controls and heterozygous carriers, which makes it usable for adjudicating variants of uncertain significance as well as for case finding.
Show evidence (3 references)
PMID:32367058 SUPPORT Human Clinical
"we next tested the fasting sorbitol level in serum from ten patients carrying the homozygous p.Ala253GlnfsTer27 mutation and ten unrelated controls and found it was over 100 times higher"
Quantifies the elevation against matched controls.
PMID:39938083 SUPPORT Human Clinical
"Fasting serum sorbitol is a reliable biomarker of the condition that can be utilized for pathogenicity assessment of identified rare SORD variants."
Establishes the clinical use of the marker, including for variant interpretation.
PMID:40580554 SUPPORT Human Clinical
"Serum sorbitol, xylitol, and D-arabinitol were measured by gas chromatography-mass spectrometry; increased sorbitol and xylitol, and decreased D-arabinitol were identified."
Independent serum measurement, which also shows that the raised polyol is not sorbitol alone: xylitol rises with it and D-arabinitol falls. Measured in serum, not urine.
Elevated Urine Sorbitol and Xylitol (INCREASED)
Context: Urinary excretion of sorbitol together with a second polyol, xylitol (CHEBI:17151), measured by gas chromatography-mass spectrometry. The pairing is what gives the test its specificity, and a urine assay avoids the fasting blood draw. The biomarker term is bound to sorbitol, the analyte the record is named for; xylitol has no separate record because it is only interpretable alongside it.
Show evidence (1 reference)
PMID:41223342 SUPPORT Human Clinical
"In this patient cohort, the combination of sorbitol and xylitol yielded 100% sensitivity and specificity for SORD-related neuropathy."
Reports the diagnostic performance of the paired urinary polyol profile.
Reduced Red Blood Cell Sorbitol Dehydrogenase Activity (DECREASED)
Context: Direct enzymatic assay of SORD in red-cell haemolysate, monitoring NADH consumption. Offers a functional read on the enzyme itself, which is particularly useful when short-read sequencing returns an ambiguous or single-variant genotype because of the SORD2P pseudogene.
Show evidence (1 reference)
PMID:42021567 SUPPORT Human Clinical
"A test cutoff of < 30% yielded 100% sensitivity and specificity to detect deficient individuals."
Gives the operating threshold of the enzymatic screening assay.
🔬

Diagnosis

2
Molecular testing of SORD with pseudogene-aware methods
Confirmatory testing is molecular, but standard short-read exome or CMT panel sequencing is not sufficient on its own. SORD2P shares near-identical sequence with SORD and carries the c.757delG position on most control chromosomes, so reads mismap and biallelic variants cannot be phased. Long-read sequencing resolves the two loci and phases the alleles, and it is the only route that detects the recurrent SORD/SORD2P inversion - which accounts for most cases in which short-read testing finds just one pathogenic variant. A patient with a single detected variant and a compatible phenotype is therefore not excluded, and the biochemical markers curated above are the practical way to adjudicate such a case.
Show evidence (2 references)
PMID:35224818 SUPPORT Human Clinical
"Subsequent Oxford Nanopore Tech (ONT) long-read sequencing was used to successfully differentiate SORD from the highly homologous non-functional SORD2P pseudogene and confirmed that the mutations were biallelic through haplotype-resolved analysis."
Demonstrates that long-read sequencing solves both the mismapping and the phasing problem in a real diagnostic case.
PMID:41282915 SUPPORT Human Clinical
"we identified novel and recurrent inversions between SORD and its pseudogene SORD2P in 13 out of 151 patients (9%) affected by SORD-related Charcot-Marie-Tooth (CMT) neuropathy, including 6 out of 8 (75%) of SORD-CMT cases where only one pathogenic variant was identified on short read..."
Quantifies the allele class that short-read testing misses, and shows it concentrates precisely in the single-variant cases.
Biochemical case finding by polyol measurement
Because the molecular route is unreliable, biochemistry does the case finding: fasting serum sorbitol, the paired urine sorbitol and xylitol profile, or a red-cell SORD activity assay. Serum sorbitol separates patients from heterozygous carriers as well as from controls, which is what lets it adjudicate a variant of uncertain significance. The individual markers and their reported performance are curated under biochemical.
Show evidence (1 reference)
PMID:39938083 SUPPORT Human Clinical
"Fasting serum sorbitol is a reliable biomarker of the condition that can be utilized for pathogenicity assessment of identified rare SORD variants."
States both diagnostic uses: identifying the condition, and adjudicating variants the molecular test cannot classify.
📈

Progression

2
Adolescent onset with slow decades-long progression
Onset is usually in the second decade, and progression is slow enough that most patients remain independently ambulatory decades later; a minority take up ankle-foot orthoses, typically in their thirties.
Show evidence (3 references)
PMID:39938083 SUPPORT Human Clinical
"Disease onset was usually in the second decade of life."
Establishes the typical age of onset in the largest assembled cohort.
PMID:39938083 SUPPORT Human Clinical
"One-fourth of patients used ankle foot orthoses, usually in their 30s, but most patients maintained independent ambulation later in life."
Quantifies the slow functional decline and preserved ambulation.
PMID:39938083 SUPPORT Human Clinical
"Foot dorsiflexion and plantar flexion decreased significantly with age."
Establishes measurable progression of distal lower-limb strength with age.
Male sex associated with greater severity and faster decline
Sex modifies expressivity rather than causing disease. In the largest cohort men were both over-represented (99 of 144) and more severely affected, with a larger longitudinal change in dorsiflexion strength. The same direction of effect was seen in the Sord-null rat, where motor conduction slowing was more pronounced in males. Whether the over-representation reflects true sex-differential expressivity or under-recognition in women is not resolved by these data.
Show evidence (2 references)
PMID:39938083 SUPPORT Human Clinical
"Male sex was significantly associated with the severity of distal lower limb weakness (plantar flexion) and a larger change over time (dorsiflexion)."
Direct statement of the sex effect on both cross-sectional severity and rate of change.
PMID:39938083 SUPPORT Human Clinical
"we identified 144 patients from 126 families, including 99 males (69%) and 45 females (31%)"
Documents the male excess in ascertainment. PARTIAL because a cohort's sex ratio cannot by itself distinguish differential expressivity from differential referral.
📊

Prevalence

3
Worldwide
Point Prevalence 1.0 per 100,000 1–9 per 100,000
Order-of-magnitude estimate quoted in the govorestat mechanistic study; the disease has been recognised only since 2020 and is generally regarded as under-ascertained, so this is a floor rather than a settled figure.
Show evidence (1 reference)
PMID:37014713 SUPPORT Other
"SORD deficiency has been identified as the most frequent autosomal recessive form of hereditary neuropathy, affecting roughly 1 per 100,000 individuals"
Gives the per-100,000 estimate used for the normalised rate.
North America and Europe
Unknown Unknown
A modelled estimate of affected patients, not a measured rate and not a literature case count: roughly 10,000 patients across North America and Europe. measure_type is UNKNOWN because the source does not say how the figure was derived.
Show evidence (1 reference)
PMID:38538210 SUPPORT Other
"Biallelic SORD mutations cause one of the most frequent forms of recessive hereditary neuropathy, estimated to affect ∼10 000 patients in North America and Europe alone."
Supplies the absolute burden estimate for the two best-studied regions.
Healthy Chinese Han controls
Carrier Frequency 460.0 per 100,000 >1 in 1,000
Heterozygous carrier frequency for the recurrent c.757delG allele, 0.0046 (3 of 650) in healthy Chinese Han controls - roughly 1 in 217. This is a carrier rate, not a disease rate, and the two must not be compared: it is the reason the disease is described as under-ascertained rather than truly rare, and it is measured for one allele in one population.
Show evidence (1 reference)
PMID:34819907 SUPPORT Human Clinical
"The carrier frequency was 0.0046 individuals in healthy controls (3/650)."
Direct measurement of the carrier rate in a defined control population.
🔬

Clinical Trials

1
NCT05397665 PHASE_III COMPLETED
INSPIRE, a randomised, double-blind, placebo-controlled study of the aldose reductase inhibitor govorestat (AT-007) in SORD deficiency, registered as a two-part phase 2/3 study with 56 participants and treatment for up to 24 months. Recorded here as PHASE_III because the schema has no combined phase 2/3 value. The two evidence items below disagree about status, and the disagreement is chronological rather than a conflict: the ClinicalTrials.gov record now reports the study as completed (actual completion 2026-06-01, status verified 2026-06), while the 2025 cohort paper cited beside it described the study as ongoing when it was written. `status: COMPLETED` is taken from the registry record, checked directly against the ClinicalTrials.gov API during curation; the cached reference file carries only the trial's title and design summary, so it cannot be quoted for the status. No peer-reviewed publication of the trial's results was found at the time of curation, and none of its outcomes are curated here.
Target Phenotypes: Distal lower limb muscle weakness HP:0009053 Human Phenotype Ontology (HP) Relation: this clinical trial targets this phenotype This clinical trial targets Distal lower limb muscle weakness (HP:0009053). HP:0009053 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
clinicaltrials:NCT05397665 SUPPORT Other
"This study is designed to assess the efficacy and safety of AT-007 treatment in patients with SORD Deficiency."
Registry record establishing the trial's agent, design and indication.
PMID:39938083 SUPPORT Human Clinical
"Notably, a multicentre phase 2/3 study to test the efficacy of govorestat (NCT05397665), a new aldose reductase inhibitor, is currently ongoing."
Independent confirmation of the trial's phase designation and agent.
🧫

Experimental Models

2
Patient-derived skin fibroblasts (SORD c.757delG homozygous) PRIMARY_CELL_CULTURE
Fibroblasts from patients homozygous for c.757delG, used to show absent SORD protein and raised intracellular sorbitol, and later as the assay system for aldose reductase inhibitor target engagement.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:32367058
Pathograph links
Loss of Sorbitol Dehydrogenase Activity recapitulates fidelity: high Human cells carrying the patient genotype, with complete absence of the enzyme protein.
Limitations: Fibroblasts are not neurons or Schwann cells, so they report the metabolic lesion but nothing about axonal vulnerability.
Show evidence (1 reference)
PMID:32367058 SUPPORT In Vitro
"In patient-derived fibroblasts, we found a complete loss of SORD protein and increased intracellular sorbitol."
Establishes the model's core finding.
Show evidence (1 reference)
PMID:32367058 SUPPORT In Vitro
"SORD protein was absent in all patients and the SORD levels were reduced in unaffected carriers compared to controls"
Confirms the fibroblast panel reports the genotype faithfully, including the intermediate carrier state.
Patient iPSC-derived motor neurons IPSC_DERIVED_MODEL
iPSC-derived motor neurons from patients, used to show that govorestat lowers sorbitol in the human cell type the disease actually targets. Patient iPSC lines carrying SORD variants have since been deposited as a shared resource.
motor neuron CL:0000100 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses motor neuron (CL:0000100). CL:0000100 is a cell type from the Cell Ontology.
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Publication
PMID:37014713
Pathograph links
Polyol Pathway Block with Sorbitol Accumulation measures fidelity: moderate Provides the sorbitol readout in a human motor neuron rather than in a fibroblast or fly.
Limitations: A two-dimensional culture without Schwann cells or long axonal compartments, so it cannot reproduce length-dependent degeneration.
Show evidence (1 reference)
PMID:37014713 SUPPORT In Vitro
"AT-007 significantly reduced sorbitol levels in patient-derived fibroblasts, induced pluripotent stem cell-derived (iPSC-derived) motor neurons, and Drosophila brains."
Names iPSC-derived motor neurons as one of the systems in which sorbitol was measured and lowered.
Show evidence (1 reference)
PMID:38796985 SUPPORT In Vitro
"Fibroblast lines from 3 different patients containing the c.753delG; p.Ala253GlnfsTer27 SORD mutations were reprogrammed into induced Pluripotent Stem Cell (iPSC) lines."
Reports the deposited patient iPSC lines that make this model a shared resource rather than a single laboratory's material.
🐁

Animal Models

3
Sord knockout Sprague Dawley rat
The best-characterised mammalian model. Sorbitol is raised in serum, CSF and peripheral nerve; motor performance and gait decline from about seven months; tibial motor conduction slows; and nerve histology shows degenerating and de/remyelinated axons with enlarged "ballooned" myelin sheaths, affecting motor axons while largely sparing sensory ones.
Species
Rat
Genotype
Sord-/- (CRISPR knockout, Sprague Dawley background)
Background
Sprague Dawley
Publication
PMID:38538210
Pathograph links
Distal Motor Axonal Degeneration and Demyelination recapitulates fidelity: high Reproduces the motor-over-sensory selectivity of the human lesion at the level of nerve pathology and conduction.
Limitations: Histology was assessed at advanced ages and electrophysiology was not followed longitudinally, so the model speaks to the established lesion rather than to its earliest steps.
Readouts
Tibial motor nerve conduction velocity
Direction: DECREASED
Interpretation: Physiological correlate of motor axonal degeneration in the model.
Show evidence (1 reference)
PMID:38538210 SUPPORT Model Organism
"Motor nerve conduction velocities of the tibial nerves were slowed."
Direct measurement of slowed motor conduction.
Serum neurofilament light chain
Direction: INCREASED
Interpretation: Fluid biomarker of ongoing axonal degeneration in the model.
Show evidence (1 reference)
PMID:38538210 SUPPORT Model Organism
"serum from Sord-/- rats contained significantly increased levels of neurofilament light chain, an established biomarker for axonal degeneration"
Quantitative fluid readout of axonal injury.
Show evidence (1 reference)
PMID:38538210 SUPPORT Model Organism
"In summary, Sord-/- rats develop a motor-predominant neuropathy that closely resembles the human phenotype."
The authors' own assessment of fidelity to the human disease.
Polyol Pathway Block with Sorbitol Accumulation recapitulates fidelity: high Establishes that sorbitol accumulates in the nervous-system compartments that patient serum measurements cannot reach.
Limitations: Rodent sugar handling and laboratory diet differ from the human setting, which is the same variable invoked to explain why one mouse model fails.
Readouts
Sorbitol concentration in serum, CSF and peripheral nerve
Direction: INCREASED
Interpretation: Compartment-resolved confirmation of the metabolic block.
Show evidence (1 reference)
PMID:38538210 SUPPORT Model Organism
"Sord-/- rats had remarkably increased levels of sorbitol in serum, CSF and peripheral nerve."
Direct measurement across three compartments.
Show evidence (1 reference)
PMID:38538210 SUPPORT Model Organism
"Therefore, we have generated a Sord knockout (KO), Sord-/-, Sprague Dawley rat, to model the human disease and to investigate the pathophysiology underlying SORD deficiency."
Establishes the model, its construction and its intended use.
C57BL/LiA mouse with reduced SORD
A mouse strain carrying an intronic splicing variant that substantially reduces SORD protein. Under standard husbandry it develops neither neuropathy nor slowed nerve conduction - a negative result that the discovery authors attribute to the low sugar content of standard mouse chow relative to human and Drosophila diets, and therefore to polyol flux rather than to a species difference in the mechanism itself.
Species
Mouse
Genotype
intronic splicing variant reducing SORD protein (C57BL/LiA)
Background
C57BL/LiA
Publication
PMID:32367058
Pathograph links
Distal Motor Axonal Degeneration and Demyelination fails to recapitulate fidelity: low Reduced SORD protein in this strain does not produce the human lesion, so the model cannot be used to test the axonal-degeneration arm.
Limitations: The allele is hypomorphic rather than null, and the proposed explanation - dietary sugar limiting polyol flux - has not been tested by feeding these animals a high-sugar diet or by ageing them, so the failure may reflect husbandry rather than a real species difference.
Show evidence (1 reference)
PMID:32367058 REFUTE Model Organism
"Mice that have significantly reduced levels of SORD protein due to an intronic splicing mutation (C57BL/LiA mice), bred and fed according to the standard laboratory conditions, do not develop neuropathy or even slowed nerve conduction velocities"
Explicit negative result: the model does not reproduce the human neuropathy.
Show evidence (1 reference)
PMID:32367058 SUPPORT Model Organism
"This is possibly due to a difference in sugar metabolism between human and mouse since standard mouse chow consists of a low-sugar diet compared to humans"
The authors' proposed explanation for the negative result, curated as PARTIAL because it is a hypothesis they did not test.
Drosophila Sodh2 loss-of-function
Fly models of SORD loss with elevated head sorbitol, age-dependent synaptic degeneration in the visual system, and progressive locomotor decline on a normal lifespan. They were the system in which aldose reductase inhibition was first shown to rescue the phenotype, and later the system used to show bioenergetic and oxidative changes.
Species
Drosophila melanogaster
Genotype
Sodh2(MB01265) homozygous, and neuronal Sodh1/Sodh2 double knockdown
Publication
PMID:32367058
Pathograph links
Mitochondrial Dysfunction and Oxidative Stress recapitulates fidelity: low Supplies the bioenergetic and oxidative-stress evidence for this node.
Limitations: An invertebrate without myelin or Schwann cells, so it cannot speak to the myelin abnormality that is central to the mammalian lesion; the readouts are brain and muscle rather than peripheral nerve.
Readouts
Brain ATP production and tissue ROS
Direction: ALTERED
Interpretation: ATP falls and ROS rises, the paired readout used to call mitochondrial dysfunction in this model.
Show evidence (1 reference)
PMID:37014713 SUPPORT Model Organism
"In addition, we found reduced ATP production in the brain and ROS accumulation in the CNS and muscle, indicating mitochondrial dysfunction."
The measurement behind this readout.
Show evidence (1 reference)
PMID:32367058 SUPPORT Model Organism
"In Drosophila, loss of SORD orthologs caused synaptic degeneration and progressive motor impairment."
Establishes the model as informative for degeneration downstream of SORD loss.
Polyol Pathway Block with Sorbitol Accumulation rescues fidelity: moderate Aldose reductase inhibitor feeding normalised sorbitol and rescued motor and eye phenotypes, which is the pharmacological proof that the metabolite and not some other consequence of the genotype drives degeneration.
Limitations: Rescue was demonstrated in flies and in patient fibroblasts, not in a mammalian nervous system.
Show evidence (1 reference)
PMID:32367058 SUPPORT Model Organism
"Reducing the polyol influx by treatment with aldose reductase inhibitors normalized intracellular sorbitol levels in patient-derived fibroblasts and in Drosophila, and also dramatically ameliorated motor and eye phenotypes."
Demonstrates that lowering the metabolite reverses the phenotype.
Show evidence (1 reference)
PMID:32367058 SUPPORT Model Organism
"Two in vivo Drosophila models recapitulated key aspects of the human phenotype"
The authors' own summary of what the fly models reproduce.
{ }

Source YAML

click to show 
name: Sorbitol Dehydrogenase Deficiency
creation_date: "2026-08-23T00:00:00Z"
category: Genetic
description: >
  Sorbitol dehydrogenase (SORD) deficiency - also called SORD deficiency with
  peripheral neuropathy (SORDD), CMT-SORD, or distal hereditary motor
  neuronopathy autosomal recessive 8 (HMNR8) - is an autosomal recessive,
  adolescent-onset, length-dependent axonal peripheral neuropathy caused by
  biallelic loss-of-function variants in SORD. It was defined as a disease
  entity only in 2020 and is now recognised as one of the most frequent
  recessive causes of axonal Charcot-Marie-Tooth disease type 2 (CMT2) and
  distal hereditary motor neuropathy (dHMN).

  The mechanism is an enzyme block in the two-step polyol pathway. Aldose
  reductase reduces glucose to sorbitol; SORD then oxidises sorbitol to
  fructose. When SORD is absent, sorbitol - a poorly membrane-permeant polyol -
  accumulates in cells, serum, CSF and peripheral nerve, and a motor-predominant
  axonal degeneration follows. This is the same pathway invoked in diabetic
  neuropathy, but here it is driven by a germline enzyme deficiency at normal
  blood glucose, which is why the disease is repeatedly described as a genetic
  window onto polyol-pathway neurotoxicity.

  Two features make the entry unusual among inherited neuropathies. First, it
  has a directly measurable biochemical readout: fasting serum sorbitol is
  roughly two orders of magnitude above control, and urine sorbitol plus
  xylitol, or a red-cell SORD activity assay, can be used for case finding -
  which matters because the SORD2P pseudogene makes short-read molecular
  diagnosis unreliable and hides a recurrent SORD/SORD2P inversion allele.
  Second, the enzyme block is therapeutically approachable from upstream:
  inhibiting aldose reductase reduces the flux into sorbitol rather than
  replacing the missing enzyme, the rationale for the govorestat (AT-007)
  programme.

  The entry deliberately spans the CMT2/dHMN boundary rather than choosing one
  label. Roughly two-thirds of patients are classified as CMT2 and one-third as
  dHMN in the largest cohort, on one genotype and one mechanism, so the split is
  a clinical description of the same disease rather than two entities.
disease_term:
  preferred_term: sorbitol dehydrogenase deficiency with peripheral neuropathy
  term:
    id: MONDO:0030055
    label: neuronopathy, distal hereditary motor, autosomal recessive 8
synonyms:
- SORD deficiency
- SORDD
- CMT-SORD
- SORD-related neuropathy
- sorbitol dehydrogenase deficiency with peripheral neuropathy
- neuronopathy, distal hereditary motor, autosomal recessive 8
- HMNR8
parents:
- distal hereditary motor neuropathy
- axonal Charcot-Marie-Tooth disease
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
references:
- reference: PMID:32367058
  title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
- reference: PMID:39938083
  title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
- reference: PMID:38538210
  title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
- reference: PMID:37014713
  title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
external_assertions:
- name: OMIM HMNR8 (SORD)
  source: OMIM
  assertion_type: disease_record
  external_id: OMIM:618912
  description: >-
    OMIM phenotype entry for neuronopathy, distal hereditary motor, autosomal
    recessive 8, the SORD-related recessive neuropathy.
- name: Orphanet sorbitol dehydrogenase deficiency
  source: Orphanet
  assertion_type: disease_record
  external_id: ORPHA:700508
  description: >-
    Orphanet disorder record for sorbitol dehydrogenase deficiency, cross-referenced
    from MONDO:0030055.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Disease requires biallelic SORD loss-of-function variants - homozygosity for
    the recurrent c.757delG frameshift allele, compound heterozygosity for that
    allele with a second variant, or (increasingly recognised) a SORD/SORD2P
    inversion in trans. Heterozygous carriers have reduced SORD protein but are
    unaffected. Just over half of probands are sporadic with neither a family
    history nor reported consanguinity, but consanguinity is not negligible: 18%
    of the largest cohort had consanguineous parents.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified 45 individuals from 38 families across multiple ancestries carrying the nonsense c.757delG (p.Ala253GlnfsTer27) variant in SORD, in either a homozygous or compound heterozygous state."
    explanation: >-
      Establishes the biallelic (homozygous or compound heterozygous)
      requirement across unrelated families and ancestries.
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "SORD protein was absent in all patients and the SORD levels were reduced in unaffected carriers compared to controls"
    explanation: >-
      Shows the gene-dosage basis of recessiveness - carriers retain partial
      protein and are unaffected, while biallelic patients have none.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thus, in 79 (55%) individuals the disease was sporadic, without report of family history of neuropathy or consanguinity."
    explanation: >-
      Quantifies the sporadic majority, which is a bare majority rather than the
      overwhelming one a looser phrasing would imply.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Forty-seven (33%) patients had a family history of neuropathy and 26 (18%) were born from consanguineous parents, including eight individuals with an additional affected family member."
    explanation: >-
      Gives the consanguinity figure, which is why the entry does not claim that
      consanguinity plays no part.
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 1.0
  notes: >-
    Order-of-magnitude estimate quoted in the govorestat mechanistic study; the
    disease has been recognised only since 2020 and is generally regarded as
    under-ascertained, so this is a floor rather than a settled figure.
  evidence:
  - reference: PMID:37014713
    reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SORD deficiency has been identified as the most frequent autosomal recessive form of hereditary neuropathy, affecting roughly 1 per 100,000 individuals"
    explanation: >-
      Gives the per-100,000 estimate used for the normalised rate.
- population: North America and Europe
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    A modelled estimate of affected patients, not a measured rate and not a
    literature case count: roughly 10,000 patients across North America and
    Europe. measure_type is UNKNOWN because the source does not say how the
    figure was derived.
  evidence:
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Biallelic SORD mutations cause one of the most frequent forms of recessive hereditary neuropathy, estimated to affect ∼10 000 patients in North America and Europe alone."
    explanation: >-
      Supplies the absolute burden estimate for the two best-studied regions.
- population: Healthy Chinese Han controls
  measure_type: CARRIER_FREQUENCY
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 460.0
  notes: >-
    Heterozygous carrier frequency for the recurrent c.757delG allele, 0.0046
    (3 of 650) in healthy Chinese Han controls - roughly 1 in 217. This is a
    carrier rate, not a disease rate, and the two must not be compared: it is
    the reason the disease is described as under-ascertained rather than truly
    rare, and it is measured for one allele in one population.
  evidence:
  - reference: PMID:34819907
    reference_title: "Clinical and Genetic Features of Biallelic Mutations in SORD in a Series of Chinese Patients With Charcot-Marie-Tooth and Distal Hereditary Motor Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The carrier frequency was 0.0046 individuals in healthy controls (3/650)."
    explanation: >-
      Direct measurement of the carrier rate in a defined control population.
progression:
- phase: Adolescent onset with slow decades-long progression
  notes: >-
    Onset is usually in the second decade, and progression is slow enough that
    most patients remain independently ambulatory decades later; a minority take
    up ankle-foot orthoses, typically in their thirties.
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Disease onset was usually in the second decade of life."
    explanation: >-
      Establishes the typical age of onset in the largest assembled cohort.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One-fourth of patients used ankle foot orthoses, usually in their 30s, but most patients maintained independent ambulation later in life."
    explanation: >-
      Quantifies the slow functional decline and preserved ambulation.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Foot dorsiflexion and plantar flexion decreased significantly with age."
    explanation: >-
      Establishes measurable progression of distal lower-limb strength with age.
- phase: Male sex associated with greater severity and faster decline
  notes: >-
    Sex modifies expressivity rather than causing disease. In the largest cohort
    men were both over-represented (99 of 144) and more severely affected, with
    a larger longitudinal change in dorsiflexion strength. The same direction of
    effect was seen in the Sord-null rat, where motor conduction slowing was more
    pronounced in males. Whether the over-representation reflects true
    sex-differential expressivity or under-recognition in women is not resolved
    by these data.
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Male sex was significantly associated with the severity of distal lower limb weakness (plantar flexion) and a larger change over time (dorsiflexion)."
    explanation: >-
      Direct statement of the sex effect on both cross-sectional severity and
      rate of change.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identified 144 patients from 126 families, including 99 males (69%) and 45 females (31%)"
    explanation: >-
      Documents the male excess in ascertainment. PARTIAL because a cohort's sex
      ratio cannot by itself distinguish differential expressivity from
      differential referral.
mechanistic_hypotheses:
- hypothesis_group_id: osmotic_myelin_injury_model
  hypothesis_label: Osmotic injury to Schwann cells and myelin
  status: CANONICAL
  description: >-
    Sorbitol is a polar polyol that crosses membranes poorly, so trapping it
    raises intracellular osmolarity and draws water in. On this model the
    primary target is the myelinating Schwann cell, and the observable signature
    is the enlarged "ballooned" myelin sheath that the Sord-null rat shows around
    otherwise intact axons, with axonal degeneration following secondarily. It is
    marked CANONICAL as the leading proposal in the mammalian literature - it is
    the only candidate with a matching structural lesion, and the same
    abnormality appears in galactosemic neuropathy, another polyol disorder -
    but leading is not the same as established: no study has measured water
    content or osmolyte composition in SORD-deficient nerve.
- hypothesis_group_id: mitochondrial_oxidative_model
  hypothesis_label: Bioenergetic failure and oxidative stress
  status: ALTERNATIVE
  description: >-
    Sorbitol accumulation is followed by falling ATP production and rising
    reactive oxygen species, and axons - the longest and most energy-hungry
    compartment - fail first. This is the best-evidenced arm in the sense of
    having direct measurements behind it, but the measurements are in Drosophila
    brain and muscle and in human skeletal muscle proteomics, neither of which is
    peripheral nerve, and none of them shows the deficit causing axonal loss.
- hypothesis_group_id: redox_cofactor_imbalance_model
  hypothesis_label: NADPH and NAD+ cofactor imbalance
  status: EMERGING
  description: >-
    Flux through the polyol pathway consumes NADPH at the aldose reductase step
    and regenerates NAD+ at the SORD step. Losing SORD leaves the reductive step
    running without its oxidative partner, depleting NADPH - and with it the
    glutathione-based antioxidant capacity - while NAD+ is not regenerated. This
    is a well-developed idea in the diabetic-neuropathy literature, but in SORD
    deficiency it is named as a plausible candidate rather than measured, which
    is why it is EMERGING and carries no node of its own.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "one or more of the known effects of decreased SORD activity, including increased sorbitol level, cellular osmolarity, oxidative stress and decreased NADPH levels, are plausible"
    explanation: >-
      The discovery authors list cofactor depletion among the candidate routes.
      PARTIAL because it is named as plausible, not demonstrated.
pathophysiology:
- name: Biallelic SORD Loss-of-Function Variants
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  description: >-
    Two loss-of-function SORD alleles. The recurrent frameshift c.757delG
    (p.Ala253GlnfsTer27) dominates the allele spectrum worldwide and is found
    homozygously in most patients; c.458C>A (p.Ala153Asp) is the commonest second
    allele. A third allele class - inversion between SORD and its highly
    homologous pseudogene SORD2P - is invisible to short-read sequencing and
    accounts for a further tranche of cases. Missense alleles act by
    destabilising the enzyme rather than by any dominant-negative or neomorphic
    route: c.404A>G produces insoluble SORD aggregates in vitro, and a splice
    allele c.908+1G>C disrupts the transcript.
  genetic_context:
    gene:
      preferred_term: SORD
      term:
        id: hgnc:11184
        label: SORD
    allele_type: frameshift, missense, splice-site, and gene-pseudogene inversion
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Homozygous in most patients and compound heterozygous in the remainder;
      all characterised alleles converge on absent or non-functional enzyme.
  genes:
  - preferred_term: SORD
    term:
      id: hgnc:11184
      label: SORD
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified 45 individuals from 38 families across multiple ancestries carrying the nonsense c.757delG (p.Ala253GlnfsTer27) variant in SORD, in either a homozygous or compound heterozygous state."
    explanation: >-
      The discovery cohort establishing c.757delG as the dominant recurrent
      allele across ancestries.
  - reference: PMID:33397963
    reference_title: "Biallelic SORD pathogenic variants cause Chinese patients with distal hereditary motor neuropathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro cell functional studies showed that c.404 A > G variant resulted in aggregate formation of SORD and low protein solubility, confirming the pathogenicity of SORD variants."
    explanation: >-
      Functional demonstration that a missense allele destroys the enzyme by
      destabilising it, supporting a loss-of-function rather than
      dominant-negative reading.
  downstream:
  - target: Loss of Sorbitol Dehydrogenase Activity
    causal_link_type: DIRECT
    description: >-
      Absent or unstable protein leaves the cell with no functional sorbitol
      dehydrogenase.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "In patient-derived fibroblasts, we found a complete loss of SORD protein and increased intracellular sorbitol."
      explanation: >-
        Cells carrying the biallelic genotype have no enzyme protein, which is
        the step this edge asserts.
- name: Loss of Sorbitol Dehydrogenase Activity
  biological_scale: MOLECULAR
  role: effector
  mechanism_confidence: ESTABLISHED
  description: >-
    Sorbitol dehydrogenase (EC 1.1.1.14), the NAD+-dependent second enzyme of the
    polyol pathway, is absent from patient cells. Protein is undetectable by
    western blot in fibroblasts homozygous for c.757delG, and red-cell enzyme
    activity is significantly reduced against run controls - a difference large
    enough that a screening assay has been built on it. The 30% figure quoted in
    the biochemical record is that assay's proposed cutoff, not a measured
    residual activity of the disease.
  molecular_functions:
  - preferred_term: sorbitol dehydrogenase activity
    term:
      id: GO:0003939
      label: L-iditol 2-dehydrogenase (NAD+) activity
    modifier: ABSENT
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "SORD protein was absent in all patients and the SORD levels were reduced in unaffected carriers compared to controls"
    explanation: >-
      Direct demonstration of absent enzyme protein in patient-derived cells.
  - reference: PMID:42021567
    reference_title: "Measurement of Red Blood Cell Sorbitol Dehydrogenase Activity for Fast Screening of SORD-Related Neuropathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RBC SORD activity was significantly reduced in individuals diagnosed with SORD deficiency when compared to within-run controls"
    explanation: >-
      Confirms the enzymatic (not merely protein-level) deficit directly in
      patient material.
  downstream:
  - target: Polyol Pathway Block with Sorbitol Accumulation
    causal_link_type: DIRECT
    description: >-
      With the oxidative step gone, sorbitol produced by aldose reductase has no
      exit and is trapped.
    evidence:
    - reference: PMID:37014713
      reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Loss of SORD causes high sorbitol levels in tissues due to the inability to convert sorbitol to fructose in the 2-step polyol pathway, leading to degenerative neuropathy."
      explanation: >-
        States the enzyme-loss to metabolite-accumulation step directly.
- name: Polyol Pathway Block with Sorbitol Accumulation
  biological_scale: CELLULAR
  role: amplifier
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Insult to Peripheral Neurons and Schwann Cells"
  description: >-
    Aldose reductase continues to reduce glucose to sorbitol, but the second step
    is blocked, so sorbitol - a polar, poorly membrane-permeant polyol -
    accumulates. Intracellular sorbitol is more than ten-fold elevated in patient
    fibroblasts and fasting serum sorbitol is roughly two orders of magnitude
    above control. In the Sord-null rat the accumulation is documented in the
    compartment that matters: serum, CSF and peripheral nerve. This is the
    metabolic insult that the conserved peripheral-axonal-degeneration module
    describes generically; here it is the whole trigger, with no toxic,
    inflammatory or hyperglycaemic component.
  biological_processes:
  - preferred_term: sorbitol catabolism
    term:
      id: GO:0006062
      label: D-sorbitol catabolic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: sorbitol
    term:
      id: CHEBI:17924
      label: D-glucitol
    modifier: INCREASED
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SORD is an enzyme that converts sorbitol into fructose in the two-step polyol pathway previously implicated in diabetic neuropathy."
    explanation: >-
      States the enzymatic step whose loss produces the block. Evidence source is
      OTHER because this is a definitional background statement, not a clinical
      observation.
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "intracellular sorbitol concentrations were over 10 times higher in patient fibroblasts compared to controls"
    explanation: >-
      Quantifies the intracellular accumulation in human patient cells.
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Sord-/- rats had remarkably increased levels of sorbitol in serum, CSF and peripheral nerve."
    explanation: >-
      Shows the accumulation reaches the peripheral nerve compartment, which
      patient serum measurements cannot establish.
  downstream:
  - target: Osmotic Stress in Schwann Cells and Myelinated Axons
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - osmotic_myelin_injury_model
    description: >-
      The osmotic arm: a trapped, poorly permeant polyol raises intracellular
      osmolarity. Curated as a competing model rather than a settled step.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "one or more of the known effects of decreased SORD activity, including increased sorbitol level, cellular osmolarity, oxidative stress and decreased NADPH levels, are plausible"
      explanation: >-
        Cellular osmolarity is named as a candidate consequence of the
        accumulation. PARTIAL because it is proposed, not measured.
  - target: Mitochondrial Dysfunction and Oxidative Stress
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - mitochondrial_oxidative_model
    description: >-
      The oxidative arm: bioenergetic failure and ROS accumulation follow the
      accumulation, but the steps linking the two are not established.
    evidence:
    - reference: PMID:37014713
      reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "AT-007 feeding in Sord-deficient Drosophila mitigated synaptic degeneration and significantly improved synaptic transduction, locomotor activity, and mitochondrial function."
      explanation: >-
        Lowering sorbitol restores mitochondrial function, which places the
        mitochondrial defect downstream of the metabolite rather than merely
        alongside it. PARTIAL because the demonstration is in Drosophila.
  - target: Distal Motor Axonal Degeneration and Demyelination
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Deliberately retained alongside the two hypothesis-tagged arms above: the
      accumulation-to-axon link is evidenced pharmacologically (removing the
      metabolite prevents degeneration) without any of the candidate routes
      being established, so this edge carries the part of the claim that
      survives whichever model turns out to be right. See the
      gap_sorbitol_to_axon_mechanism discussion.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Reducing the polyol influx by treatment with aldose reductase inhibitors normalized intracellular sorbitol levels in patient-derived fibroblasts and in Drosophila, and also dramatically ameliorated motor and eye phenotypes."
      explanation: >-
        Pharmacological reversal implicates the metabolite itself, rather than
        some other consequence of the genotype, as the cause of degeneration.
        PARTIAL because the intermediate steps remain unidentified and the
        rescue was shown in fly and fibroblast rather than in human nerve.
- name: Osmotic Stress in Schwann Cells and Myelinated Axons
  biological_scale: CELLULAR
  role: amplifier
  mechanism_confidence: HYPOTHETICAL
  description: >-
    The osmotic candidate for how a trapped metabolite injures nerve. Sorbitol
    crosses membranes poorly, so an unclearable intracellular pool should draw
    water in, and the structural finding that fits is the enlarged "ballooned"
    myelin sheath seen around otherwise intact axons in the Sord-null rat - an
    abnormality also described in galactosemic neuropathy, where a different
    polyol accumulates. The node is HYPOTHETICAL by design: the lesion is
    consistent with osmotic swelling and is the reason this is the leading
    model, but nobody has measured water content, osmolyte composition or
    volume regulation in SORD-deficient nerve, so the inference runs from
    morphology to mechanism rather than the other way round.
  cell_types:
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  biological_processes:
  - preferred_term: response to osmotic stress
    term:
      id: GO:0006970
      label: response to osmotic stress
    modifier: INCREASED
  evidence:
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Light and electron microscopy of the peripheral nervous system revealed degenerating myelinated axons, de- and remyelinated axons, and a likely pathognomonic finding-enlarged 'ballooned' myelin sheaths."
    explanation: >-
      The myelin abnormality that motivates the osmotic reading. PARTIAL because
      ballooned myelin is consistent with osmotic swelling but is not a
      measurement of it, and the authors call it pathognomonic of the disease
      rather than of a mechanism.
  downstream:
  - target: Distal Motor Axonal Degeneration and Demyelination
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - osmotic_myelin_injury_model
    description: >-
      On this model the Schwann cell is injured first and axonal degeneration is
      secondary, which is what the rat morphology - swollen sheaths around
      initially intact axons - suggests.
- name: Mitochondrial Dysfunction and Oxidative Stress
  biological_scale: CELLULAR
  role: amplifier
  mechanism_confidence: PROVISIONAL
  description: >-
    Sord-deficient Drosophila show reduced brain ATP production and reactive
    oxygen species accumulation in CNS and muscle, and both are corrected by
    aldose reductase inhibition, which ties them to sorbitol rather than to the
    genotype in general. Independent human support comes from proteomic analysis
    of patient skeletal muscle, where respiratory complex I deficiency dominated
    and the malate/oxaloacetate ratio was raised. The node is marked PROVISIONAL
    because the animal evidence is invertebrate and the human evidence is muscle
    proteomics rather than nerve.
  biological_processes:
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
    modifier: INCREASED
  evidence:
  - reference: PMID:37014713
    reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In addition, we found reduced ATP production in the brain and ROS accumulation in the CNS and muscle, indicating mitochondrial dysfunction."
    explanation: >-
      Bioenergetic and oxidative readouts in the Drosophila model of SORD loss.
  - reference: PMID:40580554
    reference_title: "Neuromuscular pathology and mitochondrial dysfunction in sorbitol dehydrogenase gene-related distal hereditary motor neuropathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complex I deficiency was dominant in the proteomic analysis and the malic acid/oxaloacetic acid ratio was significantly higher in the patients than in controls."
    explanation: >-
      Human corroboration of a mitochondrial abnormality, but measured in
      skeletal muscle rather than in peripheral nerve, hence PARTIAL.
  downstream:
  - target: Distal Motor Axonal Degeneration and Demyelination
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - mitochondrial_oxidative_model
    description: >-
      Bioenergetic failure and oxidative stress are the amplifying arm shared
      with other length-dependent axonopathies.
    evidence:
    - reference: PMID:40580554
      reference_title: "Neuromuscular pathology and mitochondrial dysfunction in sorbitol dehydrogenase gene-related distal hereditary motor neuropathies."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Mitochondrial complex I deficiency, may be a key mechanism in SORD gene-related dHMN."
      explanation: >-
        The authors propose the mitochondrial defect as a mechanism of the
        neuropathy. PARTIAL because this is an inference from muscle proteomics,
        not a demonstration that the defect causes axonal loss.
- name: Distal Motor Axonal Degeneration and Demyelination
  biological_scale: TISSUE
  role: effector
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Distal Axonal Degeneration and Demyelination"
  description: >-
    Degeneration falls on myelinated motor axons and largely spares myelinated
    sensory axons - the structural counterpart of the motor-predominant clinical
    picture. Rat nerve shows degenerating myelinated axons, de- and remyelinated
    axons, and enlarged "ballooned" myelin sheaths that the authors propose as a
    pathognomonic feature. Human sural nerve, sampled in a sensory nerve in a
    motor-predominant disease, shows correspondingly mild change: modest loss of
    large myelinated fibres with a few thinly myelinated fibres.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  - preferred_term: sensory neuron
    term:
      id: CL:0000101
      label: sensory neuron
  locations:
  - preferred_term: peripheral nerve
    term:
      id: UBERON:0001021
      label: nerve
  evidence:
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Light and electron microscopy of the peripheral nervous system revealed degenerating myelinated axons, de- and remyelinated axons, and a likely pathognomonic finding-enlarged 'ballooned' myelin sheaths."
    explanation: >-
      Primary structural description of the lesion, including the myelin
      abnormality that suggests an osmotic component.
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These findings mainly affected myelinated motor axons; myelinated sensory axons were largely spared."
    explanation: >-
      Establishes the motor-over-sensory selectivity at the level of nerve
      pathology.
  - reference: PMID:40580554
    reference_title: "Neuromuscular pathology and mitochondrial dysfunction in sorbitol dehydrogenase gene-related distal hereditary motor neuropathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sural nerve biopsies showed mild loss of large, myelinated fibers, and a few thin myelinated fibers."
    explanation: >-
      Human nerve histology; mild because the sural nerve is sensory and this is
      a motor-predominant disease.
  downstream:
  - target: Length-Dependent Motor-Predominant Nerve Fiber Dysfunction
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38538210
      reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Motor nerve conduction velocities of the tibial nerves were slowed."
      explanation: >-
        Conduction slowing measured in the same animals whose nerves show the
        degenerative pathology, linking the lesion to loss of fibre function.
- name: Length-Dependent Motor-Predominant Nerve Fiber Dysfunction
  biological_scale: TISSUE
  role: effector
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Length-Dependent Nerve Fiber Dysfunction"
  description: >-
    Nerve conduction shows a motor-predominant axonal neuropathy, with
    conduction velocities reduced into the intermediate range in a minority -
    which is why some patients are labelled intermediate CMT. Sensory conduction
    is affected in a pattern that is not simply length-dependent: upper-limb
    sensory responses are abnormal more often than lower-limb ones, an inversion
    of the usual gradient that is itself a diagnostic clue. Conformance to the
    module's length-dependent node is therefore declared for the motor arm only;
    the sensory pattern curated here is the exception to it, not an instance of
    it.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Detailed nerve conduction studies were available in 42 patients and invariably showed a motor axonal neuropathy"
    explanation: >-
      Establishes the electrophysiological signature as invariant across the
      discovery cohort.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sensory conductions in the upper limbs appeared more frequently affected than in the lower limbs."
    explanation: >-
      Records the non-length-dependent sensory pattern in the largest cohort.
  downstream:
  - target: Motor-Predominant Hereditary Neuropathy Spanning CMT2 and dHMN
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39938083
      reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In conclusion, CMT-SORD is a frequent recessive form of axonal, motor predominant CMT, with prominent foot dorsiflexion and plantar flexion involvement."
      explanation: >-
        Ties the motor-predominant axonal electrophysiology to the clinical
        picture patients present with.
- name: Motor-Predominant Hereditary Neuropathy Spanning CMT2 and dHMN
  biological_scale: ORGANISM
  role: consequence
  mechanism_confidence: ESTABLISHED
  conforms_to: "peripheral_axonal_degeneration#Peripheral Neuropathy"
  description: >-
    The clinical endpoint is a slowly progressive distal weakness and amyotrophy
    with foot deformity, beginning in the second decade. Whether an individual is
    labelled CMT2 or dHMN depends on how much sensory involvement is found, not
    on genotype: about two-thirds are classified as CMT2 and one-third as dHMN on
    the same allele spectrum.
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two-thirds of cases were diagnosed with CMT2 while one-third had distal hereditary motor neuropathy."
    explanation: >-
      Documents that one genotype produces both clinical labels.
  - reference: PMID:36943151
    reference_title: "SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eighteen had dHMN, nine had CMT2, and three had intermediate CMT."
    explanation: >-
      Independent cohort showing the same spread of clinical labels, here with
      dHMN in the majority.
phenotypes:
- category: Neurologic
  name: Distal Lower Limb Muscle Weakness
  frequency: VERY_FREQUENT
  description: >-
    Weakness of foot dorsiflexion and plantar flexion is the presenting and most
    severely affected feature, with difficulty walking the commonest initial
    complaint.
  phenotype_term:
    preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All individuals had limb weakness, but only one-half had sensory impairment."
    explanation: >-
      Limb weakness in every patient of the discovery cohort supports the
      VERY_FREQUENT band.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although foot dorsiflexion was the most affected muscle group, dorsal and plantar flexion had a similar degree of weakness in most cases"
    explanation: >-
      Localises the weakness to the distal lower limb in the largest cohort.
- category: Neurologic
  name: Foot Dorsiflexor Weakness
  description: >-
    Weakness of ankle dorsiflexion, the muscle group most affected and the one
    used as a quantitative outcome measure in natural-history and trial work.
  phenotype_term:
    preferred_term: Foot dorsiflexor weakness
    term:
      id: HP:0009027
      label: Foot dorsiflexor weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Foot dorsiflexion and plantar flexion decreased significantly with age."
    explanation: >-
      Identifies dorsiflexion as an affected and progressively declining muscle
      group.
- category: Musculoskeletal
  name: Foot Deformity
  frequency: FREQUENT
  description: >-
    Foot deformity, reported by roughly two-thirds to nine-tenths of patients
    depending on cohort, and often predating recognised weakness - evidence that
    the neuropathy begins earlier than the presenting complaint suggests. The
    term is bound at the level the sources actually report: every cohort quoted
    here says "foot deformities" rather than naming pes cavus, so the entry does
    not assert the narrower cavus morphology it cannot cite.
  phenotype_term:
    preferred_term: Foot deformity
    term:
      id: HP:0001760
      label: Abnormal foot morphology
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Disease onset was usually in the second decade of life, however, 79% of patients reported foot deformities and 46% described poor performance in sport activities at school, suggesting an earlier onset of disease."
    explanation: >-
      79% in the largest cohort supports the FREQUENT band, and the same
      sentence carries the inference that disease begins before the presenting
      complaint.
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "two thirds of the patients reported foot deformities, indicating that the neuropathy probably started earlier in life"
    explanation: >-
      Gives the frequency band and the inference about subclinical onset.
  - reference: PMID:36943151
    reference_title: "SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty patients had SORD peripheral neuropathy associating LL weakness with muscular atrophy, foot deformities (87%), and sometimes proximal LL weakness (20%) or distal upper limb weakness (50%)."
    explanation: >-
      Independent cohort reporting foot deformity in 87%.
- category: Neurologic
  name: Distal Amyotrophy
  frequency: VERY_FREQUENT
  description: >-
    Wasting of distal lower-limb, and later distal upper-limb, musculature
    accompanying the weakness. Reported in 98% of the largest cohort, and in
    every patient of a smaller European series.
  phenotype_term:
    preferred_term: Distal amyotrophy
    term:
      id: HP:0003693
      label: Distal amyotrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Distal atrophy was observed in 98% of cases."
    explanation: >-
      Direct quantitative support for the VERY_FREQUENT band (80-100%).
  - reference: PMID:36943151
    reference_title: "SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty patients had SORD peripheral neuropathy associating LL weakness with muscular atrophy, foot deformities (87%), and sometimes proximal LL weakness (20%) or distal upper limb weakness (50%)."
    explanation: >-
      Muscular atrophy accompanying lower-limb weakness in all 30 patients of an
      independent cohort.
- category: Neurologic
  name: Distal Upper Limb Weakness
  frequency: FREQUENT
  description: >-
    Hand weakness and loss of dexterity, typically appearing years after the gait
    complaint. Two independent cohorts put it at about half of patients, which
    places it in the FREQUENT band, well below the near-universal lower-limb
    involvement.
  phenotype_term:
    preferred_term: Distal upper limb muscle weakness
    term:
      id: HP:0008959
      label: Distal upper limb muscle weakness
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Half of the patients had reduced strength of intrinsic hand muscles, while most patients had reduced strength of distal lower limb muscles."
    explanation: >-
      Half of the largest cohort places this in the FREQUENT band (30-79%), and
      the same sentence records that the lower limb is affected more often.
  - reference: PMID:36943151
    reference_title: "SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "sometimes proximal LL weakness (20%) or distal upper limb weakness (50%)"
    explanation: >-
      Independent cohort giving the same 50% figure.
- category: Neurologic
  name: Distal Sensory Impairment
  frequency: FREQUENT
  description: >-
    Sensory loss is present in about half of patients and is what pushes the
    clinical label from dHMN towards CMT2; its distribution is unusual, with
    upper-limb sensory responses more often abnormal than lower-limb ones.
  phenotype_term:
    preferred_term: Distal sensory impairment
    term:
      id: HP:0002936
      label: Distal sensory impairment
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All individuals had limb weakness, but only one-half had sensory impairment."
    explanation: >-
      Direct frequency statement placing sensory impairment in the FREQUENT
      band and subordinate to the motor deficit.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SNAP amplitude or slower conduction velocities were observed in up to 76% of cases in the upper limbs but only 27% in the lower limbs, thus confirming the observation of a previous smaller case series."
    explanation: >-
      Quantifies the inverted upper-limb-over-lower-limb sensory gradient that
      the description asserts, which would otherwise be an uncited claim.
- category: Neurologic
  name: Reduced or Absent Ankle Reflexes
  frequency: FREQUENT
  description: >-
    Ankle jerks are typically reduced or lost, the expected consequence of a
    length-dependent axonopathy acting on the longest reflex arc. Curated
    separately from the upper-limb and patellar reflexes because the two behave
    in opposite directions in this disease.
  phenotype_term:
    preferred_term: Reduced tendon reflexes
    term:
      id: HP:0001315
      label: Reduced tendon reflexes
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Deep tendon reflexes in the upper limbs and knees were frequently retained or even increased, while ankle reflexes were more typically reduced or absent."
    explanation: >-
      "More typically reduced or absent" is a qualitative majority statement,
      which maps to the FREQUENT band; no cohort denominator is given, so no
      narrower band is asserted.
  - reference: PMID:34819907
    reference_title: "Clinical and Genetic Features of Biallelic Mutations in SORD in a Series of Chinese Patients With Charcot-Marie-Tooth and Distal Hereditary Motor Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They shared a common phenotype, with motor-predominant distal muscle weakness and atrophy of the lower limb and decreased or absent deep tendon reflex and foot deformities."
    explanation: >-
      Independent cohort reporting decreased or absent reflexes as part of the
      shared phenotype.
- category: Neurologic
  name: Retained or Brisk Upper Limb and Patellar Reflexes
  description: >-
    The counter-intuitive half of the reflex picture, and a diagnostic clue:
    in a disease whose lesion is a distal motor axonopathy, reflexes above the
    ankle are frequently preserved and may be frankly brisk. The reporting
    authors read the retained or brisk pattern as suggesting subclinical central
    involvement, a hypothesis rather than a demonstrated finding - imaging showed
    no relevant change - so this record asserts the reflex observation and not
    the CNS interpretation. No frequency is given: the source counts "retained or
    even increased" together, so the fraction that is actually hyperreflexic
    cannot be separated out, and the ontology term names only the brisk end.
  phenotype_term:
    preferred_term: Hyperreflexia
    term:
      id: HP:0001347
      label: Hyperreflexia
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Deep tendon reflexes in the upper limbs and knees were frequently retained or even increased, while ankle reflexes were more typically reduced or absent."
    explanation: >-
      Establishes the dissociation: preserved or increased above the ankle,
      reduced or absent at it.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Upper limb and patellar reflexes may be retained or even brisk, suggesting the presence of a possible subclinical involvement of the CNS, as also observed in other axonal CMT subtypes"
    explanation: >-
      Repeats the observation and offers the subclinical-CNS reading. PARTIAL
      because the CNS involvement is proposed, not shown - the same paper
      reports no relevant imaging change.
- category: Neurologic
  name: Motor Axonal Neuropathy on Nerve Conduction Studies
  frequency: VERY_FREQUENT
  description: >-
    Nerve conduction studies show a motor axonal pattern in essentially every
    studied patient, and a quarter have velocities in the intermediate range,
    which accounts for the intermediate-CMT labels in some series. "Essentially"
    rather than "invariably": a genetically confirmed patient with normal motor
    and sensory conduction velocities and amplitudes has been reported.
  diagnostic: true
  phenotype_term:
    preferred_term: Motor axonal neuropathy
    term:
      id: HP:0007002
      label: Motor axonal neuropathy
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Detailed nerve conduction studies were available in 42 patients and invariably showed a motor axonal neuropathy"
    explanation: >-
      Nerve conduction was abnormal in the same motor axonal pattern in all 42
      studied patients of the discovery cohort, which supports the
      VERY_FREQUENT band.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nerve conduction studies were suggestive of a motor predominant axonal neuropathy, with reduced conduction velocities in the intermediate range in a quarter of the cases."
    explanation: >-
      Confirms the pattern and quantifies the intermediate-velocity subset.
- category: Neurologic
  name: Upper Limb Tremor
  frequency: OCCASIONAL
  description: >-
    Postural tremor of the upper limbs, reported in a minority of patients in the
    discovery cohort.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seven patients had upper limb tremor, four had mild scoliosis and two had mild hearing loss."
    explanation: >-
      Seven of 45 patients gives an OCCASIONAL frequency.
- category: Musculoskeletal
  name: Mild Scoliosis
  frequency: OCCASIONAL
  description: >-
    Mild scoliosis reported in a small minority of the discovery cohort.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
    severity: MILD
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seven patients had upper limb tremor, four had mild scoliosis and two had mild hearing loss."
    explanation: >-
      Four of the 45 patients in the discovery cohort is 8.9%, which is the
      OCCASIONAL band (5-29%), not VERY_RARE.
- category: Laboratory
  name: Elevated Serum Creatine Kinase
  description: >-
    Persistently but modestly raised creatine kinase can occur and may misdirect
    the workup towards a primary myopathy; in the reported case a muscle biopsy
    was performed before whole-exome sequencing found the SORD genotype.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase concentration
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase concentration
  evidence:
  - reference: PMID:38406380
    reference_title: "Skeletal muscle involvement in biallelic SORD mutations: case report and review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Since creatine phosphokinase (CPK) values were persistently raised (1.5fold increased) and a Next-Generation Sequencing CMT-associated panel failed in identifying pathogenic variants, a muscle biopsy was performed"
    explanation: >-
      Documents raised CK and the diagnostic detour it caused. No frequency is
      asserted: the source describes itself as an isolated report and states
      that no association between SORD variants and muscle involvement had been
      described before it, so there is no cohort denominator to band.
biochemical:
- name: Elevated Fasting Serum Sorbitol
  biomarker_term:
    preferred_term: sorbitol
    term:
      id: CHEBI:17924
      label: D-glucitol
  presence: INCREASED
  frequency: OBLIGATE
  context: >-
    The defining biochemical abnormality and the practical diagnostic test.
    Fasting serum sorbitol is roughly two orders of magnitude above control and
    separates patients from both controls and heterozygous carriers, which makes
    it usable for adjudicating variants of uncertain significance as well as for
    case finding.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we next tested the fasting sorbitol level in serum from ten patients carrying the homozygous p.Ala253GlnfsTer27 mutation and ten unrelated controls and found it was over 100 times higher"
    explanation: >-
      Quantifies the elevation against matched controls.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fasting serum sorbitol is a reliable biomarker of the condition that can be utilized for pathogenicity assessment of identified rare SORD variants."
    explanation: >-
      Establishes the clinical use of the marker, including for variant
      interpretation.
  - reference: PMID:40580554
    reference_title: "Neuromuscular pathology and mitochondrial dysfunction in sorbitol dehydrogenase gene-related distal hereditary motor neuropathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Serum sorbitol, xylitol, and D-arabinitol were measured by gas chromatography-mass spectrometry; increased sorbitol and xylitol, and decreased D-arabinitol were identified."
    explanation: >-
      Independent serum measurement, which also shows that the raised polyol is
      not sorbitol alone: xylitol rises with it and D-arabinitol falls. Measured
      in serum, not urine.
  notes: >-
    Serum sorbitol also discriminates patients from heterozygous carriers, which
    is what allows it to be used on single-variant cases.
- name: Elevated Urine Sorbitol and Xylitol
  biomarker_term:
    preferred_term: sorbitol
    term:
      id: CHEBI:17924
      label: D-glucitol
  presence: INCREASED
  context: >-
    Urinary excretion of sorbitol together with a second polyol, xylitol
    (CHEBI:17151), measured by gas chromatography-mass spectrometry. The pairing
    is what gives the test its specificity, and a urine assay avoids the fasting
    blood draw. The biomarker term is bound to sorbitol, the analyte the record
    is named for; xylitol has no separate record because it is only interpretable
    alongside it.
  evidence:
  - reference: PMID:41223342
    reference_title: "Urine Sorbitol and Xylitol for the Diagnosis of Sorbitol Dehydrogenase Deficiency-Related Neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this patient cohort, the combination of sorbitol and xylitol yielded 100% sensitivity and specificity for SORD-related neuropathy."
    explanation: >-
      Reports the diagnostic performance of the paired urinary polyol profile.
  notes: >-
    The 100% sensitivity and specificity figure comes from an initial cohort of
    19 genetically confirmed patients against reference samples, so it is an
    early performance estimate rather than a validated operating characteristic.
- name: Reduced Red Blood Cell Sorbitol Dehydrogenase Activity
  presence: DECREASED
  context: >-
    Direct enzymatic assay of SORD in red-cell haemolysate, monitoring NADH
    consumption. Offers a functional read on the enzyme itself, which is
    particularly useful when short-read sequencing returns an ambiguous or
    single-variant genotype because of the SORD2P pseudogene.
  evidence:
  - reference: PMID:42021567
    reference_title: "Measurement of Red Blood Cell Sorbitol Dehydrogenase Activity for Fast Screening of SORD-Related Neuropathies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A test cutoff of < 30% yielded 100% sensitivity and specificity to detect deficient individuals."
    explanation: >-
      Gives the operating threshold of the enzymatic screening assay.
  notes: >-
    Derived from a 38-individual evaluation including only three genetically
    confirmed patients; the reported sensitivity and specificity should be read
    as preliminary.
genetic:
- name: SORD
  gene_term:
    preferred_term: SORD
    term:
      id: hgnc:11184
      label: SORD
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: PRESENT
  association: >-
    SORD (15q21.1) encodes the 357-residue cytosolic NAD+-dependent sorbitol
    dehydrogenase. Biallelic loss-of-function is necessary and sufficient for
    disease. Molecular diagnosis is complicated by SORD2P, a highly homologous
    non-functional pseudogene in which the recurrent c.757delG position is fixed
    on most control chromosomes, so short-read data mismap and biallelic status
    is hard to phase; long-read sequencing resolves both problems, and a
    recurrent SORD/SORD2P inversion is only detectable that way.
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We identified 45 individuals from 38 families across multiple ancestries carrying the nonsense c.757delG (p.Ala253GlnfsTer27) variant in SORD, in either a homozygous or compound heterozygous state."
      explanation: >-
        Biallelic requirement across unrelated families establishes recessive
        transmission at the gene level.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SORD has a non-functional highly homologous paralogue, the pseudogene SORD2P, which is thought to have arisen from the duplication of SORD within a 0.5 Mb region on chromosome 15"
    explanation: >-
      Describes the pseudogene that makes standard molecular diagnosis
      unreliable.
  - reference: PMID:35224818
    reference_title: "Long read sequencing overcomes challenges in the diagnosis of SORD neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Subsequent Oxford Nanopore Tech (ONT) long-read sequencing was used to successfully differentiate SORD from the highly homologous non-functional SORD2P pseudogene and confirmed that the mutations were biallelic through haplotype-resolved analysis."
    explanation: >-
      Demonstrates the technical solution to the pseudogene and phasing
      problems.
  - reference: PMID:41282915
    reference_title: "Gene-Pseudogene Inversions as a Hidden Source of Missing Heritability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identified novel and recurrent inversions between SORD and its pseudogene SORD2P in 13 out of 151 patients (9%) affected by SORD-related Charcot-Marie-Tooth (CMT) neuropathy, including 6 out of 8 (75%) of SORD-CMT cases where only one pathogenic variant was identified on short read sequencing, making it the third most common pathogenic allele causing SORD-CMT."
    explanation: >-
      Establishes gene-pseudogene inversion as a third recurrent allele class
      and explains apparently monoallelic cases.
  case_fractions:
  - population: German neuromuscular centre cohort of 166 patients with genetically unexplained axonal neuropathy
    case_fraction_percent: 3.0
    cohort_size: 166
    notes: >-
      Yield of SORD screening among unsolved predominantly axonal CMT/dHMN
      cases, not a share of a SORD-diagnosed cohort.
    evidence:
    - reference: PMID:38975976
      reference_title: "SORDD: mutation frequency and phenotype in predominantly axonal Charcot-Marie-Tooth disease of undefined genetic cause."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Five patients of the total cohort of 166 patients harbored pathogenic variants in SORD (3%)."
      explanation: >-
        Direct count and percentage from a single-centre screening study.
  - population: Chinese hereditary neuropathy cohort, undiagnosed subset
    case_fraction_percent: 6.4
    cohort_size: 78
    notes: >-
      Five of 78 patients remaining undiagnosed after PMP22 duplication and
      panel testing carried biallelic SORD variants.
    evidence:
    - reference: PMID:34819907
      reference_title: "Clinical and Genetic Features of Biallelic Mutations in SORD in a Series of Chinese Patients With Charcot-Marie-Tooth and Distal Hereditary Motor Neuropathy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "SORD mutation was identified in five out of 78 undiagnosed patients."
      explanation: >-
        Screening yield in an East Asian cohort, showing the allele is not
        restricted to European ancestry.
  notes: >-
    The discovery paper's abstract numbers the recurrent frameshift c.757delG
    while its main text writes c.753delG; an author correction was published
    (PMID:32457452). c.757delG (p.Ala253GlnfsTer27) is the designation used by
    every subsequent cohort and is what this entry records.
variants:
- name: SORD c.757delG (p.Ala253GlnfsTer27)
  description: >-
    Recurrent single-nucleotide deletion in SORD exon 7 producing a frameshift
    and premature termination. It is by far the commonest pathogenic allele,
    present homozygously in most reported patients and on one allele in most of
    the rest, and it recurs across European, Middle Eastern and East Asian
    ancestries rather than tracking a single founder haplotype.
  gene:
    preferred_term: SORD
    term:
      id: hgnc:11184
      label: SORD
  clinical_significance: PATHOGENIC
  type: frameshift
  evidence:
  - reference: PMID:36943151
    reference_title: "SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixteen carried a homozygous c.757delG (p.Ala253Glnfs*27) variant, and 11 carried compound heterozygous variants"
    explanation: >-
      Shows the allele dominating a 30-patient European cohort in both
      homozygous and compound heterozygous form.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We confirmed c.757delG (p.Ala253GlnfsTer27) as the most common pathogenic allele, followed by c.458C>A (p.Ala153Asp), while other variants were identified, mostly in single cases."
    explanation: >-
      Confirms the allele hierarchy in the largest multicentre cohort.
- name: SORD c.458C>A (p.Ala153Asp)
  description: >-
    Missense allele, the second commonest after c.757delG and the one most often
    found in trans with it. Curated as a variant record because the allele
    spectrum of this disease is short and top-heavy: two alleles account for most
    of it, and the rest are largely private.
  gene:
    preferred_term: SORD
    term:
      id: hgnc:11184
      label: SORD
  clinical_significance: PATHOGENIC
  type: missense
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We confirmed c.757delG (p.Ala253GlnfsTer27) as the most common pathogenic allele, followed by c.458C>A (p.Ala153Asp), while other variants were identified, mostly in single cases."
    explanation: >-
      Places this allele second in the spectrum, in the largest cohort.
  - reference: PMID:38975976
    reference_title: "SORDD: mutation frequency and phenotype in predominantly axonal Charcot-Marie-Tooth disease of undefined genetic cause."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One additional case carried this variant on one allele only and an additional pathogenic missense variant c.458C > A (p.Ala153Asp) on the other allele."
    explanation: >-
      Independent report of the allele in trans with c.757delG, the usual
      compound heterozygous configuration.
- name: SORD/SORD2P gene-pseudogene inversion
  description: >-
    A structural rearrangement between SORD and its pseudogene, and the third
    commonest pathogenic allele class. It is curated as a variant in its own
    right rather than left in the diagnostic discussion because it changes what a
    negative result means: short-read sequencing cannot see it, so it is
    concentrated precisely among the cases that look monoallelic and therefore
    unsolved.
  gene:
    preferred_term: SORD
    term:
      id: hgnc:11184
      label: SORD
  clinical_significance: PATHOGENIC
  type: inversion
  evidence:
  - reference: PMID:41282915
    reference_title: "Gene-Pseudogene Inversions as a Hidden Source of Missing Heritability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identified novel and recurrent inversions between SORD and its pseudogene SORD2P in 13 out of 151 patients (9%) affected by SORD-related Charcot-Marie-Tooth (CMT) neuropathy, including 6 out of 8 (75%) of SORD-CMT cases where only one pathogenic variant was identified on short read sequencing, making it the third most common pathogenic allele causing SORD-CMT."
    explanation: >-
      Establishes both the allele's rank in the spectrum and its concentration
      in apparently single-variant cases.
- name: SORD c.908+1G>C
  description: >-
    Splice-donor variant shown by ex vivo cDNA analysis to impair splicing of the
    SORD transcript - one of the few SORD alleles with direct transcript-level
    functional evidence.
  gene:
    preferred_term: SORD
    term:
      id: hgnc:11184
      label: SORD
  clinical_significance: PATHOGENIC
  type: splice site
  evidence:
  - reference: PMID:33397963
    reference_title: "Biallelic SORD pathogenic variants cause Chinese patients with distal hereditary motor neuropathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Ex vivo cDNA polymerase chain reaction confirmed that c.908 + 1 G > C variant was associated with impaired splicing of the SORD transcript."
    explanation: >-
      Transcript-level demonstration of the splicing defect.
diagnosis:
- name: Molecular testing of SORD with pseudogene-aware methods
  description: >-
    Confirmatory testing is molecular, but standard short-read exome or CMT
    panel sequencing is not sufficient on its own. SORD2P shares near-identical
    sequence with SORD and carries the c.757delG position on most control
    chromosomes, so reads mismap and biallelic variants cannot be phased.
    Long-read sequencing resolves the two loci and phases the alleles, and it is
    the only route that detects the recurrent SORD/SORD2P inversion - which
    accounts for most cases in which short-read testing finds just one
    pathogenic variant. A patient with a single detected variant and a
    compatible phenotype is therefore not excluded, and the biochemical markers
    curated above are the practical way to adjudicate such a case.
  evidence:
  - reference: PMID:35224818
    reference_title: "Long read sequencing overcomes challenges in the diagnosis of SORD neuropathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Subsequent Oxford Nanopore Tech (ONT) long-read sequencing was used to successfully differentiate SORD from the highly homologous non-functional SORD2P pseudogene and confirmed that the mutations were biallelic through haplotype-resolved analysis."
    explanation: >-
      Demonstrates that long-read sequencing solves both the mismapping and the
      phasing problem in a real diagnostic case.
  - reference: PMID:41282915
    reference_title: "Gene-Pseudogene Inversions as a Hidden Source of Missing Heritability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we identified novel and recurrent inversions between SORD and its pseudogene SORD2P in 13 out of 151 patients (9%) affected by SORD-related Charcot-Marie-Tooth (CMT) neuropathy, including 6 out of 8 (75%) of SORD-CMT cases where only one pathogenic variant was identified on short read sequencing, making it the third most common pathogenic allele causing SORD-CMT."
    explanation: >-
      Quantifies the allele class that short-read testing misses, and shows it
      concentrates precisely in the single-variant cases.
- name: Biochemical case finding by polyol measurement
  description: >-
    Because the molecular route is unreliable, biochemistry does the case
    finding: fasting serum sorbitol, the paired urine sorbitol and xylitol
    profile, or a red-cell SORD activity assay. Serum sorbitol separates
    patients from heterozygous carriers as well as from controls, which is what
    lets it adjudicate a variant of uncertain significance. The individual
    markers and their reported performance are curated under biochemical.
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fasting serum sorbitol is a reliable biomarker of the condition that can be utilized for pathogenicity assessment of identified rare SORD variants."
    explanation: >-
      States both diagnostic uses: identifying the condition, and adjudicating
      variants the molecular test cannot classify.
treatments:
- name: Aldose Reductase Inhibition (Investigational)
  description: >-
    Substrate reduction rather than enzyme replacement: inhibiting aldose
    reductase, the enzyme upstream of the block, reduces flux of glucose into
    sorbitol and so lowers sorbitol despite the missing SORD. Epalrestat and
    ranirestat established the principle in patient fibroblasts and in
    Drosophila; the CNS-penetrant next-generation inhibitor govorestat (AT-007)
    carried it into the clinic, lowering sorbitol in patient fibroblasts,
    iPSC-derived motor neurons and fly brain and rescuing synaptic, locomotor and
    mitochondrial phenotypes in flies. No aldose reductase inhibitor is approved
    for this indication, and this entry records no clinical efficacy claim: the
    evidence curated here is preclinical, and the clinical trial is listed
    separately under clinical_trials.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: epalrestat
      term:
        id: CHEBI:31539
        label: epalrestat
    - preferred_term: govorestat (AT-007)
  target_mechanisms:
  - target: Polyol Pathway Block with Sorbitol Accumulation
    treatment_effect: INHIBITS
    description: >-
      The drug acts one step upstream of the genetic lesion, cutting production
      of the metabolite that accumulates rather than restoring the missing
      enzyme.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "In patient fibroblasts both Epalrestat and Ranirestat significantly reduced sorbitol levels"
      explanation: >-
        Target engagement in human patient cells: inhibiting the upstream enzyme
        lowers the metabolite that accumulates. Quoted from the fibroblast
        experiment alone so the evidence source is unambiguously in vitro.
  evidence:
  - reference: PMID:37014713
    reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "AT-007 significantly reduced sorbitol levels in patient-derived fibroblasts, induced pluripotent stem cell-derived (iPSC-derived) motor neurons, and Drosophila brains."
    explanation: >-
      Target engagement for govorestat in human patient-derived cells including
      motor neurons. The quoted sentence also reports fly brain; the item is
      tagged IN_VITRO for the human-cell measurements it is cited for, and the
      Drosophila arm is carried separately by the MODEL_ORGANISM item below.
  - reference: PMID:37014713
    reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "AT-007 feeding in Sord-deficient Drosophila mitigated synaptic degeneration and significantly improved synaptic transduction, locomotor activity, and mitochondrial function."
    explanation: >-
      Phenotypic rescue in vivo, but in an invertebrate model - the basis for
      the trial, not evidence of clinical benefit.
  notes: >-
    Efficacy in humans is not established here. The phase 2/3 INSPIRE trial
    (NCT05397665) is recorded by its registry as completed, but no peer-reviewed
    report of its results was found in PubMed at the time of curation, so no
    clinical outcome is curated; company announcements are not used as evidence.
- name: Ankle-Foot Orthoses and Rehabilitation
  description: >-
    The current standard of care is supportive: ankle-foot orthoses for foot
    drop, plus physiotherapy for gait and strength maintenance. About a quarter
    of patients take up orthoses, usually in their thirties.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_phenotypes:
  - preferred_term: Foot dorsiflexor weakness
    term:
      id: HP:0009027
      label: Foot dorsiflexor weakness
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One-fourth of patients used ankle foot orthoses, usually in their 30s, but most patients maintained independent ambulation later in life."
    explanation: >-
      Documents orthotic use and its timing in the largest cohort.
- name: Genetic Counseling
  description: >-
    Autosomal recessive recurrence counselling for families, with the practical
    caveat that carrier and biallelic status cannot be read reliably off
    short-read sequencing because of SORD2P; serum sorbitol or long-read
    sequencing may be needed to settle a genotype.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    No evidence block: no cited source addresses genetic counselling practice in
    this disease. The diagnostic caveat the counselling has to work around is
    evidenced under diagnosis, and is not restated here as though it were
    evidence about counselling.
clinical_trials:
- name: NCT05397665
  phase: PHASE_III
  status: COMPLETED
  description: >-
    INSPIRE, a randomised, double-blind, placebo-controlled study of the aldose
    reductase inhibitor govorestat (AT-007) in SORD deficiency, registered as a
    two-part phase 2/3 study with 56 participants and treatment for up to 24
    months. Recorded here as PHASE_III because the schema has no combined
    phase 2/3 value.

    The two evidence items below disagree about status, and the disagreement is
    chronological rather than a conflict: the ClinicalTrials.gov record now
    reports the study as completed (actual completion 2026-06-01, status
    verified 2026-06), while the 2025 cohort paper cited beside it described the
    study as ongoing when it was written. `status: COMPLETED` is taken from the
    registry record, checked directly against the ClinicalTrials.gov API during
    curation; the cached reference file carries only the trial's title and
    design summary, so it cannot be quoted for the status.

    No peer-reviewed publication of the trial's results was found at the time of
    curation, and none of its outcomes are curated here.
  target_phenotypes:
  - preferred_term: Distal lower limb muscle weakness
    term:
      id: HP:0009053
      label: Distal lower limb muscle weakness
  evidence:
  - reference: clinicaltrials:NCT05397665
    reference_title: "A RandomIzed, Double-Blind, Placebo-CoNtrolled, Two-Part Study to Evaluate the Pharmacodynamic EffIcacy and Clinical Benefit of AT 007 in Patients With SoRbitol Dehydrogenase (SORD) DEficiency"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "This study is designed to assess the efficacy and safety of AT-007 treatment in patients with SORD Deficiency."
    explanation: >-
      Registry record establishing the trial's agent, design and indication.
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, a multicentre phase 2/3 study to test the efficacy of govorestat (NCT05397665), a new aldose reductase inhibitor, is currently ongoing."
    explanation: >-
      Independent confirmation of the trial's phase designation and agent.
animal_models:
- name: Sord knockout Sprague Dawley rat
  species: Rat
  genotype: Sord-/- (CRISPR knockout, Sprague Dawley background)
  background: Sprague Dawley
  publication: PMID:38538210
  description: >-
    The best-characterised mammalian model. Sorbitol is raised in serum, CSF and
    peripheral nerve; motor performance and gait decline from about seven months;
    tibial motor conduction slows; and nerve histology shows degenerating and
    de/remyelinated axons with enlarged "ballooned" myelin sheaths, affecting
    motor axons while largely sparing sensory ones.
  modeled_mechanisms:
  - target: Distal Motor Axonal Degeneration and Demyelination
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces the motor-over-sensory selectivity of the human lesion at the
      level of nerve pathology and conduction.
    limitations: >-
      Histology was assessed at advanced ages and electrophysiology was not
      followed longitudinally, so the model speaks to the established lesion
      rather than to its earliest steps.
    readouts:
    - name: Tibial motor nerve conduction velocity
      target: Distal Motor Axonal Degeneration and Demyelination
      direction: DECREASED
      interpretation: >-
        Physiological correlate of motor axonal degeneration in the model.
      evidence:
      - reference: PMID:38538210
        reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Motor nerve conduction velocities of the tibial nerves were slowed."
        explanation: >-
          Direct measurement of slowed motor conduction.
    - name: Serum neurofilament light chain
      target: Distal Motor Axonal Degeneration and Demyelination
      direction: INCREASED
      interpretation: >-
        Fluid biomarker of ongoing axonal degeneration in the model.
      evidence:
      - reference: PMID:38538210
        reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "serum from Sord-/- rats contained significantly increased levels of neurofilament light chain, an established biomarker for axonal degeneration"
        explanation: >-
          Quantitative fluid readout of axonal injury.
    evidence:
    - reference: PMID:38538210
      reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In summary, Sord-/- rats develop a motor-predominant neuropathy that closely resembles the human phenotype."
      explanation: >-
        The authors' own assessment of fidelity to the human disease.
  - target: Polyol Pathway Block with Sorbitol Accumulation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Establishes that sorbitol accumulates in the nervous-system compartments
      that patient serum measurements cannot reach.
    limitations: >-
      Rodent sugar handling and laboratory diet differ from the human setting,
      which is the same variable invoked to explain why one mouse model fails.
    readouts:
    - name: Sorbitol concentration in serum, CSF and peripheral nerve
      target: Polyol Pathway Block with Sorbitol Accumulation
      direction: INCREASED
      interpretation: >-
        Compartment-resolved confirmation of the metabolic block.
      evidence:
      - reference: PMID:38538210
        reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Sord-/- rats had remarkably increased levels of sorbitol in serum, CSF and peripheral nerve."
        explanation: >-
          Direct measurement across three compartments.
  evidence:
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Therefore, we have generated a Sord knockout (KO), Sord-/-, Sprague Dawley rat, to model the human disease and to investigate the pathophysiology underlying SORD deficiency."
    explanation: >-
      Establishes the model, its construction and its intended use.
- name: C57BL/LiA mouse with reduced SORD
  species: Mouse
  genotype: intronic splicing variant reducing SORD protein (C57BL/LiA)
  background: C57BL/LiA
  publication: PMID:32367058
  description: >-
    A mouse strain carrying an intronic splicing variant that substantially
    reduces SORD protein. Under standard husbandry it develops neither neuropathy
    nor slowed nerve conduction - a negative result that the discovery authors
    attribute to the low sugar content of standard mouse chow relative to human
    and Drosophila diets, and therefore to polyol flux rather than to a species
    difference in the mechanism itself.
  modeled_mechanisms:
  - target: Distal Motor Axonal Degeneration and Demyelination
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      Reduced SORD protein in this strain does not produce the human lesion, so
      the model cannot be used to test the axonal-degeneration arm.
    limitations: >-
      The allele is hypomorphic rather than null, and the proposed explanation -
      dietary sugar limiting polyol flux - has not been tested by feeding these
      animals a high-sugar diet or by ageing them, so the failure may reflect
      husbandry rather than a real species difference.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: REFUTE
      evidence_source: MODEL_ORGANISM
      snippet: "Mice that have significantly reduced levels of SORD protein due to an intronic splicing mutation (C57BL/LiA mice), bred and fed according to the standard laboratory conditions, do not develop neuropathy or even slowed nerve conduction velocities"
      explanation: >-
        Explicit negative result: the model does not reproduce the human
        neuropathy.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "This is possibly due to a difference in sugar metabolism between human and mouse since standard mouse chow consists of a low-sugar diet compared to humans"
    explanation: >-
      The authors' proposed explanation for the negative result, curated as
      PARTIAL because it is a hypothesis they did not test.
- name: Drosophila Sodh2 loss-of-function
  species: Drosophila melanogaster
  genotype: Sodh2(MB01265) homozygous, and neuronal Sodh1/Sodh2 double knockdown
  publication: PMID:32367058
  description: >-
    Fly models of SORD loss with elevated head sorbitol, age-dependent synaptic
    degeneration in the visual system, and progressive locomotor decline on a
    normal lifespan. They were the system in which aldose reductase inhibition
    was first shown to rescue the phenotype, and later the system used to show
    bioenergetic and oxidative changes.
  modeled_mechanisms:
  - target: Mitochondrial Dysfunction and Oxidative Stress
    relationship: RECAPITULATES
    fidelity: LOW
    description: >-
      Supplies the bioenergetic and oxidative-stress evidence for this node.
    limitations: >-
      An invertebrate without myelin or Schwann cells, so it cannot speak to the
      myelin abnormality that is central to the mammalian lesion; the readouts
      are brain and muscle rather than peripheral nerve.
    readouts:
    - name: Brain ATP production and tissue ROS
      target: Mitochondrial Dysfunction and Oxidative Stress
      direction: ALTERED
      interpretation: >-
        ATP falls and ROS rises, the paired readout used to call mitochondrial
        dysfunction in this model.
      evidence:
      - reference: PMID:37014713
        reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In addition, we found reduced ATP production in the brain and ROS accumulation in the CNS and muscle, indicating mitochondrial dysfunction."
        explanation: >-
          The measurement behind this readout.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In Drosophila, loss of SORD orthologs caused synaptic degeneration and progressive motor impairment."
      explanation: >-
        Establishes the model as informative for degeneration downstream of
        SORD loss.
  - target: Polyol Pathway Block with Sorbitol Accumulation
    relationship: RESCUES
    fidelity: MODERATE
    description: >-
      Aldose reductase inhibitor feeding normalised sorbitol and rescued motor
      and eye phenotypes, which is the pharmacological proof that the metabolite
      and not some other consequence of the genotype drives degeneration.
    limitations: >-
      Rescue was demonstrated in flies and in patient fibroblasts, not in a
      mammalian nervous system.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Reducing the polyol influx by treatment with aldose reductase inhibitors normalized intracellular sorbitol levels in patient-derived fibroblasts and in Drosophila, and also dramatically ameliorated motor and eye phenotypes."
      explanation: >-
        Demonstrates that lowering the metabolite reverses the phenotype.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Two in vivo Drosophila models recapitulated key aspects of the human phenotype"
    explanation: >-
      The authors' own summary of what the fly models reproduce.
experimental_models:
- name: Patient-derived skin fibroblasts (SORD c.757delG homozygous)
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:32367058
  description: >-
    Fibroblasts from patients homozygous for c.757delG, used to show absent SORD
    protein and raised intracellular sorbitol, and later as the assay system for
    aldose reductase inhibitor target engagement.
  modeled_mechanisms:
  - target: Loss of Sorbitol Dehydrogenase Activity
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Human cells carrying the patient genotype, with complete absence of the
      enzyme protein.
    limitations: >-
      Fibroblasts are not neurons or Schwann cells, so they report the metabolic
      lesion but nothing about axonal vulnerability.
    evidence:
    - reference: PMID:32367058
      reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "In patient-derived fibroblasts, we found a complete loss of SORD protein and increased intracellular sorbitol."
      explanation: >-
        Establishes the model's core finding.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "SORD protein was absent in all patients and the SORD levels were reduced in unaffected carriers compared to controls"
    explanation: >-
      Confirms the fibroblast panel reports the genotype faithfully, including
      the intermediate carrier state.
- name: Patient iPSC-derived motor neurons
  experimental_model_type: IPSC_DERIVED_MODEL
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  publication: PMID:37014713
  description: >-
    iPSC-derived motor neurons from patients, used to show that govorestat lowers
    sorbitol in the human cell type the disease actually targets. Patient iPSC
    lines carrying SORD variants have since been deposited as a shared resource.
  modeled_mechanisms:
  - target: Polyol Pathway Block with Sorbitol Accumulation
    relationship: MEASURES
    fidelity: MODERATE
    description: >-
      Provides the sorbitol readout in a human motor neuron rather than in a
      fibroblast or fly.
    limitations: >-
      A two-dimensional culture without Schwann cells or long axonal
      compartments, so it cannot reproduce length-dependent degeneration.
    evidence:
    - reference: PMID:37014713
      reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "AT-007 significantly reduced sorbitol levels in patient-derived fibroblasts, induced pluripotent stem cell-derived (iPSC-derived) motor neurons, and Drosophila brains."
      explanation: >-
        Names iPSC-derived motor neurons as one of the systems in which sorbitol
        was measured and lowered.
  evidence:
  - reference: PMID:38796985
    reference_title: "Generation of 3 patient induced Pluripotent stem cell lines containing SORD mutations linked to a recessive neuropathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Fibroblast lines from 3 different patients containing the c.753delG; p.Ala253GlnfsTer27 SORD mutations were reprogrammed into induced Pluripotent Stem Cell (iPSC) lines."
    explanation: >-
      Reports the deposited patient iPSC lines that make this model a shared
      resource rather than a single laboratory's material.
discussions:
- discussion_id: gap_sorbitol_to_axon_mechanism
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    By what route does trapped intracellular sorbitol kill long motor axons -
    osmotic stress, oxidative stress, NADPH/NAD+ cofactor imbalance, or some
    combination - and why are motor axons affected while sensory axons are
    largely spared?
  attaches_to:
  - "pathophysiology#Polyol Pathway Block with Sorbitol Accumulation"
  - "pathophysiology#Osmotic Stress in Schwann Cells and Myelinated Axons"
  - "pathophysiology#Mitochondrial Dysfunction and Oxidative Stress"
  - "pathophysiology#Distal Motor Axonal Degeneration and Demyelination"
  rationale: >-
    The genotype-to-metabolite half of the mechanism is settled, and the
    metabolite-to-axon half is not. The candidates are curated as competing
    mechanistic_hypotheses rather than argued in prose here:
    osmotic_myelin_injury_model (CANONICAL), mitochondrial_oxidative_model
    (ALTERNATIVE) and redox_cofactor_imbalance_model (EMERGING), with the first
    two carried on tagged causal edges out of the accumulation node. This
    discussion records what would settle between them. The discovery authors listed osmotic stress,
    oxidative stress and reduced NADPH as plausible and did not choose between
    them, and the govorestat study restated that the mechanisms of
    sorbitol-induced degeneration are not fully elucidated. The gap matters
    therapeutically as well as descriptively: substrate reduction works upstream
    of whichever route is correct, so it can succeed without settling the
    question, but any attempt to protect the axon downstream needs the answer.
    The motor-over-sensory selectivity is a second, related unknown - sorbitol
    accumulates systemically, yet the lesion is selective, and the ballooned
    myelin seen in the rat points at Schwann cells as at least a co-target.
  proposed_experiments:
  - experiment_id: exp_osmotic_vs_oxidative_rat_nerve
    name: Compartment-resolved osmotic versus oxidative dissection in Sord-null rat nerve
    description: >-
      In Sord-/- rat sciatic and tibial nerve, measure Schwann cell and axonal
      water content and organic-osmolyte composition alongside oxidative-damage
      markers and NADPH/NADP+ and NAD+/NADH ratios, at ages before and after the
      onset of conduction slowing, and test whether an antioxidant that does not
      lower sorbitol prevents the lesion. A dissociation between sorbitol
      lowering and antioxidant protection would separate the osmotic and
      oxidative arms.
  - experiment_id: exp_motor_vs_sensory_isogenic_ipsc
    name: Motor versus sensory neuron comparison in isogenic human cultures
    description: >-
      Differentiate isogenic patient and gene-corrected iPSC lines into motor and
      sensory neurons in microfluidic axon-compartment devices, and compare
      sorbitol handling, axonal transport, bioenergetics and axon survival
      between the two lineages under matched glucose. This tests whether the
      selectivity is cell-intrinsic or requires the Schwann cell.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Our findings do not fully elucidate yet the mechanism of axonal damage caused by SORD deficiency: one or more of the known effects of decreased SORD activity, including increased sorbitol level, cellular osmolarity, oxidative stress and decreased NADPH levels, are plausible"
    explanation: >-
      The discovery authors state the gap and enumerate the candidate routes.
  - reference: PMID:37014713
    reference_title: "Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The underlying mechanisms of sorbitol-induced degeneration have not been fully elucidated"
    explanation: >-
      Restates the gap three years later, confirming it remains open.
- discussion_id: mismatch_mouse_sord_no_neuropathy
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Why does a mouse with markedly reduced SORD protein develop no neuropathy and
    no conduction slowing, when biallelic SORD loss reliably causes neuropathy in
    humans and a motor-predominant neuropathy in the rat?
  attaches_to:
  - "pathophysiology#Distal Motor Axonal Degeneration and Demyelination"
  rationale: >-
    This is a mismatch rather than an absence of evidence: the C57BL/LiA mouse
    has been studied and is negative. The explanation offered - that standard
    mouse chow is low in sugar relative to human and Drosophila diets, so polyol
    flux never reaches the level needed to accumulate toxic sorbitol - is
    attractive because it predicts the disease is flux-dependent rather than
    purely genotype-dependent, and because SORD deficiency does aggravate
    neuropathy in diabetic rodents. It is also untested. The alternative, that
    the hypomorphic allele leaves enough residual enzyme, is not excluded. The
    distinction matters for interpreting every negative rodent result in this
    disease and for whether dietary sugar should be treated as a modifier in
    patients.
  proposed_experiments:
  - experiment_id: exp_high_sugar_diet_hypomorphic_mouse
    name: High-sugar diet and ageing challenge in the hypomorphic mouse
    description: >-
      Maintain C57BL/LiA and control mice on standard versus high-sugar diets to
      old age, with serial motor nerve conduction, nerve histology and nerve
      sorbitol. Emergence of the lesion on the high-sugar arm alone would confirm
      flux dependence; its absence under both would point instead at residual
      enzyme activity or a species difference.
  - experiment_id: exp_null_vs_hypomorph_mouse
    name: Null versus hypomorph comparison
    description: >-
      Phenotype a true Sord-null mouse alongside C57BL/LiA under identical
      husbandry, measuring residual enzyme activity, nerve sorbitol and
      conduction. This separates allele strength from diet as the explanation.
  evidence:
  - reference: PMID:32367058
    reference_title: "Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice that have significantly reduced levels of SORD protein due to an intronic splicing mutation (C57BL/LiA mice), bred and fed according to the standard laboratory conditions, do not develop neuropathy or even slowed nerve conduction velocities"
    explanation: >-
      Establishes the negative mouse result that constitutes the mismatch.
  - reference: PMID:38538210
    reference_title: "SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In summary, Sord-/- rats develop a motor-predominant neuropathy that closely resembles the human phenotype."
    explanation: >-
      The contrasting positive rodent result that makes the mouse finding a
      mismatch rather than a rule about rodents.
- discussion_id: interpretation_cmt2_dhmn_split
  kind: INTERPRETATION
  status: OPEN
  prompt: >-
    Should SORD deficiency be curated as one disease spanning CMT2 and dHMN, as
    it is here, or split along the clinical labels its patients receive?
  attaches_to:
  - "pathophysiology#Motor-Predominant Hereditary Neuropathy Spanning CMT2 and dHMN"
  rationale: >-
    Cohorts assign the same genotype to different labels in different
    proportions - roughly two-thirds CMT2 in the largest multicentre series,
    but a dHMN majority in the French and Swiss cohort - and a third label,
    intermediate CMT, is used for patients whose conduction velocities fall in
    between. The labels track how much sensory involvement was found and how
    velocities were interpreted, not genotype, mechanism, or the allele carried.
    Splitting would therefore produce entries that differ in ascertainment rather
    than in biology. MONDO indexes the disease under the dHMN branch
    (MONDO:0030055, is_a neuronopathy, distal hereditary motor, autosomal
    recessive), which this entry follows for its disease_term while recording the
    CMT2 presentation as the same disease.
  evidence:
  - reference: PMID:39938083
    reference_title: "Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two-thirds of cases were diagnosed with CMT2 while one-third had distal hereditary motor neuropathy."
    explanation: >-
      The CMT2-majority split in the largest cohort.
  - reference: PMID:36943151
    reference_title: "SORD-related peripheral neuropathy in a French and Swiss cohort: Clinical features, genetic analyses, and sorbitol dosages."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eighteen had dHMN, nine had CMT2, and three had intermediate CMT."
    explanation: >-
      The opposite split in an independent cohort, which is the argument against
      splitting the entry on these labels.
notes: >-
  Scope and boundary decisions recorded deliberately.

  Relationship to the umbrella entry: MONDO:0030055 is a child of MONDO:0015363,
  which dismech curates separately as Distal Hereditary Motor Neuronopathy,
  Autosomal Recessive - an entry that already carries a SORD block in its
  genetic section. Both are now members of the Distal_Hereditary_Motor_Neuropathies
  grouping, so a child sits beside its own parent there. That is deliberate: the
  umbrella entry covers IGHMBP2, SIGMAR1, PLEKHG5 and RTN2 as well, and splitting
  SORD out is what lets its distinct metabolic mechanism, biochemical markers and
  drug target be modelled. Anyone extending either entry should check the other
  first rather than duplicating.

  No GeneReviews chapter exists for SORD deficiency: PubMed searches for
  "sorbitol dehydrogenase deficiency GeneReviews" and "SORD deficiency
  GeneReviews" both returned zero records at the time of curation, so the
  GeneReviews phenotype baseline step was not applicable and the phenotype set
  is built from the primary cohorts instead.

  Conformance to peripheral_axonal_degeneration is declared on four nodes but
  deliberately not on the module's "Axonal Transport Impairment and
  Mitochondrial Dysfunction" amplifier. That module node bundles impaired axonal
  transport with mitochondrial dysfunction and oxidative stress; this entry has
  evidence for the mitochondrial and oxidative arms only, and none for axonal
  transport in SORD deficiency, so declaring conformance there would assert an
  unevidenced claim.

  The disease is repeatedly framed as a genetic window onto diabetic neuropathy
  because it engages the same polyol pathway. That link is not curated as
  conformance to diabetic_vascular_complications: patients are normoglycaemic,
  the upstream trigger there is chronic hyperglycaemia, and nothing in that
  module's chain is evidenced here.

  Skeletal muscle findings - raised creatine kinase, vacuoles and tubular
  aggregates on biopsy, complex I deficiency on muscle proteomics - are curated
  as a laboratory phenotype and as evidence on the mitochondrial node rather
  than as a separate myopathy arm. The reported muscle changes are described by
  their authors as subclinical and accompanied by a neurogenic pattern, so
  reading them as a primary myopathy would overstate them.
📚

References & Deep Research

References

4
PMID:32367058
Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes.
No top-level findings curated for this source.
PMID:39938083
Genotype and phenotype spectrum of Charcot-Marie-Tooth disease due to mutations in SORD.
No top-level findings curated for this source.
PMID:38538210
SORD-deficient rats develop a motor-predominant peripheral neuropathy unveiling novel pathophysiological insights.
No top-level findings curated for this source.
PMID:37014713
Sorbitol reduction via govorestat ameliorates synaptic dysfunction and neurodegeneration in sorbitol dehydrogenase deficiency.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
Sorbitol Dehydrogenase (SORD) Deficiency — Comprehensive Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 20 citations 2026-08-23T23:15:47.824759

Sorbitol Dehydrogenase (SORD) Deficiency — Comprehensive Research Report

1. Disease Information

Overview. Sorbitol dehydrogenase (SORD) deficiency — most commonly called CMT‑SORD, and clinically designated autosomal recessive distal hereditary motor neuronopathy‑8 (HMNR8) or "SORD deficiency with peripheral neuropathy (SORDD)" — is an autosomal recessive, adult/adolescent‑onset, length‑dependent peripheral neuropathy caused by biallelic loss‑of‑function variants in SORD, the gene encoding sorbitol dehydrogenase. It was first described as a distinct disease entity in 2020 and has rapidly emerged as the single most common autosomal recessive cause of axonal Charcot‑Marie‑Tooth disease type 2 (CMT2) and distal hereditary motor neuropathy (dHMN) (Cortese et al., Nat Genet 2020, PMID 32367058). Loss of the enzyme causes accumulation of the polyol sorbitol, which is directly neurotoxic to peripheral motor (and to a lesser degree sensory) axons — the same biochemical pathway implicated in diabetic peripheral neuropathy, giving the discovery broader relevance to diabetes-related neuropathy research.

Key identifiers: - OMIM phenotype: 618912 — Neuronopathy, distal hereditary motor, autosomal recessive 8 - OMIM gene: 182500 — SORBITOL DEHYDROGENASE; SORD (gene symbol SORD, chromosome 15q26.1) - MONDO: MONDO:0030055 (sorbitol dehydrogenase deficiency with peripheral neuropathy) - MedGen: C5394466 - DOID (RGD browser): DOID:9006739 - Orphanet / GeneReviews / PanelApp (Genomics England "Hereditary neuropathy" panel): SORD is listed as a validated hereditary-neuropathy gene

Synonyms: CMT‑SORD; SORD deficiency; SORD-related neuropathy; sorbitol dehydrogenase deficiency with peripheral neuropathy (SORDD); distal hereditary motor neuronopathy, autosomal recessive 8 (HMNR8); axonal CMT2 due to SORD deficiency.

Evidence basis. The disease description rests almost entirely on aggregated multi-center human clinical cohorts (the largest to date comprising 144 patients from 126 families across 43 centers, Brain 2025, PMID pending/DOI 10.1093/brain/awaf021), supplemented by mechanistic work in patient-derived fibroblasts, iPSC-derived motor neurons, Drosophila, and Sord‑deficient rat and mouse models (see Sections 6 and 15).

2. Etiology

Disease causal factor: Purely genetic — biallelic (homozygous or compound heterozygous) loss-of-function variants in SORD on chromosome 15q26.1, which abolish or severely reduce sorbitol dehydrogenase enzymatic activity.

Genetic risk factors: - The dominant pathogenic allele worldwide is the frameshift c.757delG (p.Ala253GlnfsTer27), accounting for ~87% of all disease alleles and found homozygously in ~78% of the large genotype–phenotype cohort (Brain 2025). It behaves as a founder/recurrent variant across many ancestries (European, Middle Eastern, East Asian) rather than a single-population founder effect, likely because it lies within the region shared with the SORD2P pseudogene. - Second most common allele: c.458C>A (p.Ala153Asp) (~8% of alleles). - A third recurrent pathogenic mechanism is a gene–pseudogene (SORD/SORD2P) inversion, found in ~9% of SORD-CMT patients and disproportionately (75%) among cases where short-read sequencing detected only one pathogenic variant — i.e., cryptic biallelism that standard exome/panel testing misses. - Population carrier frequency for c.757delG has been estimated at ~0.46% in Chinese controls (3/650) (Chen et al., PMC8607551) and broadly ~0.5–1% in several populations studied, consistent with SORD deficiency being present at a frequency (~1 in 100,000 homozygotes, or higher when accounting for compound heterozygotes) that makes it one of the most common recessive neuropathies overall. - Overall genotype spectrum: 82% biallelic nonsense/splicing/structural (predicted null) variants; 18% carry at least one missense allele.

Environmental / non-genetic risk factors: None established as disease-causing; this is a monogenic Mendelian disorder. However, because SORD acts in the same polyol pathway implicated in diabetic neuropathy (see Section 6), hyperglycemia is a biologically plausible modifier of polyol flux, though no formal gene–environment interaction study in SORD-deficient patients has been published.

Sex as a modifier: In the large genotype-phenotype cohort, male sex was significantly associated with greater severity of distal lower-limb (plantar flexion) weakness and a larger rate of decline in dorsiflexion strength over time — a modifier of expressivity rather than a causal factor (Brain 2025). The rat model similarly showed males more affected on motor nerve conduction velocity.

Protective factors: None specifically documented for humans. In model systems, pharmacologic inhibition of the upstream enzyme aldose reductase (AKR1B1) — which prevents glucose from ever being converted to sorbitol — is protective (see Sections 6 and 12).

Gene–environment interactions: Not formally studied in SORD-deficient humans, though the shared biochemistry with diabetic polyol-pathway neurotoxicity is repeatedly invoked as a rationale for studying SORD deficiency as a "genetic model" of diabetic neuropathy pathophysiology.

3. Phenotypes

Phenotype category: Predominantly motor/sensorimotor peripheral neuropathy signs and symptoms, plus laboratory/biochemical abnormalities (elevated serum/urine sorbitol and xylitol).

Core clinical phenotypes (from the 144-patient genotype–phenotype cohort, Brain 2025, and the original 45-patient Cortese et al. 2020 cohort):

Phenotype Frequency / detail Suggested HPO term
Distal lower-limb weakness (foot dorsiflexion) MRC ≤3 in 53% of patients; declines ~5%/year HP:0009053 (Distal lower limb muscle weakness)
Foot drop Very common presenting sign HP:0001772 (Foot drop)
Pes cavus Common structural foot deformity; 79% report foot deformity HP:0001761 (Pes cavus)
Distal muscle atrophy (legs) Common HP:0003724 (Distal amyotrophy)
Absent/decreased deep tendon reflexes Common HP:0001315 / HP:0001284
Foot plantar flexion weakness Impaired in 78%; MRC ≤3 in 33% HP:0009053
Distal upper-limb (hand) weakness/dexterity impairment ~50% motor involvement; hand dexterity impaired in 37%, onset ~8 yrs after gait symptoms HP:0009830 / HP:0007340
Sensory loss (pinprick/vibration) Reported by <1/3 patients; upper-limb sensory nerve action potentials (SNAPs) abnormal in 76% vs. only 27% in lower limbs (a distinctive "inverse" length-independent sensory pattern) HP:0003676 (Progressive sensory neuropathy)
Distal tremor 28% HP:0025278
Gait difficulty / difficulty running Walking difficulty 85%; running difficulty 88% HP:0002136 / HP:0001288
Elevated serum sorbitol 14.7 ± 4.9 mg/L (patients) vs. 0.07 ± 0.06 mg/L (controls), p<0.001 (fasting status–independent, storage-stable) (biochemical, not HP-coded)
Elevated urine sorbitol and xylitol Novel 2025 biomarker for screening/diagnosis and treatment monitoring (Neurology 2025, PMID 41223342) (biochemical)

Phenotype characteristics: - Age of onset: Typically second decade of life (childhood/adolescent onset); mean reported onset ~14 years (range 6–17) in the Chinese cohort, though many patients report subtle antecedent findings (foot deformity, poor athletic performance in school — 46%) that predate formal diagnosis. Mean age at enrollment/diagnosis in the largest cohort was 40.9 ± 14.8 years, reflecting substantial diagnostic delay (the disease was undiscovered until 2020). - Severity: Predominantly mild-to-moderate: baseline CMT Examination Score (CMTES) 6.09 ± 3.7; 72% mild (CMTES 0–7), 26% moderate (8–16), <1% severe (17–28). CMT Neuropathy Score (CMTNS) mean 12.2 (range 9–15) in an independent cohort. - Progression: Slowly progressive over decades. Foot dorsiflexion and plantar flexion strength decline significantly with age (p<0.001 both) and on longitudinal follow-up (mean 6.9 ± 7.4 years); dorsiflexion declines ~5%/year. Most patients remain independently ambulatory even late in life; only ~25% require ankle-foot orthoses (typically starting in their 30s), and only a minority need canes/crutches (13/144) or wheelchairs (2/144). - Clinical classification split: Sensorimotor CMT2 phenotype in 60% of patients vs. pure motor dHMN phenotype in 40% — i.e., SORD deficiency spans the CMT2/dHMN phenotypic continuum rather than mapping to a single discrete syndrome. - Quality of life: No dedicated EQ-5D/SF-36 study identified in the literature for CMT-SORD specifically; functional impact is documented indirectly via patient-reported walking/running difficulty rates above and use of assistive devices. General CMT quality-of-life literature (not disease-specific) applies.

4. Genetic/Molecular Information

Causal gene: SORD (HGNC symbol SORD; OMIM 182500), located at 15q26.1, encoding a 357-amino-acid cytosolic enzyme, sorbitol dehydrogenase (EC 1.1.1.14), a member of the medium-chain zinc-dependent alcohol dehydrogenase family.

Pathogenic variant classes: - Frameshift/nonsense (predicted null): c.757delG (p.Ala253GlnfsTer27) — the dominant allele (~87% of alleles); ClinVar RCV001194463 lists this as Pathogenic for both "Sorbitol dehydrogenase deficiency with peripheral neuropathy" and "Neuronopathy, distal hereditary motor, autosomal recessive 8." - Missense: c.458C>A (p.Ala153Asp) (~8% of alleles); additional missense variants reported in Chinese cohorts include c.731C>T (p.Pro244Leu), c.776C>T (p.Ala259Val), c.851T>C (p.Leu284Pro) (PMC8607551). - Structural variant: SORD/SORD2P gene–pseudogene inversion — a structural rearrangement between SORD and its highly homologous pseudogene, found in ~9% of patients and the third most common pathogenic allele class; especially important because these are frequently missed by short-read exome/panel sequencing.

A critical diagnostic complication — the SORD2P pseudogene: SORD has a paralogous pseudogene, SORD2P, that shares extremely high sequence identity (the recurrent c.757delG mutation position corresponds to a sequence present on ~95% of pseudogene-derived chromosomes), causing mis-mapping of short-read sequencing reads and complicating both variant calling and cis/trans phasing of biallelic variants. This is considered a major reason CMT-SORD was not identified as a distinct entity until 2020 despite affecting a substantial fraction of unsolved CMT2/dHMN cases. Long-read (Oxford Nanopore) sequencing has been shown to resolve SORD from SORD2P and correctly phase compound heterozygous/inversion genotypes (Cortese et al., 2022, PMID 35224818).

Functional consequence: All characterized pathogenic variants result in loss of function of sorbitol dehydrogenase. Patient-derived fibroblasts homozygous for c.757delG show complete absence of SORD protein by western blot and a ~10-fold increase in intracellular sorbitol compared with controls.

Variant origin/zygosity: Germline, autosomal recessive; homozygous (most common, ~78%) or compound heterozygous (~18%, most commonly c.757delG + a second allele) or complex (inversion) genotypes.

Modifier genes: No confirmed modifier loci; sex (male) modifies clinical severity (see Section 2), and residual polyol-pathway flux (via AKR1B1, aldose reductase, the upstream enzyme) likely modulates disease severity biochemically, though this has not been formally shown as a genetic modifier in patients.

Epigenetic information / chromosomal abnormalities: None reported; this is a straightforward Mendelian enzymopathy without known epigenetic contribution.

Population allele frequency: Carrier frequency of c.757delG ~0.46% in a Chinese control cohort (3/650) and comparably elevated in other studied populations, consistent with SORD deficiency being among the most common recessive neuropathies worldwide (estimated >3,000 cases in the USA alone; Brain 2025).

5. Environmental Information

SORD deficiency is a purely monogenic disorder; no environmental, toxin, occupational, dietary, or infectious trigger is required for disease manifestation. The relevant "environmental" biochemistry is entirely endogenous — dietary/metabolic glucose flux through the polyol pathway generates the substrate (sorbitol) that a deficient SORD enzyme cannot clear. No formal studies of dietary sorbitol/fructose intake as a disease modifier in SORD-deficient patients were identified, though this is a biologically plausible area given that the disease-defining biomarker (serum/urine sorbitol) derives from the same pathway implicated in dietary sugar-alcohol metabolism. No infectious agent is implicated.

6. Mechanism / Pathophysiology

Molecular pathway — the polyol pathway (sorbitol–aldose reductase pathway): 1. Aldose reductase (AKR1B1) — the first, rate-limiting enzyme — catalyzes the NADPH-dependent reduction of glucose → sorbitol. 2. Sorbitol dehydrogenase (SORD) — the second enzyme — normally converts sorbitol → fructose (NAD⁺-dependent). 3. When SORD is deficient, sorbitol cannot be cleared and accumulates intracellularly and extracellularly, because sorbitol is a polar polyol that diffuses poorly across cell membranes.

Causal chain (upstream → downstream): Biallelic SORD loss-of-function variant → complete/near-complete loss of SORD enzyme activity (molecular scale) → impaired conversion of sorbitol to fructose, with sorbitol trapped intracellularly (cellular scale) → osmotic/hyperosmolar stress within Schwann cells and neurons, producing pathognomonic "ballooned" myelin sheaths with bubbly disintegration (a feature also seen in galactosemic neuropathy models, implicating a shared polyol-osmotic mechanism) → secondary axonal degeneration and demyelination, disproportionately affecting motor axons (motor-predominant length-dependent axonopathy, tissue scale) → progressive distal weakness, foot drop, and gait impairment (organism scale).

Cellular processes implicated (from Drosophila and iPSC-neuron mechanistic studies, PMID 37014713, JCI Insight 2023): - Osmotic/hyperosmolar stress from sorbitol accumulation (primary proposed mechanism) - Synaptic degeneration — Sord-deficient flies show progressive motor and eye-neuron synaptic loss - Mitochondrial/energetic dysfunction — reduced brain ATP in Sord-deficient flies, restored by aldose-reductase inhibition - Oxidative stress — elevated reactive oxygen species (ROS) across CNS, ventral nerve cord (VNC), and muscle tissue in flies; reduced by treatment - NADPH/NAD⁺ cofactor imbalance — general polyol-pathway biochemistry (well documented in the diabetic-neuropathy literature via AKR1B1) diverts NADPH/NAD⁺ redox cofactors, contributing to oxidative and inflammatory injury (NF-κB activation reported in diabetic polyol pathway studies)

Biochemical abnormality: Loss-of-function enzyme deficiency (sorbitol dehydrogenase), the archetypal "enzyme deficiency" mechanism, directly analogous to inborn errors of metabolism, but manifesting as a chronic length-dependent peripheral neuropathy rather than an acute metabolic crisis.

Tissue damage mechanism: Osmotic myelin injury with secondary Wallerian-type axonal degeneration, evidenced histologically (rat model, Brain 2024, PMID pending, DOI academic.oup.com/brain/article/147/9/3131/7636456) by: - Ballooned/enlarged myelin sheaths around otherwise intact axons - Degenerating and demyelinated axons - Thinly myelinated fibers with increased g-ratios - Clusters of regenerating axons - Predominant loss of large motor fibers, especially distally, with relative sparing of sensory fibers

Molecular profiling: Elevated serum neurofilament light chain (NfL) in the rat model serves as a biomarker of ongoing axonal degeneration (present but not correlated with severity). Direct human transcriptomic/proteomic/metabolomic profiling of nerve tissue has not been widely reported; the principal "omics" readout used clinically and mechanistically is the targeted metabolomic (polyol) biomarker panel — serum and urine sorbitol and xylitol.

Suggested GO terms: - GO:0006062 (sorbitol catabolic process) - GO:0019853 (L-ascorbic acid biosynthetic process – polyol pathway crosslink, if relevant) - GO:0006970 (response to osmotic stress) - GO:0007422 (peripheral nervous system development, for context) - GO:0043524 (negative regulation of neuron apoptotic process — inverse direction relevant to axonal degeneration)

Suggested CL terms: - CL:0000011 (Schwann cell) — site of myelin ballooning - CL:0000100 (motor neuron) — preferentially affected cell type - CL:0000098 (sensory neuron) — relatively spared

7. Anatomical Structures Affected

Organ level: - Primary: Peripheral nervous system — motor and (to a lesser extent) sensory peripheral nerves, particularly the longest axons (length-dependent pattern: lower limb before upper limb). - Secondary: Skeletal muscle (secondary distal muscle atrophy from denervation); no cardiac, hepatic, renal, or CNS involvement reported as part of the core phenotype. - Body system: Peripheral/neuromuscular system (UBERON:0000010 peripheral nervous system).

Tissue/cell level: - Motor axons (CL:0000100) — predominantly affected - Schwann cells / myelin sheath (CL:0000011) — site of the pathognomonic osmotic "ballooning" - Sensory axons (CL:0000098) — relatively spared, though upper-limb sensory nerve action potentials are frequently abnormal

Subcellular level: Cytosol (GO:0005829) — SORD is a cytosolic enzyme; myelin sheath compartment (osmotic swelling).

Localization: Distal lower-limb nerves (peroneal, tibial) first and most severely; distal upper-limb (ulnar, median) nerves later (~8 years after leg symptom onset on average). Bilateral, symmetric distribution typical of an inherited length-dependent axonopathy — no lateralization reported.

Suggested UBERON terms: UBERON:0001021 (nerve), UBERON:0003714 (peripheral nerve fascicle equivalents / peroneal nerve UBERON:0009629, tibial nerve UBERON:0009028), UBERON:0001134 (skeletal muscle tissue, secondary).

8. Temporal Development

Onset: Typically childhood/adolescent onset (second decade of life), though many patients have subclinical antecedents (foot deformity, poor school athletic performance) recognized only in retrospect. Onset pattern is insidious/chronic, not acute.

Progression: Slowly progressive over decades — dorsiflexion strength declines ~5% per year on quantitative testing; statistically significant longitudinal decline in both dorsiflexion and plantar flexion strength over a mean follow-up of ~7 years. Disease severity remains predominantly mild-to-moderate even in adulthood (72% mild by CMTES); severe disease is rare (<1%).

Disease course pattern: Progressive but not typically disabling — most patients remain ambulatory without assistive devices for decades; a minority progress to requiring ankle-foot orthoses (usually starting in their 30s) or, rarely, canes/wheelchairs.

Critical periods: No formally defined therapeutic window has been established, though the ongoing govorestat trials are testing intervention in symptomatic adults; earlier (pre-symptomatic or minimally symptomatic) intervention is hypothesized to be more effective given the slow, cumulative nature of axonal loss, but this is not yet proven.

9. Inheritance and Population

Inheritance pattern: Autosomal recessive (biallelic pathogenic variants required). Nearly all reported cases are sporadic with no family history, consistent with recessive inheritance and relatively high carrier frequency rather than consanguinity-driven clustering in most populations studied. Penetrance appears to be high/complete among individuals with biallelic null variants, though expressivity (severity, motor- vs. sensorimotor-predominant phenotype) is variable.

Epidemiology: - Prevalence: Estimated to be the most common autosomal recessive axonal peripheral neuropathy; accounts for ~7–9% of dHMN and CMT2 cases in cohorts studied. At least 3,000 estimated cases in the USA alone. General hereditary neuropathy prevalence is ~1:2500; CMT-SORD represents a substantial fraction of the previously "genetically unsolved" cases within that group. - Carrier frequency: ~0.46–1% for the common c.757delG allele across multiple populations studied (Chinese, European), suggesting the disorder is under-ascertained rather than truly rare.

Genetic anticipation: Not reported/expected — this is a coding sequence loss-of-function disorder, not a repeat-expansion disease.

Germline mosaicism, founder effects, consanguinity: The c.757delG allele behaves as a recurrent (likely pseudogene-conversion-mediated) variant across many distinct ancestries rather than a classical single-founder mutation; no strong consanguinity signal has been reported (most cases sporadic, non-consanguineous).

Population demographics: - Geographic/ancestry distribution (144-patient cohort): European ancestry 75%, Middle Eastern 11%, East Asian 9%, other ancestries the remainder — i.e., globally distributed, not restricted to a single ethnic group. - Sex ratio: Cohorts show a male excess in ascertainment (99 males [69%] vs. 45 females [31%] in the largest cohort), and males show greater clinical severity, though whether this reflects true sex-differential penetrance/expressivity or ascertainment bias (e.g., under-recognition in females) is not fully resolved. - Age distribution: Diagnosed patients span 15–75 years (mean enrollment age 40.9 ± 14.8 years), reflecting long diagnostic delay typical of a disease only characterized in 2020.

10. Diagnostics

Clinical tests: - Biochemical (blood): Serum sorbitol — markedly and consistently elevated in affected patients (14.7 ± 4.9 mg/L vs. 0.07 ± 0.06 mg/L in controls, >100-fold difference in some series), stable regardless of fasting status and storage conditions, making it a robust, easily obtained diagnostic and monitoring biomarker. - Biochemical (urine): Urine sorbitol and xylitol (measured by gas chromatography–mass spectrometry) — a newer (2025) complementary/screening biomarker; xylitol elevation is specifically noted as adding diagnostic specificity (Neurology 2025, PMID 41223342; Mayo Clinic Laboratories offers a clinical urine SORD sorbitol/xylitol assay). - Electrophysiology: Nerve conduction studies show an axonal (non-demyelinating) sensorimotor or pure motor neuropathy pattern; characteristic asymmetric sensory involvement (upper-limb SNAPs abnormal far more often — 76% — than lower-limb SNAPs — 27%), a distinctive pattern that can raise suspicion for SORD deficiency specifically. - Nerve biopsy: Not part of routine diagnostic workup in humans but in animal models shows the pathognomonic ballooned/swollen myelin sheaths.

Genetic testing: - Overview: Molecular confirmation of biallelic SORD pathogenic variants is definitive, but is technically complicated by the SORD2P pseudogene, which causes false negatives/mismapping in standard short-read next-generation sequencing (exome or CMT gene panels). - Panels/exome/genome sequencing: SORD should be included in CMT2/dHMN gene panels and CMT-specific exome analyses; however, careful bioinformatic handling of the pseudogene region (or orthogonal confirmation) is needed. - Long-read sequencing (Oxford Nanopore): Increasingly used/recommended to resolve SORD from SORD2P, correctly phase compound heterozygous genotypes, and detect the SORD/SORD2P inversion allele class that short-read methods miss (up to 9% of cases, and the majority of "single-variant-detected" cases on short-read testing). - Single-gene/targeted testing: Appropriate when biochemical testing (elevated sorbitol) has already localized the defect.

Clinical criteria / differential diagnosis: SORD deficiency should be considered in any patient with an apparently sporadic, axonal, length-dependent CMT2/dHMN phenotype of childhood/adolescent onset, especially when standard CMT gene panels are negative — historically this represented a large "genetically unsolved" subgroup. Differential diagnosis includes other AR axonal CMT2/dHMN genes (e.g., HSPB1, GDAP1, TRPV4), and, when relevant, acquired causes of length-dependent neuropathy (diabetic neuropathy, toxic neuropathy) — notably, the biochemical overlap with the polyol pathway means clinicians should distinguish primary genetic SORD deficiency from the polyol-pathway hyperactivity seen in poorly controlled diabetes.

Screening: No population newborn or carrier screening program currently exists for SORD, given its relatively recent (2020) disease-gene establishment, but given the estimated carrier frequency (~0.5–1%) this may become relevant to hereditary neuropathy carrier panels in the future.

11. Outcome/Prognosis

Survival/mortality: No excess mortality has been reported; SORD deficiency is not known to shorten lifespan. No formal survival/mortality studies exist (the disease is not classically life-limiting, being restricted to peripheral motor/sensory nerve involvement).

Morbidity and function: - Most patients experience lifelong, slowly progressive distal weakness and gait impairment but retain independent ambulation for decades. - Functional impact: 85% report walking difficulty, 88% report running difficulty; ~25% eventually require ankle-foot orthoses (typically starting in their 30s); only a small minority (13/144 in the largest cohort) require canes/crutches, and very few (2/144) require wheelchairs. - No formal quality-of-life instrument (EQ-5D, SF-36) data specific to CMT-SORD were identified in the literature reviewed; general CMT disability metrics (CMTES/CMTNS) are used instead, and CMTES shows most patients (72%) fall in the "mild" category.

Disease course: Chronic and progressive but generally compatible with normal daily functioning through mid-adulthood; no described spontaneous remission. Complications are primarily musculoskeletal/orthopedic (foot deformity, gait abnormality secondary to weakness) rather than systemic.

Prognostic factors: Male sex associates with greater severity and faster progression of distal weakness. Genotype (homozygous null vs. compound heterozygous with a missense allele) may modify severity, though this has not been rigorously stratified in the literature reviewed. Elevated serum NfL (in the rat model) reflects ongoing axonal degeneration and is being explored as a prognostic/monitoring biomarker analogous to its use in other neurodegenerative conditions.

12. Treatment

Investigational disease-modifying pharmacotherapy — Govorestat (AT-007): - Mechanism: A next-generation aldose reductase (AKR1B1) inhibitor (IC50 ≈ 100 pM), CNS-penetrant. By inhibiting the upstream enzyme that converts glucose to sorbitol, govorestat reduces the total flux of sorbitol production, thereby lowering intracellular/circulating sorbitol despite the downstream SORD block — an elegant "block the tap rather than fix the drain" therapeutic logic. - Preclinical evidence: In Drosophila Sord-deficient models, govorestat normalized intracellular sorbitol, restored brain ATP, reduced ROS across CNS/VNC/muscle, and dramatically improved motor performance (climbing speed increased from 3.0 mm/s to 11.7 mm/s) and eye-phenotype degeneration (PMID 37014713, JCI Insight 2023). In patient fibroblasts, govorestat reduced sorbitol from 3.95 ng/µg protein to 0.21 ng/µg protein. - Clinical trial: The INSPIRE trial (Phase 2/3, NCT05397665) is evaluating govorestat in CMT-SORD. - 12-month interim analysis (2024): Statistically significant reduction in blood sorbitol; a significant correlation between sorbitol reduction and the composite CMT-FOM clinical endpoint (10-meter walk-run, 4-stair climb, sit-to-stand, 6-minute walk, dorsiflexion strength; p=0.05). Govorestat was safe and well tolerated with adverse-event rates similar to placebo. - 18–24 month follow-up (2025): Sustained reduction in blood sorbitol; sustained improvement in the CMT-Health Index; MRI-based lower-limb muscle-fat fraction showed a significant difference at 24 months, suggesting a slowing of disease progression, though the pre-specified primary clinical endpoint did not reach statistical significance at final analysis despite favorable trends. - Regulatory status (as of late 2025): Not yet FDA-approved for CMT-SORD; Applied Therapeutics met with the FDA (Type C meeting, Q3 2025) to discuss a potential regulatory pathway (including possible accelerated approval), with a submission strategy still under determination as of the most recent public updates.

Supportive/symptomatic care (standard of care today, in the absence of an approved disease-modifying therapy): - Physical therapy and rehabilitation for gait training and strength maintenance (NCIT:C15302 Physical Therapy) - Ankle-foot orthoses (AFOs) for foot drop (NCIT:C49236 Therapeutic Procedure / orthotic management) - Orthopedic management of secondary foot deformity (pes cavus) when indicated (NCIT:C16186 Orthopedic Surgical Procedure) - Genetic counseling for affected families given autosomal recessive inheritance (NCIT:C15240 Genetic Counseling) - General symptomatic CMT management (pain control, occupational therapy for hand involvement) as per general hereditary neuropathy guidelines

No approved gene therapy, enzyme replacement, or targeted molecular therapy currently exists for SORD deficiency; govorestat (aldose reductase inhibition) represents the leading investigational approach and is the only disease-specific pharmacotherapy in late-stage clinical development.

Suggested NCIT term for govorestat mechanism class: NCIT:C15986 (Pharmacotherapy) as treatment_term, with therapeutic_agent bound to govorestat/AT-007 (CHEBI/NCIT term to be confirmed at curation time) and therapeutic_modality: SMALL_MOLECULE.

13. Prevention

Primary prevention: Not applicable in the traditional sense (no modifiable environmental cause); the only "primary prevention" avenue is reproductive genetic counseling and carrier screening for couples with a family history or known carrier status, given the relatively high population carrier frequency (~0.5–1%) — prenatal or preimplantation genetic diagnosis is theoretically available once a family's causative variants are known, though not specifically reported as routine practice for this recently characterized disease.

Secondary prevention / early detection: Because SORD deficiency was only characterized in 2020, there is no established population screening program. However, biochemical screening (serum or urine sorbitol/xylitol) in patients with an unsolved axonal CMT2/dHMN phenotype functions as an effective secondary/case-finding strategy, given the biomarker's high sensitivity and specificity and ease of measurement compared to resolving the SORD2P pseudogene by genetic testing alone.

Tertiary prevention: Early diagnosis enables anticipatory orthopedic/rehabilitative management (AFOs, physical therapy) to minimize gait-related morbidity and secondary complications (falls, joint deformity), and positions patients for potential future disease-modifying therapy (govorestat) once approved.

Genetic counseling: Recommended for families of affected individuals given autosomal recessive inheritance and the relatively high carrier frequency in the general population.

Prophylaxis: No specific prophylactic pharmacotherapy exists; if govorestat is eventually approved, early (pre-severe) treatment initiation would represent a form of tertiary/disease-course-modifying prevention.

14. Other Species / Natural Disease

No naturally occurring SORD deficiency has been reported in companion animals or wildlife in the literature reviewed. All non-human data derive from engineered/induced models (see Section 15) rather than spontaneous veterinary disease. The polyol pathway itself (AKR1B1/SORD) is broadly conserved across mammals and is best known outside SORD deficiency in the context of diabetic complications (retinopathy, neuropathy, nephropathy) in both human diabetic patients and diabetic animal models — a related but mechanistically distinct (acquired hyperglycemia-driven vs. genetic enzyme-deficiency-driven) disease context.

15. Model Organisms

Model Type Key findings Fidelity / limitations
Drosophila Sord-ortholog loss-of-function Invertebrate genetic model Progressive synaptic degeneration, motor impairment (climbing assay), eye-neuron degeneration; ATP depletion; elevated ROS across CNS/VNC/muscle. Aldose reductase inhibition (govorestat/AT-007) normalized sorbitol and dramatically improved motor and eye phenotypes (PMID 37014713; Cortese et al. 2020, PMID 32367058) High utility for rapid mechanistic and drug-screening work; limited translational fidelity for mammalian peripheral nerve myelin biology
Patient-derived fibroblasts Human primary cell (in vitro) Complete loss of SORD protein; ~10-fold increase in intracellular sorbitol; used to validate govorestat's sorbitol-lowering effect (3.95 → 0.21 ng/µg protein) Directly human, but not neuronal/myelinating tissue
iPSC-derived motor neurons (patient-derived) Human cellular model Used alongside fibroblasts in mechanistic/drug studies of sorbitol accumulation and neurotoxicity (PMID 37014713) Captures motor-neuron-specific biology; 2D in vitro system, lacks myelinating Schwann cell/axon architecture
Naturally occurring Sord-deficient mouse (splice variant) Rodent (spontaneous hypomorphic allele) Sorbitol accumulation present, but no motor phenotype and no significant change in motor nerve conduction velocity Fails to recapitulate the human motor phenotype — an important negative/translational-mismatch result, indicating this particular mouse allele is an incomplete model
New CRISPR Sord knockout mouse (Sleigh lab, UCL; Muscular Dystrophy UK–funded, ongoing) Rodent (engineered null) Reported to show sorbitol accumulation in motor neurons with resulting muscle weakness, more faithfully recapitulating the human phenotype than the earlier splice-variant mouse Ongoing/actively developed model; full published phenotypic characterization not yet available in the literature reviewed
Sord⁻/⁻ rat Rodent (engineered null) Best-characterized rodent model to date. Motor-predominant neuropathy emerging ~7 months of age; serum sorbitol ~7-fold elevated vs. WT; CSF sorbitol ~30-fold higher than serum (suggesting independent CNS/PNS sorbitol handling); elevated serum neurofilament light chain (axonal injury biomarker); decreased motor nerve conduction velocity (more pronounced in males); abnormal hindlimb gait; nerve pathology showing degenerating/demyelinated axons, thinly myelinated fibers with increased g-ratio, regenerating axon clusters, and pathognomonic ballooned ("bubbly") myelin sheaths (also seen in galactosemic neuropathy); motor axons predominantly affected with relative sparing of sensory nerves and normal pain sensation (Brain 2024, DOI 10.1093/brain/awae170-region, full text at academic.oup.com/brain/article/147/9/3131/7636456) High fidelity for the motor-predominant axonal phenotype and the osmotic-myelin-injury mechanism; study limitation: electrophysiology not performed longitudinally across multiple ages, and histology was assessed only at advanced ages (70–85 weeks)

Applications: These models collectively support (1) mechanistic dissection of the osmotic-stress/myelin-ballooning hypothesis, (2) biomarker development (serum/CSF sorbitol, serum NfL), and (3) preclinical efficacy testing of aldose reductase inhibitors (govorestat), directly informing the ongoing human INSPIRE trial.

Resources: Alliance of Genome Resources, MGI (mouse), RGD (rat) for strain/allele tracking; no SORD-specific zebrafish, C. elegans, or yeast disease models were identified in this search.

Summary Table of Key Ontology Term Suggestions

Domain Suggested term
Disease MONDO:0030055; OMIM:618912
Gene HGNC SORD (chr15q26.1); OMIM *182500
Phenotype (HPO) HP:0009053 Distal lower limb muscle weakness; HP:0001772 Foot drop; HP:0001761 Pes cavus; HP:0003724 Distal amyotrophy; HP:0003676 Progressive sensory neuropathy; HP:0025278 Distal tremor
Biological process (GO) GO:0006062 Sorbitol catabolic process; GO:0006970 Response to osmotic stress
Cell type (CL) CL:0000100 Motor neuron; CL:0000011 Schwann cell; CL:0000098 Sensory neuron
Anatomy (UBERON) UBERON:0001021 Nerve; peripheral nerve subtypes (peroneal/tibial/ulnar/median)
Chemical (CHEBI) Sorbitol; fructose; xylitol; govorestat (AT-007)
Treatment (NCIT) NCIT:C15986 Pharmacotherapy (govorestat); NCIT:C15302 Physical Therapy; NCIT:C16186 Orthopedic Surgical Procedure; NCIT:C15240 Genetic Counseling

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  • DOI:10.1093/brain/awaf021](https://academic.oup.com/brain/article/148/10/3737/8010720 (1 mention) - Identifier did not resolve to a record
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