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Classifications

ICIMD (Inherited Metabolic Disorders)

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Mappings

MONDO

MONDO:0007777 hypotaurinemic retinal degeneration and cardiomyopathy

MONDO:0007777 carries RO:0004003 (has material basis in germline mutation in) HGNC:11052 SLC6A6 and xrefs OMIM:145350, matching this entry's causal gene and disease concept exactly. Note that the IEMbase seed row for this disorder cites OMIM 186854, which is the SLC6A6 gene entry rather than the disease entry.

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Inheritance

1

Autosomal recessive HP:0000007

All reported patients are homozygous for SLC6A6 variants, with heterozygous parents and relatives unaffected.

Autosomal recessive inheritance

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Genetic analysis identified homozygous pathogenic SLC6A6 variants in all affected individuals, while unaffected relatives were heterozygous carriers."

Homozygosity in all affected individuals with unaffected heterozygous relatives establishes recessive inheritance.

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Mechanistic Hypotheses

2

Osmolyte and Cytoprotection Model

osmotic_cytoprotection_model CANONICAL

Evidence balance 2 support

Taurine acts as an organic osmolyte and cytoprotectant supporting cell volume homeostasis, protein stabilization, antioxidation, and calcium handling. Under this model the disease is the sum of what happens to taurine-dependent tissues when that support is withdrawn: outer-retinal oxidative and metabolic stress, cardiomyocyte volume loss and atrophy, and reduced skeletal-muscle cell volume. It is the canonical framing because it accounts for the tissue distribution of disease and for the reversal of the cardiac phenotype on substrate replacement.

Retained as CANONICAL but not sufficient on its own: it does not explain why the retina fails first and most severely, nor why cardiac involvement is present in some pedigrees and absent in others despite comparable loss of transport.

Show evidence (2 references)

PMID:11772953 SUPPORT Model Organism

"Taurine is involved in cell volume homeostasis, antioxidant defense, protein stabilization, and stress responses."

States the cytoprotective functions on which the model rests.

PMID:18407290 SUPPORT Model Organism

"Our data suggest that multiple actions of taurine, including osmoregulation, regulation of mitochondrial protein expression and inhibition of apoptosis, collectively ensure proper maintenance of cardiac and skeletal muscular structure and function."

Attributes the cardiac and muscular phenotypes to taurine's osmoregulatory and cytoprotective actions.

Mitochondrial Taurine Import and Translation Model

mitochondrial_translation_model EMERGING

Evidence balance 2 support

A mitochondrial pool of SLC6A6 supplies taurine for mitochondrial tRNA modification, and its loss abrogates mitochondrial translation. Under this model taurine transporter deficiency is partly a disorder of mitochondrial protein synthesis, which would predict a bioenergetic phenotype in high-demand post-mitotic tissue — photoreceptors and cardiomyocytes are the two most oxidative-dependent tissues affected. The supporting work was done in cancer cell lines with SLC6A6 loss, not in patient material, so this is an emerging rather than established arm of the disease model.

Deliberately not asserted as an explanation of the human disease. If it is confirmed in patient tissue it has a direct therapeutic implication, because the same study reports that exogenous taurine did not substitute for the transporter in the systems tested, whereas oral taurine supplementation does benefit patients — a tension that is itself worth resolving.

Pathograph links

SLC6A6 Loss of Function -> Impaired Mitochondrial Taurine Import and mt-tRNA Modification DIRECT Beyond the plasma membrane, SLC6A6 has been shown to localize to mitochondria and to supply the taurine used for mitochondrial tRNA modification, so loss of the transporter would also deplete the mitochondrial taurine pool. This arm is demonstrated in cancer cell lines, not in patient tissue.

Impaired Mitochondrial Taurine Import and mt-tRNA Modification -> Myocardial Taurine Depletion and Energy Starvation INDIRECT UNKNOWN INTERMEDIATES Failure of mitochondrial translation would compromise respiratory-chain subunit synthesis, converging on the impaired respiratory-chain function and reduced ATP output already documented in the taurine-deficient heart. Hypothesized rather than established in this disease.

Show evidence (2 references)

PMID:41652173 SUPPORT In Vitro

"Taurine plays a crucial role in mitochondrial translation."

States the mitochondrial-translation dependence on taurine underlying this model.

PMID:41652173 SUPPORT In Vitro

"Together, these findings suggest that SLC6A6 is a mitochondrial taurine transporter and an exploitable metabolic dependency in cancer."

Confirms the authors' own framing of the mitochondrial transport function and its experimental context.

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Discussions and Knowledge Gaps

3

Why is cardiomyopathy present in some SLC6A6-deficient pedigrees and absent in others despite comparable or greater loss of taurine transport?

KNOWLEDGE GAP OPEN slc6a6_cardiac_penetrance_gap

Attached to

pathophysiology#Cardiomyocyte Atrophy and Ventricular Remodeling

The index consanguineous family carried a hypomorphic allele retaining roughly 15% of normal transport and had childhood cardiomyopathy that reversed on taurine supplementation. The later multicenter series included variants causing complete loss of transport, yet cardiac structure was normal in all seven affected individuals, with only short PR intervals. The cardiac arm therefore does not track with residual transport capacity, so something else — age at assessment, dietary taurine intake, genetic background, or a modifier of cardiac taurine handling — determines whether it manifests. This matters clinically because it determines whether cardiac surveillance and pre-emptive supplementation are warranted in every patient or only in some.

Proposed experiments

Longitudinal cardiac phenotyping of SLC6A6-deficient patients

exp_slc6a6_longitudinal_cardiac_cohort

Serial echocardiography, ECG and cardiac MRI in all known SLC6A6-deficient patients, stratified by residual transport capacity and age, to test whether cardiomyopathy is age-dependent rather than genotype-dependent.

Decision criterion

Emergence of ventricular remodeling with age in patients whose hearts were initially structurally normal would support an age-dependent arm; its absence in adults with complete loss of transport would argue for a genuine modifier.

Dietary taurine intake versus cardiac phenotype

exp_slc6a6_dietary_taurine_confounder

Quantify dietary taurine intake alongside plasma taurine in SLC6A6-deficient patients with and without cardiomyopathy, to test whether nutritional taurine masks the cardiac phenotype.

Decision criterion

Higher taurine intake in the cardiac-unaffected pedigrees would support dietary rescue as the explanation for variable penetrance.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"

Documents the absence of structural cardiomyopathy in a cohort with complete loss of transport.

PMID:31903486 SUPPORT Human Clinical

"The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."

Documents the contrasting pedigree in which cardiomyopathy was present in childhood.

Does the multisystem phenotype of the Slc6a6-null mouse predict human disease, or does it represent an allelic and physiological state no patient occupies?

HUMAN MODEL MISMATCH OPEN slc6a6_mouse_multisystem_mismatch

Attached to

pathophysiology#Skeletal Muscle Taurine Depletion

The mouse null develops hearing loss, liver fibrosis, and behavioural, heart and skeletal-muscle abnormalities in addition to retinal degeneration. In the two human brothers with 95% loss of taurine uptake, skeletal-muscle and brain taurine were severely reduced yet no extraocular dysfunction was detectable — only a subclinical oxidative-stress marker. Two explanations have different consequences for surveillance: either the human extraocular phenotypes are late and will appear with age (in which case the mouse is a valid predictor and lifelong multisystem monitoring is indicated), or humans are protected by dietary taurine and residual biosynthesis in a way mice on standard chow are not (in which case the mouse overstates human risk). The original report chose the cautious reading and recommended continuous broad surveillance.

Proposed experiments

Multisystem assessment of adult SLC6A6-deficient patients

exp_slc6a6_adult_multisystem_survey

Systematic audiological, hepatic and neuromuscular assessment of adult SLC6A6-deficient patients, to test whether the murine extraocular phenotypes emerge with age in humans.

Decision criterion

Detection of hearing loss, hepatic fibrosis or myopathy in adults would validate the mouse as predictive; their absence in adulthood would establish a species-restricted phenotype.

Cross-species comparison of taurine supply

exp_slc6a6_species_taurine_supply

Compare dietary taurine intake and endogenous taurine biosynthetic flux between mouse and human, to test the dietary and biosynthetic protection hypothesis for the species difference.

Decision criterion

Substantially greater human dietary or biosynthetic taurine supply would explain the milder human extraocular phenotype without invoking a different mechanism.

Show evidence (2 references)

PMID:31345061 SUPPORT Human Clinical

"Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"

States the human-mouse discrepancy and the surveillance recommendation that follows from it.

PMID:31345061 SUPPORT Model Organism

"mice develop multisystemic dysfunctions (hearing loss; liver fibrosis; and behavioral, heart, and skeletal muscle abnormalities) later on"

Enumerates the murine multisystem phenotypes whose human counterparts are unconfirmed.

Does SLC6A6-dependent mitochondrial taurine import contribute to the pathophysiology of inherited taurine transporter deficiency, and if so why does oral taurine help patients when exogenous taurine did not rescue SLC6A6-deficient cells?

KNOWLEDGE GAP OPEN slc6a6_mitochondrial_arm_unvalidated

Attached to

pathophysiology#Impaired Mitochondrial Taurine Import and mt-tRNA Modification

The mitochondrial-import function of SLC6A6 was established in cancer cell lines, where the transporter — and not extracellular taurine — was the requirement for mitochondrial translation. If that holds in patient tissue, then raising extracellular taurine should not correct the mitochondrial arm, and the clinical benefit of supplementation would be confined to the plasma-membrane-dependent, osmotic and antioxidant functions. Yet oral taurine reversed cardiomyopathy in the index family, where cardiac muscle is among the most mitochondria-dependent tissues affected. Either the mitochondrial arm is not rate-limiting in the inherited disease, or the residual transport of a hypomorphic allele is sufficient to serve the mitochondrial pool once extracellular taurine is high. Distinguishing these determines whether a subset of patients — particularly those with truncating alleles — would be predicted not to respond to supplementation.

Proposed experiments

Mitochondrial taurine and mt-tRNA modification in patient fibroblasts

exp_slc6a6_mito_taurine_patient_fibroblasts

Assay mitochondrial taurine content, mitochondrial tRNA taurine modification, and mitochondrial translation in patient-derived fibroblasts carrying truncating versus hypomorphic SLC6A6 alleles, with and without taurine loading.

Decision criterion

Reduced mitochondrial taurine and mt-tRNA modification in patient cells would establish the mitochondrial arm in the inherited disease; normal values would confine it to the cancer context.

Substrate-correctability of the mitochondrial arm

exp_slc6a6_mito_rescue_by_taurine_loading

Measure respiratory-chain function and mitochondrial translation products in patient fibroblasts before and after taurine supplementation, to test whether the mitochondrial arm is substrate-correctable in the inherited disease.

Decision criterion

Restoration of mitochondrial translation by taurine loading would reconcile the clinical response with the cell-line result; failure to restore would predict non-responders among truncating-allele patients.

Show evidence (2 references)

PMID:41652173 SUPPORT In Vitro

"Here we show that SLC6A6, but not exogenous taurine, is essential for mitochondrial metabolism and cancer cell growth."

The finding that extracellular taurine cannot substitute for the transporter is what creates the tension with clinical supplementation response.

PMID:31903486 SUPPORT Human Clinical

"after 24-months, the cardiomyopathy was corrected in both affected siblings"

The clinical response to supplementation that the in vitro result does not predict.

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Pathophysiology

10

SLC6A6 Loss of Function

Biallelic SLC6A6 variants abolish or severely reduce the activity of TauT, the sodium- and chloride-dependent plasma-membrane taurine transporter. The functional consequence has been measured directly in patient material: 3H-taurine uptake was reduced by 95% in peripheral blood mononuclear cells carrying p.Ala78Glu, the p.Gly399Val allele retains roughly 15% of normal capacity, and p.Thr249Ile and p.Ala294Thr abolish transport in both HEK-293 cells and patient fibroblasts. Loss of transport is not necessarily loss of the protein from the membrane — p.Ala78Glu still localizes to the plasma membrane, so the lesion is transport-functional rather than purely trafficking.

Mitochondrial Taurine Import and Translation Model

SLC6A6 hgnc:11052

taurine transmembrane transporter activity GO:0005368 ⇓ LOSS OF FUNCTION

plasma membrane GO:0005886

Downstream

Systemic Taurine Depletion Loss of TauT-mediated uptake removes the only route by which most tissues can accumulate taurine against its concentration gradient, so circulating and tissue taurine fall.

Impaired Mitochondrial Taurine Import and mt-tRNA Modification Beyond the plasma membrane, SLC6A6 has been shown to localize to mitochondria and to supply the taurine used for mitochondrial tRNA modification, so loss of the transporter would also deplete the mitochondrial taurine pool. This arm is demonstrated in cancer cell lines, not in patient tissue.

Show evidence (3 references)

PMID:31345061 SUPPORT Human Clinical

"3H-taurine uptake by peripheral blood mononuclear cells was reduced by 95%, and taurine levels were severely reduced in plasma, skeletal muscle, and brain."

Quantifies loss of taurine transport in patient cells as the proximal molecular defect.

PMID:31345061 SUPPORT Human Clinical

"TAUTp.A78E still localized in the plasma membrane but is predicted to impact structural stabilization."

Shows the defect is in transport function rather than membrane delivery for this allele.

PMID:41343195 SUPPORT In Vitro

"Functional studies demonstrated that both missense variants are associated with complete loss of taurine transport in HEK-293 cells and patient-derived fibroblasts."

Independent functional confirmation that disease missense alleles abolish taurine transport.

Systemic Taurine Depletion

Failure of TauT-mediated uptake produces profound hypotaurinemia together with depletion of the tissue taurine pool. Patient plasma taurine is reduced relative both to heterozygous carriers and to healthy controls, and taurine is severely reduced in skeletal muscle and brain as well as plasma. This is the systemic state from which every downstream tissue phenotype follows, and it is the node that oral taurine supplementation acts on.

taurine transmembrane transport GO:0015734 ↓ DECREASED

Downstream

Retinal Taurine Depletion and Photoreceptor Stress The retina is the tissue in which taurine depletion becomes clinically manifest first; taurine supports photoreceptor viability and outer-retinal homeostasis.

Myocardial Taurine Depletion and Energy Starvation Cardiac and skeletal muscle hold the largest free taurine pools of any tissue but have limited biosynthetic capacity, so they are among the first to be depleted when uptake fails.

Cellular Oxidative Stress and RNA Oxidation Taurine is an intracellular antioxidant and cytoprotectant; its loss raises oxidative burden, measurable systemically before any organ dysfunction is clinically apparent.

Skeletal Muscle Taurine Depletion Skeletal muscle taurine is severely reduced in patients, and in the mouse null this translates into decreased cell volume, structural defects, and reduced exercise capacity.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"Additionally, irrespective of the variants considered, plasma taurine levels in affected individuals were reduced compared with heterozygous carriers"

Quantitative confirmation of hypotaurinemia across all reported genotypes.

PMID:31345061 SUPPORT Human Clinical

"taurine levels were severely reduced in plasma, skeletal muscle, and brain"

Shows the depletion is systemic and extends into tissue compartments, not just plasma.

Cellular Oxidative Stress and RNA Oxidation

Taurine contributes to cell volume homeostasis, protein stabilization, cytoprotection and antioxidation, so depletion leaves cells with reduced antioxidant buffering. In the two reported brothers this was detectable as significantly increased urinary 8-oxo-7,8-dihydroguanosine — an RNA-oxidation marker — while extraocular organ function was still clinically normal, making it the earliest measurable systemic consequence of the transport defect.

cellular response to oxidative stress GO:0034599 ↑ INCREASED

Downstream

Retinal Taurine Depletion and Photoreceptor Stress Oxidative injury is the shared final stress on photoreceptors in inherited retinal degeneration and is the route by which loss of taurine's antioxidant function reaches the outer retina.

Show evidence (2 references)

PMID:31345061 SUPPORT Human Clinical

"Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"

Reports the measured RNA-oxidation marker itself — increased urinary 8-oxo-7,8-dihydroguanosine in the affected brothers — and places it upstream of any clinically apparent extraocular disease.

PMID:31345061 SUPPORT Model Organism

"Compatible with taurine's indispensability for cell volume homeostasis, protein stabilization, cytoprotection, antioxidation, and immuno- and neuromodulation, mice develop multisystemic dysfunctions (hearing loss; liver fibrosis; and behavioral, heart, and skeletal muscle abnormalities) later on."

States the cytoprotective and antioxidant roles of taurine whose loss produces the oxidative phenotype. Tagged MODEL_ORGANISM because the main clause reports the multisystem consequences in mice, not in the patients — the human counterparts of those findings are deliberately not curated here (see notes).

Impaired Mitochondrial Taurine Import and mt-tRNA Modification

A second, mitochondrial pool of SLC6A6 imports taurine into mitochondria, where it is used for taurine-dependent modification of mitochondrial tRNAs. Loss of the transporter reduces mitochondrial taurine abundance specifically and abrogates mitochondrial translation. This is an emerging arm: it was established in cancer cell lines as a metabolic dependency, and it has not been demonstrated in tissue from patients with SLC6A6 deficiency. It is curated because, if it holds in patient tissue, it would place taurine transporter deficiency partly within mitochondrial-translation disease and would complicate the therapeutic logic — the same paper reports that exogenous taurine does not substitute for the transporter in the cell systems tested.

Mitochondrial Taurine Import and Translation Model

tRNA wobble uridine modification GO:0002098 ↓ DECREASED

mitochondrion GO:0005739

Downstream

Myocardial Taurine Depletion and Energy Starvation Failure of mitochondrial translation would compromise respiratory-chain subunit synthesis, converging on the impaired respiratory-chain function and reduced ATP output already documented in the taurine-deficient heart. Hypothesized rather than established in this disease.

Show evidence (2 references)

PMID:41652173 SUPPORT In Vitro

"SLC6A6 deficiency specifically reduces mitochondrial taurine abundance and abrogates mitochondrial translation and cell proliferation."

Directly links loss of the transporter to mitochondrial taurine depletion and translation failure.

PMID:41652173 SUPPORT In Vitro

"Here we show that SLC6A6, but not exogenous taurine, is essential for mitochondrial metabolism and cancer cell growth."

Supports the transporter-specific requirement, but only in cancer cell lines — hence PARTIAL rather than SUPPORT for the inherited disease.

Retinal Taurine Depletion and Photoreceptor Stress

Photoreceptors and retinal pigment epithelium depend on imported taurine for viability, calcium signaling, and antioxidant defense; the requirement is old knowledge from taurine-deficient cats, which develop progressive retinal degeneration. In taurine transporter deficiency this dependency is unmet from birth, leaving the outer retina under chronic metabolic and oxidative stress.

photoreceptor cell CL:0000210 retinal pigment epithelial cell CL:0002586

retina UBERON:0000966

Downstream

Photoreceptor Degeneration and Outer Retinal Thinning Sustained loss of taurine-dependent support leads to photoreceptor loss and thinning of the outer nuclear layer.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"The importance of taurine in retinal development, photoreceptors maintenance, and cellular homeostasis was recognized as early as the 1970s when studies involving taurine-deficient cats demonstrated progressive retinal degeneration."

Establishes the retinal taurine requirement and that its absence alone causes progressive degeneration.

PMID:11772953 SUPPORT Model Organism

"In particular, the retinal involvement identifies the taurine transporter as an important factor for the development and maintenance of normal retinal functions and morphology."

The mouse null shows the transporter itself is required for retinal development and maintenance.

Photoreceptor Degeneration and Outer Retinal Thinning

Panretinal photoreceptor degeneration with structural loss of the outer retina. Optical coherence tomography in an affected 14-year-old showed a central island of outer nuclear layer thinning abnormally with eccentricity, with poorly delineated external limiting membrane and ellipsoid zone, and fundus examination showed attenuated retinal vasculature. Rod and cone loss are concurrent here rather than sequential — scotopic and photopic electroretinograms are both severely depressed at presentation — so this node deliberately carries no conforms_to anchor; see notes.

photoreceptor cell CL:0000210

retina UBERON:0000966

Animal models

taut-/- taurine transporter knockout mouse (retinal arm) Mouse recapitulates The null mouse loses vision from severe retinal degeneration, matching the panretinal degeneration of human TauT deficiency, and was the basis for searching for the human disease.

Downstream

Early-Onset Panretinal Dystrophy and Visual Loss Loss of photoreceptors produces the clinical LCA/EORD phenotype with severely depressed electroretinography and progressive visual failure.

Show evidence (2 references)

PMID:31345061 SUPPORT Human Clinical

"Loss of TAUT function due to a homozygous missense mutation caused panretinal degeneration in 2 brothers."

Establishes panretinal degeneration as the human tissue-level consequence.

PMID:41343195 SUPPORT Human Clinical

"Macular OCT of the right (iii) and left (iv) eyes of the same individual showing a central island of the outer nuclear layer that abnormally decreases in thickness with eccentricity."

Imaging evidence of outer nuclear layer thinning in an affected individual.

Early-Onset Panretinal Dystrophy and Visual Loss

The clinical retinal endpoint: Leber congenital amaurosis or early-onset retinal dystrophy with nystagmus, severely depressed scotopic and photopic electroretinograms, and progressive loss of visual function. Present in all reported affected individuals, and the presenting feature in every pedigree described to date.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"All 7 affected individuals exhibited LCA/EORD, with extraocular findings in some."

Establishes the retinal phenotype as the consistent clinical endpoint across the cohort.

PMID:41343195 SUPPORT Human Clinical

"These findings confirm and expand the role of biallelic variants in SLC6A6 in association with LCA/EORD due to impaired taurine transport."

States the causal association between impaired taurine transport and the LCA/EORD phenotype.

Myocardial Taurine Depletion and Energy Starvation

Taurine is the most abundant free amino acid in cardiac muscle and one of its major functions there is regulation of the respiratory chain. In the taurine-deficient heart glycolysis rises while glucose oxidation falls, pyruvate dehydrogenase flux is reduced by a raised NADH/NAD+ ratio, and long-chain fatty acid uptake into mitochondria is diminished; ATP production falls and the phosphocreatine/ATP ratio declines. The cardiomyocyte is therefore energy-starved before it is structurally abnormal. This node's evidence is rodent; the human counterpart is the taurine-responsive cardiomyopathy of the index family.

cardiac muscle cell CL:0000746

ATP biosynthetic process GO:0006754 ↓ DECREASED

heart UBERON:0000948

Downstream

Cardiomyocyte Atrophy and Ventricular Remodeling Chronic energy starvation together with loss of taurine's osmoregulatory and cytoprotective functions produces cardiomyocyte atrophy and ultrastructural damage to myofilaments and mitochondria.

Show evidence (2 references)

PMID:26475290 SUPPORT Model Organism

"These changes diminished the rate of ATP production, causing a decline in the phosphocreatine/ATP ratio, a sign of reduced energy status."

Quantifies the bioenergetic deficit produced by myocardial taurine depletion.

PMID:26475290 SUPPORT Model Organism

"The findings support the hypothesis that the taurine-deficient heart is energy starved primarily because of impaired respiratory chain function, an increase in the NADH/NAD+ ratio and diminished long chain fatty acid uptake by the mitochondria."

Identifies impaired respiratory-chain function as the primary mechanism of the energy deficit.

Cardiomyocyte Atrophy and Ventricular Remodeling

In the taurine transporter knockout mouse the heart remodels with reduced ventricular wall thickness and cardiac atrophy from smaller cardiomyocytes, reduced cardiac output, and induction of the fetal heart-failure gene programme (ANP, BNP, beta-MHC) — a dilated, atrophic cardiomyopathy rather than a hypertrophic one. The human phenotype includes cardiomyopathy in the index consanguineous family but structurally normal hearts in the later multicenter series, so penetrance of this arm is variable and unexplained.

cardiac muscle cell CL:0000746

heart UBERON:0000948

Animal models

TauTKO taurine transporter knockout mouse (cardiac and muscle arm) Mouse recapitulates The knockout develops a dilated, atrophic cardiomyopathy with reduced cardiac output and induction of fetal heart-failure genes, providing the mechanistic account of the cardiomyopathy seen in the index human family.

Show evidence (4 references)

PMID:18407290 SUPPORT Model Organism

"The TauTKO heart underwent ventricular remodeling, characterized by reductions in ventricular wall thickness and cardiac atrophy accompanied with the smaller cardiomyocytes."

Defines the remodeling phenotype produced by transporter loss.

PMID:18407290 SUPPORT Model Organism

"Associated with the structural changes in the heart was a reduction in cardiac output and increased expression of heart cardiac failure (fetal) marker genes, such as ANP, BNP and beta-MHC."

Shows the remodeling is accompanied by functional decline and the heart-failure transcriptional programme.

PMID:26475290 SUPPORT Model Organism

"A significant reduction in myocardial taurine content leads to the development of a unique dilated, atrophic cardiomyopathy."

Characterizes the cardiomyopathy as dilated and atrophic rather than hypertrophic.

+ 1 more reference

Skeletal Muscle Taurine Depletion

Skeletal muscle carries a large taurine pool with limited local synthesis. Patient skeletal-muscle taurine is severely reduced, and in the mouse null depletion produces decreased cell volume, structural defects and reduced exercise endurance. No myopathy has yet been reported in patients, so this node is curated as an established biochemical deficit with a so-far subclinical human phenotype.

skeletal muscle tissue UBERON:0001134

Animal models

TauTKO taurine transporter knockout mouse (cardiac and muscle arm) Mouse recapitulates The knockout depletes skeletal muscle taurine and produces measurable structural and exercise-capacity deficits.

Show evidence (2 references)

PMID:18407290 SUPPORT Model Organism

"Further, the skeletal muscle of the TauTKO mice also exhibited decreased cell volume, structural defects and a reduction of exercise endurance capacity."

Establishes the skeletal-muscle consequence of transporter loss in the mouse.

PMID:31345061 SUPPORT Human Clinical

"Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"

Supports the biochemical deficit while explicitly recording that no extraocular (including muscular) dysfunction was clinically detectable.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

10

Cardiovascular 1

Cardiomyopathy HP:0001638

Show evidence (2 references)

PMID:31903486 SUPPORT Human Clinical

"The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."

Cardiomyopathy in both affected siblings of the index family.

PMID:41343195 SUPPORT Human Clinical

"Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"

Recorded as PARTIAL because this series found no structural cardiomyopathy despite complete loss of taurine transport, establishing that the cardiac arm is not obligate.

Eye 4

Early-onset retinal dystrophy OBLIGATE Rod-cone dystrophy HP:0000510

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"All 7 affected individuals exhibited LCA/EORD, with extraocular findings in some."

All seven affected individuals in the largest reported series had the retinal phenotype, and it was also present in both previously reported pedigrees, supporting an obligate frequency band.

Nystagmus HP:0000639

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Four of the children had visual impairment and nystagmus since birth, with gradually deteriorating visual function over the years."

Nystagmus from birth in four affected siblings.

Visual impairment HP:0000505

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Four of the children had visual impairment and nystagmus since birth, with gradually deteriorating visual function over the years."

Congenital, progressive visual impairment in affected individuals.

Abnormal electroretinogram HP:0000512

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"All 4 patients presented with severely depressed scotopic and photopic ERG recordings in both eyes"

Documents the electrophysiological abnormality in all tested affected individuals of family 1.

Nervous System 1

Intellectual disability HP:0001249

Severity: MILD

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"The patient was examined when she was 5 years old because of mild to moderate intellectual disability (IQ, 62)"

Documented intellectual disability with a measured IQ in the Italian family.

Other 4

Retinal degeneration HP:0000546

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:31345061 SUPPORT Human Clinical

"Loss of TAUT function due to a homozygous missense mutation caused panretinal degeneration in 2 brothers."

Panretinal degeneration documented in the first reported human pedigree.

Attenuation of retinal blood vessels HP:0007843

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"showing attenuated retinal vasculature and slightly blurred optic disc margins"

Fundus photography finding in an affected 14-year-old.

Hypotaurinemia OBLIGATE HP:0500182

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Additionally, irrespective of the variants considered, plasma taurine levels in affected individuals were reduced compared with heterozygous carriers"

The "irrespective of the variants considered" phrasing establishes that hypotaurinemia was present in every affected individual, supporting an obligate band.

Shortened PR interval VERY_FREQUENT HP:0005165

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"

Reports the finding in all patients of the series. The VERY_FREQUENT band reflects "all patients" of this one cohort; the earlier pedigrees did not report PR interval, so an OBLIGATE band across the whole disorder is not supported.

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Genetic Associations

1

SLC6A6

Gene: SLC6A6 hgnc:11052 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:41343195 SUPPORT Human Clinical

"The human solute carrier family 6 member 6 gene (SLC6A6) encodes a ubiquitously expressed taurine transporter (TauT) that regulates the intracellular taurine content in many tissues, including brain, retina, heart, kidney, liver, and skeletal muscles."

Identifies SLC6A6 as the gene encoding the taurine transporter and names the tissues that depend on it.

PMID:41343195 SUPPORT Human Clinical

"Families 1 and 2 carried missense variants p.(Thr249Ile) and p.(Ala294Thr), while families 3 and 4 carried truncating variants-a deletion of exon 11 and p.(Thr113Ter), respectively."

Documents the allelic spectrum, including both missense and truncating disease alleles.

PMID:31903486 SUPPORT Human Clinical

"In a consanguineous Pakistani family with two affected individuals, a homozygous variant Gly399Val in the eighth transmembrane domain of the taurine transporter SLC6A6 was identified resulting in a hypomorph transporting capacity of ~15% compared with normal."

Establishes a hypomorphic allele with quantified residual transport capacity.

Variants (2)

SLC6A6 p.Gly399Val

Homozygous missense variant in the eighth transmembrane domain, retaining approximately 15% of normal taurine transport. Carried by the index consanguineous Pakistani family with retinal degeneration and taurine-responsive cardiomyopathy.

Show evidence (1 reference)

PMID:31903486 SUPPORT Human Clinical

"Three-dimensional modeling of this variant has indicated that it likely causes displacement of the Tyr138 (TM3) side chain, important for transport of taurine."

Gives the structural basis for the partial loss of transport by this allele.

SLC6A6 p.Ala78Glu

Homozygous missense variant in the first reported human pedigree, reducing 3H-taurine uptake in patient peripheral blood mononuclear cells by 95% while the protein still reaches the plasma membrane.

Show evidence (1 reference)

PMID:31345061 SUPPORT Human Clinical

"TAUTp.A78E still localized in the plasma membrane but is predicted to impact structural stabilization."

Distinguishes a transport-function defect from a trafficking defect for this allele.

💊

Medical Actions

1

Oral taurine supplementation

Action: oral taurine supplementation Ontology label: Nutritional Supplementation NCIT:C15425

Agent: taurine CHEBI:15891

High-dose oral taurine (100 mg/kg/day in the reported regimen) raises extracellular taurine sufficiently to restore normal blood taurine levels despite the transport defect. In the index consanguineous family, 24 months of supplementation corrected the cardiomyopathy in both affected siblings and, in the younger child, arrested the retinal degeneration with clinical improvement in vision. It is the only disease-modifying therapy reported and is explicitly proposed as a template for substrate supplementation in Mendelian transporter disease more broadly. Outside the index family it remains investigational.

Mechanism Target:

RESTORES Systemic Taurine Depletion — Oral supplementation replenishes the depleted taurine pool, restoring normal blood taurine without correcting the transporter itself.

Show evidence (1 reference)

PMID:31903486 SUPPORT Human Clinical

"Oral taurine supplementation of 100 mg/kg/day resulted in maintenance of normal blood taurine levels."

Demonstrates that supplementation restores the depleted systemic taurine pool.

Show evidence (3 references)

PMID:31903486 SUPPORT Human Clinical

"Remarkably, after 24-months, the cardiomyopathy was corrected in both affected siblings, and in the 6-years-old, the retinal degeneration was arrested, and the vision was clinically improved."

Reports the clinical outcome of long-term supplementation on both disease arms.

PMID:31903486 SUPPORT Human Clinical

"Similar therapeutic approaches could be employed in Mendelian phenotypes caused by the dysfunction of the hundreds of other molecular transporters."

The authors' generalization of the substrate-supplementation strategy to transporter disease at large.

PMID:41343195 SUPPORT Human Clinical

"These findings suggest that patients with a diagnosis of SLC6A6-related LCA/EORD may be candidates for investigational oral taurine supplementation."

Recorded as PARTIAL because the later series frames supplementation as investigational and candidate-eligible rather than established therapy.

🔬

Biochemical Markers

1

Plasma taurine (Reduced)

Context: The diagnostic biochemical marker. Plasma taurine is reduced relative both to heterozygous carriers and to healthy controls in every reported affected individual, irrespective of the underlying variant, and is almost undetectable in some. It is also the treatment-monitoring analyte: oral supplementation is titrated to maintain normal blood taurine.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"plasma taurine levels in affected individuals were reduced compared with heterozygous carriers"

Establishes the direction and comparison group for the plasma taurine abnormality.

PMID:31903486 SUPPORT Human Clinical

"Oral taurine supplementation of 100 mg/kg/day resulted in maintenance of normal blood taurine levels."

Establishes plasma taurine as the analyte used to monitor and titrate treatment.

🔬

Diagnosis

4

Fasting plasma taurine measurement

Measurement of fasting plasma taurine identifies the biochemical deficit and discriminates affected individuals from heterozygous carriers and controls.

Markers: plasma taurine

Results: Reduced or almost undetectable plasma taurine.

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"followed by measurement of fasting plasma taurine levels"

Fasting plasma taurine measurement is part of the reported diagnostic workflow.

Full-field electroretinography

ISCEV-standard full-field electroretinography characterizes the extent of rod and cone dysfunction and supports the LCA/EORD diagnosis.

Results: Severely depressed or undetectable scotopic and photopic responses.

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"All patients underwent standard clinical examinations, including visual acuity, full-field electroretinography, and multimodal retinal imaging"

Full-field electroretinography is part of the standard diagnostic assessment in this disorder.

Molecular genetic testing of SLC6A6

Whole-exome or whole-genome sequencing identifies the biallelic SLC6A6 variants and is the confirmatory test; functional taurine-uptake assays in patient fibroblasts can resolve variants of uncertain significance.

Results: Biallelic pathogenic SLC6A6 variants with segregation in heterozygous parents.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"Genetic analysis identified homozygous pathogenic SLC6A6 variants in all affected individuals, while unaffected relatives were heterozygous carriers."

Molecular testing with segregation analysis is the confirmatory diagnostic step.

PMID:41343195 SUPPORT In Vitro

"In vitro and ex vivo taurine transport and membrane trafficking assays in human embryonic kidney (HEK)-293 cells, as well as patient-derived fibroblasts, were also performed."

Functional transport assays in patient-derived fibroblasts are available to confirm variant effect.

Cardiac assessment with electrocardiography and echocardiography

Because cardiomyopathy is part of the disorder in some pedigrees, cardiac structure and conduction should be assessed at diagnosis and monitored. Conduction abnormalities may be present even when cardiac structure is normal.

Results: Cardiomyopathy in some pedigrees; short PR interval reported in all patients of one series with structurally normal hearts.

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"

Reports the ECG and echocardiographic findings that motivate cardiac assessment.

📈

Progression

2

Congenital to early-childhood retinal presentation

Age: Birth to 5 years

Visual impairment and nystagmus may be present from birth (Leber congenital amaurosis pattern) or be detected after early infancy but before age 5 (early-onset retinal dystrophy pattern), with gradual deterioration of visual function thereafter.

Show evidence (1 reference)

PMID:41343195 SUPPORT Human Clinical

"Four of the children had visual impairment and nystagmus since birth, with gradually deteriorating visual function over the years."

Documents congenital onset and progressive deterioration in the largest family reported.

Childhood progression with variable cardiac involvement

Age: Childhood

In the index consanguineous family the retinal degeneration was rapidly progressive during childhood and accompanied by cardiomyopathy. Cardiac involvement is not obligate: in the later multicenter series cardiac structure was normal in all patients, with only conduction findings.

Show evidence (1 reference)

PMID:31903486 SUPPORT Human Clinical

"The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."

Describes the rapidly progressive childhood course with cardiomyopathy in the index family.

📊

Prevalence

1

Worldwide

Cases In Literature Ultra Rare

Ultra-rare. As of the 2026 multicenter series, human SLC6A6 deficiency had been reported in a handful of pedigrees: the original two-brother family, one consanguineous Pakistani family, and seven affected individuals from four further unrelated families recruited in Pakistan, Italy, the US and France. No population frequency estimate exists.

Show evidence (2 references)

PMID:41343195 SUPPORT Human Clinical

"This was a retrospective, multicenter observational study conducted between June 2019 and March 2025, involving 7 affected and 10 unaffected individuals from 4 unrelated families recruited in Pakistan, Italy, the US, and France."

Gives the size of the largest reported cohort, from which the case-count basis for ultra-rarity follows.

PMID:41343195 SUPPORT Human Clinical

"However, a direct link between SLC6A6 and human diseases has been established only recently, following the identification of 2 unrelated pedigrees with LCA/EORD and biallelic recessive variants in this gene."

Confirms only two pedigrees were known before this series, supporting the case-in-literature framing.

🐁

Animal Models

2

taut-/- taurine transporter knockout mouse (retinal arm)

Germline disruption of the mouse taurine transporter gene, the model in which the retinal consequence of transporter loss was first established and which predated the recognition of the human disorder.

Species

Mouse

Genotype

Slc6a6 (taut) homozygous null

Publication

PMID:11772953

Pathograph links

Photoreceptor Degeneration and Outer Retinal Thinning recapitulates fidelity: high The null mouse loses vision from severe retinal degeneration, matching the panretinal degeneration of human TauT deficiency, and was the basis for searching for the human disease.

Limitations: The mouse is a complete null, whereas human disease alleles range from complete loss of transport to a hypomorph retaining roughly 15% of normal capacity; the mouse also develops later multisystem features (hearing loss, liver fibrosis, behavioural abnormalities) that have not been observed in patients.

Readouts

Retinal morphology and visual function

Direction: DECREASED

Interpretation: Structural and functional loss of the retina in the transporter-null mouse, the animal correlate of the human outer-retinal degeneration node.

Show evidence (1 reference)

PMID:11772953 SUPPORT Model Organism

"loss of vision due to severe retinal degeneration"

Reports the retinal measurement behind this readout.

Show evidence (1 reference)

PMID:11772953 SUPPORT Model Organism

"In particular, the retinal involvement identifies the taurine transporter as an important factor for the development and maintenance of normal retinal functions and morphology."

Supports treating this model as informative for the retinal degeneration node.

TauTKO taurine transporter knockout mouse (cardiac and muscle arm)

Taurine transporter knockout mouse characterized for cardiac and skeletal muscle phenotype, with myocardial and skeletal muscle taurine depletion, ventricular remodeling, cardiac atrophy and reduced exercise capacity.

Species

Mouse

Genotype

Slc6a6 (TauT) homozygous knockout

Publication

PMID:18407290

Pathograph links

Cardiomyocyte Atrophy and Ventricular Remodeling recapitulates fidelity: moderate The knockout develops a dilated, atrophic cardiomyopathy with reduced cardiac output and induction of fetal heart-failure genes, providing the mechanistic account of the cardiomyopathy seen in the index human family.

Limitations: Fidelity is only MODERATE because the cardiac arm is variably penetrant in humans: the later multicenter series found structurally normal hearts in all seven affected individuals despite complete loss of taurine transport, so the uniform murine cardiomyopathy overstates the human cardiac risk.

Readouts

Ventricular wall thickness and cardiomyocyte size

Direction: DECREASED

Interpretation: Structural correlate of the ventricular remodeling node — thinner walls and smaller cardiomyocytes rather than hypertrophy.

Show evidence (1 reference)

PMID:18407290 SUPPORT Model Organism

"reductions in ventricular wall thickness and cardiac atrophy accompanied with the smaller cardiomyocytes"

Reports the structural measurement behind this readout.

Cardiac output

Direction: DECREASED

Interpretation: Functional consequence of the remodeling in this model.

Show evidence (1 reference)

PMID:18407290 SUPPORT Model Organism

"a reduction in cardiac output and increased expression of heart cardiac failure (fetal) marker genes"

Reports the functional measurement behind this readout.

Show evidence (1 reference)

PMID:18407290 SUPPORT Model Organism

"Taurine depletion causes cardiomyocyte atrophy, mitochondrial and myofiber damage and cardiac dysfunction, effects likely related to the actions of taurine."

Supports treating this model as informative for the cardiac remodeling node.

Skeletal Muscle Taurine Depletion recapitulates fidelity: low The knockout depletes skeletal muscle taurine and produces measurable structural and exercise-capacity deficits.

Limitations: No myopathy or exercise intolerance has been reported in patients with taurine transporter deficiency, in whom skeletal muscle taurine is severely reduced but extraocular dysfunction was explicitly not detected; the murine muscle phenotype therefore has no established human counterpart.

Readouts

Skeletal muscle cell volume and exercise endurance

Direction: DECREASED

Interpretation: Muscle-level correlate of taurine depletion in this model, currently without a clinical human counterpart.

Show evidence (1 reference)

PMID:18407290 SUPPORT Model Organism

"the skeletal muscle of the TauTKO mice also exhibited decreased cell volume, structural defects and a reduction of exercise endurance capacity"

Reports the muscle measurements behind this readout.

Show evidence (1 reference)

PMID:18407290 SUPPORT Model Organism

"which exhibited a deficiency in myocardial and skeletal muscle taurine content compared with their wild-type littermates"

Supports the model as informative for the skeletal-muscle taurine depletion node.

{ }

Source YAML

click to show

name: Taurine transporter deficiency
creation_date: "2026-08-19T00:00:00Z"
category: Mendelian
synonyms:
- TauT deficiency
- SLC6A6 deficiency
- Hypotaurinemic retinal degeneration and cardiomyopathy
- SLC6A6-related Leber congenital amaurosis / early-onset retinal dystrophy
description: >-
  Taurine transporter deficiency is an autosomal recessive inborn error of amino
  acid transport caused by biallelic variants in SLC6A6, which encodes TauT, the
  ubiquitously expressed sodium- and chloride-dependent taurine transporter.
  Because most tissues have only limited capacity to synthesize taurine, they
  depend on TauT-mediated uptake against a steep concentration gradient to
  maintain a large intracellular taurine pool. Loss of that uptake produces
  profound systemic hypotaurinemia and depletes intracellular taurine in the
  tissues that need it most.

  The consistent and earliest clinical consequence is retinal: reported patients
  present in infancy or early childhood with Leber congenital amaurosis or
  early-onset retinal dystrophy, nystagmus, and severely depressed scotopic and
  photopic electroretinograms, progressing to panretinal degeneration. A
  cardiomyopathy arm is established but not obligate — the first reported
  consanguineous family had childhood cardiomyopathy, while a later multicenter
  series found structurally normal hearts (with short PR intervals) despite
  complete loss of taurine transport. Skeletal muscle, brain, and hearing
  involvement are prominent in the Slc6a6-null mouse but have so far been
  subclinical in humans.

  The disorder is mechanistically notable as a treatable transportopathy: oral
  taurine supplementation restores normal blood taurine levels, and in the index
  family corrected the cardiomyopathy and arrested the retinal degeneration over
  24 months. It is cited as a template for high-dose substrate supplementation in
  Mendelian transporter disease generally.
disease_term:
  preferred_term: hypotaurinemic retinal degeneration and cardiomyopathy
  term:
    id: MONDO:0007777
    label: hypotaurinemic retinal degeneration and cardiomyopathy
parents:
- Inborn error of metabolism
- Inborn disorder of amino acid transport
classifications:
  icimd_category:
  - classification_value: amino_acid_transport
    notes: >-
      ICIMD (Ferreira et al. 2021, PMID:33340416) group "Disorders of amino acid
      transport" under category "Disorders of amino acid metabolism"; IEMbase row
      1.11.13.01, SLC6A6-related taurine transporter deficiency.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0007777
      label: hypotaurinemic retinal degeneration and cardiomyopathy
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0007777 carries RO:0004003 (has material basis in germline mutation
      in) HGNC:11052 SLC6A6 and xrefs OMIM:145350, matching this entry's causal
      gene and disease concept exactly. Note that the IEMbase seed row for this
      disorder cites OMIM 186854, which is the SLC6A6 gene entry rather than the
      disease entry.
inheritance:
- name: Autosomal recessive
  description: >-
    All reported patients are homozygous for SLC6A6 variants, with heterozygous
    parents and relatives unaffected.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genetic analysis identified homozygous pathogenic SLC6A6 variants in all affected individuals, while unaffected relatives were heterozygous carriers."
    explanation: Homozygosity in all affected individuals with unaffected heterozygous relatives establishes recessive inheritance.
genetic:
- name: SLC6A6
  gene_term:
    preferred_term: SLC6A6
    term:
      id: hgnc:11052
      label: SLC6A6
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    SLC6A6 encodes TauT, the sodium- and chloride-dependent taurine transporter.
    Reported disease alleles span missense variants that abolish or severely
    reduce transport (p.Ala78Glu, p.Thr249Ile, p.Ala294Thr), a hypomorphic
    missense variant retaining roughly 15% of normal transport (p.Gly399Val),
    and truncating lesions (p.Thr113Ter, deletion of exon 11). All reported
    patients are homozygous, and every characterized allele acts by loss of
    transport function.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The human solute carrier family 6 member 6 gene (SLC6A6) encodes a ubiquitously expressed taurine transporter (TauT) that regulates the intracellular taurine content in many tissues, including brain, retina, heart, kidney, liver, and skeletal muscles."
    explanation: Identifies SLC6A6 as the gene encoding the taurine transporter and names the tissues that depend on it.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Families 1 and 2 carried missense variants p.(Thr249Ile) and p.(Ala294Thr), while families 3 and 4 carried truncating variants-a deletion of exon 11 and p.(Thr113Ter), respectively."
    explanation: Documents the allelic spectrum, including both missense and truncating disease alleles.
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In a consanguineous Pakistani family with two affected individuals, a homozygous variant Gly399Val in the eighth transmembrane domain of the taurine transporter SLC6A6 was identified resulting in a hypomorph transporting capacity of ~15% compared with normal."
    explanation: Establishes a hypomorphic allele with quantified residual transport capacity.
  variants:
  - name: SLC6A6 p.Gly399Val
    description: >-
      Homozygous missense variant in the eighth transmembrane domain, retaining
      approximately 15% of normal taurine transport. Carried by the index
      consanguineous Pakistani family with retinal degeneration and
      taurine-responsive cardiomyopathy.
    evidence:
    - reference: PMID:31903486
      reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Three-dimensional modeling of this variant has indicated that it likely causes displacement of the Tyr138 (TM3) side chain, important for transport of taurine."
      explanation: Gives the structural basis for the partial loss of transport by this allele.
  - name: SLC6A6 p.Ala78Glu
    description: >-
      Homozygous missense variant in the first reported human pedigree, reducing
      3H-taurine uptake in patient peripheral blood mononuclear cells by 95%
      while the protein still reaches the plasma membrane.
    evidence:
    - reference: PMID:31345061
      reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "TAUTp.A78E still localized in the plasma membrane but is predicted to impact structural stabilization."
      explanation: Distinguishes a transport-function defect from a trafficking defect for this allele.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Ultra-rare. As of the 2026 multicenter series, human SLC6A6 deficiency had
    been reported in a handful of pedigrees: the original two-brother family, one
    consanguineous Pakistani family, and seven affected individuals from four
    further unrelated families recruited in Pakistan, Italy, the US and France.
    No population frequency estimate exists.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This was a retrospective, multicenter observational study conducted between June 2019 and March 2025, involving 7 affected and 10 unaffected individuals from 4 unrelated families recruited in Pakistan, Italy, the US, and France."
    explanation: Gives the size of the largest reported cohort, from which the case-count basis for ultra-rarity follows.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, a direct link between SLC6A6 and human diseases has been established only recently, following the identification of 2 unrelated pedigrees with LCA/EORD and biallelic recessive variants in this gene."
    explanation: Confirms only two pedigrees were known before this series, supporting the case-in-literature framing.
progression:
- phase: Congenital to early-childhood retinal presentation
  age_range: Birth to 5 years
  notes: >-
    Visual impairment and nystagmus may be present from birth (Leber congenital
    amaurosis pattern) or be detected after early infancy but before age 5
    (early-onset retinal dystrophy pattern), with gradual deterioration of
    visual function thereafter.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four of the children had visual impairment and nystagmus since birth, with gradually deteriorating visual function over the years."
    explanation: Documents congenital onset and progressive deterioration in the largest family reported.
- phase: Childhood progression with variable cardiac involvement
  age_range: Childhood
  notes: >-
    In the index consanguineous family the retinal degeneration was rapidly
    progressive during childhood and accompanied by cardiomyopathy. Cardiac
    involvement is not obligate: in the later multicenter series cardiac
    structure was normal in all patients, with only conduction findings.
  evidence:
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."
    explanation: Describes the rapidly progressive childhood course with cardiomyopathy in the index family.
pathophysiology:
- name: SLC6A6 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Biallelic SLC6A6 variants abolish or severely reduce the activity of TauT,
    the sodium- and chloride-dependent plasma-membrane taurine transporter. The
    functional consequence has been measured directly in patient material:
    3H-taurine uptake was reduced by 95% in peripheral blood mononuclear cells
    carrying p.Ala78Glu, the p.Gly399Val allele retains roughly 15% of normal
    capacity, and p.Thr249Ile and p.Ala294Thr abolish transport in both HEK-293
    cells and patient fibroblasts. Loss of transport is not necessarily loss of
    the protein from the membrane — p.Ala78Glu still localizes to the plasma
    membrane, so the lesion is transport-functional rather than purely
    trafficking.
  genes:
  - preferred_term: SLC6A6
    term:
      id: hgnc:11052
      label: SLC6A6
  molecular_functions:
  - preferred_term: taurine transmembrane transporter activity
    term:
      id: GO:0005368
      label: taurine transmembrane transporter activity
    modifier: LOSS_OF_FUNCTION
  cellular_components:
  - preferred_term: plasma membrane
    term:
      id: GO:0005886
      label: plasma membrane
  evidence:
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "3H-taurine uptake by peripheral blood mononuclear cells was reduced by 95%, and taurine levels were severely reduced in plasma, skeletal muscle, and brain."
    explanation: Quantifies loss of taurine transport in patient cells as the proximal molecular defect.
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TAUTp.A78E still localized in the plasma membrane but is predicted to impact structural stabilization."
    explanation: Shows the defect is in transport function rather than membrane delivery for this allele.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional studies demonstrated that both missense variants are associated with complete loss of taurine transport in HEK-293 cells and patient-derived fibroblasts."
    explanation: Independent functional confirmation that disease missense alleles abolish taurine transport.
  downstream:
  - target: Systemic Taurine Depletion
    description: >-
      Loss of TauT-mediated uptake removes the only route by which most tissues
      can accumulate taurine against its concentration gradient, so circulating
      and tissue taurine fall.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31903486
      reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."
      explanation: Links the transporter defect directly to near-absent circulating taurine in affected individuals.
  - target: Impaired Mitochondrial Taurine Import and mt-tRNA Modification
    description: >-
      Beyond the plasma membrane, SLC6A6 has been shown to localize to
      mitochondria and to supply the taurine used for mitochondrial tRNA
      modification, so loss of the transporter would also deplete the
      mitochondrial taurine pool. This arm is demonstrated in cancer cell lines,
      not in patient tissue.
    causal_link_type: DIRECT
    hypothesis_groups:
    - mitochondrial_translation_model
    evidence:
    - reference: PMID:41652173
      reference_title: "SLC6A6 imports taurine into mitochondria to sustain mitochondrial translation and tumour growth."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We discover that SLC6A6 also localizes to mitochondria and imports taurine for mitochondrial transfer RNA modifications."
      explanation: Establishes a mitochondrial localization and mitochondrial-taurine-import function for the same transporter.
- name: Systemic Taurine Depletion
  biological_scale: ORGANISM
  description: >-
    Failure of TauT-mediated uptake produces profound hypotaurinemia together
    with depletion of the tissue taurine pool. Patient plasma taurine is reduced
    relative both to heterozygous carriers and to healthy controls, and taurine
    is severely reduced in skeletal muscle and brain as well as plasma. This is
    the systemic state from which every downstream tissue phenotype follows, and
    it is the node that oral taurine supplementation acts on.
  chemical_entities:
  - preferred_term: taurine
    term:
      id: CHEBI:15891
      label: taurine
    modifier: DECREASED
  biological_processes:
  - preferred_term: taurine transmembrane transport
    term:
      id: GO:0015734
      label: taurine transmembrane transport
    modifier: DECREASED
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Additionally, irrespective of the variants considered, plasma taurine levels in affected individuals were reduced compared with heterozygous carriers"
    explanation: Quantitative confirmation of hypotaurinemia across all reported genotypes.
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "taurine levels were severely reduced in plasma, skeletal muscle, and brain"
    explanation: Shows the depletion is systemic and extends into tissue compartments, not just plasma.
  downstream:
  - target: Retinal Taurine Depletion and Photoreceptor Stress
    description: >-
      The retina is the tissue in which taurine depletion becomes clinically
      manifest first; taurine supports photoreceptor viability and outer-retinal
      homeostasis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41343195
      reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Subsequent research has shown that cellular intake of taurine supports photoreceptors viability, regulates intracellular calcium signaling, and acts as an antioxidant."
      explanation: States the cellular dependence of photoreceptors on taurine uptake that the depletion removes.
  - target: Myocardial Taurine Depletion and Energy Starvation
    description: >-
      Cardiac and skeletal muscle hold the largest free taurine pools of any
      tissue but have limited biosynthetic capacity, so they are among the first
      to be depleted when uptake fails.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:18407290
      reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "we generated taurine transporter- (TauT-) knockout mice (TauTKO), which exhibited a deficiency in myocardial and skeletal muscle taurine content compared with their wild-type littermates."
      explanation: Shows that loss of the transporter depletes the myocardial taurine pool specifically.
  - target: Cellular Oxidative Stress and RNA Oxidation
    description: >-
      Taurine is an intracellular antioxidant and cytoprotectant; its loss
      raises oxidative burden, measurable systemically before any organ
      dysfunction is clinically apparent.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31345061
      reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"
      explanation: Measured oxidative-stress and RNA-oxidation marker elevation in patients with taurine depletion.
  - target: Skeletal Muscle Taurine Depletion
    description: >-
      Skeletal muscle taurine is severely reduced in patients, and in the mouse
      null this translates into decreased cell volume, structural defects, and
      reduced exercise capacity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31345061
      reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "taurine levels were severely reduced in plasma, skeletal muscle, and brain"
      explanation: Documents measured skeletal-muscle taurine depletion in a patient.
- name: Cellular Oxidative Stress and RNA Oxidation
  biological_scale: CELLULAR
  description: >-
    Taurine contributes to cell volume homeostasis, protein stabilization,
    cytoprotection and antioxidation, so depletion leaves cells with reduced
    antioxidant buffering. In the two reported brothers this was detectable as
    significantly increased urinary 8-oxo-7,8-dihydroguanosine — an RNA-oxidation
    marker — while extraocular organ function was still clinically normal,
    making it the earliest measurable systemic consequence of the transport
    defect.
  biological_processes:
  - preferred_term: cellular response to oxidative stress
    term:
      id: GO:0034599
      label: cellular response to oxidative stress
    modifier: INCREASED
  evidence:
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"
    explanation: Reports the measured RNA-oxidation marker itself — increased urinary 8-oxo-7,8-dihydroguanosine in the affected brothers — and places it upstream of any clinically apparent extraocular disease.
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Compatible with taurine's indispensability for cell volume homeostasis, protein stabilization, cytoprotection, antioxidation, and immuno- and neuromodulation, mice develop multisystemic dysfunctions (hearing loss; liver fibrosis; and behavioral, heart, and skeletal muscle abnormalities) later on."
    explanation: States the cytoprotective and antioxidant roles of taurine whose loss produces the oxidative phenotype. Tagged MODEL_ORGANISM because the main clause reports the multisystem consequences in mice, not in the patients — the human counterparts of those findings are deliberately not curated here (see notes).
  downstream:
  - target: Retinal Taurine Depletion and Photoreceptor Stress
    description: >-
      Oxidative injury is the shared final stress on photoreceptors in inherited
      retinal degeneration and is the route by which loss of taurine's
      antioxidant function reaches the outer retina.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Loss of taurine-dependent antioxidant buffering in outer-retinal cells.
    - Oxidative damage to photoreceptor lipids, proteins and RNA.
    evidence:
    - reference: PMID:41343195
      reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Subsequent research has shown that cellular intake of taurine supports photoreceptors viability, regulates intracellular calcium signaling, and acts as an antioxidant."
      explanation: Names the antioxidant role of imported taurine in photoreceptors.
- name: Impaired Mitochondrial Taurine Import and mt-tRNA Modification
  biological_scale: MOLECULAR
  description: >-
    A second, mitochondrial pool of SLC6A6 imports taurine into mitochondria,
    where it is used for taurine-dependent modification of mitochondrial tRNAs.
    Loss of the transporter reduces mitochondrial taurine abundance specifically
    and abrogates mitochondrial translation. This is an emerging arm: it was
    established in cancer cell lines as a metabolic dependency, and it has not
    been demonstrated in tissue from patients with SLC6A6 deficiency. It is
    curated because, if it holds in patient tissue, it would place taurine
    transporter deficiency partly within mitochondrial-translation disease and
    would complicate the therapeutic logic — the same paper reports that
    exogenous taurine does not substitute for the transporter in the cell
    systems tested.
  biological_processes:
  - preferred_term: tRNA wobble uridine modification
    term:
      id: GO:0002098
      label: tRNA wobble uridine modification
    modifier: DECREASED
  cellular_components:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  chemical_entities:
  - preferred_term: taurine
    term:
      id: CHEBI:15891
      label: taurine
    modifier: DECREASED
  evidence:
  - reference: PMID:41652173
    reference_title: "SLC6A6 imports taurine into mitochondria to sustain mitochondrial translation and tumour growth."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "SLC6A6 deficiency specifically reduces mitochondrial taurine abundance and abrogates mitochondrial translation and cell proliferation."
    explanation: Directly links loss of the transporter to mitochondrial taurine depletion and translation failure.
  - reference: PMID:41652173
    reference_title: "SLC6A6 imports taurine into mitochondria to sustain mitochondrial translation and tumour growth."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here we show that SLC6A6, but not exogenous taurine, is essential for mitochondrial metabolism and cancer cell growth."
    explanation: >-
      Supports the transporter-specific requirement, but only in cancer cell
      lines — hence PARTIAL rather than SUPPORT for the inherited disease.
  downstream:
  - target: Myocardial Taurine Depletion and Energy Starvation
    description: >-
      Failure of mitochondrial translation would compromise respiratory-chain
      subunit synthesis, converging on the impaired respiratory-chain function
      and reduced ATP output already documented in the taurine-deficient heart.
      Hypothesized rather than established in this disease.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - mitochondrial_translation_model
    evidence:
    - reference: PMID:26475290
      reference_title: "Impaired energy metabolism of the taurine-deficient heart."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "One of the major functions of taurine in the heart is the regulation of the respiratory chain."
      explanation: Independent evidence that taurine deficiency in the heart acts through the respiratory chain, the output of mitochondrial translation.
- name: Retinal Taurine Depletion and Photoreceptor Stress
  biological_scale: CELLULAR
  description: >-
    Photoreceptors and retinal pigment epithelium depend on imported taurine for
    viability, calcium signaling, and antioxidant defense; the requirement is old
    knowledge from taurine-deficient cats, which develop progressive retinal
    degeneration. In taurine transporter deficiency this dependency is unmet from
    birth, leaving the outer retina under chronic metabolic and oxidative stress.
  conforms_to: "photoreceptor_degeneration#Photoreceptor Metabolic and Oxidative Stress"
  cell_types:
  - preferred_term: photoreceptor cell
    term:
      id: CL:0000210
      label: photoreceptor cell
  - preferred_term: retinal pigment epithelial cell
    term:
      id: CL:0002586
      label: retinal pigment epithelial cell
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  chemical_entities:
  - preferred_term: taurine
    term:
      id: CHEBI:15891
      label: taurine
    modifier: DECREASED
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The importance of taurine in retinal development, photoreceptors maintenance, and cellular homeostasis was recognized as early as the 1970s when studies involving taurine-deficient cats demonstrated progressive retinal degeneration."
    explanation: Establishes the retinal taurine requirement and that its absence alone causes progressive degeneration.
  - reference: PMID:11772953
    reference_title: "Disruption of the taurine transporter gene (taut) leads to retinal degeneration in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In particular, the retinal involvement identifies the taurine transporter as an important factor for the development and maintenance of normal retinal functions and morphology."
    explanation: The mouse null shows the transporter itself is required for retinal development and maintenance.
  downstream:
  - target: Photoreceptor Degeneration and Outer Retinal Thinning
    description: >-
      Sustained loss of taurine-dependent support leads to photoreceptor loss and
      thinning of the outer nuclear layer.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:11772953
      reference_title: "Disruption of the taurine transporter gene (taut) leads to retinal degeneration in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "These mice show markedly decreased taurine levels in a variety of tissues, a reduced fertility, and loss of vision due to severe retinal degeneration."
      explanation: Directly connects tissue taurine depletion to severe retinal degeneration and vision loss.
- name: Photoreceptor Degeneration and Outer Retinal Thinning
  biological_scale: TISSUE
  description: >-
    Panretinal photoreceptor degeneration with structural loss of the outer
    retina. Optical coherence tomography in an affected 14-year-old showed a
    central island of outer nuclear layer thinning abnormally with eccentricity,
    with poorly delineated external limiting membrane and ellipsoid zone, and
    fundus examination showed attenuated retinal vasculature. Rod and cone loss
    are concurrent here rather than sequential — scotopic and photopic
    electroretinograms are both severely depressed at presentation — so this
    node deliberately carries no conforms_to anchor; see notes.
  cell_types:
  - preferred_term: photoreceptor cell
    term:
      id: CL:0000210
      label: photoreceptor cell
  locations:
  - preferred_term: retina
    term:
      id: UBERON:0000966
      label: retina
  evidence:
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Loss of TAUT function due to a homozygous missense mutation caused panretinal degeneration in 2 brothers."
    explanation: Establishes panretinal degeneration as the human tissue-level consequence.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Macular OCT of the right (iii) and left (iv) eyes of the same individual showing a central island of the outer nuclear layer that abnormally decreases in thickness with eccentricity."
    explanation: Imaging evidence of outer nuclear layer thinning in an affected individual.
  downstream:
  - target: Early-Onset Panretinal Dystrophy and Visual Loss
    description: >-
      Loss of photoreceptors produces the clinical LCA/EORD phenotype with
      severely depressed electroretinography and progressive visual failure.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:41343195
      reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "All 4 patients presented with severely depressed scotopic and photopic ERG recordings in both eyes"
      explanation: Functional confirmation that photoreceptor loss translates into abolished rod and cone responses.
- name: Early-Onset Panretinal Dystrophy and Visual Loss
  biological_scale: ORGANISM
  description: >-
    The clinical retinal endpoint: Leber congenital amaurosis or early-onset
    retinal dystrophy with nystagmus, severely depressed scotopic and photopic
    electroretinograms, and progressive loss of visual function. Present in all
    reported affected individuals, and the presenting feature in every pedigree
    described to date.
  conforms_to: "photoreceptor_degeneration#Progressive Visual Field Loss and Blindness"
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All 7 affected individuals exhibited LCA/EORD, with extraocular findings in some."
    explanation: Establishes the retinal phenotype as the consistent clinical endpoint across the cohort.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These findings confirm and expand the role of biallelic variants in SLC6A6 in association with LCA/EORD due to impaired taurine transport."
    explanation: States the causal association between impaired taurine transport and the LCA/EORD phenotype.
- name: Myocardial Taurine Depletion and Energy Starvation
  biological_scale: CELLULAR
  description: >-
    Taurine is the most abundant free amino acid in cardiac muscle and one of its
    major functions there is regulation of the respiratory chain. In the
    taurine-deficient heart glycolysis rises while glucose oxidation falls,
    pyruvate dehydrogenase flux is reduced by a raised NADH/NAD+ ratio, and
    long-chain fatty acid uptake into mitochondria is diminished; ATP production
    falls and the phosphocreatine/ATP ratio declines. The cardiomyocyte is
    therefore energy-starved before it is structurally abnormal. This node's
    evidence is rodent; the human counterpart is the taurine-responsive
    cardiomyopathy of the index family.
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  locations:
  - preferred_term: heart
    term:
      id: UBERON:0000948
      label: heart
  biological_processes:
  - preferred_term: ATP biosynthetic process
    term:
      id: GO:0006754
      label: ATP biosynthetic process
    modifier: DECREASED
  chemical_entities:
  - preferred_term: taurine
    term:
      id: CHEBI:15891
      label: taurine
    modifier: DECREASED
  evidence:
  - reference: PMID:26475290
    reference_title: "Impaired energy metabolism of the taurine-deficient heart."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These changes diminished the rate of ATP production, causing a decline in the phosphocreatine/ATP ratio, a sign of reduced energy status."
    explanation: Quantifies the bioenergetic deficit produced by myocardial taurine depletion.
  - reference: PMID:26475290
    reference_title: "Impaired energy metabolism of the taurine-deficient heart."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The findings support the hypothesis that the taurine-deficient heart is energy starved primarily because of impaired respiratory chain function, an increase in the NADH/NAD+ ratio and diminished long chain fatty acid uptake by the mitochondria."
    explanation: Identifies impaired respiratory-chain function as the primary mechanism of the energy deficit.
  downstream:
  - target: Cardiomyocyte Atrophy and Ventricular Remodeling
    description: >-
      Chronic energy starvation together with loss of taurine's osmoregulatory
      and cytoprotective functions produces cardiomyocyte atrophy and
      ultrastructural damage to myofilaments and mitochondria.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:18407290
      reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Taurine depletion causes cardiomyocyte atrophy, mitochondrial and myofiber damage and cardiac dysfunction, effects likely related to the actions of taurine."
      explanation: Directly connects taurine depletion to cardiomyocyte atrophy and myofibrillar/mitochondrial damage.
- name: Cardiomyocyte Atrophy and Ventricular Remodeling
  biological_scale: TISSUE
  description: >-
    In the taurine transporter knockout mouse the heart remodels with reduced
    ventricular wall thickness and cardiac atrophy from smaller cardiomyocytes,
    reduced cardiac output, and induction of the fetal heart-failure gene
    programme (ANP, BNP, beta-MHC) — a dilated, atrophic cardiomyopathy rather
    than a hypertrophic one. The human phenotype includes cardiomyopathy in the
    index consanguineous family but structurally normal hearts in the later
    multicenter series, so penetrance of this arm is variable and unexplained.
  conforms_to: "cardiomyopathy_maladaptive_remodeling#Ventricular Remodeling"
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  locations:
  - preferred_term: heart
    term:
      id: UBERON:0000948
      label: heart
  evidence:
  - reference: PMID:18407290
    reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The TauTKO heart underwent ventricular remodeling, characterized by reductions in ventricular wall thickness and cardiac atrophy accompanied with the smaller cardiomyocytes."
    explanation: Defines the remodeling phenotype produced by transporter loss.
  - reference: PMID:18407290
    reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Associated with the structural changes in the heart was a reduction in cardiac output and increased expression of heart cardiac failure (fetal) marker genes, such as ANP, BNP and beta-MHC."
    explanation: Shows the remodeling is accompanied by functional decline and the heart-failure transcriptional programme.
  - reference: PMID:26475290
    reference_title: "Impaired energy metabolism of the taurine-deficient heart."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "A significant reduction in myocardial taurine content leads to the development of a unique dilated, atrophic cardiomyopathy."
    explanation: Characterizes the cardiomyopathy as dilated and atrophic rather than hypertrophic.
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Remarkably, after 24-months, the cardiomyopathy was corrected in both affected siblings, and in the 6-years-old, the retinal degeneration was arrested, and the vision was clinically improved."
    explanation: >-
      Human evidence that the cardiac remodeling is taurine-dependent and
      reversible, which is why the node is placed downstream of taurine depletion
      rather than treated as an independent structural defect.
- name: Skeletal Muscle Taurine Depletion
  biological_scale: TISSUE
  description: >-
    Skeletal muscle carries a large taurine pool with limited local synthesis.
    Patient skeletal-muscle taurine is severely reduced, and in the mouse null
    depletion produces decreased cell volume, structural defects and reduced
    exercise endurance. No myopathy has yet been reported in patients, so this
    node is curated as an established biochemical deficit with a so-far
    subclinical human phenotype.
  locations:
  - preferred_term: skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  chemical_entities:
  - preferred_term: taurine
    term:
      id: CHEBI:15891
      label: taurine
    modifier: DECREASED
  evidence:
  - reference: PMID:18407290
    reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Further, the skeletal muscle of the TauTKO mice also exhibited decreased cell volume, structural defects and a reduction of exercise endurance capacity."
    explanation: Establishes the skeletal-muscle consequence of transporter loss in the mouse.
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"
    explanation: >-
      Supports the biochemical deficit while explicitly recording that no
      extraocular (including muscular) dysfunction was clinically detectable.
mechanistic_hypotheses:
- hypothesis_group_id: osmotic_cytoprotection_model
  hypothesis_label: Osmolyte and Cytoprotection Model
  status: CANONICAL
  description: >-
    Taurine acts as an organic osmolyte and cytoprotectant supporting cell volume
    homeostasis, protein stabilization, antioxidation, and calcium handling. Under
    this model the disease is the sum of what happens to taurine-dependent
    tissues when that support is withdrawn: outer-retinal oxidative and metabolic
    stress, cardiomyocyte volume loss and atrophy, and reduced skeletal-muscle
    cell volume. It is the canonical framing because it accounts for the tissue
    distribution of disease and for the reversal of the cardiac phenotype on
    substrate replacement.
  evidence:
  - reference: PMID:11772953
    reference_title: "Disruption of the taurine transporter gene (taut) leads to retinal degeneration in mice."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Taurine is involved in cell volume homeostasis, antioxidant defense, protein stabilization, and stress responses."
    explanation: States the cytoprotective functions on which the model rests.
  - reference: PMID:18407290
    reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our data suggest that multiple actions of taurine, including osmoregulation, regulation of mitochondrial protein expression and inhibition of apoptosis, collectively ensure proper maintenance of cardiac and skeletal muscular structure and function."
    explanation: Attributes the cardiac and muscular phenotypes to taurine's osmoregulatory and cytoprotective actions.
  notes: >-
    Retained as CANONICAL but not sufficient on its own: it does not explain why
    the retina fails first and most severely, nor why cardiac involvement is
    present in some pedigrees and absent in others despite comparable loss of
    transport.
- hypothesis_group_id: mitochondrial_translation_model
  hypothesis_label: Mitochondrial Taurine Import and Translation Model
  status: EMERGING
  description: >-
    A mitochondrial pool of SLC6A6 supplies taurine for mitochondrial tRNA
    modification, and its loss abrogates mitochondrial translation. Under this
    model taurine transporter deficiency is partly a disorder of mitochondrial
    protein synthesis, which would predict a bioenergetic phenotype in
    high-demand post-mitotic tissue — photoreceptors and cardiomyocytes are the
    two most oxidative-dependent tissues affected. The supporting work was done
    in cancer cell lines with SLC6A6 loss, not in patient material, so this is an
    emerging rather than established arm of the disease model.
  evidence:
  - reference: PMID:41652173
    reference_title: "SLC6A6 imports taurine into mitochondria to sustain mitochondrial translation and tumour growth."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Taurine plays a crucial role in mitochondrial translation."
    explanation: States the mitochondrial-translation dependence on taurine underlying this model.
  - reference: PMID:41652173
    reference_title: "SLC6A6 imports taurine into mitochondria to sustain mitochondrial translation and tumour growth."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Together, these findings suggest that SLC6A6 is a mitochondrial taurine transporter and an exploitable metabolic dependency in cancer."
    explanation: Confirms the authors' own framing of the mitochondrial transport function and its experimental context.
  notes: >-
    Deliberately not asserted as an explanation of the human disease. If it is
    confirmed in patient tissue it has a direct therapeutic implication, because
    the same study reports that exogenous taurine did not substitute for the
    transporter in the systems tested, whereas oral taurine supplementation does
    benefit patients — a tension that is itself worth resolving.
phenotypes:
- name: Early-onset retinal dystrophy
  category: Ophthalmological
  description: >-
    Leber congenital amaurosis or early-onset retinal dystrophy, present in all
    reported affected individuals.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Rod-cone dystrophy
    term:
      id: HP:0000510
      label: Rod-cone dystrophy
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All 7 affected individuals exhibited LCA/EORD, with extraocular findings in some."
    explanation: >-
      All seven affected individuals in the largest reported series had the
      retinal phenotype, and it was also present in both previously reported
      pedigrees, supporting an obligate frequency band.
- name: Retinal degeneration
  category: Ophthalmological
  phenotype_term:
    preferred_term: Retinal degeneration
    term:
      id: HP:0000546
      label: Retinal degeneration
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Loss of TAUT function due to a homozygous missense mutation caused panretinal degeneration in 2 brothers."
    explanation: Panretinal degeneration documented in the first reported human pedigree.
- name: Nystagmus
  category: Ophthalmological
  phenotype_term:
    preferred_term: Nystagmus
    term:
      id: HP:0000639
      label: Nystagmus
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four of the children had visual impairment and nystagmus since birth, with gradually deteriorating visual function over the years."
    explanation: Nystagmus from birth in four affected siblings.
- name: Visual impairment
  category: Ophthalmological
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four of the children had visual impairment and nystagmus since birth, with gradually deteriorating visual function over the years."
    explanation: Congenital, progressive visual impairment in affected individuals.
- name: Abnormal electroretinogram
  category: Ophthalmological
  description: >-
    Severely depressed scotopic and photopic full-field electroretinogram
    responses, reflecting loss of both rod and cone function.
  phenotype_term:
    preferred_term: Abnormal electroretinogram
    term:
      id: HP:0000512
      label: Abnormal electroretinogram
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All 4 patients presented with severely depressed scotopic and photopic ERG recordings in both eyes"
    explanation: Documents the electrophysiological abnormality in all tested affected individuals of family 1.
- name: Attenuation of retinal blood vessels
  category: Ophthalmological
  phenotype_term:
    preferred_term: Attenuation of retinal blood vessels
    term:
      id: HP:0007843
      label: Attenuation of retinal blood vessels
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "showing attenuated retinal vasculature and slightly blurred optic disc margins"
    explanation: Fundus photography finding in an affected 14-year-old.
- name: Hypotaurinemia
  category: Metabolic
  description: >-
    Reduced or almost undetectable plasma taurine, the biochemical signature of
    the disorder.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Hypotaurinemia
    term:
      id: HP:0500182
      label: Hypotaurinemia
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Additionally, irrespective of the variants considered, plasma taurine levels in affected individuals were reduced compared with heterozygous carriers"
    explanation: >-
      The "irrespective of the variants considered" phrasing establishes that
      hypotaurinemia was present in every affected individual, supporting an
      obligate band.
- name: Cardiomyopathy
  category: Cardiovascular
  description: >-
    Childhood cardiomyopathy, reported in the index consanguineous family and
    corrected by taurine supplementation. Not present in all pedigrees.
  phenotype_term:
    preferred_term: Cardiomyopathy
    term:
      id: HP:0001638
      label: Cardiomyopathy
  evidence:
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."
    explanation: Cardiomyopathy in both affected siblings of the index family.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"
    explanation: >-
      Recorded as PARTIAL because this series found no structural cardiomyopathy
      despite complete loss of taurine transport, establishing that the cardiac
      arm is not obligate.
- name: Shortened PR interval
  category: Cardiovascular
  description: >-
    Short PR interval on electrocardiography, present in every affected
    individual of the 2026 multicenter series and the only cardiac abnormality
    found in that cohort, whose hearts were structurally normal. It is therefore
    the one cardiac finding that does not track with the variably penetrant
    structural cardiomyopathy.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Shortened PR interval
    term:
      id: HP:0005165
      label: Shortened PR interval
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"
    explanation: >-
      Reports the finding in all patients of the series. The VERY_FREQUENT band
      reflects "all patients" of this one cohort; the earlier pedigrees did not
      report PR interval, so an OBLIGATE band across the whole disorder is not
      supported.
- name: Intellectual disability
  category: Neurological
  description: >-
    Mild to moderate intellectual disability, reported in one affected individual
    alongside oculomotor abnormalities and a developmental motor coordination
    disorder.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
    severity: MILD
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was examined when she was 5 years old because of mild to moderate intellectual disability (IQ, 62)"
    explanation: Documented intellectual disability with a measured IQ in the Italian family.
biochemical:
- name: Plasma taurine
  presence: Reduced
  context: >-
    The diagnostic biochemical marker. Plasma taurine is reduced relative both to
    heterozygous carriers and to healthy controls in every reported affected
    individual, irrespective of the underlying variant, and is almost
    undetectable in some. It is also the treatment-monitoring analyte: oral
    supplementation is titrated to maintain normal blood taurine.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "plasma taurine levels in affected individuals were reduced compared with heterozygous carriers"
    explanation: Establishes the direction and comparison group for the plasma taurine abnormality.
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Oral taurine supplementation of 100 mg/kg/day resulted in maintenance of normal blood taurine levels."
    explanation: Establishes plasma taurine as the analyte used to monitor and titrate treatment.
diagnosis:
- name: Fasting plasma taurine measurement
  description: >
    Measurement of fasting plasma taurine identifies the biochemical deficit and
    discriminates affected individuals from heterozygous carriers and controls.
  markers: plasma taurine
  results: Reduced or almost undetectable plasma taurine.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "followed by measurement of fasting plasma taurine levels"
    explanation: Fasting plasma taurine measurement is part of the reported diagnostic workflow.
- name: Full-field electroretinography
  description: >
    ISCEV-standard full-field electroretinography characterizes the extent of rod
    and cone dysfunction and supports the LCA/EORD diagnosis.
  results: Severely depressed or undetectable scotopic and photopic responses.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients underwent standard clinical examinations, including visual acuity, full-field electroretinography, and multimodal retinal imaging"
    explanation: Full-field electroretinography is part of the standard diagnostic assessment in this disorder.
- name: Molecular genetic testing of SLC6A6
  description: >
    Whole-exome or whole-genome sequencing identifies the biallelic SLC6A6
    variants and is the confirmatory test; functional taurine-uptake assays in
    patient fibroblasts can resolve variants of uncertain significance.
  results: Biallelic pathogenic SLC6A6 variants with segregation in heterozygous parents.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genetic analysis identified homozygous pathogenic SLC6A6 variants in all affected individuals, while unaffected relatives were heterozygous carriers."
    explanation: Molecular testing with segregation analysis is the confirmatory diagnostic step.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro and ex vivo taurine transport and membrane trafficking assays in human embryonic kidney (HEK)-293 cells, as well as patient-derived fibroblasts, were also performed."
    explanation: Functional transport assays in patient-derived fibroblasts are available to confirm variant effect.
- name: Cardiac assessment with electrocardiography and echocardiography
  description: >
    Because cardiomyopathy is part of the disorder in some pedigrees, cardiac
    structure and conduction should be assessed at diagnosis and monitored.
    Conduction abnormalities may be present even when cardiac structure is
    normal.
  results: >-
    Cardiomyopathy in some pedigrees; short PR interval reported in all patients
    of one series with structurally normal hearts.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"
    explanation: Reports the ECG and echocardiographic findings that motivate cardiac assessment.
treatments:
- name: Oral taurine supplementation
  description: >-
    High-dose oral taurine (100 mg/kg/day in the reported regimen) raises
    extracellular taurine sufficiently to restore normal blood taurine levels
    despite the transport defect. In the index consanguineous family, 24 months
    of supplementation corrected the cardiomyopathy in both affected siblings
    and, in the younger child, arrested the retinal degeneration with clinical
    improvement in vision. It is the only disease-modifying therapy reported and
    is explicitly proposed as a template for substrate supplementation in
    Mendelian transporter disease more broadly. Outside the index family it
    remains investigational.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: oral taurine supplementation
    term:
      id: NCIT:C15425
      label: Nutritional Supplementation
    therapeutic_agent:
    - preferred_term: taurine
      term:
        id: CHEBI:15891
        label: taurine
  target_mechanisms:
  - target: Systemic Taurine Depletion
    treatment_effect: RESTORES
    description: >-
      Oral supplementation replenishes the depleted taurine pool, restoring
      normal blood taurine without correcting the transporter itself.
    evidence:
    - reference: PMID:31903486
      reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Oral taurine supplementation of 100 mg/kg/day resulted in maintenance of normal blood taurine levels."
      explanation: Demonstrates that supplementation restores the depleted systemic taurine pool.
  evidence:
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Remarkably, after 24-months, the cardiomyopathy was corrected in both affected siblings, and in the 6-years-old, the retinal degeneration was arrested, and the vision was clinically improved."
    explanation: Reports the clinical outcome of long-term supplementation on both disease arms.
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Similar therapeutic approaches could be employed in Mendelian phenotypes caused by the dysfunction of the hundreds of other molecular transporters."
    explanation: The authors' generalization of the substrate-supplementation strategy to transporter disease at large.
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These findings suggest that patients with a diagnosis of SLC6A6-related LCA/EORD may be candidates for investigational oral taurine supplementation."
    explanation: >-
      Recorded as PARTIAL because the later series frames supplementation as
      investigational and candidate-eligible rather than established therapy.
animal_models:
- name: taut-/- taurine transporter knockout mouse (retinal arm)
  species: Mouse
  genotype: Slc6a6 (taut) homozygous null
  publication: PMID:11772953
  description: >-
    Germline disruption of the mouse taurine transporter gene, the model in which
    the retinal consequence of transporter loss was first established and which
    predated the recognition of the human disorder.
  modeled_mechanisms:
  - target: Photoreceptor Degeneration and Outer Retinal Thinning
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The null mouse loses vision from severe retinal degeneration, matching the
      panretinal degeneration of human TauT deficiency, and was the basis for
      searching for the human disease.
    limitations: >-
      The mouse is a complete null, whereas human disease alleles range from
      complete loss of transport to a hypomorph retaining roughly 15% of normal
      capacity; the mouse also develops later multisystem features (hearing loss,
      liver fibrosis, behavioural abnormalities) that have not been observed in
      patients.
    readouts:
    - name: Retinal morphology and visual function
      target: Photoreceptor Degeneration and Outer Retinal Thinning
      direction: DECREASED
      interpretation: >-
        Structural and functional loss of the retina in the transporter-null
        mouse, the animal correlate of the human outer-retinal degeneration node.
      evidence:
      - reference: PMID:11772953
        reference_title: "Disruption of the taurine transporter gene (taut) leads to retinal degeneration in mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "loss of vision due to severe retinal degeneration"
        explanation: Reports the retinal measurement behind this readout.
    evidence:
    - reference: PMID:11772953
      reference_title: "Disruption of the taurine transporter gene (taut) leads to retinal degeneration in mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In particular, the retinal involvement identifies the taurine transporter as an important factor for the development and maintenance of normal retinal functions and morphology."
      explanation: Supports treating this model as informative for the retinal degeneration node.
- name: TauTKO taurine transporter knockout mouse (cardiac and muscle arm)
  species: Mouse
  genotype: Slc6a6 (TauT) homozygous knockout
  publication: PMID:18407290
  description: >-
    Taurine transporter knockout mouse characterized for cardiac and skeletal
    muscle phenotype, with myocardial and skeletal muscle taurine depletion,
    ventricular remodeling, cardiac atrophy and reduced exercise capacity.
  modeled_mechanisms:
  - target: Cardiomyocyte Atrophy and Ventricular Remodeling
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      The knockout develops a dilated, atrophic cardiomyopathy with reduced
      cardiac output and induction of fetal heart-failure genes, providing the
      mechanistic account of the cardiomyopathy seen in the index human family.
    limitations: >-
      Fidelity is only MODERATE because the cardiac arm is variably penetrant in
      humans: the later multicenter series found structurally normal hearts in
      all seven affected individuals despite complete loss of taurine transport,
      so the uniform murine cardiomyopathy overstates the human cardiac risk.
    readouts:
    - name: Ventricular wall thickness and cardiomyocyte size
      target: Cardiomyocyte Atrophy and Ventricular Remodeling
      direction: DECREASED
      interpretation: >-
        Structural correlate of the ventricular remodeling node — thinner walls
        and smaller cardiomyocytes rather than hypertrophy.
      evidence:
      - reference: PMID:18407290
        reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "reductions in ventricular wall thickness and cardiac atrophy accompanied with the smaller cardiomyocytes"
        explanation: Reports the structural measurement behind this readout.
    - name: Cardiac output
      target: Cardiomyocyte Atrophy and Ventricular Remodeling
      direction: DECREASED
      interpretation: Functional consequence of the remodeling in this model.
      evidence:
      - reference: PMID:18407290
        reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "a reduction in cardiac output and increased expression of heart cardiac failure (fetal) marker genes"
        explanation: Reports the functional measurement behind this readout.
    evidence:
    - reference: PMID:18407290
      reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Taurine depletion causes cardiomyocyte atrophy, mitochondrial and myofiber damage and cardiac dysfunction, effects likely related to the actions of taurine."
      explanation: Supports treating this model as informative for the cardiac remodeling node.
  - target: Skeletal Muscle Taurine Depletion
    relationship: RECAPITULATES
    fidelity: LOW
    description: >-
      The knockout depletes skeletal muscle taurine and produces measurable
      structural and exercise-capacity deficits.
    limitations: >-
      No myopathy or exercise intolerance has been reported in patients with
      taurine transporter deficiency, in whom skeletal muscle taurine is severely
      reduced but extraocular dysfunction was explicitly not detected; the murine
      muscle phenotype therefore has no established human counterpart.
    readouts:
    - name: Skeletal muscle cell volume and exercise endurance
      target: Skeletal Muscle Taurine Depletion
      direction: DECREASED
      interpretation: >-
        Muscle-level correlate of taurine depletion in this model, currently
        without a clinical human counterpart.
      evidence:
      - reference: PMID:18407290
        reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "the skeletal muscle of the TauTKO mice also exhibited decreased cell volume, structural defects and a reduction of exercise endurance capacity"
        explanation: Reports the muscle measurements behind this readout.
    evidence:
    - reference: PMID:18407290
      reference_title: "Taurine depletion caused by knocking out the taurine transporter gene leads to cardiomyopathy with cardiac atrophy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "which exhibited a deficiency in myocardial and skeletal muscle taurine content compared with their wild-type littermates"
      explanation: Supports the model as informative for the skeletal-muscle taurine depletion node.
discussions:
- discussion_id: slc6a6_cardiac_penetrance_gap
  prompt: >-
    Why is cardiomyopathy present in some SLC6A6-deficient pedigrees and absent
    in others despite comparable or greater loss of taurine transport?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Cardiomyocyte Atrophy and Ventricular Remodeling
  rationale: >-
    The index consanguineous family carried a hypomorphic allele retaining
    roughly 15% of normal transport and had childhood cardiomyopathy that
    reversed on taurine supplementation. The later multicenter series included
    variants causing complete loss of transport, yet cardiac structure was normal
    in all seven affected individuals, with only short PR intervals. The cardiac
    arm therefore does not track with residual transport capacity, so something
    else — age at assessment, dietary taurine intake, genetic background, or a
    modifier of cardiac taurine handling — determines whether it manifests. This
    matters clinically because it determines whether cardiac surveillance and
    pre-emptive supplementation are warranted in every patient or only in some.
  proposed_experiments:
  - experiment_id: exp_slc6a6_longitudinal_cardiac_cohort
    name: Longitudinal cardiac phenotyping of SLC6A6-deficient patients
    description: >-
      Serial echocardiography, ECG and cardiac MRI in all known SLC6A6-deficient
      patients, stratified by residual transport capacity and age, to test
      whether cardiomyopathy is age-dependent rather than genotype-dependent.
    decision_criterion: >-
      Emergence of ventricular remodeling with age in patients whose hearts were
      initially structurally normal would support an age-dependent arm; its
      absence in adults with complete loss of transport would argue for a genuine
      modifier.
  - experiment_id: exp_slc6a6_dietary_taurine_confounder
    name: Dietary taurine intake versus cardiac phenotype
    description: >-
      Quantify dietary taurine intake alongside plasma taurine in
      SLC6A6-deficient patients with and without cardiomyopathy, to test whether
      nutritional taurine masks the cardiac phenotype.
    decision_criterion: >-
      Higher taurine intake in the cardiac-unaffected pedigrees would support
      dietary rescue as the explanation for variable penetrance.
  evidence:
  - reference: PMID:41343195
    reference_title: "Early-Onset Retinopathy in Patients With Variants in SLC6A6 Leading to Impaired Taurine Transport."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac structure was normal in all patients; however, short PR intervals were observed in all patients"
    explanation: Documents the absence of structural cardiomyopathy in a cohort with complete loss of transport.
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels."
    explanation: Documents the contrasting pedigree in which cardiomyopathy was present in childhood.
- discussion_id: slc6a6_mouse_multisystem_mismatch
  prompt: >-
    Does the multisystem phenotype of the Slc6a6-null mouse predict human
    disease, or does it represent an allelic and physiological state no patient
    occupies?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Skeletal Muscle Taurine Depletion
  rationale: >-
    The mouse null develops hearing loss, liver fibrosis, and behavioural, heart
    and skeletal-muscle abnormalities in addition to retinal degeneration. In the
    two human brothers with 95% loss of taurine uptake, skeletal-muscle and brain
    taurine were severely reduced yet no extraocular dysfunction was detectable —
    only a subclinical oxidative-stress marker. Two explanations have different
    consequences for surveillance: either the human extraocular phenotypes are
    late and will appear with age (in which case the mouse is a valid predictor
    and lifelong multisystem monitoring is indicated), or humans are protected by
    dietary taurine and residual biosynthesis in a way mice on standard chow are
    not (in which case the mouse overstates human risk). The original report
    chose the cautious reading and recommended continuous broad surveillance.
  proposed_experiments:
  - experiment_id: exp_slc6a6_adult_multisystem_survey
    name: Multisystem assessment of adult SLC6A6-deficient patients
    description: >-
      Systematic audiological, hepatic and neuromuscular assessment of adult
      SLC6A6-deficient patients, to test whether the murine extraocular
      phenotypes emerge with age in humans.
    decision_criterion: >-
      Detection of hearing loss, hepatic fibrosis or myopathy in adults would
      validate the mouse as predictive; their absence in adulthood would
      establish a species-restricted phenotype.
  - experiment_id: exp_slc6a6_species_taurine_supply
    name: Cross-species comparison of taurine supply
    description: >-
      Compare dietary taurine intake and endogenous taurine biosynthetic flux
      between mouse and human, to test the dietary and biosynthetic protection
      hypothesis for the species difference.
    decision_criterion: >-
      Substantially greater human dietary or biosynthetic taurine supply would
      explain the milder human extraocular phenotype without invoking a
      different mechanism.
  evidence:
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Extraocular dysfunctions were not yet detected, but significantly increased urinary excretion of 8-oxo-7,8-dihydroguanosine indicated generally enhanced (yet clinically unapparent) oxidative stress and RNA oxidation, warranting continuous broad surveillance"
    explanation: States the human-mouse discrepancy and the surveillance recommendation that follows from it.
  - reference: PMID:31345061
    reference_title: "Biallelic mutation of human SLC6A6 encoding the taurine transporter TAUT is linked to early retinal degeneration."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "mice develop multisystemic dysfunctions (hearing loss; liver fibrosis; and behavioral, heart, and skeletal muscle abnormalities) later on"
    explanation: Enumerates the murine multisystem phenotypes whose human counterparts are unconfirmed.
- discussion_id: slc6a6_mitochondrial_arm_unvalidated
  prompt: >-
    Does SLC6A6-dependent mitochondrial taurine import contribute to the
    pathophysiology of inherited taurine transporter deficiency, and if so why
    does oral taurine help patients when exogenous taurine did not rescue
    SLC6A6-deficient cells?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Impaired Mitochondrial Taurine Import and mt-tRNA Modification
  rationale: >-
    The mitochondrial-import function of SLC6A6 was established in cancer cell
    lines, where the transporter — and not extracellular taurine — was the
    requirement for mitochondrial translation. If that holds in patient tissue,
    then raising extracellular taurine should not correct the mitochondrial arm,
    and the clinical benefit of supplementation would be confined to the
    plasma-membrane-dependent, osmotic and antioxidant functions. Yet oral
    taurine reversed cardiomyopathy in the index family, where cardiac muscle is
    among the most mitochondria-dependent tissues affected. Either the
    mitochondrial arm is not rate-limiting in the inherited disease, or the
    residual transport of a hypomorphic allele is sufficient to serve the
    mitochondrial pool once extracellular taurine is high. Distinguishing these
    determines whether a subset of patients — particularly those with truncating
    alleles — would be predicted not to respond to supplementation.
  proposed_experiments:
  - experiment_id: exp_slc6a6_mito_taurine_patient_fibroblasts
    name: Mitochondrial taurine and mt-tRNA modification in patient fibroblasts
    description: >-
      Assay mitochondrial taurine content, mitochondrial tRNA taurine
      modification, and mitochondrial translation in patient-derived fibroblasts
      carrying truncating versus hypomorphic SLC6A6 alleles, with and without
      taurine loading.
    decision_criterion: >-
      Reduced mitochondrial taurine and mt-tRNA modification in patient cells
      would establish the mitochondrial arm in the inherited disease; normal
      values would confine it to the cancer context.
  - experiment_id: exp_slc6a6_mito_rescue_by_taurine_loading
    name: Substrate-correctability of the mitochondrial arm
    description: >-
      Measure respiratory-chain function and mitochondrial translation products
      in patient fibroblasts before and after taurine supplementation, to test
      whether the mitochondrial arm is substrate-correctable in the inherited
      disease.
    decision_criterion: >-
      Restoration of mitochondrial translation by taurine loading would
      reconcile the clinical response with the cell-line result; failure to
      restore would predict non-responders among truncating-allele patients.
  evidence:
  - reference: PMID:41652173
    reference_title: "SLC6A6 imports taurine into mitochondria to sustain mitochondrial translation and tumour growth."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here we show that SLC6A6, but not exogenous taurine, is essential for mitochondrial metabolism and cancer cell growth."
    explanation: The finding that extracellular taurine cannot substitute for the transporter is what creates the tension with clinical supplementation response.
  - reference: PMID:31903486
    reference_title: "Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "after 24-months, the cardiomyopathy was corrected in both affected siblings"
    explanation: The clinical response to supplementation that the in vitro result does not predict.
notes: >-
  Curated as an increment of IEMbase metabolic package WP-004 (issue #5559), row
  1.11.13.01 "SLC6A6-related Taurine transporter deficiency".

  Identity check performed before curation: MONDO:0007777 carries RO:0004003
  HGNC:11052 (SLC6A6) and xref OMIM:145350, matching the causal gene named in
  every cited human report. Note that the IEMbase seed row cites OMIM 186854,
  which is the SLC6A6 gene entry rather than the disease entry — the disease MIM
  is 145350.

  Claims deliberately NOT curated, so a future curator does not re-add them:

  - No hearing loss, liver fibrosis or behavioural phenotype is curated as a
    human phenotype. These are Slc6a6-null mouse findings; the human reports
    state that extraocular dysfunction was not detected. They are represented
    only inside the HUMAN_MODEL_MISMATCH discussion.
  - No dilated cardiomyopathy HP term is used. The dilated/atrophic
    characterization comes from the rodent literature; the human reports say
    "cardiomyopathy" without a structural subtype, so the generic HP:0001638 is
    used.
  - No taurine reference range is curated. The 2026 series reports differences
    in means between groups rather than a reference interval, and no
    LOINC-coded interval for plasma taurine was verified.
  - The SLC6A6 cancer literature (breast, cholangiocarcinoma, colon; PROTAC
    degraders; Mendelian-randomization associations) is out of scope for this
    entry. Only the mitochondrial-transport mechanism paper is cited, and only
    as an EMERGING hypothesis with IN_VITRO evidence.
  - The "Photoreceptor Degeneration and Outer Retinal Thinning" node does NOT
    declare conforms_to photoreceptor_degeneration#Secondary Cone Degeneration
    and Outer Retinal Thinning, and the anchor should not be re-added. That
    module node defines cone loss as non-cell-autonomous and consequent on rods
    having already been largely eliminated, in a disease whose mutation is "not
    expressed in cones". Neither holds here: scotopic AND photopic ERGs are
    severely depressed from presentation (the LCA/EORD pattern), so cone
    involvement is concurrent rather than secondary, and SLC6A6 loss is systemic
    so cones carry the lesion themselves. The entry correspondingly does not
    conform to the module's #Rod Photoreceptor Apoptosis node either. Retinal
    conformance is asserted only at #Photoreceptor Metabolic and Oxidative
    Stress and #Progressive Visual Field Loss and Blindness, which are
    mechanism-neutral as to which photoreceptor class fails first.

  - No finer retinal descriptors are curated beyond the six retinal phenotypes
    above. The deep-research artifact surfaces macular atrophy (HP:0007401),
    clumped pigmentary retinal degeneration, nyctalopia (HP:0000662),
    strabismus and a colour-vision defect. All are expected components of the
    curated HP:0000510 rod-cone dystrophy / HP:0000546 retinal degeneration
    pair, and the artifact reports them either as individual-patient findings
    (macular atrophy with clumped pigmentation progressing between ages 11 and
    18 in one patient) or as an unquantified symptom list. They are omitted for
    want of a frequency band that could be honestly justified, not because they
    were missed.
  - Taurine's roles in intracellular calcium handling and in
    proteostasis/apoptosis regulation are not modeled as pathophysiology nodes.
    The deep-research artifact cites them only to a review and to a
    non-peer-reviewed preprint, neither of which measures them in
    SLC6A6-deficient human tissue, so they do not meet the evidence bar for a
    causal node here.

  Correction to an earlier draft of this entry: it claimed HPO had no term for
  short PR interval and flagged an ontology gap warranting a new-term request.
  That was wrong — HP:0005165 "Shortened PR interval" exists, is inside the
  PhenotypeTerm enum root, and is already used in Pompe_Disease.yaml. The
  finding is now curated as a phenotype and no NTR is warranted.

📚

References & Deep Research

Deep Research

1

Falcon ▸

Taurine Transporter Deficiency: Comprehensive Disease-Characteristics Report

Edison Scientific Literature 25 citations 2026-08-20T01:11:55.035774

Taurine Transporter Deficiency: Comprehensive Disease-Characteristics Report

Executive summary

Taurine transporter deficiency is an exceptionally rare autosomal-recessive disorder caused by biallelic pathogenic variants in SLC6A6, which encodes the sodium/chloride-dependent taurine transporter TauT. Its most reproducible human manifestation is congenital or early-childhood retinal dystrophy; cardiomyopathy is clinically important but variably expressed. Affected patients have markedly reduced plasma taurine and severely impaired cellular taurine uptake. The only reported disease-directed treatment is oral taurine supplementation. In two siblings with a hypomorphic allele, 100 mg/kg/day normalized blood taurine, reversed systolic cardiomyopathy after 24 months, and stabilized retinal disease in the younger child. These results are promising but remain case-level evidence, not evidence from a controlled trial. (ansar2020taurinetreatmentof pages 1-2, ullah2026earlyonsetretinopathyin pages 1-2)

The human evidence base is extremely small: the original report comprised two siblings, while the latest multicenter study—conducted during 2019–2025 and published online December 4, 2025—added seven affected individuals from four families. No disease-specific primary human publication from 2023–2024 was identified; recent 2023–2024 literature primarily advances broader understanding of taurine biology rather than this Mendelian condition itself. (ullah2026earlyonsetretinopathyin pages 1-2)

domain	best-supported finding	evidence type/strength	suggested ontology terms
Disease / gene / inheritance	Taurine transporter deficiency is a Mendelian disorder caused by biallelic loss-of-function or severe hypomorphic variants in SLC6A6 (TauT), with autosomal recessive segregation in all reported families. Human evidence currently includes 2 affected siblings in one consanguineous family and 7 affected individuals from 4 unrelated families. (ansar2020taurinetreatmentof pages 1-2, ullah2026earlyonsetretinopathyin pages 1-2)	Direct human genetic and clinical evidence; strongest available but based on very small case series	SLC6A6; taurine transporter deficiency; autosomal recessive inheritance; MONDO term label if added in future
Retinal phenotype	Core phenotype is early-onset retinal degeneration spanning Leber congenital amaurosis / early-onset retinal dystrophy with poor vision or nystagmus from birth or early childhood, extinguished or severely depressed ERG, macular atrophy, pigmentary degeneration, and photoreceptor loss on OCT. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 3-4, ullah2026earlyonsetretinopathyin pages 1-2)	Direct human clinical evidence; consistent across all known cases	HP: Nystagmus; HP: Visual impairment; HP: Night blindness; HP: Abnormal electroretinogram; HP: Macular atrophy; HP: Retinal degeneration; Leber congenital amaurosis; early-onset retinal dystrophy
Cardiac phenotype	Cardiomyopathy was prominent in the 2020 family, with mild hypokinetic cardiomyopathy, systolic dysfunction, and LV dilation; in the expanded cohort, a shared structural cardiomyopathy phenotype was not consistently present, though short PR intervals were recurrent and cardiology follow-up was advised. (ansar2020taurinetreatmentof pages 2-4, ansar2020taurinetreatmentof pages 4-5, ullah2026earlyonsetretinopathyin pages 3-4, ullah2026earlyonsetretinopathyin pages 7-8)	Direct human evidence; variable expressivity, small numbers	HP: Cardiomyopathy; HP: Left ventricular dilatation; HP: Systolic dysfunction; HP: Short PR interval; cardiovascular system
Biochemical marker	Fasting plasma taurine is markedly reduced in affected individuals; the index family had nearly undetectable levels (6–7 μmol/L), and the multicenter cohort showed significantly lower taurine versus carriers and controls. (ansar2020taurinetreatmentof pages 1-2, ullah2026earlyonsetretinopathyin pages 1-2)	Direct human biochemical evidence; strong disease biomarker	taurine (CHEBI:15891); HP: Abnormal circulating amino acid concentration; low plasma taurine
Pathogenic variants	Reported disease-associated variants include NM_003043.5:c.1196G>T p.(Gly399Val) with ~15% residual transport, NM_003043.6:c.746C>T p.(Thr249Ile), c.880G>A p.(Ala294Thr), c.1210-2389_1348-331del p.(Phe404_Glu449del), and c.338G>A p.(Trp113Ter). Missense variants showed severe to complete transport loss; truncating/deletion alleles support loss of function. (ansar2020taurinetreatmentof pages 1-2, ullah2026earlyonsetretinopathyin pages 5-6, ullah2026earlyonsetretinopathyin pages 3-4, ullah2026earlyonsetretinopathyin pages 1-2)	Direct human molecular evidence with functional validation for key alleles	SLC6A6 missense variant; nonsense variant; exon deletion; loss of function; hypomorphic allele
Diagnosis	Best-supported diagnostic approach is molecular testing of SLC6A6 in patients with LCA/EORD plus fasting plasma taurine measurement, retinal phenotyping (visual acuity, full-field ERG, multimodal imaging/OCT), and where possible functional transport or membrane-trafficking assays in HEK-293 cells or patient fibroblasts. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 1-2)	Direct human evidence; practical but not yet standardized by guidelines	whole-exome sequencing; genome sequencing; Sanger confirmation; electroretinography; optical coherence tomography; plasma taurine assay
Treatment	Oral taurine supplementation is the only disease-directed intervention reported. In the index family, 100 mg/kg/day normalized blood taurine, reversed systolic cardiomyopathy after 24 months, and arrested retinal degeneration with clinical visual improvement in the younger child; a later retinal-only case normalized plasma taurine on 1–2 g/day but had no short-term ophthalmic improvement. No side effects were reported in the treated family. (ansar2020taurinetreatmentof pages 1-2, ansar2020taurinetreatmentof pages 4-5, ullah2026earlyonsetretinopathyin pages 4-5)	Direct human therapeutic evidence; promising but limited to anecdotal/case evidence	taurine supplementation; oral administration; NCIT term label: Dietary Supplementation; investigational therapy
Mechanism / pathophysiology	Disease mechanism is impaired TauT-mediated taurine uptake from biallelic SLC6A6 dysfunction, causing cellular taurine deficiency. Human functional work shows markedly reduced or absent transport; modeling places pathogenic residues in transmembrane regions important for ligand recognition, folding, trafficking, and transport cycling. Review/model literature supports downstream osmotic, mitochondrial, oxidative-stress, calcium-handling, and anti-apoptotic defects. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 5-6, baliou2020significanceoftaurine pages 4-6, baliou2020significanceoftaurine pages 8-9)	Mixed evidence: direct human functional evidence for transport loss; broader downstream mechanisms mainly model/review inference	sodium/chloride-dependent taurine transport; plasma membrane; mitochondrial dysfunction; oxidative stress; apoptosis; osmoregulation
Affected anatomy / cells	Highest-confidence affected structures are retina and heart. Within retina, human OCT/ERG data and model literature support major involvement of photoreceptors; retinal ganglion cell vulnerability is supported mainly by depletion models. Cardiac myocytes are implicated by the cardiomyopathy phenotype. (ansar2020taurinetreatmentof pages 2-4, ansar2020taurinetreatmentof pages 4-5, surai2021taurineasa pages 3-5)	Retina/heart: direct human evidence; specific cell-type detail partly inferred from models	UBERON: retina; UBERON: heart; photoreceptor cell; retinal ganglion cell; cardiomyocyte
Animal models	Slc6a6/TauT knockout mice develop retinal degeneration, cardiomyopathy/cardiac atrophy, skeletal muscle abnormalities, reproductive defects, and age-related multi-organ manifestations; chemically induced taurine depletion also causes photoreceptor and retinal ganglion cell loss. Taurine-deficient cats and dogs provide natural/comparative evidence for retinal degeneration and reversible cardiomyopathy. (ansar2020taurinetreatmentof pages 4-5, baliou2020significanceoftaurine pages 6-7, baliou2020significanceoftaurine pages 7-8, ullah2026earlyonsetretinopathyin pages 9-9)	Model and veterinary evidence; strong biologic support but indirect for human disease spectrum	knockout mouse model; taurine depletion model; retinal degeneration; dilated cardiomyopathy
Epidemiology / gaps	Prevalence, incidence, carrier frequency, penetrance, genotype-phenotype correlations, long-term natural history, and formal management guidelines are not established. No disease-specific registered interventional trial was identified in the tool search; current evidence remains based on rare case reports/series. (ullah2026earlyonsetretinopathyin pages 1-2, ullah2026earlyonsetretinopathyin pages 7-8)	Evidence gap / absence of data	rare disease; unknown prevalence; unknown penetrance; research gap
Recent developments	The key recent advance is the expanded multicenter cohort published online in 2025 showing 7 affected individuals from 4 families, broader allelic heterogeneity, consistent retinal phenotype, and functional confirmation of complete taurine transport loss for missense variants. No disease-specific 2023–2024 primary human expansion was identified in the retrieved evidence. (ullah2026earlyonsetretinopathyin pages 1-2, ullah2026earlyonsetretinopathyin pages 5-6)	Direct human evidence for 2025 expansion; explicit 2023–2024 evidence gap	cohort expansion; variant spectrum; functional validation

Table: This table summarizes the best-supported knowledge for SLC6A6-related taurine transporter deficiency across clinical, molecular, mechanistic, and translational domains. It is designed for knowledge-base use and clearly separates direct human evidence from model-based inference and current evidence gaps.

1. Disease information

Definition and scope

Taurine transporter deficiency is a Mendelian membrane-transport disorder in which deficient TauT activity prevents normal cellular accumulation of taurine. The clinical spectrum currently includes SLC6A6-related Leber congenital amaurosis/early-onset retinal dystrophy (LCA/EORD) and, in some patients, hypokinetic or dilated cardiomyopathy. The name should not be applied to acquired low-taurine states caused by diet, prematurity, parenteral nutrition, drugs, or unrelated systemic disease.

Names and identifiers

Preferred names: taurine transporter deficiency; SLC6A6-related taurine transporter deficiency.
Phenotypic names: SLC6A6-related early-onset retinal dystrophy, SLC6A6-related Leber congenital amaurosis, and SLC6A6 retinopathy with cardiomyopathy.
Gene: SLC6A6, approved name solute carrier family 6 member 6; protein TauT; Ensembl ENSG00000131389. (OpenTargets Search: taurine transporter deficiency-SLC6A6)
Gene OMIM/MIM: 186854, as stated in the index report. (ansar2020taurinetreatmentof pages 1-2)
Disease OMIM, Orphanet, MONDO, MeSH, ICD-10, and ICD-11: a confidently disease-specific identifier was not established in the retrieved authoritative evidence. The condition may presently be represented under broader inherited retinal dystrophy or cardiomyopathy concepts. A dedicated MONDO assignment should not be inferred from similarly named taurine or amino-acid disorders.

The evidence is aggregated from published family studies, clinical examinations, molecular assays, and disease-level literature—not EHR-derived population data.

2. Etiology, risk, and protective factors

Primary cause

The cause is germline biallelic SLC6A6 dysfunction. Reported disease alleles are severe loss-of-function or hypomorphic variants that reduce transporter activity, surface trafficking, or cycling. Unaffected heterozygous relatives retained sufficient transport and did not exhibit the retinal phenotype, supporting recessive inheritance and absence of clinically important haploinsufficiency in the observed families. (ullah2026earlyonsetretinopathyin pages 7-8, ullah2026earlyonsetretinopathyin pages 1-2)

Genetic risk factors

Established risk factors are:

Two pathogenic SLC6A6 alleles in trans or homozygously;
parental consanguinity or shared ancestry, which increases homozygosity risk;
an affected sibling in an autosomal-recessive family.

The index Pakistani family and several subsequently reported families were consanguineous. No susceptibility loci, modifier genes, digenic interactions, founder allele, or germline mosaicism have been demonstrated. (ansar2020taurinetreatmentof pages 4-5, ullah2026earlyonsetretinopathyin pages 3-4)

Environmental and protective factors

No environmental exposure causes the inherited disorder. Because taurine is obtained from endogenous synthesis and animal-derived foods, dietary supply could plausibly influence residual tissue availability, but no human gene–diet interaction has been quantified. Normal diet did not prevent disease in individuals with severe transporter dysfunction.

Oral taurine is the only demonstrated potentially protective intervention after diagnosis. Benefit appears greatest when residual transport remains and treatment begins before irreversible photoreceptor loss. This is a mechanistic and case-based inference, not a validated prevention guideline. The elder sibling who had already lost vision by age eight did not recover vision, whereas the younger sibling retained central photoreceptors and stabilized after treatment. (ansar2020taurinetreatmentof pages 4-5, ansar2020taurinetreatmentof pages 2-4)

Smoking, alcohol, exercise, toxins, infections, sex, and occupational exposures have no established disease-specific effect. There are no known genetically protective variants.

3. Phenotypes

Ocular phenotype

The core phenotype is severe, bilateral, progressive retinal degeneration.

Onset: birth to early childhood. Four individuals in one family had visual impairment and nystagmus from birth; another developed night blindness at one to two years. (ullah2026earlyonsetretinopathyin pages 3-4)
Symptoms/signs: poor vision, nystagmus, night blindness, progressive daytime and color-vision loss, strabismus, and eventual blindness.
Electrophysiology: severely reduced or extinguished scotopic and photopic ERGs; multifocal ERG may retain only minimal central responses early in disease. (ullah2026earlyonsetretinopathyin pages 3-4, ansar2020taurinetreatmentof pages 2-4)
Imaging: attenuated retinal vessels, macular atrophy, pigmentary or salt-and-pepper degeneration, photoreceptor/outer nuclear layer loss, and a residual central island on OCT. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 4-5)
Severity/course: variable but commonly severe and progressive. In the index family, the older male had only light perception at 15 years and had complete visual loss by age eight; the younger child retained central photoreceptors. A separate patient demonstrated progression of macular atrophy and clumped pigmentation between ages 11 and 18. (ansar2020taurinetreatmentof pages 4-5, ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 3-4)
Frequency: retinal dystrophy was present in all seven affected individuals in the expanded cohort and both affected siblings in the index family, making it the most penetrant recognized manifestation. (ullah2026earlyonsetretinopathyin pages 1-2)

Suggested HPO terms: Retinal degeneration, Leber congenital amaurosis, Visual impairment, Blindness, Nystagmus, Nyctalopia, Abnormal electroretinogram, Macular atrophy, Photoreceptor degeneration, Pigmentary retinal degeneration, Strabismus, and Color vision defect.

Cardiac phenotype

The index siblings had mild hypokinetic cardiomyopathy with systolic dysfunction, left-ventricular systolic dilation, and fractional shortening of 24–27%. Exercise testing was normal. After treatment, fractional shortening normalized to 32% in both. (ansar2020taurinetreatmentof pages 2-4)

Cardiac expression is variable. In the later cohort, cardiac structure and systolic function were generally preserved. Short PR intervals were observed in one family; one proband met ECG voltage criteria for left-ventricular hypertrophy with mild repolarization abnormalities, but echocardiography did not confirm hypertrophy. Other reported ejection fractions were 56%, 60%, and 65%. (ullah2026earlyonsetretinopathyin pages 3-4, ullah2026earlyonsetretinopathyin pages 4-5)

Suggested HPO terms: Cardiomyopathy, Dilated cardiomyopathy, Left ventricular dilatation, Abnormal left ventricular systolic function, Short PR interval, and Abnormal ECG.

Other findings

Mild intellectual disability, motor-coordination dysfunction, facial dysmorphism, and oculomotor abnormalities occurred in isolated patients, but substantial autozygosity and possible additional recessive defects make attribution to SLC6A6 uncertain. One child had IQ 62. Brain MRI and hepatic ultrasound were normal in the index siblings. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 5-6, ullah2026earlyonsetretinopathyin pages 4-5)

No disease-specific validated quality-of-life instrument has been used. Severe childhood visual impairment would predict major effects on mobility, education, independence, and psychosocial well-being, while cardiomyopathy adds exercise and medical-monitoring burdens; these impacts have not been quantified with EQ-5D, SF-36, or PROMIS.

4. Genetic and molecular information

Gene and protein

SLC6A6 encodes a plasma-membrane, high-affinity, sodium- and chloride-dependent transporter belonging to the SLC6/GABA-transporter family. TauT is predicted to have 12 transmembrane helices. It concentrates taurine intracellularly against a steep gradient, especially in retina, myocardium, skeletal muscle, brain, kidney, and leukocytes. (surai2021taurineasa pages 3-5, yadav2025thetaurinetautaxis pages 5-7)

Reported pathogenic variants

NM_003043.5:c.1196G>T, p.(Gly399Val): homozygous hypomorphic missense allele; approximately 15% residual transport. Modeling predicts displacement of Tyr138, a ligand-recognition/transport residue. Reduced transport arose predominantly from impaired transporter cycling rather than reduced surface abundance. (ansar2020taurinetreatmentof pages 2-4, ansar2020taurinetreatmentof pages 1-2)
NM_003043.6:c.746C>T, p.(Thr249Ile): homozygous missense allele in TM5; absent from gnomAD v4.1 and GME in the study; classified likely pathogenic. (ullah2026earlyonsetretinopathyin pages 5-6)
NM_003043.6:c.880G>A, p.(Ala294Thr): homozygous pathogenic missense allele in TM6; gnomAD frequency 5.45 × 10⁻⁵, with no homozygotes reported. It caused a 94% reduction in surface expression in the transfected system, 99% reduction in transport in patient fibroblasts, and 76% lower fibroblast surface expression, consistent with misfolding and trafficking failure. (ullah2026earlyonsetretinopathyin pages 5-6)
NM_003043.6:c.1210-2389_1348-331del, p.(Phe404_Glu449del): homozygous 3,320-bp deletion affecting exon 11 and a transmembrane segment. (ullah2026earlyonsetretinopathyin pages 5-6, ullah2026earlyonsetretinopathyin pages 3-4)
NM_003043.6:c.338G>A, p.(Trp113Ter): homozygous truncating nonsense allele. (ullah2026earlyonsetretinopathyin pages 3-4)

All reported disease variants are germline. No somatic mechanism, dominant-negative effect, gain of function, repeat expansion, or recurrent chromosomal abnormality is established. No validated modifier genes or disease-specific epigenetic signature is known.

5. Environmental information

No toxin, radiation exposure, infection, smoking behavior, or occupational factor is known to initiate this genetic disease. Chemically induced taurine depletion in animals—using the competitive transporter inhibitor guanidinoethane sulfonate or high β-alanine exposure—can reproduce retinal injury and illustrates biological vulnerability, but it is not evidence of a common human environmental cause. (ansar2020taurinetreatmentof pages 4-5)

A taurine-poor diet might worsen systemic deficiency where transport is residual, but this remains untested. Conversely, dietary taurine alone may be inadequate when TauT function is absent. Vaccination, antimicrobial prophylaxis, and pollution control are not disease-specific interventions.

6. Mechanism and pathophysiology

Upstream causal chain

Biallelic SLC6A6 variant → reduced TauT abundance or transport cycling → impaired Na⁺/Cl⁻-coupled cellular taurine uptake → very low plasma/tissue taurine → failure of high-taurine tissues, particularly retina and heart → photoreceptor degeneration and variable cardiomyopathy.

The human mechanistic link is strong: p.Gly399Val retained approximately 15% transport, while p.Ala294Thr and other severe missense alleles showed near-complete or complete transport loss. Plasma taurine in the index family was only 6–7 μmol/L. (ansar2020taurinetreatmentof pages 1-2, ullah2026earlyonsetretinopathyin pages 5-6, ullah2026earlyonsetretinopathyin pages 1-2)

Downstream mechanisms

The following downstream processes are biologically plausible and well supported in models, but are not all directly measured in patient tissues:

Mitochondrial dysfunction. Taurine contributes to mitochondrial tRNA uridine modification and accurate translation of respiratory-chain proteins. Deficiency impairs complex I/NADH dehydrogenase function, ATP synthesis, and fatty-acid oxidation while increasing NADH, acetylcarnitine, and superoxide. (baliou2020significanceoftaurine pages 7-8, baliou2020significanceoftaurine pages 8-9)
Oxidative stress. High-taurine tissues lose antioxidant and membrane-stabilizing support. TauT-null hearts generate more mitochondrial ROS; retinal depletion causes oxidative injury, glial activation, synaptic loss, and photoreceptor damage. (surai2021taurineasa pages 3-5)
Osmoregulation and cell-volume control. Taurine acts as an organic osmolyte, with TauT regulation involving NFAT5/TonEBP and osmotic signaling. (baliou2020significanceoftaurine pages 7-8, baliou2020significanceoftaurine pages 8-9)
Calcium handling and excitability. Taurine modulates ion channels, calcium homeostasis, neuronal activity, and myocardial contractility; disruption may contribute to retinal signaling and cardiac dysfunction. (yadav2025thetaurinetautaxis pages 5-7)
Proteostasis and cell death. Deficiency increases unfolded-protein responses and protein aggregation and reduces anti-apoptotic protection. Photoreceptor apoptosis is prominent in knockout models. (baliou2020significanceoftaurine pages 6-7, baliou2020significanceoftaurine pages 7-8)

Suggested GO terms include taurine transport, transmembrane transport, sodium ion transmembrane transport, chloride transmembrane transport, cellular osmoregulation, mitochondrial translation, oxidative phosphorylation, response to oxidative stress, regulation of calcium ion homeostasis, photoreceptor cell maintenance, and apoptotic process. Suggested cellular component terms are plasma membrane, integral component of plasma membrane, mitochondrion, and mitochondrial respiratory-chain complex I.

No disease-specific human single-cell, spatial-transcriptomic, proteomic, lipidomic, epigenomic, CRISPR-screen, or multi-omic study was identified.

7. Anatomical structures affected

Primary organs

Retina: strongest and most consistent evidence. Suggested UBERON term: retina.
Heart/myocardium: directly affected in some patients. Suggested UBERON terms: heart, myocardium, left ventricle.

Tissues and cells

Photoreceptors—both cone and rod systems—are strongly implicated by OCT and ERG.
Retinal ganglion cells and retinal pigment epithelium are vulnerable in depletion models, but their contribution to the human phenotype is less directly established.
Cardiomyocytes are implicated by systolic cardiomyopathy.

Suggested Cell Ontology labels: photoreceptor cell, rod photoreceptor cell, cone photoreceptor cell, retinal ganglion cell, retinal pigment epithelial cell, and cardiac muscle cell/cardiomyocyte.

Disease is bilateral in the eyes. Cardiac involvement is systemic rather than lateralized. Model organisms suggest possible skeletal-muscle, liver, kidney, brain, auditory, olfactory, reproductive, and immune involvement, but these are not yet established components of the human disorder. (baliou2020significanceoftaurine pages 6-7, baliou2020significanceoftaurine pages 7-8)

8. Temporal development

Onset is congenital or pediatric and usually insidious/progressive. LCA-like disease presents at birth or within the first six months, whereas EORD becomes evident after infancy but before age five. Visual deterioration can continue through childhood and adolescence, progressing from night blindness and nystagmus to macular atrophy and profound visual loss. (ullah2026earlyonsetretinopathyin pages 1-2)

Cardiomyopathy may be childhood-onset but could also be age dependent. Current numbers are insufficient to define stages or progression rates. The disease is lifelong; spontaneous remission has not been reported.

The likely therapeutic window is before irreversible photoreceptor loss and myocardial remodeling. Stabilization rather than regeneration is a realistic retinal goal. Treatment-induced cardiac recovery appears more feasible, as demonstrated by complete normalization in two children after 24 months. (ansar2020taurinetreatmentof pages 4-5)

9. Inheritance and population

Inheritance is autosomal recessive. All affected individuals in the expanded cohort were homozygous, while available unaffected relatives were heterozygous carriers. Both sexes are affected. (ullah2026earlyonsetretinopathyin pages 1-2)

Prevalence, incidence, carrier frequency, penetrance, and sex ratio are unknown. The published patients originated from Pakistani, Italian, Egyptian/US, French, and Turkish-associated families, arguing against restriction to one population. Consanguinity was common but is not required. No founder effect has been demonstrated. (ullah2026earlyonsetretinopathyin pages 1-2, ullah2026earlyonsetretinopathyin pages 3-4, ullah2026earlyonsetretinopathyin pages 4-5)

Retinal penetrance appears high among known biallelic cases, but ascertainment through ophthalmic cohorts creates substantial bias. Cardiac expressivity is clearly variable. Genetic anticipation is not expected and has not been observed.

For two carrier parents, each pregnancy has the standard recessive probabilities: 25% affected, 50% carrier, and 25% unaffected/non-carrier, assuming both variants are fully pathogenic and no unusual reproductive mechanism.

10. Diagnostics

Recommended clinical approach

Recognize the phenotype: congenital/early childhood bilateral retinal dystrophy, particularly with low taurine or cardiomyopathy.
Ophthalmic assessment: visual acuity, refraction, fundus examination, full-field ERG, OCT, fundus autofluorescence, and widefield imaging. Full-field stimulus testing may be useful where visual acuity is extremely poor. (ullah2026earlyonsetretinopathyin pages 4-5, ullah2026earlyonsetretinopathyin pages 1-2)
Biochemistry: fasting quantitative plasma amino acids with specific taurine measurement. Values of 6–7 μmol/L were seen in the index family; one later patient had 5 nmol/mL, rising to 29 nmol/mL on therapy against a stated age-adjusted range of 21–123 nmol/mL. (ansar2020taurinetreatmentof pages 1-2, ullah2026earlyonsetretinopathyin pages 4-5)
Cardiac assessment: ECG, echocardiography with EF and fractional shortening, and periodic surveillance even if baseline imaging is normal.
Molecular confirmation: inherited-retinal-disease panel including SLC6A6, WES, or WGS; confirm and phase variants by Sanger/family testing. WGS may be preferable when WES is negative because it can identify exon-level or intronic structural deletions.
Functional confirmation where needed: radiolabeled taurine uptake and surface-biotinylation/trafficking assays in patient fibroblasts or transfected cells. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 5-6)

Chromosomal microarray, karyotyping, FISH, mitochondrial DNA testing, and repeat-expansion testing are not first-line unless the broader phenotype suggests another disorder. CMA could detect a large deletion but will miss most single-nucleotide alleles.

Differential diagnosis

The principal differential is genetically heterogeneous LCA/EORD, including RPE65-, CEP290-, GUCY2D-, CRB1-, AIPL1-, and other IRD-related disease. Distinguishing clues for SLC6A6 deficiency are markedly reduced plasma taurine, cardiomyopathy or conduction findings, and biallelic SLC6A6 variants. Other considerations include nutritional/acquired taurine deficiency, mitochondrial disease, syndromic retinal dystrophies, and primary pediatric cardiomyopathy.

No consensus diagnostic criteria, newborn-screening program, or validated population cutoff for taurine transporter deficiency exists. A normal plasma taurine result should not automatically exclude a partial transporter defect, particularly after supplementation.

11. Outcome and prognosis

No survival curves, mortality rates, life-expectancy estimates, or formal disability statistics exist. Major morbidity is progressive visual disability. Untreated severe disease can lead to childhood blindness. Cardiac prognosis is uncertain but potentially modifiable.

Prognostic factors likely include:

residual TauT activity;
age at treatment;
remaining central photoreceptor structure;
baseline plasma taurine;
presence and severity of cardiomyopathy;
ability of supplementation to normalize circulating taurine.

These factors are biologically compelling but not validated in a prognostic model. The index family suggests that myocardium can recover and residual retina can stabilize, whereas established blindness is unlikely to reverse. No prognostic biomarker beyond plasma taurine, functional transport, and organ-specific testing has been validated. (ansar2020taurinetreatmentof pages 4-5, ansar2020taurinetreatmentof pages 2-4)

12. Treatment

Oral taurine supplementation

Taurine—2-aminoethanesulfonic acid, suggested CHEBI CHEBI:15891—is the only reported disease-directed therapy.

Index-family regimen: an oral loading dose of 100 mg/kg, followed by 100 mg/kg/day in three divided doses of approximately 33 mg/kg every eight hours. Blood taurine rose above 40 μmol/L. After 24 months, left-ventricular fractional shortening normalized from 24–27% to 32%; cardiomyopathy resolved in both siblings. The younger child's visual acuity reached 20/100 right eye and 20/160 left eye, with anatomical stability and preserved foveal photoreceptors. No adverse effects were reported. (ansar2020taurinetreatmentof pages 4-5, ansar2020taurinetreatmentof pages 2-4)

The authors’ abstract states: “Remarkably, after 24-months, the cardiomyopathy was corrected in both affected siblings, and in the 6-years-old, the retinal degeneration was arrested, and the vision was clinically improved.” (ansar2020taurinetreatmentof pages 1-2)

Later case: oral taurine began at 1 g/day and increased to 2 g/day. Plasma taurine rose from 5 to 12 and then 29 nmol/mL over 17 months, but ophthalmic examination and full-field stimulus testing remained essentially unchanged. This supports biochemical target engagement but not reversal of established retinal degeneration. (ullah2026earlyonsetretinopathyin pages 4-5)

Suggested NCIT intervention labels: Dietary Supplementation, Oral Therapy, Supportive Care, and Investigational Agent. Taurine treatment should presently be regarded as investigational and supervised by metabolic, ophthalmic, and cardiac specialists.

Supportive management

low-vision services, mobility training, educational accommodation, assistive technology, and occupational therapy;
routine cardiology surveillance and guideline-based heart-failure therapy if needed;
genetic counseling and cascade testing;
monitoring plasma taurine, renal/liver chemistry, ECG/echo, visual function, and retinal structure during supplementation.

There is no established gene therapy, CRISPR therapy, ASO, siRNA, cell therapy, surgery, or immunotherapy. No disease-specific registered interventional trial was identified. Evidence from general heart-failure studies must not be treated as proof for SLC6A6 deficiency.

13. Prevention

Primary prevention is genetic rather than behavioral. Options for an identified family include carrier testing, cascade testing, reproductive counseling, prenatal diagnosis, and preimplantation genetic testing for the known familial variants.

Secondary prevention centers on early recognition: measure plasma taurine and test SLC6A6 in unexplained LCA/EORD, especially when cardiomyopathy is present. Early supplementation could prevent additional tissue injury, but this remains unproven outside case reports.

Tertiary prevention includes continued taurine supplementation where clinically chosen, cardiac surveillance, retinal monitoring, and low-vision rehabilitation. There is no relevant vaccine, antimicrobial prophylaxis, or population screening program.

14. Other species and natural disease

Domestic cat, Felis catus (NCBI Taxonomy 9685): dietary taurine deficiency naturally causes retinal degeneration and dilated cardiomyopathy. Historical veterinary cardiomyopathy was reversible with taurine repletion, providing important comparative evidence. (ullah2026earlyonsetretinopathyin pages 9-9, ansar2020taurinetreatmentof pages 5-6)
Domestic dog, Canis lupus familiaris (NCBI Taxonomy 9615): taurine-deficiency-associated dilated cardiomyopathy occurs in susceptible animals and can improve after diet change and supplementation. (ansar2020taurinetreatmentof pages 5-6, ansar2020taurinetreatmentof pages 4-5)
No zoonotic transmission exists; the disorder is genetic/metabolic, not infectious.

These animal diseases phenocopy low-taurine physiology but are not necessarily caused by naturally occurring biallelic SLC6A6 variants. A breed-specific VBO annotation for SLC6A6 deficiency itself is therefore not justified from current evidence.

15. Model organisms

Mouse

Global Slc6a6/TauT knockout mice are the principal genetic model. They exhibit 95–100% taurine loss in cardiac and skeletal muscle and 74–96% loss in other tissues. Phenotypes include early photoreceptor apoptosis and vision loss; cardiomyopathy with myofibrillar fragmentation, mitochondrial disruption, and swelling; skeletal-muscle necrosis and myofilament disorganization; auditory/olfactory and synaptic abnormalities; impaired reproduction; and later liver inflammation, fibrosis, and tumors. (baliou2020significanceoftaurine pages 6-7)

Cardiac mitochondrial findings include impaired complex I activity and fatty-acid oxidation. Aged knockout mice develop sarcopenia and up to a tenfold increase in p16INK4A. Exercise endurance is severely impaired, with more than an 80% reduction in treadmill running distance in reported models. (baliou2020significanceoftaurine pages 7-8, surai2021taurineasa pages 3-5)

Strength: excellent construct validity for systemic taurine-transport loss and good face validity for retinal and cardiac disease. Limitations: global null mice have broader and more severe multi-organ disease than currently documented in humans; human alleles include hypomorphs; species-specific taurine synthesis and diet complicate translation.

Induced retinal-depletion models

Guanidinoethane sulfonate or β-alanine-mediated taurine depletion in rodents causes photoreceptor and retinal-ganglion-cell injury, oxidative stress, glial activation, synaptic loss, and increased susceptibility to light damage. These models are useful for testing supplementation timing and downstream neuroprotection but lack the exact human genotype. (ansar2020taurinetreatmentof pages 4-5)

Cellular models

HEK-293/HEK-derived cells expressing mutant TauT and patient-derived fibroblasts are established functional systems. They quantify radiolabeled taurine uptake, kinetic parameters, membrane abundance, protein folding, and trafficking. Patient fibroblasts showed approximately 99% transport loss for p.Ala294Thr, making them a practical personalized model for variant classification and therapy screening. (ansar2020taurinetreatmentof pages 2-4, ullah2026earlyonsetretinopathyin pages 5-6)

No disease-specific iPSC-retinal organoid, engineered cardiac tissue, zebrafish knockout, Drosophila, or humanized knock-in model was identified in the retrieved literature.

Recent developments and expert assessment

The principal recent advance is the expanded multicenter cohort published online on December 4, 2025 in JAMA Ophthalmology (DOI: 10.1001/jamaophthalmol.2025.4875). It expanded the allelic spectrum to TM5/TM6 missense, nonsense, and exon-deletion variants; established a consistent LCA/EORD phenotype across four unrelated families; quantified lower taurine against carriers and controls; and showed complete transport loss for key missense alleles. The authors concluded that affected patients “may be candidates for investigational oral taurine supplementation.” (ullah2026earlyonsetretinopathyin pages 1-2)

The foundational therapeutic report was published online December 31, 2019 and in Human Molecular Genetics volume 29 (2020), DOI: 10.1093/hmg/ddz303. Its treatment response is biologically persuasive because biochemical correction, cardiac normalization, and retinal stabilization were concordant, but expert interpretation must remain cautious: only two siblings were treated, there was no untreated comparator, and retinal improvement was age- and stage-dependent. (ansar2020taurinetreatmentof pages 4-5, ansar2020taurinetreatmentof pages 1-2)

The most defensible current management principle is therefore rapid molecular diagnosis plus early, monitored consideration of oral taurine, accompanied by formal retinal and cardiac outcome measurement. Multicenter natural-history studies, standardized taurine pharmacokinetics, genotype-stratified dosing, and prospective controlled trials are the highest priorities.

Major evidence gaps

No reliable prevalence, incidence, carrier-frequency, mortality, or life-expectancy estimate.
No formal OMIM disease number, Orphanet entry, MONDO identifier, ICD code, or MeSH heading was verified from the retrieved material.
No prospective natural-history cohort or randomized trial.
Uncertain penetrance and age dependence of cardiomyopathy.
No validated treatment threshold, target plasma level, duration, or long-term safety protocol.
No evidence that supplementation restores advanced retinal tissue.
No disease-specific newborn screening, clinical guideline, patient-reported outcome, multi-omic profile, or advanced therapeutic program.
Disease-specific 2023–2024 primary human literature was not identified; the decisive clinical expansion appeared online in late 2025.

References

(ansar2020taurinetreatmentof pages 1-2): Muhammad Ansar, Emmanuelle Ranza, Madhur Shetty, Sohail A Paracha, Maleeha Azam, Ilse Kern, Justyna Iwaszkiewicz, Omer Farooq, Constantin J Pournaras, Ariane Malcles, Mateusz Kecik, Carlo Rivolta, Waqar Muzaffar, Aziz Qurban, Liaqat Ali, Yacine Aggoun, Federico A Santoni, Periklis Makrythanasis, Jawad Ahmed, Raheel Qamar, Muhammad T Sarwar, L Keith Henry, and Stylianos E Antonarakis. Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with slc6a6 taurine transporter deficiency. Human molecular genetics, 29:618-623, Dec 2020. URL: https://doi.org/10.1093/hmg/ddz303, doi:10.1093/hmg/ddz303. This article has 75 citations and is from a domain leading peer-reviewed journal.
(ullah2026earlyonsetretinopathyin pages 1-2): Mukhtar Ullah, Atta Ur Rehman, Madhur Shetty, Michael D. Allen, Ehsan Ullah, Sabrina G. Signorini, Cyril Burin des Roziers, Rosalie M. Grijalva, Abdur Rashid, Asad Munir, Alessandra Pia Porretta, Enza Maria Valente, Aime R. Agather, Ioannis Dimopoulos, Robert B. Hufnagel, Edouard Malandain, Juliette Coursimault, Muhammad Ansar, Stylianos E. Antonarakis, Andrea Superti-Furga, Sanaullah Jan, Brian P. Brooks, Giacomo Calzetti, Bin Guan, Mathieu Quinodoz, L. Keith Henry, and Carlo Rivolta. Early-onset retinopathy in patients with variants in slc6a6 leading to impaired taurine transport. JAMA Ophthalmology, 144(1):70, Jan 2026. URL: https://doi.org/10.1001/jamaophthalmol.2025.4875, doi:10.1001/jamaophthalmol.2025.4875. This article has 2 citations and is from a highest quality peer-reviewed journal.
(ansar2020taurinetreatmentof pages 2-4): Muhammad Ansar, Emmanuelle Ranza, Madhur Shetty, Sohail A Paracha, Maleeha Azam, Ilse Kern, Justyna Iwaszkiewicz, Omer Farooq, Constantin J Pournaras, Ariane Malcles, Mateusz Kecik, Carlo Rivolta, Waqar Muzaffar, Aziz Qurban, Liaqat Ali, Yacine Aggoun, Federico A Santoni, Periklis Makrythanasis, Jawad Ahmed, Raheel Qamar, Muhammad T Sarwar, L Keith Henry, and Stylianos E Antonarakis. Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with slc6a6 taurine transporter deficiency. Human molecular genetics, 29:618-623, Dec 2020. URL: https://doi.org/10.1093/hmg/ddz303, doi:10.1093/hmg/ddz303. This article has 75 citations and is from a domain leading peer-reviewed journal.
(ullah2026earlyonsetretinopathyin pages 3-4): Mukhtar Ullah, Atta Ur Rehman, Madhur Shetty, Michael D. Allen, Ehsan Ullah, Sabrina G. Signorini, Cyril Burin des Roziers, Rosalie M. Grijalva, Abdur Rashid, Asad Munir, Alessandra Pia Porretta, Enza Maria Valente, Aime R. Agather, Ioannis Dimopoulos, Robert B. Hufnagel, Edouard Malandain, Juliette Coursimault, Muhammad Ansar, Stylianos E. Antonarakis, Andrea Superti-Furga, Sanaullah Jan, Brian P. Brooks, Giacomo Calzetti, Bin Guan, Mathieu Quinodoz, L. Keith Henry, and Carlo Rivolta. Early-onset retinopathy in patients with variants in slc6a6 leading to impaired taurine transport. JAMA Ophthalmology, 144(1):70, Jan 2026. URL: https://doi.org/10.1001/jamaophthalmol.2025.4875, doi:10.1001/jamaophthalmol.2025.4875. This article has 2 citations and is from a highest quality peer-reviewed journal.
(ansar2020taurinetreatmentof pages 4-5): Muhammad Ansar, Emmanuelle Ranza, Madhur Shetty, Sohail A Paracha, Maleeha Azam, Ilse Kern, Justyna Iwaszkiewicz, Omer Farooq, Constantin J Pournaras, Ariane Malcles, Mateusz Kecik, Carlo Rivolta, Waqar Muzaffar, Aziz Qurban, Liaqat Ali, Yacine Aggoun, Federico A Santoni, Periklis Makrythanasis, Jawad Ahmed, Raheel Qamar, Muhammad T Sarwar, L Keith Henry, and Stylianos E Antonarakis. Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with slc6a6 taurine transporter deficiency. Human molecular genetics, 29:618-623, Dec 2020. URL: https://doi.org/10.1093/hmg/ddz303, doi:10.1093/hmg/ddz303. This article has 75 citations and is from a domain leading peer-reviewed journal.
(ullah2026earlyonsetretinopathyin pages 7-8): Mukhtar Ullah, Atta Ur Rehman, Madhur Shetty, Michael D. Allen, Ehsan Ullah, Sabrina G. Signorini, Cyril Burin des Roziers, Rosalie M. Grijalva, Abdur Rashid, Asad Munir, Alessandra Pia Porretta, Enza Maria Valente, Aime R. Agather, Ioannis Dimopoulos, Robert B. Hufnagel, Edouard Malandain, Juliette Coursimault, Muhammad Ansar, Stylianos E. Antonarakis, Andrea Superti-Furga, Sanaullah Jan, Brian P. Brooks, Giacomo Calzetti, Bin Guan, Mathieu Quinodoz, L. Keith Henry, and Carlo Rivolta. Early-onset retinopathy in patients with variants in slc6a6 leading to impaired taurine transport. JAMA Ophthalmology, 144(1):70, Jan 2026. URL: https://doi.org/10.1001/jamaophthalmol.2025.4875, doi:10.1001/jamaophthalmol.2025.4875. This article has 2 citations and is from a highest quality peer-reviewed journal.
(ullah2026earlyonsetretinopathyin pages 5-6): Mukhtar Ullah, Atta Ur Rehman, Madhur Shetty, Michael D. Allen, Ehsan Ullah, Sabrina G. Signorini, Cyril Burin des Roziers, Rosalie M. Grijalva, Abdur Rashid, Asad Munir, Alessandra Pia Porretta, Enza Maria Valente, Aime R. Agather, Ioannis Dimopoulos, Robert B. Hufnagel, Edouard Malandain, Juliette Coursimault, Muhammad Ansar, Stylianos E. Antonarakis, Andrea Superti-Furga, Sanaullah Jan, Brian P. Brooks, Giacomo Calzetti, Bin Guan, Mathieu Quinodoz, L. Keith Henry, and Carlo Rivolta. Early-onset retinopathy in patients with variants in slc6a6 leading to impaired taurine transport. JAMA Ophthalmology, 144(1):70, Jan 2026. URL: https://doi.org/10.1001/jamaophthalmol.2025.4875, doi:10.1001/jamaophthalmol.2025.4875. This article has 2 citations and is from a highest quality peer-reviewed journal.
(ullah2026earlyonsetretinopathyin pages 4-5): Mukhtar Ullah, Atta Ur Rehman, Madhur Shetty, Michael D. Allen, Ehsan Ullah, Sabrina G. Signorini, Cyril Burin des Roziers, Rosalie M. Grijalva, Abdur Rashid, Asad Munir, Alessandra Pia Porretta, Enza Maria Valente, Aime R. Agather, Ioannis Dimopoulos, Robert B. Hufnagel, Edouard Malandain, Juliette Coursimault, Muhammad Ansar, Stylianos E. Antonarakis, Andrea Superti-Furga, Sanaullah Jan, Brian P. Brooks, Giacomo Calzetti, Bin Guan, Mathieu Quinodoz, L. Keith Henry, and Carlo Rivolta. Early-onset retinopathy in patients with variants in slc6a6 leading to impaired taurine transport. JAMA Ophthalmology, 144(1):70, Jan 2026. URL: https://doi.org/10.1001/jamaophthalmol.2025.4875, doi:10.1001/jamaophthalmol.2025.4875. This article has 2 citations and is from a highest quality peer-reviewed journal.
(baliou2020significanceoftaurine pages 4-6): Stella Baliou, Anthony Kyriakopoulos, Maria Goulielmaki, Michalis Panayiotidis, Demetrios Spandidos, and Vassilios Zoumpourlis. Significance of taurine transporter (taut) in homeostasis and its layers of regulation. Molecular Medicine Reports, 22:2163-2173, Jul 2020. URL: https://doi.org/10.3892/mmr.2020.11321, doi:10.3892/mmr.2020.11321. This article has 111 citations and is from a peer-reviewed journal.
(baliou2020significanceoftaurine pages 8-9): Stella Baliou, Anthony Kyriakopoulos, Maria Goulielmaki, Michalis Panayiotidis, Demetrios Spandidos, and Vassilios Zoumpourlis. Significance of taurine transporter (taut) in homeostasis and its layers of regulation. Molecular Medicine Reports, 22:2163-2173, Jul 2020. URL: https://doi.org/10.3892/mmr.2020.11321, doi:10.3892/mmr.2020.11321. This article has 111 citations and is from a peer-reviewed journal.
(surai2021taurineasa pages 3-5): Peter F. Surai, Katie Earle-Payne, and Michael T. Kidd. Taurine as a natural antioxidant: from direct antioxidant effects to protective action in various toxicological models. Antioxidants, 10:1876, Nov 2021. URL: https://doi.org/10.3390/antiox10121876, doi:10.3390/antiox10121876. This article has 219 citations.
(baliou2020significanceoftaurine pages 6-7): Stella Baliou, Anthony Kyriakopoulos, Maria Goulielmaki, Michalis Panayiotidis, Demetrios Spandidos, and Vassilios Zoumpourlis. Significance of taurine transporter (taut) in homeostasis and its layers of regulation. Molecular Medicine Reports, 22:2163-2173, Jul 2020. URL: https://doi.org/10.3892/mmr.2020.11321, doi:10.3892/mmr.2020.11321. This article has 111 citations and is from a peer-reviewed journal.
(baliou2020significanceoftaurine pages 7-8): Stella Baliou, Anthony Kyriakopoulos, Maria Goulielmaki, Michalis Panayiotidis, Demetrios Spandidos, and Vassilios Zoumpourlis. Significance of taurine transporter (taut) in homeostasis and its layers of regulation. Molecular Medicine Reports, 22:2163-2173, Jul 2020. URL: https://doi.org/10.3892/mmr.2020.11321, doi:10.3892/mmr.2020.11321. This article has 111 citations and is from a peer-reviewed journal.
(ullah2026earlyonsetretinopathyin pages 9-9): Mukhtar Ullah, Atta Ur Rehman, Madhur Shetty, Michael D. Allen, Ehsan Ullah, Sabrina G. Signorini, Cyril Burin des Roziers, Rosalie M. Grijalva, Abdur Rashid, Asad Munir, Alessandra Pia Porretta, Enza Maria Valente, Aime R. Agather, Ioannis Dimopoulos, Robert B. Hufnagel, Edouard Malandain, Juliette Coursimault, Muhammad Ansar, Stylianos E. Antonarakis, Andrea Superti-Furga, Sanaullah Jan, Brian P. Brooks, Giacomo Calzetti, Bin Guan, Mathieu Quinodoz, L. Keith Henry, and Carlo Rivolta. Early-onset retinopathy in patients with variants in slc6a6 leading to impaired taurine transport. JAMA Ophthalmology, 144(1):70, Jan 2026. URL: https://doi.org/10.1001/jamaophthalmol.2025.4875, doi:10.1001/jamaophthalmol.2025.4875. This article has 2 citations and is from a highest quality peer-reviewed journal.
(OpenTargets Search: taurine transporter deficiency-SLC6A6): Open Targets Query (taurine transporter deficiency-SLC6A6, 3 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(yadav2025thetaurinetautaxis pages 5-7): Anshu Yadav, Bishal Patgiri, Jitendra Kumar, and Uddalak Das. The taurine-taut axis in hematologic malignancies: a review on redox homeostasis, mitochondrial trna stabilization, leukemic stem cell persistence, and therapeutic vulnerabilities. Unknown journal, Oct 2025. URL: https://doi.org/10.20944/preprints202510.1439.v1, doi:10.20944/preprints202510.1439.v1.
(ansar2020taurinetreatmentof pages 5-6): Muhammad Ansar, Emmanuelle Ranza, Madhur Shetty, Sohail A Paracha, Maleeha Azam, Ilse Kern, Justyna Iwaszkiewicz, Omer Farooq, Constantin J Pournaras, Ariane Malcles, Mateusz Kecik, Carlo Rivolta, Waqar Muzaffar, Aziz Qurban, Liaqat Ali, Yacine Aggoun, Federico A Santoni, Periklis Makrythanasis, Jawad Ahmed, Raheel Qamar, Muhammad T Sarwar, L Keith Henry, and Stylianos E Antonarakis. Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with slc6a6 taurine transporter deficiency. Human molecular genetics, 29:618-623, Dec 2020. URL: https://doi.org/10.1093/hmg/ddz303, doi:10.1093/hmg/ddz303. This article has 75 citations and is from a domain leading peer-reviewed journal.

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Mechanistic Hypotheses

Discussions and Knowledge Gaps

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Biochemical Markers

Diagnosis

Progression

Prevalence

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Taurine Transporter Deficiency: Comprehensive Disease-Characteristics Report

Executive summary

1. Disease information

Definition and scope

Names and identifiers

2. Etiology, risk, and protective factors

Primary cause

Genetic risk factors

Environmental and protective factors

3. Phenotypes

Ocular phenotype

Cardiac phenotype

Other findings

4. Genetic and molecular information

Gene and protein

Reported pathogenic variants

5. Environmental information

6. Mechanism and pathophysiology

Upstream causal chain

Downstream mechanisms

7. Anatomical structures affected

Primary organs

Tissues and cells

8. Temporal development

9. Inheritance and population

10. Diagnostics

Recommended clinical approach

Differential diagnosis

11. Outcome and prognosis

12. Treatment

Oral taurine supplementation

Supportive management

13. Prevention

14. Other species and natural disease

15. Model organisms

Mouse

Induced retinal-depletion models

Cellular models

Recent developments and expert assessment

Major evidence gaps

Artifacts

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