Infantile Tay-Sachs Disease Research Articles

Biochemical and mutational analyses of HEXA in a cohort of Egyptian patients with infantile Tay-Sachs disease. Expansion of the mutation spectrum

BackgroundTay-Sachs disease (TSD), an autosomal recessively inherited neurodegenerative lysosomal storage disease, reported worldwide with a high incidence among population of Eastern European and Ashkenazi Jewish descent. Mutations in the alpha subunit of HEXA that encodes for the β-hexosaminidase-A lead to deficient enzyme activity and TSD phenotype. This study is the first to highlight the HEXA sequence variations spectrum in a cohort of Egyptian patients with infantile TSD.ResultsThis study involved 13 Egyptian infant/children patients presented with the infantile form of TSD, ten of the 13 patients were born to consanguineous marriages. β-hexosaminidase-A enzyme activity was markedly reduced in the 13 patients with a mean activity of 3 µmol/L/h ± 1.56. Sanger sequencing of the HEXA’ coding regions and splicing junctions enabled a detection rate of ~ 62% (8/13) in our patients revealing the molecular defects in eight patients; six homozygous-mutant children (five of them were the product of consanguineous marriages) and two patients showed their mutant alleles in heterozygous genotypes, while no disease-causing mutation was identified in the remaining patients. Regulatory intragenic mutations or del/dup may underlie the molecular defect in those patients showing no relevant pathogenic sequencing variants or in the two patients with a heterozygous genotype of the mutant allele. This research identified three novel, likely pathogenic variants in association with the TSD phenotype; two missense, c.920A > C (E307A) and c.952C > G (H318D) in exon 8, and a single base deletion c.484delG causing a frameshift E162Rfs*37 (p.Glu162ArgfsTer37) in exon 5. Three recurrent disease-causing missense mutations; c.1495C > T (R499C), c.1511G > A(R504H), and c.1510C > T(R504C) in exon 13 were identified in five of the eight patients. None of the variants was detected in 50 healthy Egyptians’ DNA. Five variants, likely benign or of uncertain significance, S3T, I436V, E506E, and T2T, in exons 1, 11,13, & 1 were detected in our study.ConclusionsFor the proper diagnostics, genetic counseling, and primary prevention, our study stresses the important role of Next Generation Sequencing approaches in delineating the molecular defect in TSD-candidate patients that showed negative Sanger sequencing or a heterozygous mutant allele in their genetic testing results. Interestingly, the three recurrent TSD associated mutations were clustered on chromosome 13 and accounted for 38% of the HEXA mutations detected in this study. This suggested exon 13 as the first candidate for sequencing screening in Egyptian patients with infantile TSD. Larger studies involving our regional population are recommended, hence unique disease associated pathogenic variations could be identified.

Infantile Tay-Sachs disease: The need for improved prenatal screening

Infantile Tay-Sachs disease: The need for improved prenatal screening

Storage of GM2 ganglioside and altered gene expression in infantile Tay-Sachs disease during fetal development has implications for therapeutic timing and efficacy

Storage of GM2 ganglioside and altered gene expression in infantile Tay-Sachs disease during fetal development has implications for therapeutic timing and efficacy

AAV gene therapy for Tay-Sachs disease.

Tay-Sachs disease (TSD) is an inherited neurological disorder caused by deficiency of hexosaminidase A (HexA). Here, we describe an adeno-associated virus (AAV) gene therapy expanded-access trial in two patients with infantile TSD (IND 18225) with safety as the primary endpoint and no secondary endpoints. Patient TSD-001 was treated at 30 months with an equimolar mix of AAVrh8-HEXA and AAVrh8-HEXB administered intrathecally (i.t.), with 75% of the total dose (1 × 1014 vector genomes (vg)) in the cisterna magna and 25% at the thoracolumbar junction. Patient TSD-002 was treated at 7 months by combined bilateral thalamic (1.5 × 1012 vg per thalamus) and i.t. infusion (3.9 × 1013 vg). Both patients were immunosuppressed. Injection procedures were well tolerated, with no vector-related adverse events (AEs) to date. Cerebrospinal fluid (CSF) HexA activity increased from baseline and remained stable in both patients. TSD-002 showed disease stabilization by 3 months after injection with ongoing myelination, a temporary deviation from the natural history of infantile TSD, but disease progression was evident at 6 months after treatment. TSD-001 remains seizure-free at 5 years of age on the same anticonvulsant therapy as before therapy. TSD-002 developed anticonvulsant-responsive seizures at 2 years of age. This study provides early safety and proof-of-concept data in humans for treatment of patients with TSD by AAV gene therapy.

Article on Tay-Sachs Disease

Tay–Sachs disease is a genetic disorder that results in the destruction of nerve cells in the brain and spinal cord..also known as GM2 gangliosidosis or Hexosaminidase A deficiency) is an autosomal recessive genetic disorder. In its most common variant known as infantile Tay-Sachs disease it presents with a relentless deterioration of mental and physical abilities which commences at 6 months of age and usually results in death by the age of four.It is caused by a genetic defect in a single gene with one defective copy of that gene inherited from each parent. The disease occurs when harmful quantities of gangliosides accumulate in the nerve cells of the brain, eventually leading to the premature death of those cells. There is currently no cure or treatment. Tay- Sachs disease is a rare disease. Other autosomal disorders such as cystic fibrosis and sickle cell anemia are far more common. TSD is an autosomal recessive genetic disorder, meaning that when both parents are carriers, there is a 25% risk of giving birth to an affected child.

Supporting Families Considering Participation in a Clinical Trial: Parent-Provider Perspectives.

* Abbreviation: CPN — : Courageous Parents Network The emergence of efficacious human gene therapy for life-limiting genetic diseases such as spinal muscular atrophy type 11 has raised hopes among families of children with previously incurable genetic disorders. However, a number of concerns have surfaced regarding the gene therapy trial process. Two bereaved parents, both deeply engaged in their disease communities, collaborated with an experienced gene therapy researcher to create patient education materials to aid parents in critical decision-making. In this Family Partnerships article, we present a summary of the module, as well the reflections of each of the 3 contributors describing the impetus for the Courageous Parents Network (CPN) unit Evaluating the Clinical Trial Option, and their hopes for its impact, as captured in an interview conducted after completion of the educational module. The Evaluating the Clinical Trial Option unit (https://courageousparentsnetwork.org/topics/clinical-trial) offers an overview of the fundamental elements of clinical trial participation, written for a nonmedical audience to help families understand and evaluate their options. It is disease and therapy agnostic and does not advocate for any particular path or decision. Content areas include a glossary of terms; informed consent; clinical trial basics, such as efficacy; trial design, including the phases; participation criteria; and the emotional impact of decision-making. Its elements include a variety of media types: 85 short videos (average 2–4 minutes each, a total of ∼240 minutes); downloadable guides in English and Spanish; 3 podcasts; 4 blog posts written by parents; and a curated educational digital experience (“Guided Pathway”) that, through videos and text, walks parents … Address correspondence to Terence R. Flotte, MD, Medical School, University of Massachusetts and Dean’s Office, 55 Lake Ave North, Worcester, MA 01655. E-mail: terry.flotte{at}umassmed.edu

In silico analysis of the effects of disease-associated mutations of β-hexosaminidase A in Tay‒Sachs disease

Tay-Sachs disease (TSD), a deficiency of b-hexosaminidase A (Hex A), is a rare but debilitating hereditary metabolic disorder. Symptoms include extensive neurodegeneration and often result in death in infancy. We report an in silico study of 42 Hex A variants associated with the disease. Variants were separated into three groups according to the age of onset: infantile (n=28), juvenile (n=9) and adult (n=5). Protein stability, aggregation potential and the degree of conservation of residues were predicted using a range of in silico tools. We explored the relationship between these properties and the age of onset of TSD. There was no significant relationship between proteinstability and disease severity or between protein aggregation and disease severity. Infantile TSD had a significantly higher mean conservation score than nondisease associated variants. This was not seen in either juvenile or adult TSD. This study has established that the degree of residue conservation may be predictive of infantile TSD. It is possible that these more highly conserved residues are involved in trafficking of the protein to the lysosome. In addition, we developed and validated software tools to automate the process of in silico analysis of proteins involved in inherited metabolic diseases. Further work is required to identify the function of well-conserved residues to establish an in silico predictive model of TSD severity.

The incidence and carrier frequency of Tay-Sachs disease in the French-Canadian population of Quebec based on retrospective data from 24 years, 1992-2015.

Tay-Sachs disease (TSD) is a hereditary neurodegenerative condition inherited through an autosomal recessive pattern. The incidence and carrier frequency of infantile TSD were found to be increased among French Canadians in specific areas of the province of Quebec or calculated from New England populations with French-Canadian heritage. No accurate infantile TSD carrier frequency for the whole French-Canadian population in Quebec has been published. In this study, we estimate the incidence and carrier frequency of infantile TSD in the Quebec French-Canadian population. The number of TSD cases was ascertained during the 1992-2015 period, as well as the number of births to mothers whose language of use is French. Seven cases of TSD have been diagnosed in Quebec during the period of ascertainment. This corresponds to an incidence of 1/218,144, which in turn corresponds to a carrier frequency of 1/234. In the same 24-year period, there are two French-Canadian couples who had a fetus prenatally diagnosed with TSD. If these cases are included, the incidence of TSD in the French-Canadian population of Quebec is 1/169,668 and the carrier frequency 1/206. These findings can be used for genetic counseling and policy decisions regarding carrier screening for TSD in populations of French-Canadian descent.

Identification of novel variants in a large cohort of children with Tay-Sachs disease: An initiative of a multicentric task force on lysosomal storage disorders by Government of India.

Tay-Sachs disease (TSD) (OMIM) is a neurodegenerative lysosomal storage disorder caused due to mutations in the HEXA gene. To date, nearly 190 mutations have been reported in HEXA gene. Here, we have characterized 34 enzymatically confirmed TSD families to investigate the presence of novel as well as known variants in HEXA gene. Overall study detected 25 variants belonging to 31 affected TSD patients and 3 carrier couples confirmed by enzyme study. Of these 17 patients harbors 15 novel variants, including seven missense variants [p.V206L, p.Y213H, p.R252C, p.F257S, p.C328G, p.G454R, and p.P475R], four nonsense variant [p.S9X, p.E91X, p.W420X, and p.W482X], two splice site variants [c.347-1G>A and c.460-1G>A], and two small deletion [c.1349delC (p.A450VfsX3) and c.52delG (p.G18Dfs*82)]. While remaining 17 patients harbors 10 previously reported variants that includes six missense variants [p.M1T, p.R170Q, p.D322Y, p.D322N, p.E462V, and p.R499C], one nonsense variant [p.Q106X], two splice site variants [c.1073+1G>A and c.459+4A>G] and one 4 bp insertion [c.1278insTATC (p.Y427IfsX5)]. In conclusion, Indian infantile TSD patients provide newer insight into the molecular heterogeneity of the TSD. Combining present study and our earlier studies, we have observed that 67% genotypes found in Indian TSD patients are novel, which are associated with severe infantile phenotypes, while rest 33% genotypes found in our cohort were previously reported in various populations. In addition, higher frequency of the p.E462V and c.1278insTATC mutations in the present study further support and suggest the prevalence of p.E462V mutation in the Indian population.

Amyotrophy, cerebellar impairment and psychiatric disease are the main symptoms in a cohort of 14 Czech patients with the late-onset form of Tay-Sachs disease.

Tay-Sachs disease (TSD) is an inherited neurodegenerative disorder caused by a lysosomal β-hexosaminidase A deficiency due to mutations in the HEXA gene. The late-onset form of disease (LOTS) is considered rare, and only a limited number of cases have been reported. The clinical course of LOTS differs substantially from classic infantile TSD. Comprehensive data from 14 Czech patients with LOTS were collated, including results of enzyme assays and genetic analyses. 14 patients (9 females, 5 males) with LOTS were diagnosed between 2002 and 2018 in the Czech Republic (a calculated birth prevalence of 1 per 325,175 live births). The median age of first symptoms was 21years (range 10-33years), and the median diagnostic delay was 10.5years (range 0-29years). The main clinical symptoms at the time of manifestation were stammering or slurred speech, proximal weakness of the lower extremities due to anterior horn cell neuronopathy, signs of neo- and paleocerebellar dysfunction and/or psychiatric disorders. Cerebellar atrophy detected through brain MRI was a common finding. Residual enzyme activity was 1.8-4.1% of controls. All patients carried the typical LOTS-associated c.805G>A (p.Gly269Ser) mutation on at least one allele, while a novel point mutation, c.754C>T (p.Arg252Cys) was found in two siblings. LOTS seems to be an underdiagnosed cause of progressive distal motor neuron disease, with variably expressed cerebellar impairment and psychiatric symptomatology in our group of adolescent and adult patients. The enzyme assay of β-hexosaminidase A in serum/plasma is a rapid and reliable tool to verify clinical suspicions.

Prenatal Diagnosis of Tay-Sachs Disease.

Tay-Sachs disease (TSD) is an autosomal recessive lysosomal storage disorder caused by mutations of the HEXA gene resulting in the deficiency of hexosaminidase A (Hex A) and subsequent neuronal accumulation of GM2 gangliosides. Infantile TSD is a devastating and fetal neurodegenerative disease with death before the age of 3-5years. A small proportion of TSD patients carry milder mutations and may present juvenile or adult onset milder disease. TSD is more prevalent among Ashkenazi Jewish (AJ) individuals and some other genetically isolated populations with carrier frequencies of approximately ~1:27 which is much higher than that of 1:300 in the general population. Carrier screening and prenatal testing for TSD are effective in preventing the birth of affected fetuses greatly diminishing the incidence of TSD. Testing of targeted HEXA mutations by genotyping or sequencing can detect 98% of carriers in AJ individuals; however, the detection rate is much lower for most other ethnic groups. When combined with enzyme analysis, above 98% of carriers can be reliably identified regardless of ethnic background. Multiplex PCR followed by allele-specific primer extension is one method to test for known and common mutations. Sanger sequencing or other sequencing methods are useful to identify private mutations. For prenatal testing, only predefined parental mutations need to be tested. In the event of unknown mutational status or the presence of variants of unknown significance (VUS), enzyme analysis must be performed in conjunction with DNA-based assays to enhance the diagnostic accuracy. Enzymatic assays involve the use of synthetic substrates 4-methylumbelliferyl-N-acetyl-β-glucosamine (4-MUG) and 4-methylumbelliferyl-6-sulfo-2-acetamido-2-deoxy-β-D-glucopyranoside (4-MUGS) to measure the percentage Hex A activity (Hex A%) and specific Hex A activity respectively. These biochemical and molecular tests can be performed in both direct specimens and cultured cells from chorionic villi sampling or amniocentesis.

Infantile Tay-Sachs disease: a case report

Infantile Tay-Sachs disease: a case report

Generation of HEXA-deficient hiPSCs from fibroblasts of a Tay-Sachs disease patient

Human iPSC line TSD-01-hiPSC was generated from fibroblasts of a patient with infantile Tay-Sachs disease (TSD). The patient is compound heterozygous at the HEXA gene by carrying a 1278insTATC allele and an IVS12+1G>C allele. STEMCCA lentivirus, which expresses OCT4, SOX2, KLF4, and c-MYC from a polycistronic transcript, were used for reprogramming. TSD-01-hiPSC express pluripotency markers such as OCT4, SOX2, NANOG, Tra-1-60, and alkaline phosphatase, and can differentiate into tissues from all the three embryonic germ layers. This TSD patient-derived hiPSC line may serve as a valuable in vitro tool for disease modeling and drug test.

Choroidal coloboma in a case of tay-sachs disease.

Coloboma as an ocular finding has been documented in various syndromes. Here we have a case of infantile Tay-Sachs disease associated with unilateral choroidal coloboma. To the best of our knowledge, such an association has not been documented in the literature. Whether such an association is a matter of chance or signifies the involvement of ganglioside metabolism in ocular embryogenesis remains to be elucidated.

The Natural History of Late Onset Tay-Sachs Disease (P01.243)

Objective: To investigate whether late onset Tay-Sachs (LOTS) Disease phenotypes (juvenile and adult) overlap and whether LOTS can be better characterized. Background LOTS has a more chronic course than infantile Tay-Sachs disease and is divided into juvenile and adult phenotypes. Design/Methods: We reviewed retrospective surveys and performed prospective examinations using a brief ataxia rating scale. Results: Retrospective data from 55 LOTS patients (45 adult, 10 juvenile), showed a heterogeneous population with overlap in age of onset. Median onset in adults was 10 years (range 1 to 40) and in juveniles 2 years (range 1 to 4). Median progression from first symptom to becoming wheelchair-bound was 22 (adult) and 3.75 years (juvenile). Among both juvenile and adult LOTS the most common presenting symptoms were gait and speech abnormalities. Forty-five percent presented with gait difficulties as their first symptom (21/45 adult, age range 3 to 40 years; 4/10 juvenile, age range 1 to 4 years). Eighteen percent presented with speech difficulties (9/45 adult, age range 3 to 30 years; 2/10 juvenile, age range 1 to 1.5 years). Fifteen percent had motor problems without speech difficulties (8/45 adult, age range 7 to 40 years; 2/10 juvenile, age range 1.5 to 1.8 years). Prospective data from ten LOTS patients showed 80% (8/10) had muscle weakness and cerebellar dysfunction (range of onset 24 to 64 years) and 20% had selective lower motor neuron weakness with no cerebellar dysfunction (ages of onset 23 and 25 years), confirming the distribution and/or variation in phenotype of our retrospective cohort. Conclusions: Our studies confirm an overlap in age of first symptoms among juvenile and adult LOTS and consistent variation in phenotypes in both retrospective and prospective cohorts, with absence of cerebellar findings in 15 to 20% of LOTS patients. This research highlights the need for a better understanding of the natural history of LOTS. Supported by: National Tay-Sachs & Allied Disease Association. Disclosure: Dr. Yerramilli-Rao has nothing to disclose. Dr. Giannikopoulos has nothing to disclose. Dr. Kublis has nothing to disclose. Dr. Pan has nothing to disclose. Dr. Eichler has nothing to disclose.

Educational corner of the issue

Genetics Unit, Pediatrics Department, Faculty of Medicine, Ain Shams University, Cairo, EgyptReceived 17 June 2011; accepted 12 July 2011Available online 3 December 2011Part I: Educational caseA 3.5-year-old boy, the second in order of birth of first cousinparents presented to the genetics clinic for counseling. The pa-tient had normal development till the age of 2 years then hestarted to have abnormal ataxic gait with frequent falls. Atthe age of 2.5 years, he started to lose previously acquired cog-nitive skills and speech and to develop convulsions. Neurolog-ical examination showed hypotonia and increased deep tendonreflexes. The patient had a sister and a paternal cousin with thesame clinical picture who both died at the age of 5 and 6 years.MRI brain showed brain atrophy. Fundus examinationshowed cherry-red spot (Fig. 1). The mother is 10 weeks preg-nant and asks about prenatal diagnosis.Q1: What is the most probable diagnosis?The most probable diagnosis is Tay Sachs disease which is aneurodegenerative disorder caused by intralysosomal storageof the specific glycosphingolipid GM2 ganglioside. Commonclinical findings include progressive weakness and loss of mo-tor and cognitive skills, decreased attentiveness and an in-creased startle response. The typical findings on physicalexamination are generalized muscular hypotonia, ankle clonus,hyperreflexia and normal-sized liver and spleen. This is fol-lowed by signs of progressive neurodegeneration, seizures,blindness, and spasticity. A cherry-red spot of the fovea cen-tralis of the macula of the retina is usually found on fundusexamination [1].Our patient has the juvenile (subacute) form. The diseaseoften begins between the age of 2 and 10 years by loss of pre-viously acquired skills and speech followed by spasticity andseizures. Loss of vision occurs much later than in the acuteinfantile form of the disease, and a cherry-red spot – in con-trary to our case – is not consistently observed. Instead, opticatrophy and retinitis pigmentosa may be seen late in thecourse. A vegetative state with decerebrate rigidity developsby age 10–15 years, followed within few years by death, usuallyfrom infection. In some cases, the disease pursues a particu-larly aggressive course, culminating in death in 2–4 years [2].Q2: Are there other phenotypes of the disease?Other phenotypes include [1]: Acute infantile (Tay-Sachs disease) with rapid progressionand death before age 4 years. Chronic and adult-onset Tay Sachs disease with long-termsurvival. Affected individuals have several different pheno-types, including progressive dystonia, spinocerebellardegeneration, motor neuron disease with muscle weaknessand fasciculations, and/or psychosis. ActivatordeficientTaysachsdisease:itisarareinfantileform(phenotype identical to classic disease) where the enzymaticactivityofbothhexosaminidaseA(HEXA)andhexosamin-idase B (HEX B) are normal, but GM2 ganglioside accumu-lation occurs because of a deficit of the intralysosomal

Identification of two HEXA mutations causing infantile-onset Tay–Sachs disease in the Persian population

The β-hexosaminidase A (HEXA) mutations in the first reported cases of infantile Tay-Sachs disease in the Persian population were identified in two unrelated consanguineous families. The clinical diagnoses of the affected infants were confirmed by their markedly deficient levels of HEXA activity in plasma or peripheral leukocytes. The specific causative mutation in each family was determined by sequencing the HEXA alleles in both sets of related parents. Two mutations were identified: c.1A>G (p.MIV), which obliterated the initiating methionine in codon 1, and c.1177C>T (p.R393X), which predicted a termination codon or nonsense mutation.

Mice Doubly-Deficient in Lysosomal Hexosaminidase A and Neuraminidase 4 Show Epileptic Crises and Rapid Neuronal Loss

Tay-Sachs disease is a severe lysosomal disorder caused by mutations in the HexA gene coding for the α-subunit of lysosomal β-hexosaminidase A, which converts GM2 to GM3 ganglioside. Hexa−/− mice, depleted of β-hexosaminidase A, remain asymptomatic to 1 year of age, because they catabolise GM2 ganglioside via a lysosomal sialidase into glycolipid GA2, which is further processed by β-hexosaminidase B to lactosyl-ceramide, thereby bypassing the β-hexosaminidase A defect. Since this bypass is not effective in humans, infantile Tay-Sachs disease is fatal in the first years of life. Previously, we identified a novel ganglioside metabolizing sialidase, Neu4, abundantly expressed in mouse brain neurons. Now we demonstrate that mice with targeted disruption of both Neu4 and Hexa genes (Neu4 −/−;Hexa −/−) show epileptic seizures with 40% penetrance correlating with polyspike discharges on the cortical electrodes of the electroencephalogram. Single knockout Hexa −/− or Neu4 −/− siblings do not show such symptoms. Further, double-knockout but not single-knockout mice have multiple degenerating neurons in the cortex and hippocampus and multiple layers of cortical neurons accumulating GM2 ganglioside. Together, our data suggest that the Neu4 block exacerbates the disease in Hexa−/− mice, indicating that Neu4 is a modifier gene in the mouse model of Tay-Sachs disease, reducing the disease severity through the metabolic bypass. However, while disease severity in the double mutant is increased, it is not profound suggesting that Neu4 is not the only sialidase contributing to the metabolic bypass in Hexa −/− mice.

Evaluation of the Risk for Tay-Sachs Disease in Individuals of French Canadian Ancestry Living in New England

The assessment of risk for Tay-Sachs disease (TSD) in individuals of French Canadian background living in New England is an important health issue. In preliminary studies of the enzyme-defined carrier frequency for TSD among Franco-Americans in New England, we found frequencies (1:53) higher than predicted from the incidence of infantile TSD in this region. We have now further evaluated the risk for TSD in the Franco-American population of New England. Using a fluorescence-based assay for beta-hexosaminidase activity, we determined the carrier frequencies for TSD in 2783 Franco-Americans. DNA analysis was used to identify mutations causing enzyme deficiency in TSD carriers. We determined the enzyme-defined carrier frequency for TSD as 1:65 (95% confidence interval 1:49 to 1:90). DNA-based analysis of 24 of the enzyme-defined carriers revealed 21 with sequence changes: 9 disease-causing, 4 benign, and 8 of unknown significance. Six of the unknowns were identified as c.748G>A p.G250S, a mutation we show by expression analysis to behave similarly to the previously described c.805G>A p.G269S adult-onset TSD mutation. This putative adult-onset TSD c.748G>A p.G250S mutation has a population frequency similar to the common 7.6 kb deletion mutation that occurs in persons of French Canadian ancestry. We estimate the frequency of deleterious TSD alleles in Franco-Americans to be 1:73 (95% confidence interval 1:55 to 1:107). These data provide a more complete data base from which to formulate policy recommendations regarding TSD heterozygosity screening in individuals of French Canadian background.

Molecular analysis of theHEXAgene in Italian patients with infantile and late Onset Tay-Sachs disease: detection of fourteen novel alleles

Tay-Sachs disease (TSD) is a recessively inherited disorder caused by the hexosaminidase A deficiency. We report the molecular characterization performed on 31 Italian patients, 22 with the infantile, acute form of TSD and nine patients with the subacute juvenile form, biochemically classified as B1 Variant. Of the 29 different alleles identified, fourteen were due to 15 novel mutations, two being in-cis on a new complex allele. The new alleles caused four frameshifts, three premature stop codons, three amino acid changes, two amino acid deletions and two splicing alterations. As previously reported, the c.533G>A (p.R178H) mutation was present either in homozygosity or as compound heterozygote, in all the patients with the late onset TSD form (B1 Variant); the allele frequency in this group is discussed by comparison with that found in infantile TSD.