LETTERS TO THE EDITOR
|Year : 2022 | Volume
| Issue : 3 | Page : 502-505
Juvenile tay sachs disease due to compound heterozygous mutation in Hex-A gene, with early sign of bilateral tremors
Jayesh Sheth1, Ira Mohapatra1, Gangotri Patra1, Riddhi Bhavsar1, Chandni Patel1, Siddharth Shah2, Aadhira Nair1
1 Department of Biochemical and Molecular Genetics, FRIGE's Institute of Human Genetics, FRIGE House, Jodhpur Gam Road, Satellite, Ahmedabad, India
2 Consultant Pediatric Neurologist, Royal Institute of Child Neurosciences, Vastrapur, Ahmedabad, Gujarat, India
|Date of Submission||22-Jun-2021|
|Date of Decision||11-Aug-2021|
|Date of Acceptance||25-Aug-2021|
|Date of Web Publication||05-Jan-2022|
Biochemical Genetics, FRIGE House, Jodhpur Gam Road, Satellite, Ahmedabad - 380 015, Gujarat
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sheth J, Mohapatra I, Patra G, Bhavsar R, Patel C, Shah S, Nair A. Juvenile tay sachs disease due to compound heterozygous mutation in Hex-A gene, with early sign of bilateral tremors. Ann Indian Acad Neurol 2022;25:502-5
|How to cite this URL:|
Sheth J, Mohapatra I, Patra G, Bhavsar R, Patel C, Shah S, Nair A. Juvenile tay sachs disease due to compound heterozygous mutation in Hex-A gene, with early sign of bilateral tremors. Ann Indian Acad Neurol [serial online] 2022 [cited 2022 Aug 14];25:502-5. Available from: https://www.annalsofian.org/text.asp?2022/25/3/502/335000
Tay–Sachs disease (TSD) is one of the common glycolipid storage disorders with an incidence of 1 in 100,000 live births. TSD (OMIM # 272800) is a result of biallelic pathogenic variants in the HEXA gene that causes deficiency of β-hexosaminidase A (HexA) enzyme (EC 22.214.171.124). This is further categorized into a classic infantile form, sub-acute juvenile form, and late-onset form, depending on the age of onset of symptoms. Notably, India has a TSD case mostly with the infantile phenotype whereas juvenile or late-onset forms have been rarely reported.
Here we describe the second case of juvenile TSD from India along with a review of previously reported juvenile TSD cases having confirmed genetic study.
The proband is the first child born to a non-consanguineous couple and was referred to us at 12 years of age. He had a normal development till the age of 5 years and progressive deterioration of the learned skill with bilateral tremors thereafter. On presentation at our centre, he had gait ataxia, difficulty in climbing stairs, slurred speech, difficulty in getting up and down. Magnetic Resonance Imaging (MRI) scans of the brain showed mild cortical atrophic changes [Figure 1]. On eye examination, cherry red spot was absent. An IQ assessment study showed IQ level to be 33.3. The clinical presentation suggested a neurodegenerative disorder with a strong suspicion of TSD. Our differentials included Sandhoff disease, neuronal ceroid lipofuscinosis, Friedreich ataxia and late-onset spinal muscular atrophy.
To confirm the clinical diagnosis, a lysosomal enzyme β-hexosaminidase A study was carried out from the leucocytes. The test showed β-hexosaminidase A activity to be 3.1 nmol/hr/mg protein, which was less than 10% of the normal range (62.7–659.4 nmol/hr/mg protein). Further, genomic DNA extracted from blood sample was used to carry out neurology gene panel study. This identified a compound heterozygous variant c.1496G>A (chr15-72637817) (p.Arg499His) in exon 13 and c.902T>G (chr15-72641504) (p.Met301Arg) in exon 8 of the HEXA gene. As per ACMG guidelines, these variants were classified as pathogenic and likely pathogenic, respectively. The results were validated in the proband and both parents by bidirectional sequencing of the coding region of the HEXA gene (ENST00000268097). This study confirmed the presence of both variants in compound heterozygous state in the proband and heterozygous state in both parents.
The juvenile form of TSD is a rare and progressive neurodegenerative disorder with a heterogeneous clinical course. To date, 155 cases of juvenile TSD have been reported in the literature including a single case from India. The mean age of onset was 5.24 ± 3.9 years. We found that dysarthria and gait ataxia are the most common clinical signs, seen in 96.5% and 93.1% of the cases, respectively.,,,,, In the present case also, there was a similar observation with an additional sign of bilateral tremors in hand at 5 years of age which has been seen in only 26.72% of the previously reported cases. The MRI findings showing cortical atrophy in our case are consistent with those observed in other juvenile TSD cases.
Sandhoff et al. have suggested an inverse correlation between the heterogeneity of onset and the residual activity of the β-hexosaminidase enzyme. Patients with the juvenile forms of TSD may have 5-10% of wild-type enzyme activity that lies in the range of 2 to 9 nmol/hr/mg protein.,,,,, Though, previous large study of infantile cases and present case of juvenile TSD could not find a correlation between enzyme activity and the onset of disease. In the present case, this could be due to presence of one heterozygous variant (c.902T>G) which is commonly associated with infantile TSD.
On literature review, we found, forty-one variants in HEXA to be observed with juvenile TSD [Table 1], [Figure 2]. The two most common variants found in juvenile TSD are c.1496G>A (p.Arg499His) and c.533G>A (p.Arg178His) found in exon 13 and 5, respectively, in 25.4% of the 67 patients including the present case.,,,,,
|Figure 2: Schematic diagram of HEXA gene structure with functional domains showing the 41 reported variants in juvenile TSD|
Click here to view
Both variants in the present case: c.1496G>A (p.Arg499His) and c.902T>G (p.Met301Arg) have been previously reported in the literature in multiple ethnicity. Interestingly, c.1496G>A has been observed in affected TSD patients from various ethnic backgrounds like Caucasian, Argentinean, Portuguese and Italian populations., This variant is located outside the catalytic domain, and hence causes minor structural changes, which explains the late-onset clinical phenotype. While the other variant, c.902T>G (p.Met301Arg), has been reported only twice in the literature for infantile TSD. In one case, it was in homozygous state, whereas in another case, it was present in combination with another pathogenic HEXA variant p.Arg504His. This variant is located in the catalytic domain of the α- subunit of β-hexosaminidase A. Although the effect of this variant on the enzyme is unclear, it has been hypothesized that the association process of the two subunits (α and β) of the enzyme might be affected.
Thus, based on the reported cases in the literature and present case, it is likely possible to predict the onset of symptoms and the disease severity depending on the mutation in HEXA gene and its subsequent effect on the residual β-hexosaminidase A activity. Hence, establishing genotype-phenotype correlation is critical to understand the patient prognosis and plan effective management of the condition.
Present case highlights the rarity of juvenile TSD in India and shows bilateral tremors as an early sign in this condition. The variant c.902T>G in the HEXA has been reported in infantile forms of TSD. Nonetheless, due to presence of c.1496G>A, a common variant in juvenile TSD, the index case has shown a milder phenotype with juvenile onset.
We express our thanks to the patient and his parents for their cooperation. We thank Dr. Heli Shah for referring this case. We also thank Dr. Harsh Sheth for his partial help in the reading and making critical suggestions for the manuscript.
Financial support and sponsorship
This work was partly supported by Gujarat State Biotechnology Mission (GSBTM) (grant no: GSBTM/JDR &D/608/2020/459-461).
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]