title: Expanding the spectrum ofHEXAmutations in Indian patients with Tay-Sachs disease.
abstract: Tay-Sachs disease is an autosomal recessive neurodegenerative disorder occurring due to impaired activity of β-hexosaminidase-A (EC 3.2.1.52), resulting from the mutation inHEXAgene. Very little is known about the molecular pathology of TSD in Indian children except for a few mutations identified by us. The present study is aimed to determine additional mutations leading to Tay-Sachs disease in nine patients confirmed by the deficiency of β-hexosaminidase-A (< 2% of total hexosaminidase activity for infantile patients) in leucocytes. The enzyme activity was assessed by using substrates 4-methylumbelliferyl-N-acetyl-β-d-glucosamine and 4-methylumbelliferyl-N-acetyl-β-d-glucosamine-6-sulfate for total-hexosaminidase and hexosaminidase-A respectively, and heat inactivation method for carrier detection. The exons and exon-intron boundaries of theHEXAgene were bi-directionally sequenced on an automated sequencer. 'In silico' analyses for novel mutations were carried out using SIFT, Polyphen2 and MutationT@ster software programs. The structural study was carried out by UCSF Chimera software using the crystallographic structure of β-hexosaminidase-A (PDB-ID: 2GJX) as the template. Our study identified four novel mutations in three cases. These include a compound heterozygous missense mutation c.524A>C (D175A) and c.805G>C (p.G269R) in one case; and one small 1 bp deletion c.426delT (p.F142LfsX57) and one splice site mutation c.459+4A>C in the other two cases respectively. None of these mutations were detected in 100 chromosomes from healthy individuals of the same ethnic group. Three previously reported missense mutations, (i) c.532C>T (p.R178C), (ii) c.964G>T (p.D322Y), and (iii) c.1385A>T (p.E462V); two nonsense mutations (i) c.709C>T (p.Q237X) and (ii) c.1528C>T (p.R510X), one 4 bp insertion c.1277_1278insTATC (p.Y427IfsX5) and one splice site mutation c.459+5G>A were also identified in six cases. We observe from this study that novel mutations are more frequently observed in Indian patients with Tay-Sachs disease with clustering of ~ 73% of disease causing mutations in exons 5 to 12. This database can be used for a carrier rate screening in the larger population of the country.
authors.affiliation: Department of Biochemical and Molecular Genetics, FRIGE's Institute of Human Genetics, FRIGE House, Satellite, Ahmedabad 380015, India.
authors.forename: Jayesh
authors.initials: J
authors.lastname: Sheth
authors.affiliation: Department of Biochemical and Molecular Genetics, FRIGE's Institute of Human Genetics, FRIGE House, Satellite, Ahmedabad 380015, India.
authors.forename: Mehul
authors.initials: M
authors.lastname: Mistri
authors.affiliation: Department of Genetics, Clinical Geneticist, Sahyadri Medical Genetics and Tissue Engineering Facility (SMGTEF), Pune, India.
authors.forename: Chaitanya
authors.initials: C
authors.lastname: Datar
authors.affiliation: Department of Genetics, Clinical Geneticist, Sahyadri Medical Genetics and Tissue Engineering Facility (SMGTEF), Pune, India.
authors.forename: Umesh
authors.initials: U
authors.lastname: Kalane
authors.affiliation: Department of Pediatric Neurology, Hiranandani Hospital, Mumbai, Maharashtra, India.
authors.forename: Shekhar
authors.initials: S
authors.lastname: Patil
authors.affiliation: Department of Pediatric Neurology, KLES Prabhakar Kore Hospital, Belgaum, Karnataka, India.
authors.forename: Mahesh
authors.initials: M
authors.lastname: Kamate
authors.affiliation: Rajvee Child Neuro Hospital, Memnagar, Ahmedabad, India.
authors.forename: Harshuti
authors.initials: H
authors.lastname: Shah
authors.affiliation: Department of Pediatric Genetics, Amrita Institute of Medical Science & Research Centre, AIMS Ponekkara PO, Cochin, Kerala, India.
authors.forename: Sheela
authors.initials: S
authors.lastname: Nampoothiri
authors.affiliation: Department of Biochemistry, Faculty of Science, M.S. University of Baroda, Vadodara, Gujarat, India.
authors.forename: Sarita
authors.initials: S
authors.lastname: Gupta
authors.affiliation: Department of Biochemical and Molecular Genetics, FRIGE's Institute of Human Genetics, FRIGE House, Satellite, Ahmedabad 380015, India.
authors.forename: Frenny
authors.initials: F
authors.lastname: Sheth
keywords: HEXA gene; Hex-A, β-Hexosaminidase A; LSDs, Lysosomal storage disorders; Lysosomal enzyme; MUG, 4-Methylumbelliferyl-N-acetyl-β-d-glucosamine; MUGS, 4-Methylumbelliferyl-N-acetyl-β-d-glucosamine-6-sulfate; SD, Sandhoff disease; TSD, Tay–Sachs disease; Tay–Sachs disease; β-Hexosaminidase-A