Identification of a novel mutation in metabotropic glutamate receptor 1 causing autosomal recessive spinocerebellar ataxia-13 in a Pakistani family.

BACKGROUND: Autosomal recessive spinocerebellar ataxia-13 is a rare multifactorial disorder characterized by physical disability, cerebellar ataxia, adaptive behavior, intellectual disability, response to sudden noise and light, sensation, skeletal, and oculomotor abnormalities. It affects both males and females equally. So far, only seven variants have been identified in the glutamate metabotropic receptor 1 ( GRM1 ) gene in 18 familial cases of Roma, Iranian, Pakistani, and Tunisian origins.

METHODS: In the present study, we have investigated a large consanguineous family of Pakistani origin presenting severe phenotypes like intellectual disability, delayed developmental milestones, severe ataxia, and nonprogressive neuropathy. Whole exome sequencing was done, followed by Sanger sequencing.

RESULTS: Sequence analysis revealed a novel homozygous deletion mutation (c.1715del) in the GRM1 gene (NM_001278064.2) that led to the substitution of Asn with Met at the 572 amino acid position, leading to frame shift and premature termination (p. Asn572MetfsTer4).

CONCLUSION: This study raised the total number of GRM1 variants to eight and would be helpful in prenatal screening, genetic counseling, and carrier testing of other members in the Pakistani community.