Functional characterization of novel variants in SMPD1 in Indian patients with acid sphingomyelinase deficiency.

Pathogenic variations in SMPD1 lead to acid sphingomyelinase deficiency (ASMD), that is, Niemann-Pick disease (NPD) type A and B (NPA, NPB), which is a recessive lysosomal storage disease. The knowledge of variant spectrum in Indian patients is crucial for early and accurate NPD diagnosis and genetic counseling of families. In this study, we recruited 40 unrelated pediatric patients manifesting symptoms of ASMD and subnormal ASM enzyme activity. Variations in SMPD1 were studied using Sanger sequencing for all exons, followed by interpretation of variants based on American College of Medical Genetics and Genomics & Association for Molecular Pathology (ACMG/AMP) criteria. We identified 18 previously unreported variants and 21 known variants, including missense, nonsense, deletions, duplications, and splice site variations with disease-causing potential. Eight missense variants were functionally characterized using in silico molecular dynamic simulation and in vitro transient transfection in HEK293T cells, followed by ASM enzyme assay, immunoblot, and immunofluorescence studies. All the variants showed reduced ASM activity in transfected cells confirming their disease-causing potential. The study provides data for efficient prenatal diagnosis and genetic counseling of families with NPD type A and B.

Newborn screening in India.

Expanded newborn screening (NBS) is aimed for early detection and intervention of treatable inborn errors of metabolism and also to establish incidence of these disorders in this part of the globe. The first expanded NBS programme initiated in the capital city of Andhra Pradesh to screen all the newborns born in four major Government Maternity Hospitals in Hyderabad by heel prick capillary blood collected on S&S 903 filter paper. Chromatographic (TLC and HPLC), electrophoretic (cellulose acetate and agarose) and ELISA based assays have been employed for screening of common inborn errors of metabolism. This study has shown a high prevalence of treatable Inborn errors of metabolism. Congenital hypothyroidsm is the most common disorder (1 in 1700) followed by congenital Adrenal Hyperplasia (1 in 2575) and Hyperhomocystenemia (1 in 100). Interestingly, a very high prevalence of inborn errors of metabolism to the extent of 1 in every thousand newborns was observed. The study reveals the importance of screening in India, necessitating nation wide large-scale screening.