Mutational spectrum and identification of five novel mutations in G6PC1 gene from a cohort of Glycogen Storage Disease Type 1a.

BACKGROUND: Glycogen storage disease type-1a is an inherited, autosomal recessive disorder caused by mutations in G6PC1 gene leading to deficiency of glucose-6-phosphatase-α specifically in the liver/kidney/intestine. PATIENTS AND METHODS: DNA of six unrelated Indian GSD-1a patients were screened for mutations in the entire coding region of G6PC1 gene followed by direct DNA sequencing and functional was tested using glucose-6-phosphatase assay. RESULTS: Mutational screening of GSD-1a patients identified five novel mutations, viz., 1) p.V99Cfs*3, 2) p.G125R, 3) IVS1-2A > T, 4) IVS3 + 39G > A and 5) IVS3 + 42G > A along with three previously reported mutations p.G118D, p.R149Q and p.A331V. Interestingly, each of the p.V99Cfs*3, IVS1-2A > T and p.G118D mutations are identified in two unrelated GSD-1a cases. Further allelic distribution of p.V99Cfs*3 and p.A331V mutations were confirmed by RFLP analysis, consistent with autosomal recessive inheritance. Functional characterization revealed that glucose-6-phosphatase activity was completely abrogated with the mutant proteins p.G125R, p.R149Q, p.G118D, p.A331V and p.V99Cfs*3 than wild-type. However, no significant changes were observed in the expression of mutant constructs at transcription and translation level. CONCLUSION: Five novel mutations, p.V99Cfs*3, p.G125R, IVS1-2A > T, IVS3 + 39G > A and IVS3 + 42G > A are reported first time to cause GSD-1a among Indian ethnicity and are not yet reported elsewhere, suggesting separate ethnic founder effects for some mutations among Indian ethnicity.

Novel nonsense mutation (p.Ile411Metfs*12) in the SLC19A2 gene causing Thiamine Responsive Megaloblastic Anemia in an Indian patient.

Thiamine-responsive megaloblastic anemia (TRMA), an autosomal recessive disorder, is caused by mutations in SLC19A2 gene encodes a high affinity thiamine transporter (THTR-1). The occurrence of TRMA is diagnosed by megaloblastic anemia, diabetes mellitus, and sensorineural deafness. Here, we report a female TRMA patient of Indian descent born to 4th degree consanguineous parents presented with retinitis pigmentosa and vision impairment, who had a novel homozygous mutation (c.1232delT/ter422; p.Ile411Metfs*12) in 5th exon of SLC19A2 gene that causes premature termination of hTHTR-1. PROSITE analysis predicted to abrogate GPCRs family-1 signature motif in the variant by this mutation c.1232delT/ter422, suggesting uncharacteristic rhodopsin function leading to cause RP clinically. Thiamine transport activity by the clinical variant was severely inhibited than wild-type THTR-1. Confocal imaging had shown that the variant p.I411Mfs*12 is targeted to the cell membrane and showed no discrepancy in membrane expression than wild-type. Our findings are the first report, to the best of our knowledge, on this novel nonsense mutation of hTHTR-1 causing TRMA in an Indian patient through functionally impaired thiamine transporter activity.

Riboflavin transporter-2 (rft-2) of Caenorhabditis elegans: Adaptive and developmental regulation.

Riboflavin transporters (rft-1 and rft-2), orthologous to human riboflavin transporter-3 (hRVFT-3), are identified and characterized in Caenorhabditis elegans. However, studies pertaining to functional contribution of rft-2 in maintaining body homeostatic riboflavin levels and its regulation are very limited. In this study, the expression pattern of rft-2 at different life stages of C. elegans was studied through real-time PCR, and found to be consistent from larval to adult stages that demonstrate its involvement in maintaining the body homeostatic riboflavin levels at whole animal level all through its life. A possible regulation of rft-2 expression at mRNA levels at whole animal was studied after adaptation to low and high concentrations of riboflavin. Abundance of rft-2 transcript was upregulated in riboflavin-deficient conditions (10 nM), while it was downregulated with riboflavin-supplemented conditions (2 mM) as compared with control (10 meu M). Further, the 5'-regulatory region of the rft-2 gene was cloned, and transgenic nematodes expressing transcriptional rft-2 promoter::GFP fusion constructs were generated. The expression of rft-2 was found to be adaptively regulated in vivo when transgenic worms were maintained under different extracellular riboflavin levels, which was also mediated partly via changes in the rft-2 levels that directs towards the possible involvement of transcriptional regulatory events.