Introduction Genetic variants contribute to differential responses to non-insulin antidiabetic drugs (NIADs), and consequently to variable plasma glucose control. Optimal control of plasma glucose is paramount to minimizing type 2 diabetes-related long-term complications. India’s distinct genetic architecture and its exploding burden of type 2 diabetes warrants a population-specific survey of NIAD-associated pharmacogenetic (PGx) variants. The recent availability of large-scale whole genomes from the Indian population provides a unique opportunity to generate a population-specific map of NIAD-associated PGx variants. Research design and methods We mined 1029 Indian whole genomes for PGx variants, drug–drug interaction (DDI) and drug–drug–gene interactions (DDGI) associated with 44 NIADs. Population-wise allele frequencies were estimated and compared using Fisher’s exact test. Results Overall, we found 76 known and 52 predicted deleterious common PGx variants associated with response to type 2 diabetes therapy among Indians. We report remarkable interethnic differences in the relative cumulative counts of decreased and increased response-associated alleles across NIAD classes. Indians and South Asians showed a significant excess of decreased metformin response-associated alleles compared with other global populations. Network analysis of shared PGx genes predicts high DDI risk during coadministration of NIADs with other metabolic disease drugs. We also predict an increased CYP2C19-mediated DDGI risk for CYP3A4/3A5-metabolized NIADs, saxagliptin, linagliptin and glyburide when coadministered with proton-pump inhibitors (PPIs). Conclusions Indians and South Asians have a distinct PGx profile for antidiabetes drugs, marked by an excess of poor treatment response-associated alleles for various NIAD classes. This suggests the possibility of a population-specific reduced drug response in atleast some NIADs. In addition, our findings provide an actionable resource for accelerating future diabetes PGx studies in Indians and South Asians and reconsidering NIAD dosing guidelines to ensure maximum efficacy and safety in the population.

INTRODUCTION: The gene-environment interaction of the REarranged during Transfection (RET) gene with vitamin A in the etiopathogenesis of Hirschsprung disease (HSCR) has been suggested in rodents. The aim of this study was to evaluate vitamin A status in mothers of children with HSCR and to assess its association with pathogenic variants of the RET gene in affected children. METHODS: This was a case-control study of stable isotope–based vitamin A measurement stores of mothers of children diagnosed with HSCR (within 8 months from birth, n = 7) and age-matched mothers of normal children (n = 6). Next-generation sequencing of RET exons, along with their upstream promoter region, was performed in the 7 HSCR proband-parent triads to evaluate pathogenic variants. RESULTS: Maternal vitamin A stores in the HSCR group was almost 50% that of those in controls, tending toward significance (0.50 ± 0.17 vs 0.89 ± 0.51 μmol/g respectively, P = 0.079). Two novel pathogenic de novo mutations were identified in 2 cases, and a rare single-nucleotide deletion was detected in the 3.5-kb RET upstream region, in a heterozygous state, in all 7 proband-parent triads. Low-penetrance RET haplotypes associated with HSCR were detected in 5 cases. DISCUSSION: Mothers with children with HSCR had lower vitamin A liver stores than mothers with normal children, and the children who were affected had HSCR despite having no established pathogenic RET variants. Lower maternal vitamin A status may increase the penetrance of genetic mutations in RET, and vitamin-A mediated gene-environment interactions may underpin some of the etiology of HSCR.

Background/Objectives: The bioavailability of crystalline vitamin B₁₂ (B₁₂) through active absorption is reported to have a maximum capacity of 1.5–2.5 µg per dose. A small passive bioavailability has also been suggested at high doses. The present study aimed to determine the dose-dependency of active B₁₂ absorption and to quantify its passive absorption at higher doses. Methods: The dose-dependency of crystalline B₁₂ bioavailability was determined in nine healthy adults, using oral [¹³C]-cyanocobalamin, in a cross-over design at doses of 2.5, 5, and 10 µg. The dose order was randomised, with a washout of one month. Literature data from was added to the present study data in a meta-analysis of the relation between B₁₂ bioavailability and dose, to evaluate its pattern at different doses. Results: Bioavailability, as a function of dose, was significantly different between 2.5, 5, and 10 µg doses of [¹³C]-cyanocobalamin at 50.9 ± 32.5%, 26.7 ± 22.3%, 15.4 ± 13.6%, respectively, (p < 0.01), while the absolute bioavailability trended upward, at 1.16 ± 0.74 µg, 1.22 ± 1.02 µg, and 1.39 ± 1.23 µg (p = 0.46). The meta-analysis showed two distinct phases of bioavailability. Up to a dose of 2.6 µg, there was a significant steep positive correlation, with a slope (bioavailability) of 43%/µg suggesting an active process with a maximum of 1.2 µg. At higher doses, the slope was 1%/µg, not significantly different from zero, possibly a passive process. Conclusions: The active bioavailability of crystalline B₁₂ is not dose-dependent, saturating at ~1.2 µg.

Aim: The CYP2D6 gene is highly polymorphic, causing large interindividual variability in the metabolism of several clinically important drugs. Materials & methods: The authors investigated the dive...