Vitamin D Pathway Genetic Variation and Type 1 Diabetes: A Case-Control Association Study.

Vitamin D has immunomodulatory effects, and its deficiency has been implicated in the autoimmune process of type 1 diabetes. Serum vitamin D levels are influenced by variants in genes involved in the synthesis, transport, hydroxylation and degradation of vitamin D. The aim of this study was to assess if single nucleotide polymorphisms (SNPs) at the DHCR7 (rs12785878), GC (rs2282679), CYP2R1 (rs2060793) and CYP24A1 (rs6013897) loci are associated with type 1 diabetes in the Portuguese population. Genotype and allele frequencies were determined in 350 cases of type 1 diabetes and in 490 controls. The frequency of each SNP alone was not significantly different between patients and controls. However, the combined analysis of the four SNPs showed that minor alleles of these variants clustered more frequently in patients. The proportion of individuals with three or more minor alleles was significantly higher in patients than in controls (56.3% vs. 48.5; odds ratio (OR) 1.37; 95% confidence interval (CI) 1.04-1.81; p-value 0.027). These results suggest a cumulative effect of SNPs at the DHCR7, GC, CYP2R1 and CYP24A1 loci on the susceptibility to type 1 diabetes, due to the roles of these genes in the vitamin D metabolic pathway.

Maturity-Onset Diabetes of the Young (MODY) in Portugal: Novel GCK, HNFA1 and HNFA4 Mutations.

Maturity-onset diabetes of the young (MODY) is a frequently misdiagnosed type of diabetes, which is characterized by early onset, autosomal dominant inheritance, and absence of insulin dependence. The most frequent subtypes are due to mutations of the GCK (MODY 2), HNF1A (MODY 3), and HNF4A (MODY 1) genes. We undertook the first multicenter genetic study of MODY in the Portuguese population. The GCK, HNF1A, and HNF4A genes were sequenced in 46 unrelated patients that had at least two of the three classical clinical criteria for MODY (age at diagnosis, family history, and clinical presentation). The functional consequences of the mutations were predicted by bioinformatics analysis. Mutations were identified in 23 (50%) families. Twelve families had mutations in the GCK gene, eight in the HNF1A gene, and three in the HNF4A gene. These included seven novel mutations (GCK c.494T>C, GCK c.563C>G, HNF1A c.1623G>A, HNF1A c.1729C>G, HNF4A c.68delG, HNF4A c.422G>C, HNF4A c.602A>C). Mutation-positive patients were younger at the time of diagnosis when compared to mutation-negative patients (14.3 vs. 23.0 years, p = 0.011). This study further expands the spectrum of known mutations associated with MODY, and may contribute to a better understanding of this type of diabetes and a more personalized clinical management of affected individuals.

Association of Vitamin D Pathway Genetic Variation and Thyroid Cancer.

Vitamin D is mostly known for its role in bone and calcium metabolism. However, studies have suggested that it also has inhibitory effects on tumor development and progression. Genetic variants close to genes that encode crucial enzymes for the synthesis (DHCR7 rs12785878), metabolism (CYP2R1 rs2060793) and degradation (CYP24A1 rs6013897) of vitamin D have been associated with serum levels of vitamin D. The aim of this case-control study was to determine the effect of these variants in the vitamin D pathway on the susceptibility to thyroid cancer. Five hundred patients with differentiated thyroid cancer and 500 controls were genotyped for the DHCR7 rs12785878, CYP2R1 rs2060793, and CYP24A1 rs6013897 variants. Genotype and allele frequencies were compared between patients and controls. The DHCR7 rs12785878 minor allele was associated with thyroid cancer under an additive (OR 1.38, 95% CI 1.15-1.65, p = 0.0004) and codominant (OR 1.88, 95% CI 1.30-2.74, p = 0.0021) model. These findings suggest that DHCR7 polymorphisms may be associated with an increased risk of thyroid cancer due to an effect of this gene on circulating vitamin D levels.