The -514C>T polymorphism in the LIPC gene modifies type 2 diabetes risk through modulation of HDL-cholesterol levels in Mexicans.

PURPOSE: Both type 2 diabetes (T2D) and low levels of high-density lipoprotein cholesterol (HDL-C) are very prevalent conditions among Mexicans. Genetic variants in the LIPC gene have been associated with both conditions. This study aimed to evaluate the association of the -514C < T (rs1800588) LIPC gene polymorphism with different metabolic traits, particularly the effects of this polymorphism on HDL-C plasma levels and T2D risk. METHODS: Mediation analysis was used to assess the direct and indirect effects of the -514C>T LIPC gene variant on HDL-C levels, T2D risk, and body mass index (BMI), in 2105 Mexican mestizo participants. We also assessed the functional effect of the -514C>T LIPC variant on the promoter activity of a reporter gene in the HepG2 cell line. RESULTS: Direct effects show that the -514C>T LIPC polymorphism is significantly associated with increased HDL-C plasma levels (ß = 0.03; p < 0.001). The -514C>T variant resulted in an indirect protective effect on T2D risk through increasing HDL-C levels (ß = - 0.03; p < 0.001). Marginal direct association between -514C>T and T2D was found (ß = 0.08; p = 0.06). Variables directly influencing T2D status were European ethnicity (ß = - 7.20; p < 0.001), age (ß = 0.04; p < 0.001), gender (ß = - 0.15; p = 0.017) and HDL-C (ß = - 1.07; p < 0.001). In addition, we found that the -514C>T variant decreases the activity of LIPC promoter by 90% (p < 0.001). CONCLUSIONS: The -514C>T polymorphism was not directly associated with T2D risk. HDL-C acts as a mediator between -514C>T LIPC gene variant and T2D risk in the Mexican population.

R230C but not - 565C/T variant of the ABCA1 gene is associated with type 2 diabetes in Mexicans through an effect on lowering HDL-cholesterol levels.

PURPOSE: Type 2 diabetes (T2D) and low serum concentration of high-density lipoprotein cholesterol (HDL-c) are common coexisting metabolic disorders. ABCA1 variants have been shown to be associated to these conditions. We sought to test the combined effect of two ABCA1 gene common variants, rs2422493 (- 565C > T) and rs9282541 (R230C) on HDL-c levels and T2D risk. METHODS: Path analysis was conducted in 3,303 Mexican-mestizos to assess the specific contributions of rs2422493 and rs9282541 ABCA1 variants, insulin resistance, waist-to-height ratio (WHtR), and age on HDL-c levels and T2D risk. Participants were classified into four groups according to their ABCA1 variants carrier status: (i) the reference group carried wild type alleles for both ABCA1 variants (-/-), (ii) +/- were carriers of rs2422493 but non-carriers of rs9282541, (iii) -/+ for carriers of rs9282541 but not carriers of rs2422493 and (iv) carriers of minor alleles for both SNPs (+/+). Principal components from two previous genome-wide association studies were used to control for ethnicity. RESULTS: We identified significant indirect effects on T2D risk mediated by HDL-c in groups -/+ and +/+ (ß = 0.04; p = 0.03 and ß = 0.06; p < 0.01, respectively) in comparison to the -/- reference group. Low concentrations of HDL-c were directly and significantly associated with increased T2D risk (ß = -0.70; p < 0.01). WHtR, male gender, age, and insulin resistance were also associated with T2D risk (p < 0.05). There was no significant direct effect for any of the ABCA1 groups on T2D risk: p = 0.99, p = 0.58, and p = 0.91 for groups +/-, -/+, and +/+ respectively. CONCLUSIONS: The ABCA1 rs9282541 (R230C) allele is associated with T2D in Mexicans through its effect on lowering HDL-c levels. This is the first report demonstrating that HDL-c levels act as an intermediate factor between an ABCA1 variant and T2D.

A cis-acting element in the promoter of human ether à go-go 1 potassium channel gene mediates repression by calcitriol in human cervical cancer cells.

The human ether à go-go 1 potassium channel (hEAG1) is required for cell cycle progression and proliferation of cancer cells. Inhibitors of hEAG1 activity and expression represent potential therapeutic drugs in cancer. Previously, we have shown that hEAG1 expression is downregulated by calcitriol in a variety of cancer cells. Herein, we provided evidence on the regulatory mechanism involved in such repressive effect in cells derived from human cervical cancer. Our results indicate that repression by calcitriol occurs at the transcriptional level and involves a functional negative vitamin D response element (nVDRE) E-box type in the hEAG1 promoter. The described mechanism in this work implies that a protein complex formed by the vitamin D receptor-interacting repressor, the vitamin D receptor, the retinoid X receptor, and the Williams syndrome transcription factor interact with the nVDRE in the hEAG1 promoter in the absence of ligand. Interestingly, all of these transcription factors except the vitamin D receptor-interacting repressor are displaced from hEAG1 promoter in the presence of calcitriol. Our results provide novel mechanistic insights into calcitriol mode of action in repressing hEAG1 gene expression.

Early-onset type 2 diabetes: metabolic and genetic characterization in the mexican population.

The objective of this study was to investigate possible defects in the insulin sensitivity and/or the acute insulin response in a group of Mexican patients displaying early-onset type 2 diabetes and to evaluate the contribution of mutations in three of the genes linked to maturity-onset diabetes of the young. We studied 40 Mexican patients with an age of diagnosis between 20 and 40 yr in which the insulin sensitivity as well as the insulin secretory response were measured using the minimal model approach. A partial screening for possible mutations in 3 of the 5 genes linked to maturity-onset diabetes of the young was carried out by PCR-single strand conformation polymorphism analysis. A low insulin secretory capacity (AIRg = 68.5 +/- 5 muU/mL.min) and a near-normal insulin sensitivity (3.43 +/- 0.2 min/muU.mL x 10(4)) were found in these patients. Among this group we found two individuals carrying missense mutations in exon 4 of the hepatocyte nuclear factor-1alpha (HNF-4alpha) gene (Asp(126)-->His/Tyr and Arg(154)-->Gln, respectively) and one carrying a nonsense mutation in exon 7 of the HNF-1alpha gene (Gln(486)-->stop codon); 7.5% had positive titers for glutamic acid decarboxylase antibodies. Thirty-five percent of cases had insulin resistance; these subjects had the lipid abnormalities seen in the metabolic syndrome. A defect in insulin secretion is the hallmark in Mexican diabetic patients diagnosed between 20 and 40 yr of age. Mutations in either the HNF-1alpha or the HNF-4alpha genes are present among the individuals who develop early-onset diabetes in our population. These particular sequence changes have not been previously reported and therefore represent putative new mutations. Even in the absence of endogenous hyperinsulinemia, insulin resistance is associated with an adverse lipid profile.

Mutation analysis in patients with congenital adrenal hyperplasia in the Spanish population: identification of putative novel steroid 21-hydroxylase deficiency alleles associated with the classic form of the disease.

Steroid 21-hydroxylase deficiency, due to the genetic impairment of the CYP21 gene, is a major cause of congenital adrenal hyperplasia (CAH). In about 80% of the cases, the defect is related with the transfer of deleterious point mutations from the CYP21P pseudogene to the active CYP21 gene. Sixteen different point mutations have been searched for in 60 Spanish patients with the classic form of CAH and 171 unaffected family members, using selective amplification of the CYP21 gene followed by allele-specific oligonucleotide hybridization (PCR-ASOH) and sequencing analysis. While 31.9% of the disease alleles carry CYP21 deletions or large gene conversions, around 58% of the alleles carry single point mutations. Corresponding segregation of mutations was found in every case indicating that none of them has apparently appeared de novo. The most frequent mutations found in our sample are i2G, V281L, R356W, Q318X, P453S and F306+t, with rates of 30, 14.2, 10, 9.2, 9.2 and 7. 5%, respectively. We found similar frequencies for the A and C polymorphism at position 656 (40 and 31.5%, respectively) in wild-type alleles for the i2G mutation. Around 10% of the alleles, for which no mutations were identified by searching for the sixteen previously known mutations, are currently being sequenced and new possible mutations and polymorphisms have been identified.

Uniparental disomy for chromosome 6 results in steroid 21-hydroxylase deficiency: evidence of different genetic mechanisms involved in the production of the disease.

Congenital adrenal hyperplasia (CAH) is an inherited recessive disorder of adrenal steroidogenesis caused by mutations in the steroid 21-hydroxylase gene (CYP21) in more than 90% of affected patients. The CYP21 gene is located within the HLA complex locus on chromosome 6 (6p21.3). During a molecular characterisation study of a group of 47 Mexican families with 21-hydroxylase deficiency, we identified nine in which the mutation or mutations found in the patient did not appear to originate from one of the parents. Through DNA fingerprinting, paternity was established in all nine families with a probability of non-paternity in the range of 10(-19) to 10(-23). Among these families, we identified one patient with exclusive paternal inheritance of all eight markers tested on chromosome 6p, despite normal maternal and paternal contributions for eight additional markers on three different chromosomes. We did not identify duplication of paternal information for markers in the 6q region, consistent with lack of expression of transient neonatal diabetes owing to genomic imprinting in this patient. Our results substantiate evidence for the existence of different genetic mechanisms involved in the expression of this recessive condition in a substantial portion (approximately 19%) of affected Mexican families. In addition to the identification of a patient with paternal uniparental disomy, the occurrence of germline mutations may explain the unusual pattern of segregation in the majority of the remaining eight families.

Molecular genetic analysis of patients carrying steroid 21-hydroxylase deficiency in the Mexican population: identification of possible new mutations and high prevalence of apparent germ-line mutations.

Steroid 21-hydroxylase deficiency is the underlying cause in over 90% of patients with congenital adrenal hyperplasia, an inherited metabolic disorder of adrenal steroidogenesis. We have characterized 94 mutant alleles from 47 unrelated Mexican patients and the corresponding mutant alleles in their parents by amplification of the functional CYP21 gene by PCR, followed by direct sequence analysis. The study included patients diagnosed with the three clinical forms of the disease. Our results revealed: (1) the presence of relatively few mutations or combinations of mutations associated with particular phenotypes; (2) the presence of putative new mutations; (3) the finding of identical genotypes in patients displaying discordant phenotypes; (4) the identification of patients lacking all previous reported mutations; and (5) an apparent high frequency of germ-line mutations. The absence of previously reported mutations in about 22% of the disease alleles, the finding of putative new mutations in some of the patients lacking previously known mutations, and the apparent high prevalence of germ-line mutations make evident the differences in the genetic background leading to this disorder between the Caucasian and the Mexican populations.

Low frequency of deletion alleles in patients with steroid 21-hydroxylase deficiency in a Mexican population.

Steroid 21-hydroxylase deficiency is caused by mutations in the CYP21 gene. Approximately 95% of mutant alleles are generated by recombination events between the active gene CYP21 and its highly homologous pseudogene, CYP21P. Deletion alleles are generated by unequal crossing over, while point mutations are the result of gene conversion events. Deletions account for 20-25% of the 21-hydroxylase deficiency alleles in most populations studied. We have looked for deletions among 53 unrelated Mexican patients with steroid 21-hydroxylase deficiency and found that deletions represent less than 1% of the disease alleles. These findings suggest that nearly all mutant alleles in our patient population contain point mutations and that the low representation of deletion alleles among clinically diagnosed patients may be due to missing detection of salt wasters, mainly males, who may die during the neonatal period.