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.

Objective: A haplotype at chromosome 17p13 that reduces expression and function of the solute carrier transporter SLC16A11 is associated with increased risk for type 2 diabetes in Mexicans. We aim to investigate the detailed metabolic profile of SLC16A11 risk haplotype carriers to identify potential physiological mechanisms explaining the increased type 2 diabetes risk. Design: Cross-sectional study. Methods: We evaluated carriers (n = 72) and non-carriers (n = 75) of the SLC16A11 risk haplotype, with or without type 2 diabetes. An independent sample of 1069 subjects was used to replicate biochemical findings. The evaluation included euglycemic-hyperinsulinemic clamp, frequently sampled intravenous glucose tolerance test (FSIVGTT), dual-energy X-ray absorptiometry (DXA), MRI and spectroscopy and subcutaneous abdominal adipose tissue biopsies. Results: Fat-free mass (FFM)-adjusted M value was lower in carriers of the SLC16A11 risk haplotype after adjusting for age and type 2 diabetes status (β = −0.164, P = 0.04). Subjects with type 2 diabetes and the risk haplotype demonstrated an increase of 8.76 U/L in alanine aminotransferase (ALT) (P = 0.02) and of 7.34 U/L in gammaglutamyltransferase (GGT) (P = 0.05) compared with non-carriers and after adjusting for gender, age and ancestry. Among women with the risk haplotype and normal BMI, the adipocyte size was higher (P < 0.001). European Journal of Endocrinology180:2 100 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com Conclusions: Individuals carrying the SLC16A11 risk haplotype exhibited decreased insulin action. Higher serum ALT and GGT levels were found in carriers with type 2 diabetes, and larger adipocytes in subcutaneous fat in the size distribution in carrier women with normal weight. European Journal of Endocrinology 180:2 101 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com European Journal of Endocrinology 180:2 102 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com European Journal of Endocrinology 180:2 103 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com European Journal of Endocrinology 180:2 104 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com European Journal of Endocrinology 180:2 105 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com European Journal of Endocrinology 180:2 106 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity https://eje.bioscientifica.com European Journal of Endocrinology 180:2 107 Clinical Study P Almeda-Valdes and others SLC16A11 and insulin sensitivity

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.

Steroid 21-hydroxylase deficiency is the major cause of congenital adrenal hyperplasia, an autosomic recessive disorder that affects the synthesis of aldosterone and cortisol. The disease presents a wide spectrum of clinical phenotypes as a result of the combination of different mutant alleles. Due to the adrenal-specific expression of the enzyme, the study of the functional effect of different mutations is only possible through in vitro expression studies. Determination of the functional effect of independent mutations does not always result in clear phenotype-genotype correlations, particularly in those patients with different mutations in the two alleles (compound heterozygotes). In this study we show that co-expression of the mutant proteins I172N, V281L or I236N/V237E/M239K with the wild-type enzyme resulted in an apparent dominant negative effect on the enzymatic activity of the latter, while co-expression with the mutant enzyme R356W does not show this effect.