Examination of chromosome 7p22 candidate genes RBaK, PMS2 and GNA12 in familial hyperaldosteronism type II.

1. There are two types of familial hyperaldosteronism (FH): FH-I and FH-II. FH-I is caused by a hybrid CYP11B1/CYP11B2 gene mutation. The genetic cause of FH-II, which is more common, is unknown. Adrenal hyperplasia and adenomas are features. We previously reported linkage of FH-II to a approximately 5 Mb region on chromosome 7p22. We subsequently reported finding no causative mutations in the retinoblastoma-associated Kruppel-associated box gene (RBaK), a candidate at 7p22 involved in tumorigenesis and cell cycle control. 2. In the current study we investigated RBaK regulatory regions and two other candidate genes: postmeiotic segregation increased 2 (PMS2, involved in DNA mismatch repair and tumour predisposition) and guanine nucleotide-binding protein alpha-12 (GNA12, a transforming oncogene). 3. The GNA12 and PMS2 genes were examined in two affected (A1, A2) and two unaffected (U1, U2) subjects from a large 7p22-linked FH-II family (family 1). No mutations were found. 4. The RBaK and PMS2 distal promoters were sequenced to -2150 bp from the transcription start site for RBaK and-2800 bp for PMS2. Five unreported single nucleotide polymorphisms (SNPs) were found in subjects A1, A2 but not in U1 or U2; A(-2031 bp)T, T(-2030 bp)G, G(-834 bp)C, C(-821 bp)G in RBaK and A(-876 bp)G in PMS2. Additional affected and unaffected subjects from family 1 and from two other 7p22-linked FH-II families and 58 unrelated normotensive control subjects were genotyped for these SNPs. 5. The five novel SNPs were found to be present in a significant proportion of normotensive controls. The four RBaK promoter SNPs were found to be in linkage disequilibrium in the normal population. The RBaK promoter (-)2031T/2030G/834C/821T allele was found to be in linkage disequilibrium with the causative mutation in FH-II family 1, but not in families 2 and 3. The PMS2 promoter (-)876G allele was also found to be linked to affected phenotypes in family 1. 6. The RBaK and PMS2 promoter SNPs alter the binding sites for several transcription factors. Although present in the normal population, it is possible that the RBaK (-)2031T/2030G/834C/821T and PMS2 (-)876G alleles may have functional roles contributing to the FH-II phenotype in family 1.

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