Mutation identification and functional analysis of mutant dax-1 proteins found in Thai patients with x-linked adrenal hypoplasia congenita

Abstract

Mutations in the DAX-1 gene result in X-linked adrenal hypoplasia congenita (X-linked AHC), a rare congenital disorder of adrenal insufficiency with defects in adrenal gland development and steroid biosynthesis. Male patients usually develop severe adrenal insufficiency in early infancy or childhood. In some cases, hypogonadotropic hypogonadonism (HH) is presented in puberty. DAX-1 gene product, DAX-1 protein, acts as a transcriptional repressor of genes in the steroidogenic pathway by interacting with, and repressing the steroidogenic factor 1 (SF-1) protein. In contrast, the SF-1 protein transactivates the steroidogenic acute regulatory (StAR) protein that functions in the steroid biosynthetic pathway. The aim of this study is to identify mutations in the DAX-1 gene and to analyze functions of mutant DAX-1 proteins found in Thai patients with X-linked AHC. Seven Thai patients in six families with typical and atypical symptoms of X-linked AHC and HH were investigated in the present study. The DAX-1 gene was sequenced from all patients, and the mutant DAX-1 proteins were functionally analyzed by luciferase assays. Sequence data identified three novel mutations: c.363delG (p.Gly122Valfs*142), c.1062delC (p.Ala355Profs*17), c.1156C>T (p.Leu386Phe), and three known mutations: c.805_807delGTC (p.Val269del), c.1148_1149delGG (p.Gly383Aspfs*5), c.501_502insG (p.Ala170Argfs*15) in the DAX-1 gene. DAX-1 mutants showed lower levels of repressor activity on the StAR gene promoter when compared with wild-type. Moderate genotype-phenotype correlation was observed in the patients. These results support the diagnosis, and extend the phenotypic and mutational spectrum of DAX-1 mutations. Moreover, molecular analysis and functional studies pave ways to better understanding towards the disease pathogenesis.