GNRHR biallelic and digenic mutations in patients with normosmic congenital hypogonadotropic hypogonadism

OBJECTIVE: Normosmic congenital hypogonadotropic hypogonadism (nCHH) is a rare disorder characterised by lack of pubertal development and infertility, due to deficient production, secretion or action of gonadotropin-releasing hormone (GnRH) and, unlike Kallmann syndrome, is associated with a normal sense of smell. Mutations in the GNRHR gene cause autosomal recessive nCHH. The aim of this study was to determine the prevalence of GNRHR mutations in a group of 40 patients with nCHH. DESIGN: Cross-sectional study of 40 unrelated patients with nCHH. METHODS: Patients were screened for mutations in the GNRHR gene by DNA sequencing. RESULTS: GNRHR mutations were identified in five of 40 patients studied. Four patients had biallelic mutations (including a novel frameshift deletion p.Phe313Metfs*3, in two families) in agreement with autosomal recessive inheritance. One patient had a heterozygous GNRHR mutation associated with a heterozygous PROKR2 mutation, thus suggesting a possible role of synergistic heterozygosity in the pathogenesis of the disorder. CONCLUSIONS: This study further expands the spectrum of known genetic defects associated with nCHH. Although GNRHR mutations are usually biallelic and inherited in an autosomal recessive manner, the presence of a monoallelic mutation in a patient should raise the possibility of a digenic/oligogenic cause of nCHH.