Background: Disorders (or differences) of sex development (DSD) are rare congenital conditions in which the development of chromosomal, gonadal, or anatomical sex is atypical. The luteinizing hormone/chorionic gonadotropin receptor (LHCGR) is important for male sex development. LHCGR mutations can cause Leydig cell hypoplasia, which is an autosomal recessive disorder.
Objective and hypotheses: We found two heterozygous mutations in the LHCGR, a new p.F138S mutation in combination with the previously described c.580A>G mutation in exon 6A in two sisters with 46,XY DSD and complete inconspicuous female appearance. Deleterious effect of the p.F138S mutation was assessed by functional analysis.
Methods: Expression vectors containing LHCGR mutation were generated an employed for functional assay by cAMP RIA, cAMP-responsive element containing reporter genes (pCRE-Luc) and cAMP binding luciferases (GloSensor). Localisation was analysed by immunoimaging and glycosylation was studied by glycosidase F treatment and immunoblot.
Results: The three different cAMP assays demonstrated a complete loss of function of the p.F138S mutant. Immunoimaging showed that the mutant receptor is expressed internally, but did not reach the membrane surface. Treatment with glycosidase F and subsequent immunoblot revealed an incomplete glycosylation of the receptor. Compound heterozygosity was proven by long range PCR and subcloning of the fragment containing both mutants.
Conclusion: The mutation p.F138S in Exon 5 leads to a loss of function of LHCGR. Together with the second previously described mutation in cryptic exon 6A these compound heterozygous mutations explain the autosomal recessive disorder. The functional data fully support the observed clinical phenotype.
10 Sep 2016 - 12 Sep 2016