Leydig cell hypoplasia: absent luteinizing hormone receptor cell surface expression caused by a novel homozygous mutation in the extracellular domain

Leydig cell hypoplasia is a rare autosomal recessive condition that interferes with normal development of male external genitalia in 46,XY individuals. We have studied a family with a 46,XY girl due to a new homozygous mutation (V144F) in the extracellular ligand-binding domain. HEK 293 cells transfected with the mutant LH receptor exhibited a marked impairment of human chorionic gonadotropin binding. Using Western blotting of the expressed V144F mutant LH receptor protein showed the absence of the glycosylated cell surface form. Treatment of the mutant LH receptor with N-glycosidase F or endoglycosidase-H demonstrated that the mutant receptor is retained in the endoplasmic reticulum. Expression and study of enhanced green fluorescent protein-tagged receptors confirmed that the mutant LHR-V144F receptors do not migrate to the cell surface, and the fluorescence remains intracellular and colocalizes with an endoplasmic reticulum marker, ER-tracker Blue-white DPX. Comparison of the theoretical molecular models of the extracellular domain of the wild-type and the mutant receptor suggests that the mutation LHR-V144F, located in the outer circumference in a alpha-helix of the leucine-rich repeat 4, may induce a conformational strain on the molecule. F144 of the mutant LH receptor has overlapping interactions with F119, which V144 in the wild-type receptor has not.