The prevalence of digenic mutations in patients with normosmic hypogonadotropic hypogonadism and Kallmann syndrome

Objective: To determine the prevalence of digenic mutations in patients with idiopathic hypogonadotropic hypogonadism (IHH) and Kallmann syndrome (KS).

Design: Molecular analysis of DNA in IHH/KS patients.

Setting: Academic medical center.

Patient(s): Twenty-four IHH/KS patients with a known mutation (group 1) and 24 IHH/KS patients with no known mutation (group 2).

Intervention(s): DNA from IHH/KS patients was subjected to polymerase chain reaction-based DNA sequencing of the 13 most common genes (KAL1, GNRHR, FGFR1, KISS1R, TAC3, TACR3, FGF8, PROKR2, PROK2, CHD7, NELF, GNRH1, and WDR11).

Main outcome measure(s): The identification of mutations absent in ≥188 ethnically matched controls. Both SIFT (sorting intolerant from tolerant) and conservation among orthologs provided supportive evidence for pathologic roles.

Result(s): In group 1, 6 (25%) of 24 IHH/KS patients had a heterozygous mutation in a second gene, and in group 2, 13 (54.2%) of 24 had a mutation in at least one gene, but none had digenic mutations. In group 2, 7 (29.2%) of 24 had a mutation considered sufficient to cause the phenotype.

Conclusion(s): When the 13 most common IHH/KS genes are studied, the overall prevalence of digenic gene mutations in IHH/KS was 12.5%. In addition, approximately 30% of patients without a known mutation had a mutation in a single gene. With the current state of knowledge, these findings suggest that most IHH/KS patients have a monogenic etiology.