NMDA (N-Methyl-D-aspartic acid) receptors have been shown to control the timing of sexual maturation in laboratory animals. Therefore, variants in genes impacting NMDA receptor signaling might be predicted to affect human puberty. We studied an extended family with extremely delayed puberty (menarche at 16.5 - 18 years for female family members and pubertal onset at 16 years for male family members). Exome sequencing revealed a rare missense variant (F900V) in DLG2, which co-segregated precisely with the delayed puberty phenotype in the 5 affected members of the 11-member family. Interestingly, recent genome-wide association studies (GWAS) have implicated DLG2 in the normal timing of human puberty in males and females. DLG2 encodes PSD-93, an anchoring protein of NMDA receptors. The functional effects of PSD-93 F900V were studied in vitro. First, we assessed the effect of F900V on the interaction between PSD-93 and Fyn, a known binding partner of PSD-93 that phosphorylates NMDA receptors to increase signaling. Co-immunoprecipitation showed that the F900V variant impaired the interaction between PSD-93 and Fyn (P=0.005). Second, the impact of F900V on the expression of Gnrh1 was studied in the hypothalamic cell line, GT1-7. Compared to wild-type Dlg2/PSD-93, F900V decreased expression of Gnrh1 both in mRNA expression by real time-PCR (P=0.003) and GnRH peptide/total protein ratio by ELISA (P=0.008). We next looked for DLG2 sequence variants in a large cohort of 1,327 individuals with hypogonadotropic hypogonadism (HH) and identified missense variants in DLG2 that also significantly diminished Gnrh1 mRNA expression in vitro in 3 unrelated families with HH: two siblings with normosmic HH, 2 siblings with Kallmann syndrome, and a single subject with Kallmann syndrome. However, incomplete penetrance indicated that the DLG2 variants alone were not sufficient to cause HH, suggesting a digenic or oligogenic inheritance. We observed mRNA expression of Dlg2 in the rat preoptic area and protein expression in mouse hypothalamus which varied with age. However, the temporal pattern of expression did not match the temporal pattern of reproductive maturation suggesting that, although Dlg2/PSD-93 may be important for normal puberty, rising expression may not be a trigger for pubertal onset.
In conclusion, variants in DLG2/PSD-93, an anchoring protein of NMDA receptors, were found in an extended family with extremely delayed puberty and in subjects with HH. In vitro studies indicated that the variants affect GnRH expression. The findings provide evidence that abnormalities in NMDA receptor signaling are involved in the pathogenesis of human pubertal disorders.
19 Sep 2019 - 21 Sep 2019