Endocrine Abstracts

Mini-puberty is the period of transient hypothalamic-pituitary-gonadal (HPG) axis activity shortly after birth, before the axis is ‘switched-off’ until puberty. The amplitude of mini-puberty is exaggerated in preterm babies, with potential consequences for neuronal maturation, pubertal disorders, behavioural and metabolic conditions. Nitric oxide (NO) is a key player in regulation of mini-puberty and reproductive development, with Nitric oxide synthase 1 (NOS1) deficiency causing abnormal mini-puberty in mice and congenital hypogonadotropic hypogonadism in humans. We interrogated 63 patient samples from the Finnish mini-puberty cohort (‘miniNO’ project, grant 847941), for variants in genes associated with NO signalling pathways. Whole genome sequencing was filtered for rare, predicted pathogenic variants. We identified two preterm infants with variants of interest. One female patient, born at 24.7 weeks, carried a rare missense heterozygous variant (c.1855A>T, p.M619L) in NOS1. She displayed a very exaggerated mini-puberty. At 14.8 years the patient was pre-menarchal, suggesting pubertal delay. The variant is in the highly conserved oxygenase domain of NOS1. In vitro, the NO output from cells transiently expressing the p.M619L mutant was significantly attenuated compared to wild-type NOS1, suggesting decreased NOS1 activity. Additionally, the p.M619L variant dimerised with wildtype NOS1, suggesting impaired functional homodimer formation, potentially underlying pathogenicity. A second female patient, born at 32.1 weeks had a missense heterozygous variant (c.296G>A, p.S99N) in NOS1 associated protein 1 (NOS1AP). The variant has gnomAD European frequency of 0.57%. The patient demonstrated a flat mini-puberty profile and pubertal delay. NOS1AP is expressed in GnRH neurons and co-expressed with NOS1. Ongoing functional characterisation thus far suggests no impact on NO output. Measurement of GnRH is ongoing. Here we identify rare exonic variants in genes within the NO synthesis pathway in patients with preterm birth and abnormal mini-puberty, providing potential human evidence for the role of NO signalling in prematurity and HPG axis regulation.