Endocrine Abstracts

JOINT2823

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 has been shown to be exaggerated in babies born preterm, with potential consequences later in life 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 leading to abnormal mini-puberty in mice and congenital hypogonadotropic hypogonadism in humans. We interrogated 63 patient samples from the Finnish mini-puberty cohort (75% born <37/40 gestation) part of the ‘miniNO’ project (grant 847941), for variants in genes associated with NO signalling pathways. Whole genome sequencing was filtered for rare and predicted in-silico to be pathogenic to protein function. We identified two preterm infants with variants of interest. One female patient, born at 24.7 weeks, carried a missense heterozygous variant (c.1855A>T, p.M619L) in NOS1. The variant is rare in the healthy population (gnomAD European frequency of 0.39%). She displayed a very exaggerated mini-puberty with peak urinary luteinising hormone (LH) of 208 IU/l, with corresponding oestradiol of 16662 pmol/l. At follow-up aged 14.8 years the patient is pre-menarche, suggesting pubertal delay. The affected residue is located in the highly conserved oxygenase domain of NOS1. in vitro, the maximal NO output from cells transiently expressing the p.M619L mutant was significantly attenuated compared to wild-type NOS1, suggesting decreased NOS1 activity. In addition, the p.M619L variant was able to dimerise with wildtype NOS1 in co-immunoprecipitation experiments, suggesting an impairment of functional homodimer formation, which may underly pathogenicity of the heterozygous variant. A second female patient, born at 32.1 weeks had a missense heterozygous variant (c.296G>A, p.S99N) in the NOS1 associated protein 1 gene (NOS1AP). The variant has gnomAD European frequency of 0.57%. The patient demonstrated a flat mini-puberty profile with peak LH of 0.97 IU/l and at the current age of 12.5 years has mild puberty delay (Tanner stage B2). NOS1AP is expressed in GnRH neurons and co-expressed with NOS1. The S99N variant is located within the phosphotyrosine-binding domain of NOS1AP, with a role in neuronal dendritic development and cell proliferation and migration. Functional characterisation is in progress. 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.