FRI285 Evidence For ZIC1 As A Novel Gene For Isolated Hypogonadotropic Hypogonadism With Phenotypic Pleiotropic Intersection With Cerebellar Malformation

Disclosure: J. Cassin: None. D.L. Keefe: None. K.E. Sung: None. C.C. Bojo: None. G. Santiago: None. L. Plummer: None. K.B. Salnikov: None. S.B. Seminara: None. R. Balasubramania: None. P.L. Mellon: None. Isolated Hypogonadotropic Hypogonadism (IHH) is a condition marked by absent pubertal development and low sex steroids in the setting of low/normal gonadotropins. Mutations in known IHH genes only explain <50% of the genetic etiology suggesting significant missing heritability in IHH. To explore this missing IHH heritability, we examined whole exome sequencing data from approximately 1400 IHH probands for rare genetic variants in novel genes that are enriched in IHH patients. We identified four IHH probands with rare, novel heterozygous variants in ZIC1 (p.H134Rfs*21, p.Y287X, p.E299K, p.S413Y), a gene encoding C2H2-type zinc finger protein (rare variant enrichment p <0.0001 for both truncating and missense alleles). Prior literature review show that heterozygous deletions affecting the ZIC1 gene have been linked to Dandy Walker malformation [DWM], a cerebellar malformation, while gain-of-function ZIC1 single nucleotide variants have been linked to coronal craniosynostosis (premature cranial suture fusion). Notably, two IHH subjects with novel ZIC1 variants in our cohort exhibited posterior fossa abnormalities (DWM [p.H134Rfs*21] and ventriculomegaly [E299K]) but none had any cranial suture defects. Given the above genetic enrichment, phenotypic overlap between DWM and IHH, and ZIC1’s known high expression in the hypothalamus, we explored whether ZIC1 regulates the expression of hypothalamic releasing factors. We determined that ZIC1 overexpression increases GNRH1 luciferase expression in the immortalized GnRH cell line, GT1-7. We next explored whether the rare ZIC1 variants identified in the four IHH probands would affect this phenotype. We discovered that three of the four ZIC1 variants significantly reduced GNRH1-luciferase expression. Of those, one truncating mutation, p.H134Rfs*21, resulted in lower ZIC1 protein content in the cell and failure to localize to the nucleus, suggesting a hypomorphic mechanism of action. These findings implicate ZIC1 variants as putatively causal for IHH. Further studies will define the precise ZIC1 transcriptional targets that relate to ZIC1’s pleotropic effects on GnRH transcription, neuronal function, cerebellar development, and cranial suture fusion. Presentation: Friday, June 16, 2023