SUN-032 Digenic Inheritance of PCSK1 and CHD7 Mutations in PAX4 Homozygous Diabetic Male with Normosmic Hypogonadotropic Hypogonadism

Abstract

Background: Normosmic congenital hypogonadotropic hypogonadism denotes Kallmann syndrome not associated with anosmia or hyposmia. Over the past few years, the availability of next-generation sequencing has started to unravel the complex molecular basis of congenital hypogonadotrophic hypogonadism including digenic or oligogenic pathogenecity in addition to classic monogenic causality (1). Clinical Case: A 22-year-old male patient was referred to the endocrine clinic in 2018 with recent -onset hyperglycemia. His weight was 82.2 kg with a height of 180 cm (BMI of 25.3 kg/m2). Physical examination revealed small testes, micropenis, and no axillary and pubic terminal hair. His smell sense was intact. His hormonal test reveals low testosterone (0.10 ng/mL) and low free testosterone (0.65 pg/mL) levels with inappropriately low gonadotrophins levels. Secretion of LH and FSH increased 2-fold after GnRH stimulation. His bone age was 13-years 6-months old, and brain magnetic resonance imaging showed the presence of olfactory bulbs, and unremarkable findings except for small size of the pituitary gland. There were no signs associated with CHARGE syndrome (coloboma ocular, heart defects, atresia or stenosis of the choanae, retardation of growth and/or development, genitourinary anomalies, and ear abnormalities). Biochemical investigation demonstrated high serum glucose level and high HbA1c (13.8%). To identify variants to cause the phenotype of the proband, we adopted trio-based whole exome sequencing (WES) and candidate gene approach. Candidate genes was listed from the orphanet (https://www.orpha.net). WES of the proband revealed the presence of heterozygote missense mutations of the CHD7 gene (c.6107C>T, p.Pro2036Leu, rs369543203) and PCSK1 gene (c.239G>A, p.Arg80Gln, rs1799904). The missense variants were predicted to have a damaging effect on the encoded protein, by SIFT and PolyPhen-2 analyses. Genetic analyses of his family revealed that his father had the same heterozygote missense mutations of the CHD7 gene, but wild type of PCSK1. Proband’s mother had the same heterozygote missense mutations of PCSK1, but wild type of CHD7. Furthermore, the proband had homozygote missense mutation of PAX4 (c.575G>A, p.Arg192His, rs2233580) known as maturity-onset diabetes of the young (MODY) 9 gene. Both parents have the same but heterozygous mutation of PAX4 p.Arg192His, and pre-diabetic range of hyperglycemia. Conclusion: This is the first case demonstrating digenic inheritance of mutations in PCSK1 and CHD7 as a potential cause of normosmic hypogonadotrophic hypogonadism, interestingly in PAX4 homozygous diabetic male. Reference: (1) Maione L, et al. Genetic counseling for congenital hypogonadotropic hypogonadism and Kallmann syndrome: new challenges in the era of oligogenism and next-generation sequencing. Eur J Endocrinol. 2018;178(3):R55-R80.