ESPE Abstracts

Background: Isolated gonadotropin-releasing hormone deficiency (IGD) is a genetically heterogeneous disorder caused by >60 genes resulting in a broad range of clinical manifestations and classified into Kallmann syndrome (KS) with anosmia and normosmic isolated hypogonadotropic hypogonadism (nIHH). Despite the advent of next-generation sequencing technology, ~50% of the cases remain genetically undiagnosed. Previously, copy number variations (CNVs) in known IGD genes contribute ~2% of IGD pathogenesis. This study aims to investigate frequency of CNVs and clinical characteristics in patients with KS and nIHH.

Methods: This study included 77 patients (45 with KS, 27 with nIHH, and 5 prepubertal children with anosmia or micropenis). Clinical features and endocrine findings were retrospectively analyzed. Genetic testing was performed using Sanger sequencing for select genes (n = 39), multiplex ligation-dependent probe amplification (MLPA) analysis for ANOS1 (n = 32), targeted gene panel sequencing (n = 27), whole-exome sequencing (WES, n = 29), or whole-genome sequencing (WGS, n = 16). One neonate with Xp22 deletion detected by G-scanning was included.

Results: Among the 77 patients, 45 (58.4%) harbored rare sequence variants, including 28 (36.4%) with pathogenic or likely pathogenic variants and 17 (22.1%) with variants of uncertain significance. Additional four patients (5.2%) had structural variants, including inv(X)(p22.23p22.2) encompassing ANOS1, deletion of exon 7 in ANOS1, Xp22.31 microdeletion, and a 20p12.3 deletion involving exon 3 to 3’-untranslated region of PROKR2. The patient who diagnosed with KS harboring inv(X)(p22.23p22.2) presented with hearing loss, developmental delay, ptosis, myopia, and unilateral renal agenesis. Among 3 patients with CNVs, two were diagnosed with KS, whereas the other one was a prepubertal child with micropenis and bilateral cryptorchidism.

Conclusion: The frequency of CNVs was 3.8% in our cohort with IGD. Comprehensive analysis using WGS or MLPA analysis is required to detect CNVs. The diagnostic yield of next-generation sequencing for IGD is still not more than 50%, suggesting that the impact of oligogenic inheritance, epigenetic modifications, and variants in non-coding regions on the etiology and variability of IGD.