Endocrine Abstracts

Introduction: Hypoparathyroidism (HPT), pseudohypoparathyroidism (PHP), and end-organ parathyroid hormone (PTH)-resistance are rare metabolic disorders characterized by low serum calcium and increased serum phosphorus due to a PTH-deficient or resistant state. Various genes/loci have been identified as responsible for the development of congenital/familial forms of HPT, PHP and related diseases.

Patients and Methods: A total of 39 patients with a clinical diagnostic suspicion of congenital forms of HPT (n=30) or PHP (n=9), previously resulted negative to monogenic genetic screening with PCR-based Sanger sequencing (n=13) or not yet being genetically analyzed (n=26), were collected by 4 major endocrinology centers in Italy. They were all analyzed by Next Generation Sequencing (NGS) using a customized multigenic panel containing 24 human genes whose mutations have been associated with the development of congenital forms of HPT and PHP. Obtained sequences were mapped on the HG38 human reference genome; genetic variants were annotated and analyzed using human gene variant databases and variant allele frequency projects. Variants were classified as “common” or “rare” with a frequency over or less than 1% in the general population, respectively, and then as benign (B), likely benign (LB), variants of uncertain clinical significance (VUS), likely pathogenic (LP), or pathogenic (P), according to the Standards and Guidelines for the Interpretation of Human Sequence Variants of the American College of Medical Genetics and Genomics (ACMG).

Results: Twenty-two patients (56.4%) were found not bearing any rare genetic variant, while in 4 patients (10.3%) we identified 4 different rare variants classified as benign. Thirteen patients (33.3%) were found to be carriers of at least one rare variant classified as VUS, LP, or P, out of them 8 (20.5%) had a single VUS, 3 (7.7%) had one VUS and one LP variant, one (2.6%) had a single LP variant, and one (2.6%) had a P variant. A total of 14 different VUS, LP and P variants were identified, all being heterozygous, 3 in AIRE gene (2 VUS, 1 P), 2 in GCM2 gene (1 VUS, 1 LP), and one in ACADM (VUS), CaSR (LP), CDH7 (VUS), FAM111A (VUS), GATA3 (LP), GNAS (VUS), PTH1R (VUS), TBCE (VUS) and TBX1 (VUS) genes.

Conclusions: Multigenic panel screening by NGS allowed the identification of rare VUS, LP, or P variants in patients previously resulted negative to monogenic Sanger’s sequencing (6/13; 46.2%). Segregation analysis is needed to assess the real clinical significance of identified variants.