P163: Clinical and molecular investigation of 89 Brazilian patients with Cornelia de Lange syndrome*

Introduction: Cornelia de Lange Syndrome (CdLS) is a rare genetic disease with a broad phenotypic spectrum, including facial dysmorphisms, short stature, hirsutism, upper limb defects, intellectual disability and behavioral disorders, including self-injury, anxiety, autistic characteristics, and sleep problems.Other common findings include congenital heart disease, gastroesophageal reflux disease (GERD), sensorineural deafness, myopia and cryptorchidism in boys.The variants in the NIPBL gene are the most frequent, affecting ~60% of cases and SMC1A, SMC3, RAD21, and HDAC8 genes affect 10% of CdLS cases and usually result in milder phenotypes.Mosaic variants mainly involving the NIPBL gene are very recurrent in CdLS patients, with a prevalence of 15%-20% of cases, that usually are not identified in blood, requiring the investigation of other tissues, such as buccal cells and fibroblasts variants.Our objectives were: To confirm the genetic etiology through exome sequencing (ES) analysis from patients with clinical diagnosis of CdLS including mosaic form; To describe the clinical findings with correlation phenotype and genotype.Methods: From 2017 to 2024, 89 patients with clinical suspect of CdLS selected from Associao Brasileira de CdLS were examined at the Genetics Unit from the Instituto da Criana do Hospital das Clnicas da Universidade de So Paulo; blood samples of the probands and their parents were submitted to ES in Yokohama City University and ES of buccal cells were performed in negative ES patients in Brazil.Results: All 89 patients included scored at least 4 points in Kline criteria (indication of molecular testing for CdLS).The age at the evaluation ranged from 6 months to 43 years old (mean 11,4 yo).Pathogenic and likely pathogenic causative variants were identified in CdLS causative genes in 55/89 patients (61,8%).NIPBL variants were found in 50/55 patients (91%), (31-male:19-female) and SMC1A variants in 5 patients (9%), (1 male: 4-female).Mosaicism in buccal cells was found in 6 NIPBL patients (6%), that was negative in blood sample.DNA was available from both parents in 40 families and of these, all variants were de novo.Causative variants include: 29 truncating (21 frameshift and 8 nonsense), 1 deletion in frame, 16 missense, 6 splicing, and 3 non-coding.Variants of uncertain significance were found in 4 probands.Interestingly, 26 probands (29,2%) other causative variants or copy number variations (CNVs) were identified with clinical overlap of CdLS phenotype.We were not able to find a molecular etiology in 8 cases.Among 55 patients with molecular confirmation of CdLS, the maternal age at pregnancy ranged from 16 to 39 years (mean: 27,6 yo) There were reports of 32 complicated pregnancies (58%), especially IUGR.Csection was done in 39 (70%) of cases, preterm delivery in 23 probands (42%) and 31(56%) with low birth weight.Complications in the perinatal period were present in 33 patients.The age at clinical diagnosis ranged from birth to 9 yo (mean:15,1mo).Most of the diagnosis was made by geneticist (41%).Almost all patients (96%) presented medical complications: ophthalmologic (40%), hearing disturbance (40%), cardiac malformation (56%), gastroesophageal reflux (85%), renal (13%), genital anomalies (58%), failure to thrive (93%).Behavioral disorders were common: self-injury (42%), aggressive (36%), autistic features in (29%), sleep problems (24%).All 55 patients presented some degree of developmental delay and/or intellectual disability.One 22 years old male patient died due to infectious respiratory disease.According to Kline criteria 44 patients were classified as classic (score >11), 6 patients as non-classic (score 9-10) and 5 patients as molecular investigation indicated (score4-8).Conclusion: Exome sequencing by NGS is an important method for confirmation for CdLS and buccal cells for mosaicism in negative ES patients should be included for investigation.