Antonio Percesepe

Novel approaches to uncover the molecular etiology of neurodevelopmental disorders (NDD) are highly needed. Even using a powerful tool such as whole exome sequencing (WES), the diagnostic process may still prove long and arduous due to the high clinical and genetic heterogeneity of these conditions. The main strategies to improve the diagnostic rate are based on family segregation, re-evaluation of the clinical features by reverse-phenotyping, re-analysis of unsolved NGS-based cases and epigenetic functional studies. In this article, we described three selected cases from a cohort of patients with NDD in which trio WES was applied, in order to underline the typical challenges encountered during the diagnostic process: (1) an ultra-rare condition caused by a missense variant in MEIS2, identified through the updated Solve-RD re-analysis; (2) a patient with Noonan-like features in which the NGS analysis revealed a novel variant in NIPBL causing Cornelia de Lange syndrome; and (3) a case with de novo variants in genes involved in the chromatin-remodeling complex, for which the study of the epigenetic signature excluded a pathogenic role. In this perspective, we aimed to (i) provide an example of the relevance of the genetic re-analysis of all unsolved cases through network projects on rare diseases; (ii) point out the role and the uncertainties of the reverse phenotyping in the interpretation of the genetic results; and (iii) describe the use of methylation signatures in neurodevelopmental syndromes for the validation of the variants of uncertain significance.

Introduction Haemophilias are X‐linked inherited bleeding disorders, due to de novo F8/F9 gene variants in 30–50% of cases. The identification of causative variant in index cases (IC) is crucial for genetic counselling in related women. Over the last 20 years the Emilia‐Romagna Regional Haemophilia Registry documented high proportions of sporadic severe haemophilia. Aim To clarify if carriers’ reproductive choices influence the sporadic/familial ratio of severe haemophilia. Methods Genetic counselling and genotyping in 221 relatives of severe IC were retrospectively reviewed, retrieving reproductive choices and pregnancy history of childbearing‐age carriers from familial and sporadic pedigrees and according to the IC degree of relationship (mothers, daughters, II/other). Results Carriers’ identification rates were lower in sporadic women and in other‐degree relatives. Among childbearing age women (n = 140), carriers were 37/48 (77%) and 57/92 (62%) of familial and sporadic relatives, respectively. Forty‐five/57 sporadic carriers experienced 67 pregnancies, while 21/37 familial carriers had 39 pregnancies (four voluntary terminations), with a significantly higher number of affected sons in the former (40/67 vs. 12/35, P = .025). Prenatal diagnosis was chosen by 40% and 47% of sporadic and familial aware carriers, respectively. Sporadic mothers often avoided further pregnancies (17/38, 45%) after a firstborn affected child, while familial mothers tended to face pregnancies without prenatal approaches (6/10, 60%). Conclusion In this cohort sporadic offspring account for more than 70% of severe haemophilia cases. This increasing proportion is likely to reflect the influence in reproductive choices of awareness of carriers’ status, particularly in sporadic mothers, and of prenatal diagnosis options.