Sotos syndrome is a rare genetic disorder caused by haploinsufficiency of the NSD1 (nuclear receptor binding SET domain containing protein 1) gene. No clinical diagnostic consensus criteria are published yet, and molecular analysis reduces the clinical diagnostic uncertainty. We screened 1530 unrelated patients enrolled from 2003 to 2021 at Galliera Hospital and Gaslini Institute in Genoa. NSD1 variants were identified in 292 patients including nine partial gene deletions, 13 microdeletions of the entire NSD1 gene, and 115 novel intragenic variants never previously described. Thirty-two variants of uncertain significance (VUS) out of 115 identified were re-classified. Twenty-five missense NSD1 VUS (25/32, 78.1%) changed class to likely pathogenic or likely benign, showing a highly significant shift in class (p < 0.01). Apart from NSD1, we identified variants in additional genes (NFIX, PTEN, EZH2, TCF20, BRWD3, PPP2R5D) in nine patients analyzed by the NGS custom panel. We describe the evolution of diagnostic techniques in our laboratory to ascertain molecular diagnosis, the identification of 115 new variants, and the re-classification of 25 VUS in NSD1. We underline the utility of sharing variant classification and the need to improve communication between the laboratory staff and the referring physician.

Mitral annular disjunction (MAD) is associated with an increased risk of ventricular arrhythmias and sudden cardiac death, yet its genetic background remains poorly defined. We report the case of a 50-year-old man with MAD who survived cardiac arrest and carries three variants of unknown significance (VUS) in genes involved in cardiomyopathy pathogenesis. To explore the genetic basis of non-syndromic MAD, we performed a systematic review of the literature, identifying five case reports and one retrospective cohort study. The case reports described patients with MAD harboring four pathogenic variants and ten VUS. Two pathogenic variants were linked to cardiomyopathies, involving proteins of the nuclear envelope and cytoskeleton, while two were associated with channelopathies. The retrospective cohort study identified a recurrent variant in a gene involved in intercellular adhesion segregating within a family affected by MAD. Overall, available evidence suggests that genetic factors may hypothetically modulate susceptibility to MAD, not only in connective tissue disorders but also in isolated mitral valve disease. Variants associated with arrhythmogenic cardiomyopathies and channelopathies appear to cluster in families with non-syndromic MAD and arrhythmic phenotypes, suggesting a role in the arrhythmic substrate. However, in absence of definitive functional, segregation, or longitudinal data, the contribution of genetic variants to MAD should be interpreted with caution. Further genomic studies are needed to clarify their genetic contribution and prognostic implications.