The rapid accrual of knowledge in genomic medicine has prompted the reanalysis of preexisting data. 1,2 We clinically reanalyzed data from two patient series that had undergone diagnostic proband-only exome sequencing.

PurposeTruncating mutations in the maternally imprinted, paternally expressed gene MAGEL2, which is located in the Prader-Willi critical region 15q11-13, have recently been reported to cause Schaaf-Yang syndrome, a Prader-Willi-like disease, manifesting developmental delay/intellectual disability, hypotonia, feeding difficulties, and autism spectrum disorder. The causality of the reported variants in the context of the patients’ phenotypes was questioned, as MAGEL2 whole gene deletions appear to cause little to no clinical phenotype.MethodsHere we report a total of 18 new individuals with Schaaf-Yang syndrome from 14 families, including one family with three individuals found to be affected with a truncating variant of MAGEL2, 11 individuals clinically affected, but not tested molecularly, and a presymptomatic fetal sibling with carrying the pathogenic MAGEL2 variant.ResultsAll cases harbor truncating mutations of MAGEL2, and nucleotides c.1990-1996 arise as a mutational hotspot, with 10 individuals and one fetus harboring a c.1996dupC (p.Q666fs) mutation and two fetuses harboring a c.1996delC (p.Q666fs). The phenotypic spectrum of Schaaf-Yang syndrome ranges from fetal akinesia to individuals with neurobehavioral disease and contractures of the small finger joints.ConclusionThis study provides strong evidence for the pathogenicity of truncating mutations of the paternal allele of MAGEL2, refines the associated clinical phenotypes, and highlights implications for genetic counseling of affected families.

SON is a key component of the spliceosomal complex and a critical mediator of constitutive and alternative splicing. Additionally, SON has been shown to influence cell-cycle progression, genomic integrity, and maintenance of pluripotency in stem cell populations. The clear functional relevance of SON in coordinating essential cellular processes and its presence in diverse human tissues suggests that intact SON might be crucial for normal growth and development. However, the phenotypic effects of deleterious germline variants in SON have not been clearly defined. Herein, we describe seven unrelated individuals with de novo variants in SON and propose that deleterious variants in SON are associated with a severe multisystem disorder characterized by developmental delay, persistent feeding difficulties, and congenital malformations, including brain anomalies.

We report 281 individuals carrying a pathogenic recurrent NF1