Expanding the phenotype of MTOR-related disorders and the Smith-Kingsmore syndrome

Semaglutide as a potential treatment for obesity in Smith-Kingsmore syndrome (SKS) patients: A mosaic mutation case report

We present for the first-time efficacy and tolerability of GLP-1-RA (Semaglutide) in Smith-Kingsmore syndrome (SKS). SKS is a rare genetic disorder characterized by intellectual disability, macrocephaly, seizures and distinctive facial features due to MTOR gene mutation. We present a 22-year-old woman with mosaic SKS and severe obesity (Body Mass Index ≥40 kg/m²), treated with semaglutide. She achieved a 9 kg (7.44%) weight loss over 12 months without adverse effects.This case highlights semaglutide's potential in managing obesity in SKS patients, emphasizing the need for further research in this rare genetic disorder.

Delineating the Smith-Kingsmore syndrome phenotype: Investigation of 16 patients with the MTOR c.5395G > A p.(Glu1799Lys) missense variant

Smith-Kingsmore Syndrome (SKS) is a rare genetic syndrome associated with megalencephaly, a variable intellectual disability, autism spectrum disorder, and MTOR gain of function variants. Only 30 patients with MTOR missense variants are published, including 14 (47%) with the MTOR c.5395G>A p.(Glu1799Lys) variant. Limited phenotypic data impacts the quality of information delivered to families and the robustness of interpretation of novel MTOR missense variation. This study aims to improve our understanding of the SKS phenotype through the investigation of 16 further patients with the MTOR c.5395G>A p.(Glu1799Lys) variant. Through the careful phenotypic evaluation of these 16 patients and integration with data from 14 previously reported patients, we have defined major (100% patients) and frequent (>15%) SKS clinical characteristics and, using these data, proposed guidance for evidence-based management. In addition, in the absence of functional studies, we suggest that the combination of the SKS major clinical features of megalencephaly (where the head circumference is at least 3SD) and an intellectual disability with a de novo MTOR missense variant (absent from population databases) should be considered diagnostic for SKS.

A new case of Smith-Kingsmore syndrome with somatic MTOR pathogenic variant expands the phenotypic spectrum to lateralized overgrowth

Smith-Kingsmore syndrome (SKS) is a rare autosomal dominant disorder caused by heterozygous germline activating pathogenic variants in mammalian target of rapamycin (MTOR) on chromosome 1p36. A few patients with disseminated mosaicism have been described so far and they seem to display a different phenotype when compared to germline cases. Here we report the sixth case with a disseminated mosaic MTOR pathogenic variant, a 7-year-old boy with hemimegalencephaly, epilepsy, developmental delay, hypomelanosis of Ito, and lateralized overgrowth. Genetic testing revealed a pathogenic variant (c.4448G > A, p.Cys1483Tyr) in MTOR with a frequency of 32% in the DNA extracted from a skin sample, 3% in saliva and 0.46% in blood. The clinical features observed in our patient further corroborate the existence of differences in phenotypic presentation of germline and mosaic SKS cases. Moreover, lateralized overgrowth, a finding never described so far in SKS, further expands the phenotypic spectrum of SKS and allows the inclusion of MTOR pathogenic variants among the several causes of asymmetric body overgrowth.