Joint hypermobility as a manifestation of neonatal Sotos syndrome

SummarySotos syndrome is associated with hypergrowth, macrocephaly, intellectual disability and characteristic facial features, the diagnosis of which becomes more evident during childhood. We present the case of a full-term newborn, who was admitted to the Neonatology Unit with early hypoglycaemia, hypotonia, a peculiar phenotype and joint hyperlaxity, with dislocation of both wrists. An interventricular communication with haemodynamic repercussions was detected. During his hospitalisation, he presented with feeding difficulties and cholestasis of multifactorial aetiology. Genetic testing detected a pathogenic variant in heterozygosity in the NSD1 gene (c.5990A>G p.Tyr1997Cys) with an autosomal dominant de novo inheritance pattern. Therefore, in a newborn with hypotonia associated with typical facial features, together with joint hyperlaxity, jaundice, hypoglycaemia and feeding difficulties, this syndrome should be suspected and a genetic study requested. In more than 95% of cases, Sotos syndrome is caused by mutations or microdeletions in the NSD1 gene. Given the associated complications, multidisciplinary follow-up is recommended.