Snyder-Robinson syndrome: a novel nonsense mutation in spermine synthase and expansion of the phenotype
Snyder-Robinson syndrome is a rare form of X-linked intellectual disability caused by mutations in the spermine synthase (SMS) gene, and characterized by intellectual disability, thin habitus with diminished muscle mass, osteoporosis, kyphoscoliosis, facial dysmorphism (asymmetry, full lower lip), long great toes, and nasal or dysarthric speech. Physical signs seem to evolve from childhood to adulthood. We describe the first Italian patient with Snyder-Robinson syndrome and a novel nonsense mutation in SMS (c.200G>A; p.G67X). Apart from the typical features of the syndrome, the index patient presented with an ectopic right kidney and epilepsy from the first year of age that was characterized by focal motor seizures and negative myoclonus. The clinical and molecular evaluation of this family and the review of the literature expand the phenotype of Snyder-Robinson syndrome to include myoclonic or myoclonic-like seizures (starting even in the first years of life) and renal abnormalities in affected males.