X-linked intellectual disability, Snyder type

X-linked intellectual disability, Snyder type (also known as Snyder-Robinson syndrome or SRS) is a rare genetic condition that primarily affects males and is characterized by intellectual disability, skeletal abnormalities, and distinctive facial features. The condition was first described by Snyder and Robinson in 1969. It is caused by mutations in the SMS gene on the X chromosome, which encodes spermine synthase, an enzyme involved in polyamine metabolism. Reduced spermine synthase activity leads to decreased spermine levels and accumulation of spermidine, disrupting normal cellular function. The condition affects multiple body systems. Key clinical features include mild to moderate intellectual disability, thin body habitus (asthenic build), muscle hypotonia, osteoporosis with a tendency toward fractures, kyphoscoliosis, facial asymmetry, a nasal or high-pitched voice, and unsteady gait. Some individuals may also experience seizures. Facial features can include a long face, prominent lower lip, and deep-set eyes. Skeletal involvement is significant, with osteoporosis often leading to recurrent fractures even from minor trauma. There is currently no cure or specific targeted therapy for Snyder-Robinson syndrome. Management is supportive and multidisciplinary, focusing on addressing individual symptoms. This may include physical therapy for motor difficulties, educational support for intellectual disability, orthopedic management for skeletal complications including osteoporosis treatment, and anticonvulsant medications if seizures are present. Genetic counseling is recommended for affected families. Research into polyamine metabolism continues to explore potential therapeutic avenues.

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