Snyder–Robinson syndrome

Snyder–Robinson syndrome
Other names	Spermine synthase deficiency
Specialty	Medical genetics
Symptoms	Intellectual disability, facial asymmetry, kyphoscoliosis, osteoporosis, hypotonia, asthenic build, seizures
Usual onset	Adolescence, childhood, infancy
Causes	Genetic[1]
Differential diagnosis	Glycerol kinase deficiency, Urban syndrome, Rett syndrome, cerebral palsy, Prader–Willi syndrome
Frequency	<1 per 1,000,000

Snyder–Robinson syndrome (SRS) is an extremely rare inherited genetic disorder^[1] characterized by muscular and skeletal abnormalities, varying degrees of intellectual disability, seizures,^[2] and slow development.^[3]

SRS is caused by a mutated SMS gene at chromosome Xp21.3-p22.12, which carries instructions for producing the enzyme spermine synthase.^[4] Spermine synthase in turn helps the body produce spermine, a polyamine critical to cell processes such as cell division, tissue repair, and apoptosis.^[5] The resulting shortage of spermine in cells causes problems with development and brain function, though the exact mechanism is not understood.

The syndrome has also been referred to as Snyder–Robinson X-linked mental retardation syndrome (MRXSSR) and spermine synthase deficiency. SRS exclusively affects males.^[1] Only about ten families currently have a child with SRS, and 50 people have been diagnosed worldwide since 1969.^[6]

Presentation[]

Snyder–Robinson usually is noticeable in infants, causing hypotonia and declining muscle tone with age. Seizures can occur in childhood, and children are especially susceptible to broken bones.^[3]

During early childhood, SRS causes mild to profound intellectual disability; speech difficulties; problems with walking; osteoporosis; marfanoid habitus; and scoliosis, kyphosis, or both (kyphoscoliosis). Distinctive facial features include a cleft palate, facial asymmetry, and a prominent lower lip. Kidney problems may also occur, such as nephrocalcinosis and renal cysts.^{[citation needed]}

Cause[]

SRS is a recessive X-linked condition.^[7] There are no known female cases, as both copies of the X chromosome would need to be mutated.^{[citation needed]}

Diagnosis[]

When SRS is suspected, doctors will order a molecular genetic test to confirm a mutation in the SMS gene—specifically a "hemizygous loss-of-function... pathogenic variant". However, there are currently no formal criteria for a diagnosis.^[3]

Management[]

Individuals with Snyder–Robinson may be assisted by occupational therapy, physical or speech therapy. Anti-seizure medications such as carbamazepine, phenobarbital, and clobazam can be used to manage seizures^[2]—the medication used often is influenced by the type of seizure. Bone density can be determined via a DXA scan and may be improved with calcium supplements.^[3]

In 2014, several parents of individuals with SRS founded the Snyder–Robinson Foundation, a 501(c)(3) non-profit based in the US.^[8][6] It is a member of the National Organization for Rare Disorders.^[9]

History[]

SRS was first reported in a 1969 paper published in Clinical Pediatrics by Russell D. Snyder^[10] and Arthur Robinson, who described the syndrome as "recessive sex-linked mental retardation in the absence of other recognizable abnormalities".^[11]

References[]

External links[]

• The Snyder–Robinson Foundation
• Albert, Jessica; Schwartz, Charles E.; Boerkoel, Cornelius F.; Stevenson, Roger E. (June 27, 2013). "Snyder-Robinson Syndrome". GeneReviews. Seattle: University of Washington, Seattle. PMID 23805436. Retrieved 1 July 2019.
• Snyder, Russell D.; Robinson, Arthur (November 1, 1969). "Recessive Sex-Linked Mental Retardation in the Absence of Other Recognizable Abnormalities: Report of a Family". Clinical Pediatrics. 8 (11): 669–674. doi:10.1177/000992286900801114. PMID 5823961. S2CID 32198336.