Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type

Qu'est-ce que Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type?

It is a rare genetic syndrome marked by intellectual disability and developmental delay. The symptoms progress from mild developmental delay to more severe intellectual disability. The syndrome also leads to muscle and bone anomalies. The syndrome affects males only and currently affects only around 10 families worldwide.

This syndrome is also known as:
Snyder-robinson Mental Retardation Syndrome; Srs Snyder-Robinson syndrome Spermine Synthase Deficiency

Quelles sont les causes des changements génétiques Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type?

Les modifications du gène SMS sont responsables de la syndrome.

le syndrome est héritée dans un modèle récessif lié à l'X, et ce mode de transmission le rend présent chez les hommes presque exclusivement.

Quels sont les principaux symptômes de Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type?

The main symptoms of the syndrome include intellectual disability and delayed development which get progressively worse with age. This delay includes speech and language development with speech difficulties. In some individuals this means the lack of any speech at all.

Low and thin muscle mass is common with the syndrome. As is a thin and long body with low muscle tone. Muscle tone continues to be lost with age. This in turn can create issues with walking and the development of an unsteady gait. A short stature is also a common physical feature of the syndrome.
Skeletal issues are also common with the syndrome. These include a thinning of the bones (osteoporosis) leading to brittle bones that break easily even without significant trauma or impact. Kyphoscoliosis- a curving of the spine is also common.
Unique facial features of the syndrome include a prominent lower lip, narrow roof of the mouth, cleft palate and facial asymmetry.

Possible clinical traits/features:
Decreased muscle mass, Dental crowding, Cryptorchidism, Facial asymmetry, Dysarthria, High, narrow palate, Hyperextensibility of the finger joints, Hypertelorism, Nasal speech, Short stature, Tall stature, Mandibular prognathia, Pectus excavatum, Muscular hypotonia, Kyphoscoliosis, Intellectual disability, Long fingers, Long hallux, Long palm, Narrow palm, Wide intermamillary distance, Phenotypic variability, Recurrent fractures, Thick lower lip vermilion, Short philtrum, High myopia, X-linked recessive inheritance, Talipes equinovarus, Bifid uvula, Abnormality of the pinna, Broad-based gait, Cleft palate, Osteoporosis, Pectus carinatum, Seizure, Webbed neck

Comment quelqu'un se fait-il tester pour Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type?

Les premiers tests de Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type peut commencer par un dépistage par analyse faciale, en passant par le FDNA Telehealth plateforme de télégénétique, qui permet d'identifier les marqueurs clés de la syndrome et souligner la nécessité de tests supplémentaires. Une consultation avec un conseiller génétique puis un généticien suivra. 

Sur la base de cette consultation clinique avec un généticien, les différentes options pour les tests génétiques seront partagées et le consentement sera recherché pour des tests supplémentaires.

Informations médicales sur Mental Retardation, X-Linked, Syndromic, Snyder-Robinson Type

Snyder-Robinson syndrome is an X-linked intellectual disability syndrome associated with loss-of-function mutations in SMS, the gene encoding spermine synthase. Initially described as a nonsyndromal form of intellectual disability with hypotonia, the disorder is now defined by its craniofacial and skeletal manifestations. Affected males typically show facial asymmetry, high or cleft palate, malar flattening, prominent lower lip, general asthenia, spinal curvature, long digits, and osteoporosis. The cognitive impairment is variable, and seizures are frequent. Female carriers have no cognitive impairment but may have osteoporosis or scoliosis.

Clinical manifestations of Snyder-Robinson syndrome appear in infancy and typically include general asthenia, hypotonia, and global developmental delays. The face may have mild asymmetry and prominence of the lower lip. The majority can walk but with an unsteady gait. The majority speak but speech has a nasal or dysarthric quality. Height and head circumference tend to be in the upper centiles. Seizures of variable types occur in most children with onset in the first couple of years. Generalized osteoporosis and kyphoscoliosis become apparent in the first decade and may lead to recurrent fractures.

Craniofacial: large cranium, long palpebral fissures and eyelashes, malar flattening, tall palate, prominent lower lip, facial asymmetry
Nervous system: developmental delay, cognitive impairment, seizures, variable hearing impairment
Sensory system: hearing loss
Muscles: hypotonia, decreased muscle mass
Gastrointestinal: GERD, swallowing difficulties, constipation, chronic diarrhea
Genitourinary: hypospadias, cryptorchidism
Bones and joints: asthenic build, kyphoscoliosis, pectus excavatum or carinatum, osteoporosis, long digits, fractures
Blood: rare thrombocytopenia in neonatal period
Infections: recurrent respiratory infections in childhood

PREVALENCE: Unknown but rare, less than 50 cases have been recognized
LIFE EXPECTANCY: Unknown, but survival into late 50s has occurred
PRENATAL PRESENTATION: Usually normal prenatal history

ASSOCIATED GENE: Spermine synthase (SMS)
RECURRENT MUTATIONS: No mutation hotspots or founder mutations
TYPE OF MUTATIONS: Missense, frameshifts and splice site; all loss-of-function
GENOTYPE/PHENOTYPE CORRELATION: No genotype-phenotype correlations available to date

Snyder and Robinson (1969) described five males in one family with nonsyndromal X-linked intellectual disability and hypotonia.

Arena et al., (1996) revisited the original family and noted facial asymmetry, high palate, nasal speech, prominent lower lip, reduced muscle mass, kyphoscoliosis, osteoporosis and long great toes in affected males and mapped the gene to Xp21.2-p12.12.

Cason et al., (2003) reported a splice site mutation in spermine synthase, which constitutes the first recognized defect of polyamine metabolism in the original family.

Kesler et al., (2009) described volume loss of the hippocampus, red nucleus and cerebellum in affected males.

Families with confirmed mutations in SMS have been reported by de Alencastro et al. (2008), Becerra-Solano et al. (2009), Zhang et al. (2013), Peron et al. (2013), and Albert et al. (2015).

Starks et al., (2018) reported autopsy findings in a 4-year-old boy.

Li et al., (2018) reported evidence in the Drosophila model of Snyder-Robinson syndrome for oxidative stress and lysosomal dysfunction secondary to the generation of toxic metabolites produced by excessive spermidine catabolism.

Seizure activity in early childhood
Developmental assessment for motor, speech, and cognitive delays
DEXA-scan radiographs for osteoporosis
Audiology for hearing impairment

Speech, occupational and physical therapies for developmental delays
Anticonvulsants for seizures
Fracture precautions, avoid high contact sports
Surgical procedures as necessary for hypospadias and cryptorchidism
GERD and constipation intervention with diet or medications
Aids as necessary for hearing loss



(1) Child Neuropsychiatry Unit - Epilepsy Center (Medical Genetics), San Paolo Hospital, Department of Health Sciences, Università degli Studi di Milano, Milan, Italy
(2) Department of Pediatrics, Division of Medical Genetics, University of Utah School of Medicine, Salt Lake City, UT, USA
(3) Greenwood Genetic Center, Greenwood, SC, USA

novembre 23, 2018

* This information is courtesy of the L M D.
If you find a mistake or would like to contribute additional information, please email us at: [email protected]

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