Mental Retardation, Autosomal Recessive 35

Alternative Names

  • MRT35
  • Short Ulna-Dysmorphism-Hypotonia-Intellectual Disability Syndrome
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Other congenital malformations

OMIM Number

615162

Mode of Inheritance

Autosomal recessive

Gene Map Locus

17q21.31-q22

Description

MRT35 is a syndrome characterized by severe cognitive impairment, dysmorphic facies and skeletal abnormalities. Affected patients present with signs of delayed global development, thin body build with stooped posture, hypotonia, short ulna and hypertrichosis on the face and extremities. Facial dysmorphic features include a flat and broad occiput, synophrys, hypertelorism, malar hypoplasia, broad nose with thick alae nasi, low set small ears, everted lower lip and micrognathia. Skeletal abnormalities may also consist of clinodactyly, mild thickening of the calvarium and minimal scoliosis. So far, MRT35 has only been diagnosed in four siblings of a consanguineous Saudi family.

Molecular Genetics

MRT35 appears to follow an autosomal recessive mode of inheritance. Homozygosity mapping and linkage analysis have mapped the syndrome to chromosome 17q21.31-q22 spanning a region of 12.2 Mb. However, the exact genetic defect leading to the syndrome has not been uncovered.

Epidemiology in the Arab World

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Other Reports

Saudi Arabia

Al-Owain et al. (2011) reported a ten year old Saudi girl with severe developmental delays, limited communication skills, thin body build, stooped posture and facial dysmorphisms, which included a flat and broad occiput, synophrys, hypertelorism, malar hypoplasia, broad nose with thick alae nasi, low set small ears, everted lower lip and micrognathia. Further skeletal examination revealed mild hand camptodactyly, thickening of the calvarium, minimal scoliosis and short ulna. Her 18 year old brother showed similar symptoms of developmental delay and dysmorphic facies. He was also found to have indirect hyperbilirubinemia which was confirmed to be due to Gilbert syndrome. Their 19 year old sister showed mild developmental delay, mildly coarse facial features, mild thickening of the calvarium and lumbar scoliosis. The patient’s 28 month old brother showed mild developmental delay, dysmorphic facies and minimal levoscoliosis. All patients showed normal urinary glycosaminoglycans which ruled out the possibility of mucopolysaccharidosis. The patient’s parents were first cousins and had four other non-affected children. Linkage analysis and homozygosity mapping uncovered a 12.2 Mb region of homozygosity on chromosome 17q21.31-q22. This study suggests that MRT35 is a novel syndromic autosomal recessive form of cognitive impairment caused by a genetic defect in a locus that is located in 17q21.31-q22.

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