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X-linked intellectual disability-hypotonic face syndrome
Mental retardation-hypotonic facies covers a group of X-linked syndromes characterized by severe intellectual deficit and facial dysmorphism, with variable other features.
ORPHA:73220Classification level: Group of disorders
- Synonym(s): -
- Prevalence: Unknown
- Inheritance: X-linked recessive
- Age of onset: Infancy, Neonatal
- ICD-10: -
- OMIM: 309580
- UMLS: -
- MeSH: -
- GARD: -
- MedDRA: -
Prevalence is unknown but most of these syndromes have been reported in only a few families.
At present this group includes the Juberg-Marsidi, Carpenter-Waziri, Holmes-Gang, Renier-Gabreels-Jasper, Smith-Fineman-Myers and Chudley-Lowry syndromes (see these terms).
These syndromes are caused by a mutation in the helicase 2 (XH2/ATRX; Xq13.3) gene.
These syndromes show clinical similarity to alpha-thalassemia-X-linked mental retardation (ATR-X syndrome; see this term), which is also caused by a mutation in the ATRX gene, but all patients with a mental retardation-hypotonic facies syndrome display normal haematologic indices and do not appear to exhibit the haemoglobin H inclusions characteristic of ATR-X.
Transmission is X-linked recessive. A highly skewed X-inactivation pattern was identified in female carriers and some of the heterozygous mothers were reported to have manifestations such as subnormal intelligence and microcephaly.