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An X-linked mental retardation (XLMR) syndrome belonging to the group of conditions characterised by the association of intellectual deficit with hypotonic facies (Mental retardation, X-linked-hypotonic facies).
ORPHA:93974Classification level: Disorder
Prevalence is unknown. Since its initial description in 1980, SFMS has been described in males from 11 families and in one isolated case.
SFMS is characterised by facial dysmorphism (slanted palpebral fissures, narrow face, micrognathia, patulous lower lip, flat or small philtrum, and alternating exotropia and ptosis), short stature, early hypotonia and later hypertonia, prominent upper central incisors, foot deformities (pes planus, metatarsus varus, equinovarus), psychomotor retardation, and behavioural problems.
In most cases the syndrome is caused by mutations in the ATRX gene (Xq13.3), however, the causative gene in a large Chinese family with SFMS has been mapped to a 19.8 Mb interval on Xq25.
Transmission is X-linked recessive.