Résumé
Abstract Mutations in the ARX gene cause both nonsyndromic and several forms of syndromic mental retardation (MR). Two polyalanine (polyA) expansions of ARX are recurrent mutations. The most common one, the c.428\₄51dup, is associated with a wide spectrum of phenotypes, ranging from the most severe West syndrome to Partington syndrome (MR and hand dystonia), and even nonsyndromic X-linked mental retardation (NS-XLMR). Studies of patients not selected for specific clinical signs showed that the c.428\₄51dup is relatively frequent in families harboring X-linked MR (7.5%), but less common in familial cases compatible with X-linked NR (1%), and very rare in sporadic cases (0.1%). The c.333\₃34ins(GCG)7 expansion is less frequent and mainly associated with West syndrome. We screened for both ARX polyA expansions in 98 unrelated patients selected for the presence of NR associated with different types of epilepsy and/or with hand dystonia. We also studied two families with an initial diagnosis of NS-XLMR, one of which was identified as showing linkage to the ARX locus. The c.428\₄51dup was identified in three patients and the c.333\₃34ins(GCG)7 in one; all of the patients were from families with two affected brothers. We also found the c.428\₄51dup in the family linked to ARX , and clinical re-evaluation showed subtle, previously undetected signs. Our study illustrates that ARX polyA expansions are primarily associated with syndromic MR and shows a higher yield (18% in our cohort) when these mutations are screened in familial cases of MR with epilepsy and/or dystonia. © 2010 Wiley-Liss, Inc.