12p13.33 microdeletion including ELKS/ERC1, a new locus associated with childhood apraxia of speech

Speech sound disorders are heterogeneous conditions, and sporadic and familial cases have been described. However, monogenic inheritance explains only a small proportion of such disorders, in particular in cases with childhood apraxia of speech (CAS). Deletions of <5 Mb involving the 12p13.33 locus is one of the least commonly deleted subtelomeric regions. Only four patients have been reported with such a deletion diagnosed with fluorescence in situ hybridisation telomere analysis or array CGH. To further delineate this rare microdeletional syndrome, a French collaboration together with a search in the Decipher database allowed us to gather nine new patients with a 12p13.33 subtelomeric or interstitial rearrangement identified by array CGH. Speech delay was found in all patients, which could be defined as CAS when patients had been evaluated by a speech therapist (5/9 patients). Intellectual deficiency was found in 5/9 patients only, and often associated with psychiatric manifestations of various severity. Two such deletions were inherited from an apparently healthy parent, but reevaluation revealed abnormal speech production at least in childhood, suggesting variable expressivity. The ELKS/ERC1 gene, which encodes for a synaptic factor, is found in the smallest region of overlap. These results reinforce the hypothesis that deletions of the 12p13.33 locus may be responsible for variable phenotypes including CAS associated with neurobehavioural troubles and that the presence of CAS justifies a genetic work-up.