<i>ARID1B</i>mutations are the major genetic cause of corpus callosum anomalies in patients with intellectual disability

Sir, In their extensive review article in Brain , Edwards et al. (2014) presented physiological processes underlying the formation of the corpus callosum, as well as pathological conditions in mice and humans leading to agenesis of the corpus callosum (AgCC). They reviewed most human syndromes associated with AgCC and emphasized the great heterogeneity of known genetic causes of AgCC in humans by listing more than 70 single gene mutations and copy number variations (CNV), which altogether explain 30–45% of all cases. Most of these genetic anomalies are responsible for AgCC associated with other cerebral or extra-cerebral malformations and/or intellectual disability (ID). The association between AgCC and intellectual disability is further highlighted by the higher prevalence of AgCC in individuals with intellectual disability (2–3%) versus in the general population (0.025–0.02%) (Paul et al. , 2007; Sotiriadis and Makrydimas, 2012). Thereby, given the extreme genetic heterogeneity of intellectual disability (Deciphering Developmental Disorders Study, 2015) and the number of genes involved in the formation of the corpus callosum in humans, it is not surprising that genetic causes of syndromes associating AgCC and intellectual disability are so numerous. However, the prevalence of each of these genetic anomalies in individuals with this association is currently unknown. To improve our knowledge on genetic causes of AgCC with intellectual disability, we collected prospectively clinical and molecular data from 177 individuals with anomalies of the corpus callosum (ACC, comprising patients with AgCC, or with short corpus callosum or with dysplastic corpus callosum), and intellectual disability (or developmental delay for young children; ACC-ID) between 2009 and 2015. A clinical diagnosis, further confirmed by targeted sequencing of the corresponding gene, when possible, was made for 15 patients. Among these patients, one had a diagnosis of Coffin-Siris syndrome (CSS) and a mutation in ARID1B , the major gene for Coffin-Siris …