CACNA1C haploinsufficiency accounts for the common features of interstitial 12p13.33 deletion carriers.

We identified a de novo 44.7 Kb interstitial 12p13.33 micro-deletion that involves solely the first exon of the CACNA1C (MIM 114205), using microarray-based comparative genomic hybridization (aCGH). The associated main phenotype is characterized by expressive language impairment, tremors, fine motor-skills delay, muscular hypotonia, and joint laxity. A careful comparison between the clinical and genomic characteristics between our proband and 20 previously reported patients, led us to propose CACNA1C haploinsufficiency as the main cause of both expressive language delay and motor-skills impairment. Pathogenic variants of CACNA1C have been associated to a plethora of clinical phenotypes, such as Timothy syndrome (TS, OMIM 601005), Brugada syndrome (BRGDA3, OMIM 611875) and a variety of neuropsychiatric disorders (bipolar disorder, major depression, schizophrenia, autism spectrum disorder, psychotic manifestations). In this report we describe a 12p13.33 micro-deletion involving one coding gene only, in contrast with previous studies that mostly concluded that a multi-genes deletion in the 12p13.33 sub-telomeric region is responsible of the minimum clinical phenotype of patients with 12p13.33 monosomy. Certainly, larger deletions spanning multiple Mb in 12p13.33 are responsible for more severe phenotypes, associated to a variable degree of dysmorphic features.