Critical region in 2q31.2q32.3 deletion syndrome: Report of two phenotypically distinct patients, one with an additional deletion in Alagille syndrome region

Abstract

Abstract Background: Standard cytogenetic analysis has revealed to date more than 30 reported cases presenting interstitial deletions involving region 2q31-q32, but with poorly defined breakpoints. After the postulation of 2q31.2q32.3 deletion as a clinically recognizable disorder, more patients were reported with a critical region proposed and candidate genes pointed out. Results: We report two female patients with de novo chromosome 2 cytogenetically visible deletions, one of them with an additional de novo deletion in chromosome 20p12.2p12.3. Patient I presents a 16.8 Mb deletion in 2q31.2q32.3 while patient II presents a smaller deletion of 7 Mb in 2q32.1q32.3, entirely contained within patient I deleted region, and a second 4 Mb deletion in Alagille syndrome region. Patient I clearly manifests symptoms associated with the 2q31.2q32.3 deletion syndrome, like the muscular phenotype and behavioral problems, while patient II phenotype is compatible with the 20p12 deletion since she manifests problems at the cardiac level, without significant dysmorphisms and an apparently normal psychomotor development. Conclusions: Whereas Alagille syndrome is a well characterized condition mainly caused by haploinsufficiency of JAG1 gene, with manifestations that can range from slight clinical findings to major symptoms in different domains, the 2q31.2q32.3 deletion syndrome is still being delineated. The occurrence of both imbalances in reported patient II would be expected to cause a more severe phenotype compared to the individual phenotype associated with each imbalance, which is not the case, since there are no manifestations due to the 2q32 deletion. This, together with the fact that patient I deleted region overlaps previously reported cases and patient II deletion is outside this common region, reinforces the existence of a critical region in 2q31.3q32.1, between 181 to 185 Mb, responsible for the clinical phenotype.