Three new cases of Ataxia-Telangiectasia-Like Disorder: no impairment of the ATM pathway, but S-phase checkpoint defect.

Ataxia-Telangiectasia-Like Disorder (ATLD) is a rare genomic instability syndrome caused by bi-allelic variants of MRE11 characterized by progressive cerebellar ataxia and typical karyotype abnormalities. These symptoms are common to those of Ataxia-Telangiectasia, which is consistent with the key role of MRE11 in ATM activation after DNA double-strand breaks. Three unrelated French patients were referred with ataxia. Only one had typical karyotype abnormalities. Unreported bi-allelic MRE11 variants were found in these three cases. Interestingly, one variant (c.424G>A) was present in two cases and haplotype analysis strongly suggested a French founder variant. Variants c.544G>A and c.314+4_314+7del lead to splice defects. The level of MRE11 in lymphoblastoid cell lines was consistently and dramatically reduced. Functional consequences were evaluated on activation of the ATM pathway via phosphorylation of ATM targets (KAP1 and CHK2), but no consistent defect was observed. However, an S-phase checkpoint activation defect after camptothecin was observed in these ATLD patients. In conclusion, we report the first three French ATLD patients and a French founder variant, and propose an S-phase checkpoint activation study to evaluate the pathogenicity of MRE11 variants. This article is protected by copyright. All rights reserved.

This article is protected by copyright. All rights reserved.