Rovelet-Lecrux Anne, Bonnevalle Antoine, Quenez Olivier, Delcroix Wandrille, Cassinari Kévin, Richard Anne-Claire, Boland Anne, Deleuze Jean-François, Goizet Cyril, Rucar Alice, Verny Christophe, Nguyen Karine, Lecourtois Magalie, Nicolas Gaël
Univ Rouen Normandie, Inserm U1245 and CHU Rouen, Department of Genetics, CNRMAJ and Reference Center for Neurogenetics Disorders, F-76000, Rouen, France.
Univ Rouen Normandie, Inserm U1245 and CHU Rouen, Department of Neurology, CNRMAJ and Reference Center for Neurogenetics Disorders, F-76000, Rouen, France.
Eur J Hum Genet. 2024 Jul;32(7):779-785. doi: 10.1038/s41431-024-01580-4. Epub 2024 Mar 4.
More than 50% of patients with primary familial brain calcification (PFBC), a rare neurological disorder, remain genetically unexplained. While some causative genes are yet to be identified, variants in non-coding regions of known genes may represent a source of missed diagnoses. We hypothesized that 5'-Untranslated Region (UTR) variants introducing an AUG codon may initiate mRNA translation and result in a loss of function in some of the PFBC genes. After reannotation of exome sequencing data of 113 unrelated PFBC probands, we identified two upstream AUG-introducing variants in the 5'UTR of PDGFB. One, NM_002608.4:c.-373C>G, segregated with PFBC in the family. It was predicted to create an upstream open reading frame (ORF). The other one, NM_002608.4:c.-318C>T, was found in a simplex case. It was predicted to result in an ORF overlapping the natural ORF with a frameshift. In a GFP reporter assay, both variants were associated with a dramatic decrease in GFP levels, and, after restoring the reading frame with the GFP sequence, the c.-318C>T variant was associated with a strong initiation of translation as measured by western blotting. Overall, we found upstream AUG-introducing variants in the 5'UTR of PDGFB in 2/113 (1.7%) undiagnosed PFBC cases. Such variants thus represent a source of putative pathogenic variants.
原发性家族性脑钙化（PFBC）是一种罕见的神经系统疾病，超过50%的患者在基因方面仍无法解释病因。虽然一些致病基因尚未被鉴定出来，但已知基因非编码区的变异可能是漏诊的一个原因。我们推测，引入AUG密码子的5'-非翻译区（UTR）变异可能会启动mRNA翻译，并导致某些PFBC基因功能丧失。在对113名无亲缘关系的PFBC先证者的外显子测序数据进行重新注释后，我们在PDGFB的5'UTR中鉴定出两个引入上游AUG的变异。其中一个，NM_002608.4:c.-373C>G，在家族中与PFBC共分离。预计它会产生一个上游开放阅读框（ORF）。另一个，NM_002608.4:c.-318C>T，在一个散发病例中被发现。预计它会导致一个ORF与天然ORF重叠并发生移码。在绿色荧光蛋白（GFP）报告基因检测中，这两个变异都与GFP水平的显著降低有关，并且在用GFP序列恢复阅读框后，通过蛋白质印迹法检测，c.-318C>T变异与强烈的翻译起始有关。总体而言，我们在113例未确诊的PFBC病例中的2例（1.7%）中发现了PDGFB的5'UTR中引入上游AUG的变异。因此，这些变异是潜在致病变异的一个来源。
