Aslaksen Sigrid, Aukrust Ingvild, Molday Laurie, Holtan Josephine Prener, Jansson Ragnhild Wivestad, Berland Siren, Rødahl Eyvind, Bredrup Cecilie, Bragadóttir Ragnheiður, Bratland Eirik, Molday Robert S, Knappskog Per Morten
Department of Clinical Science, University of Bergen, Bergen, Norway.
Department of Medical Genetics, Haukeland University Hospital, Bergen, Norway.
Invest Ophthalmol Vis Sci. 2024 Aug 1;65(10):2. doi: 10.1167/iovs.65.10.2.
Biallelic pathogenic variants in the gene encoding the ATP-binding cassette transporter ABCA4 are the leading cause of irreversible vision loss in inherited retinal dystrophies (IRDs). Interpretation of ABCA4 variants is challenging, due to cis-modifying and hypomorphic variants. We have previously detected 10 missense variants of unknown significance (VUS) in patients with suspected ABCA4-retinal dystrophies (ABCA4-RDs) in Norway. In this study, we functionally characterized the VUS to aid interpretation of the variants and to determine if they are associated with the disease.
The ABCA4 VUS were expressed in HEK293T cells and the ABCA4 expression level and ATPase activity were determined and correlated with the patients' phenotype. The functional data further used for reclassification of the VUS following the American College of Medical Genetics and Genomics (ACMG) guidelines.
Of the 10 VUSs, 2 variants, Cys205Phe and Asn415Thr, were categorized as functionally severe. The age at presentation in the 2 patients carrying these variants was divergent and seemed to be driven by the patients' second pathogenic variants Gly1961Glu and c.5461-10T>C, respectively. Three variants, Val643Gly, Pro799Leu, and Val1433Ile were categorized as functionally moderate, and were found in patients with intermediate/late age at presentation. The remaining five variants were categorized as functionally normal/mild. Based on our data, c.614G>T p.(Cys205Phe), c.1244A>C p.(Asn415Thr), and c.2396C>T p.(Pro799Leu) were reclassified to (likely) pathogenic, while 4 of the functionally normal/mild variants could be reclassified to likely benign.
Functional analyses of ABCA4 variants are a helpful tool in variant classification and enable us to better predict the disease severity in patients with ABCA4-RDs.
编码ATP结合盒转运蛋白ABCA4的基因中的双等位基因致病变异是遗传性视网膜营养不良（IRD）中不可逆视力丧失的主要原因。由于顺式修饰和亚效变异，对ABCA4变异的解读具有挑战性。我们之前在挪威疑似ABCA4视网膜营养不良（ABCA4-RD）患者中检测到10个意义未明的错义变异（VUS）。在本研究中，我们对这些VUS进行功能表征，以辅助变异解读并确定它们是否与疾病相关。
将ABCA4 VUS在HEK293T细胞中表达，测定ABCA4表达水平和ATP酶活性，并与患者表型相关联。功能数据进一步用于按照美国医学遗传学与基因组学学会（ACMG）指南对VUS进行重新分类。
在这10个VUS中，2个变异，即Cys205Phe和Asn415Thr，被归类为功能严重。携带这些变异的2名患者的发病年龄不同，似乎分别由患者的第二个致病变异Gly1961Glu和c.5461-10T>C驱动。3个变异，Val643Gly、Pro799Leu和Val1433Ile被归类为功能中等，在发病年龄为中年/老年的患者中发现。其余5个变异被归类为功能正常/轻度。根据我们的数据，c.614G>T p.(Cys205Phe)、c.1244A>C p.(Asn415Thr)和c.2396C>T p.(Pro799Leu)被重新分类为（可能）致病，而4个功能正常/轻度的变异可重新分类为可能良性。
ABCA4变异的功能分析是变异分类的有用工具，使我们能够更好地预测ABCA4-RD患者的疾病严重程度。
