Tian Lu, Chen Chunjie, Song Yuning, Zhang Xiaohui, Xu Ke, Xie Yue, Jin Zi-Bing, Li Yang
Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology & Visual Sciences Key Lab, Beijing, China.
Invest Ophthalmol Vis Sci. 2022 Jun 1;63(6):5. doi: 10.1167/iovs.63.6.5.
To identify the missing heritability of ABCA4-related retinopathy in a Chinese cohort.
We recruited 33 unrelated patients with ABCA4-related retinopathy carrying a monoallelic variant in ABCA4. All patients underwent ophthalmic examinations. Next-generation sequencing of the whole ABCA4 sequence, including coding and noncoding regions, was performed to detect deep intronic variants (DIVs) and copy number variations (CNVs).
We identified eight missing pathogenic ABCA4 variants in 60.6% of the patients (20/33), which comprised five DIVs and three CNVs. The five DIVs, including four novel (c.1555-816T>G, c.2919-169T>G, c.2919-884G>T, and c.5461-1321A>G) and one reported (c.4539+1100A>G), accounted for the missing alleles in 51.5% of the patients. Minigene assays showed that four novel DIVs activated cryptic splice sites leading to the insertions of pseudoexons. The three novel CNVs consisted of one gross deletion of 1273 bp (exon 2) and two gross duplications covering 25.2 kb (exons 28-43) and 9.4 kb (exons 38-44). The microhomology domains were identified at the breakpoints and revealed the potential mechanisms of CNV formation.
DIVs and CNVs explained approximately two-thirds of the unresolved Chinese cases with ABCA4-related retinopathy. Combining results from phenotypic-directed screening, targeting the whole ABCA4 sequencing and in silico tools can help to identify the missing heritability.
在中国队列中确定ABCA4相关视网膜病变缺失的遗传度。
我们招募了33名携带ABCA4单等位基因变异的ABCA4相关视网膜病变无关患者。所有患者均接受眼科检查。对整个ABCA4序列（包括编码区和非编码区）进行二代测序，以检测内含子深处变异（DIVs）和拷贝数变异（CNVs）。
我们在60.6%的患者（20/33）中鉴定出8个缺失的致病性ABCA4变异，其中包括5个DIVs和3个CNVs。这5个DIVs，包括4个新的（c.1555-816T>G、c.2919-169T>G、c.2919-884G>T和c..5461-1,321A>G）和1个已报道的（c.4539+1,100A>G），占51.5%患者中缺失的等位基因。小基因检测表明，4个新的DIVs激活了隐蔽剪接位点，导致假外显子插入。3个新的CNVs包括1个1273 bp（外显子2）的大片段缺失和2个分别覆盖25.2 kb（外显子28-43）和9.4 kb（外显子38-44）的大片段重复。在断点处鉴定出微同源结构域，并揭示了CNV形成的潜在机制。
DIVs和CNVs解释了约三分之二未解决的中国ABCA4相关视网膜病变病例。结合表型导向筛查、针对整个ABCA4测序的结果和计算机工具，有助于识别缺失的遗传度。
