Andreadi Anneliza, Hallam Thomas M, Brocklebank Vicky, Sharp Scott J, Walsh Patrick R, Southerington Tom, Hautalahti Marco, Steel David H, Lotery Andrew J, Harris Claire L, Marchbank Kevin J, Kavanagh David, Jones Amy V
Complement Therapeutics Research Group, Translational and Clinical Research Institute, Newcastle University, Framlington Place Newcastle upon Tyne, NE2 4HH, United Kingdom.
National Renal Complement Therapeutics Centre, Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne, NE1 4LP, United Kingdom.
Hum Mol Genet. 2025 Feb 1;34(3):218-228. doi: 10.1093/hmg/ddae165.
Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the developed world. The alternative pathway (AP) of complement has been linked to the pathogenesis of AMD. In particular, rare variants (RVs) in the complement factor I (CFI) gene encoding the Factor I (FI) protein confer increased AMD risk. The prevalence of CFI RVs are well characterised in European AMD, however little is known about other populations. The Finnish population underwent genetic restriction events which have skewed allele frequencies in unexpected ways. A series of novel or enriched CFI RVs were identified in individuals with dry AMD from the Finnish Biobank Cooperative (FINBB), but the relationship between these genotypes and contribution to disease was unclear. Understanding how RVs impact the ability of FI to regulate the complement system is important to inform mechanistic understanding for how different genotypes contribute to disease development. To explore this a series of in vitro assays were used to functionally characterise the protein products of 3 CFI RVs enriched in FINBB dry AMD, where no prior data were available. The G547R variant resulted in almost complete loss of both classical pathway and AP regulatory potential. The c.982 g>a variant encoding G328R FI perturbed an exon splice enhancer site which resulted in exon skipping and a premature stop codon in vitro and low levels of FI in vivo. Despite detailed analysis no defect in levels or function was demonstrated in T107A. Functional characterization of all Finnish CFI RVs in the cohort allowed us to demonstrate that in Finnish dry AMD, collectively the type 1 CFI RVs (associated with FI haploinsufficiency) were significantly enriched with odds ratio (ORs) of 72.6 (95% confidence interval; CI 16.92 to 382.1). Meanwhile, type 2 CFI RVs (associated with FI dysfunction) collectively conferred a significant OR of 4.97 (95% CI 1.522 to 15.74), and non-impaired or normal CFI RV collectively conferred an of OR 3.19 (95% CI 2.410 to 4.191) although this was driven primarily by G261D. Overall, this study for the first time determined the ORs and functional effect for all CFI RVs within a Geographic Atrophy (GA) cohort, enabling calculations of combined risk scores that underline the risk conferred by type 1 and 2 CFI RVs in GA/AMD.
年龄相关性黄斑变性（AMD）是发达国家不可逆失明的主要原因。补体替代途径（AP）与AMD的发病机制有关。特别是，编码I因子（FI）蛋白的补体因子I（CFI）基因中的罕见变异（RVs）会增加AMD风险。CFI RVs在欧洲AMD中的患病率已得到充分表征，但对其他人群知之甚少。芬兰人群经历了基因限制事件，这些事件以意想不到的方式扭曲了等位基因频率。在芬兰生物银行合作组织（FINBB）的干性AMD个体中鉴定出一系列新的或富集的CFI RVs，但这些基因型与疾病贡献之间的关系尚不清楚。了解RVs如何影响FI调节补体系统的能力，对于深入理解不同基因型如何导致疾病发展的机制很重要。为了探索这一点，我们使用了一系列体外试验来对FINBB干性AMD中富集的3种CFI RVs的蛋白质产物进行功能表征，此前尚无相关数据。G547R变异导致经典途径和AP调节潜力几乎完全丧失。编码G328R FI的c.982 g>a变异扰乱了一个外显子剪接增强子位点，导致体外外显子跳跃和提前终止密码子，以及体内FI水平较低。尽管进行了详细分析，但未发现T107A在水平或功能上存在缺陷。对队列中所有芬兰CFI RVs的功能表征使我们能够证明，在芬兰干性AMD中，1型CFI RVs（与FI单倍体不足相关）总体上显著富集，优势比（ORs）为72.6（95%置信区间；CI 16.92至382.1）。同时，2型CFI RVs（与FI功能障碍相关）总体上赋予显著的OR值为4.97（95%CI 1.522至15.74），而未受损或正常的CFI RV总体上赋予OR值为3.19（95%CI 2.410至4.191），尽管这主要由G261D驱动。总体而言，本研究首次确定了地理萎缩（GA）队列中所有CFI RVs的OR值和功能效应，能够计算综合风险评分，突出了1型和2型CFI RVs在GA/AMD中所带来的风险。
