探讨4.1埃兹蛋白－根蛋白－膜突蛋白结构域包含的7(FRMD7)基因新突变位点导致先天性眼球震颤(CN)一家系的遗传学特征。

2021年10月，收集于北京大学人民医院眼视光中心确诊CN家系四代19例的临床资料。采集家系中3例CN患者和9例眼正常者的外周血样本，检查受试者的最佳矫正视力(BCVA)、眼前节及眼底；评估眼球震颤的类型、头位、是否有中间带及眼位等。应用GenCap液相仪抓取目标基因技术，获取与眼部疾病相关的811个基因的外显子区域及其侧翼区域，对先证者进行高通量测序，筛选出致病基因和突变位点，并在家系中进行Sanger测序和共分离验证。使用Mutation Taster软件分析突变位点的基因突变类型；预测突变型蛋白质的三维结构和功能改变。

该家系的先证者(Ⅲ6)男性，11岁。此患者右眼BCVA 0.7，左眼BCVA 0.8。先证者表弟(Ⅲ9)男性，2岁，双眼视力检查配合度不佳。先证者祖父(Ⅰ1)男性，73岁。此患者右眼BCVA 0.3，左眼BCVA 0.4，双眼晶状体混浊。3患者均双眼正位，眼球震颤呈水平钟摆型，无中间带及代偿头位，眼底检查未见明显异常。此家系患者均为男性，呈现隔代遗传特征，符合X连锁隐性遗传。家系中12例受试者外周血基因检测结果显示，3例患者FRMD7基因第9外显子编码区发生半合子变异，Ⅱ6、Ⅱ8及Ⅲ8等3例眼正常女性者在该区域发生杂合变异，核苷酸变异c.822C>A，氨基酸变异p.Y274X，使终止密码子提前出现，造成蛋白质编码提前终止，大量氨基酸丢失。根据美国医学遗传学与基因组学学会遗传变异分类标准与指南，该变异被评定为疑似致病性变异。经Mutation Taster软件分析，结果显示突变性质为无义突变；突变型蛋白质三维结构和功能的预测显示该突变影响FRMD7蛋白结构的稳定性，可能使其功能受损。

FRMD7基因核苷酸变异c.822C>A(p.Y274X)为无义突变，属于新突变位点，此变异是该家系CN的可能致病原因，扩大了FRMD7基因突变频谱。

The aim of this study was to investigate the genetic characteristics of the mutation site of four-point-one ezrin-radixin-moesin domain-containing 7 (FRMD7) gene in a family with congenital nystagmus (CN).

Clinical data of 19 cases in four-generation of a Chinese family with a diagnosised CN in the Department of Ophthalmology and Clinical Centre of Optometry, Peking University People′s Hospital in October 2021 were collected. The leukocytes of the peripheral blood was extracted from 3 cases with CN and 9 cases with normal eyes. The best corrected visual acuity (BCVA) of patients, anterior segment and fundus were performed; the type of CN, head position, whether there is median and eye position were evaluated. Targeted gene was captrued using liquid chromatography and exon region and its flanking region containing 811 candidate genes related to ophthalmic disorders was captured. The high throughput sequencing technology was performed for the proband, then the pathogenic genes and mutation sites were selected and Sanger sequencing was performed for the other family members to verify the candidate disease-causing mutation. The gene mutation type of mutation sites was analyzed by MutationTaster software; 3D structure and function of mutated protein was evaluated.

The proband (Ⅲ6) was a 11-year old male, whose BCVA of right eye and left eye were 0.7 and 0.8, respectively. Proband′s cousin (Ⅲ9) was a 2-year old male, whose BCVA examination was failed. The proband′s grandfather (Ⅰ1) was a 73-year old male, whose BCVA of right eye and left eye were 0.3 and 0.4, respectively and his bilateral lens were opacite. Three patients had a pendular oscillation in both eyes, and normal ocular alignment, no abnormal head posture; the anterior segment and fundus of patients were normal. 3 patients in this family with CN were male, showing intergenerational genetic characteristics, which was consistent with X-linked recessive inheritance. Sequencing analysis identified a hemizygote mutation (c.822C>A) in exon9 of FRMD7 gene in this Chinese family with CN. Three females (Ⅱ6, Ⅱ8, Ⅲ8) had a heterozygous mutation in this region. This mutation resulted in a amino acid mutation (p.Y274X) due to a single nucleotide substitution of C→A at position c. 822. It caused the earlier appearance of the termination codon stopping proteins encoding, which causing numerous missing of amino acids. According to the standard and guide of genomics classification of genetic mutation of American Society for Medical Genetics, it has been estimated that this mutation was likely pathogenic. The mutagenesis nature was a nonsense mutation through MutationTaster software. The analysis of 3D structure and function of mutated protein was shown that there was a unstable protein structure, which probably causing the damaged function.

The mutation c. 822C>A (p.Y274X) of FRMD7 was a nonsense mutation, which was a novel site. This mutation had a capability of causing CN, and broaden the muation spectrum of FRMD7.