[Homozygous familial hypobetalipoproteinemia caused by APOB gene variations: a case report and review of literature].

Objective: To summarize the genotypes and clinical characteristics of homozygous family hypobetalipoproteinemia (Ho-FHBL) caused by apolipoprotein B (APOB) gene variations. Methods: The clinical, laboratory, genetic, and liver histology data of a boy with Ho-FHBL managed in the hepatology ward of the Children's Hospital of Fudan University in May 2021 were retrospectively analyzed. The literature was searched from China National Knowledge Infrastructure, Wanfang Data Knowledge Service Platform, China VIP database, China Biology Medicine disc and PubMed database (up to May 2022) with "familial hypobetalipoproteinemia" or "hypobetalipoproteinemias" or "hypo beta lipoproteinemia" or "hypolipoproteinemias" as the search terms. All relevant literatures were reviewed to summarize the clinical and genetic features of Ho-FHBL caused by APOB gene variations. Results: The male patient was admitted to the hospital due to abnormal liver function tests for 8 months at the age of 4 years and 6 months. Blood biochemistry showed transaminitis and abnormally low serum levels of lipids. Liver biopsy revealed fatty liver with inflammation and early cirrhosis (Brunt score was F3G2S4). Whole exome sequencing revealed two novel variants of APOB gene (c.3745C>T, p.Q1249 * from the father and c.4589_4592delinsAGGTAGGAGGTTTAACTCCTCCTACCT, p.T1530Kfs * 12 from the mother). He was diagnosed as Ho-FHBL caused by APOB gene compound heterozygous variations. Literature search retrieved 36 English literatures and 0 Chinese literature. A total of 55 (23 males and 32 females) Ho-FHBL cases, including this one, were caused by 54 APOB gene pathogenic variants (23 frameshift, 15 nonsense, 7 missense, 8 splice and 1 gross deletions). The age of the last follow-up was between 1 month and 75 years. Among them, 28 cases had lipid malabsorption, 19 cases had early dysplasia, 12 cases had no symptoms. Twenty-one patients had symptoms related to fat soluble vitamin deficiency, including 14 cases of acanthocytosis, 10 cases of neurological symptoms, and 6 cases of ocular lesions. Thirty-four patients had liver involvement, including 25 cases of elevated transaminase, 21 cases of fatty liver, 15 cases of hepatomegaly, 9 cases of liver fibrosis, 3 cases of liver cirrhosis, 1 case of hepatic hemangioma and 1 case of liver neoplastic nodule. Conclusions: The variants of APOB gene in Ho-FHBL are mainly frameshift and nonsense variations. Patients may have lipid malabsorption and (or) early dysplasia, or symptom-free. Liver involvement is common.目的： 总结APOB基因变异致纯合型家族性低β脂蛋白血症（Ho-FHBL）的基因型与临床特点。 方法： 回顾性病例总结2021年5月复旦大学附属儿科医院肝病病区诊治的1例Ho-FHBL患儿的病史、体征、实验室检查、肝脏病理等临床资料及基因检测的特点，并分别以“家族性低β脂蛋白血症”“低β脂蛋白血症”“低β-脂蛋白血症”“低脂蛋白血症”“familial hypobetalipoproteinemia”“hypobetalipoproteinemias”“hypo beta lipoproteinemia”“hypolipoproteinemias”为检索词，对中国知网、万方、维普、中国生物医学文献数据库、PubMed数据库建库至2022年5月的相关文献进行检索，总结APOB基因变异致Ho-FHBL的临床及遗传学特点。 结果： 患儿，男，4岁6月龄，因“发现肝功能异常8个月”入院，血生化检测提示转氨酶升高，血脂减低。肝组织活检提示脂肪性肝炎伴早期肝硬化形成（Brunt评分F3G2S4），全外显子组测序发现APOB基因2种新变异（c.3745C>T，p.Q1249*，父亲杂合携带；c.4589_4592delinsAGGTAGGAGGTTTAACTCCTCCTACCT，p.T1530Kfs*12，母亲杂合携带），诊断为APOB基因复合杂合变异所致的Ho-FHBL。文献检索到英文文献36篇，中文文献0篇，结合本例，合计55例APOB基因变异致Ho-FHBL，其中男23例、女32例，末次随访年龄1月龄至75岁。共检测到APOB基因致病性变异54种，包括23种移码变异、15种无义变异、8种剪接位点变异、7种错义变异与1种大片段缺失。55例Ho-FHBL患者中28例表现为脂质吸收不良、19例表现为早期生长发育不良、12例无症状。21例患者出现脂溶性维生素缺乏相关表现，其中棘红细胞增多症14例、神经症状10例、眼部病变6例。34例患者肝脏受累，包括转氨酶升高25例、脂肪肝21例、肝肿大15例、肝纤维化9例、肝硬化3例、肝血管瘤和肝肿瘤性结节各1例。 结论： Ho-FHBL中APOB基因变异以移码变异与无义变异为主，患者可表现为脂质吸收不良和（或）早期生长发育不良，也可无任何症状，肝脏受累多见。.