微绒毛包涵体病一家系临床特点和MYO5B基因突变分析

微绒毛包涵体病(MVID)是MYO5B或STX3基因突变导致的一种常染色体隐性遗传病,以难治性腹泻和营养吸收障碍为主要临床表现。本文探讨1例MVID患儿的临床特征及MYO5B基因突变特点。患儿为21 d女婴,因"解稀便20 d"收住院。体查发现患儿体重和身长落后,皮肤巩膜黄染;双肺呼吸音清,心音有力;腹部膨隆,腹壁静脉显露,肝脾肋下未触及。血生化结果发现总胆汁酸、胆红素、转氨酶、谷氨酰转肽酶等指标均升高,而血钠、氯、磷和镁水平均降低。血气分析提示代谢性酸中毒。初步诊断先天性腹泻,给予肠外营养及对症支持治疗。患儿腹泻顽固,代谢性酸中毒和电解质絮乱难以纠正,且转氨酶、谷氨酰转肽酶、总胆汁酸、胆红素等胆汁淤积指标持续高于正常。住院1月余自动出院,出院后失访。遗传学分析在患儿MYO5B基因检测到c.1966CT(p.R656C)和c.310+2Tdup两个突变,分别来源于其母亲和父亲;其中c.310+2Tdup为新的剪接位点突变,最终患儿确诊为MVID。

Clinical features and MYO5B mutations of a family affected by microvillus inclusion disease

Microvillus inclusion disease (MVID) is an autosomal recessive disorder caused by biallelic mutations in the MYO5B or STX3 gene. Refractory diarrhea and malabsorption are the main clinical manifestations. The aim of this study was to investigate the clinical features and MYO5B gene mutations of an infant with MVID. A 21-day-old female infant was referred to the hospital with the complaint of diarrhea for 20 days. On physical examination, growth retardation of the body weight and length was found along with moderately jaundiced skin and sclera. Breath sounds were clear in the two lungs and the heart sounds were normal. The abdomen was distended and the veins in the abdominal wall were observed. The liver and spleen were not palpable. Biochemical analysis revealed raised serum total bile acids, bilirubin, transaminases and γ-glutamyl transpeptidase while decreased levels of serum sodium, chloride, phosphate and magnesium. Blood gas analysis indicated metabolic acidosis. The preliminary diagnosis was congenital diarrhea, and thus parenteral nutrition was given along with other symptomatic and supportive measures. However, diarrhea, metabolic acidosis and electrolyte disturbance were intractable, and the cholestatic indices, including transaminases, γ-glutamyl transpeptidase, bilirubin and total bile acids, remained at increased levels. One month later, the patient was discharged and then lost contact. On genetic analysis, the infant was proved to be a compound heterozygote of the c.310+2Tdup and c.1966C>T(p.R656C) variants of the gene MYO5B, with c.310+2Tdup being a novel splice-site mutation. MVID was thus definitely diagnosed.