以急性脑干脑炎及脊髓炎起病的单纯型甲基丙二酸尿症1例

Acute brainstem encephalitis and myelitis in a girl with isolated methylmalonic aciduria due to MUT gene defect

摘要:

MUT 基因突变引起的甲基丙二酰辅酶A 变位酶缺陷是我国单纯型甲基丙二酸尿症的主要病因。该文报道我国首例以急性脑干脑炎和脊髓炎样形式起病的MUT 型患者,探讨甲基丙二酸尿症的复杂临床表型。患儿,女,3 岁2 个月时因发热伴肢体进行性无力3 d,呼吸困难伴意识障碍1 d 就诊。头颅MRI 扫描提示双侧苍白球及脑干背侧对称片状高信号,脊髓MRI 扫描提示急性脊髓炎样改变。临床诊断为"病毒性脑炎、中枢型呼吸衰竭?",血液丙酰肉碱(6.83 μmol/L,参考值1.0~5.0 μmol/L)增高,尿甲基丙二酸(133.2 mmol/mol肌酐,参考值 0.2~3.6 mmol/mol 肌酐)显著增高,血清总同型半胱氨酸正常。MUT 基因存在c.1663C>T 和c.1630_1631GG>TA 突变,其中c.1663C>T(p.A555T)为新突变,确诊为MUT 型甲基丙二酸尿症。经特殊饮食、维生素B12、左卡尼汀治疗后,患儿病情逐渐好转。甲基丙二酸尿症临床表现复杂,早期的代谢筛查及基因诊断是鉴别病型、指导治疗的关键技术。

Abstract:

Methylmalonyl CoA mutase deficiency due to MUT gene defect has been known as the main cause of isolated methylmalonic acidemia in Mainland China. This study reported a patient with isolated methylmalonic aciduria (MUT type) characterized as acute brainstem encephalitis and myelitis. The previously healthy girl presented with fever, lethargy and progressive weakness in her extremities at the age of 3 years and 2 months. Three day later, she had respiratory distress and consciousness. Cranial MRI revealed bilateral symmetrical lesion of pallidum, brain stem and spinal cord, indicating acute brainstem encephalitis and myelitis. Her blood propionylcarnitine (6.83 μmol/L vs normal range 1.0 to 5.0 μmol/L) and urinary methylmalonic acid (133.22 mmol/mol creatinine vs normal range 0.2 to 3.6 mmol/mol creatinine) increased significantly. Plasma total homocysteine was normal. On her MUT gene, a reported mutation (c.1630_1631GG>TA) and a novel mutation (c.1663C>T, p.A555T) were identified, which confirmed the diagnosis of methylmalonic aciduria (MUT type). After cobalamin injection, protein-restricted diet with the supplements of special formula and L-carnitine, progressive improvement has been observed. The clinical manifestation of patients with methylmalonic aciduria is complex. Metabolic study and gene analysis are keys for the diagnosis and treatment of the disorder.