TK2-related mitochondrial DNA depletion syndrome:two cases report and review of literature / 中华实用儿科临床杂志

ABSTRACT

Objective To study the clinical characteristics,muscle pathological features,diagnosis and prognosis of TK2-related mitochondrial DNA depletion syndrome(MDS).Methods Clinical and laboratory data of 2 cases of TK2-related myopathic MDS were reported.And data of previously reported 58 TK2-related MDS cases were reviewed.Results Total 60 patients consisted of 35 male and 25 female.The age of onset ranged from the birth to the age of 74 years old,and 54 of the patients were attacked at the age younger than 3 years old.Muscle weakness and hypotonia were detected in all patients,with 40 patients(including the newly diagnosed 2 cases) manifested as pure myopathic form,and 20 patients with other multiple organs involvement.Serum creatine kinase was mildly increased (211-6 500 IU/L) in 53 patients.Elevated serum lactic acid level (2.3-12.0 mmol/L)was observed in 24 patients.Muscle biopsy was available from 55 patients,and ragged red fibers and/or cytochrome C oxidase (COX)-negative fibers were detected in 48 out of them.Nine out of 11 patients received electronic microscope study showed proliferation of abnormal mitochondria.Respiratory chain enzymatic activities in skeletal muscle were reduced in 31 out of 33 patients.Marked mtDNA content reduction was observed in 36 out of 41 patients (4％-25％ of age-and tissue-matched controls).A total of 42 TK2 mutations were found in 60 patients,including 2 novel mutations c.923A ＞ G and c.619-2A ＞ T in this study.Conclusions The most common clinical manifestations of TK2-related MDS are severely,rapidly progressing myopathy with infantile or early childhood onset.As the detection rate of characteristic pathologic features in muscle is high,muscle biopsy is important for the diagnosis of TK2-related MDS.