Study progress of mitochondrial DNA depletion syndromes / 中华实用儿科临床杂志

Mitochondrial DNA(mtDNA)depletion syndromes(MDS)is a type of autosomal recessive genetic disease characterized by a severe reduction in mtDNA content caused by mutations in the nuclear gene,which results in impaired energy production in affected tissues and organs. According to phenotype,MDS are usually classified as 4 forms:myopathic,encephalomyopathic,hepa - tocerebarl and neurogastrointestinal. The following 9 types of related genes have been reported:a myopathic form associated with mutations in TK2;an encephalomyopathic form associated with mutations in SUCLA2,SUCLGl,or RRM2B;a hepa-tocerebral form associated with mutations in DGUOK,MPVl7, POLG,or Cl0orf2;and a neurogastrointestinal form associated with mutations in TYMP. Some MDS can lead to early death in newborns and infants,so early identification is very important. Combination of biochemical testing,histopatholo-gy,respiratory chain complex testing and mtDNA quantification is needed for the diagnosis. The final diagnosis requires genetic testing.

A case of SUCLG1-related infantile encephalomyopathy mitochondrial DNA depletion syndrome / 临床儿科杂志

Objective Mitochondrial DNA depletion syndrome is a rare autosomal recessive disorder characterized by complex genetic and clinical manifestations.This study aimed to investigate the clinical and laboratory features of a boy with mitochondrial encephalomyopathy caused by SUCLG1 mutation.Methods The clinical data and genetic test of a patient with mitochondrial DNA depletion syndrome were retrospectively analyzed.Result The proband presented with limb weakness at the 4th month after birth,and presented dystrophic appearance,muscular hypotonia,psychomotor retardation,failure to thrive,hearing impairment,scoliosis,thoracocyllosis and facial features at 9 months old.Laboratory tests showed blood lactic acid and pymvate increased,liver damage and abnormal myocardial enzymes.Plasma camitine ester profiling showed that amino acids decreased and C4-dicarboxylic-carnitine increased.Urinary organic acid analysis showed increased concentration of methylmalonic acid and its metabolites indicating methyl malonic aciduria.MRI showed bilateral T2 hyperintensities in bilateral caudate nuelei and lenticular and brain atrophy-like changes.Brainstem auditory evoked potential showed severe hearing loss.His development quotient was 35.Genetic sequencing of MUT,,MMAA,MMAB and other classic mitochondrial disease related genes of the proband revealed no mutation.Two heterozygous mutations,c.961C＞G and c.713T＞C,inherited from the phenotype of normal parents were detected in his SUCLG1 gene.The copy number of mitochondrial DNA was 244/cell in peripheral blood leukocytes,equivalent to 68.4％ of that in normal control.Conclusion In this study,an infant with muscular hypotonia,psychomotor retardation,deafness and slightly increased urine methyl malonic acid was diagnosed by genetic test.For patients with unexplained hypotonia,mental retardation,abnormal movements,hearing disorder together with increased blood pyruvic acid and lactic acid,mild methylmalonic acidemia and abnormal acylcarnitine,mitochondrial DNA depletion syndrome should be considered.Gene analysis is important for diagnosis and prenatal diagnosis of the next pregnancy.

Recent advances in the diagnosis and treatment of pediatric genetic cholestasis / 中华实用儿科临床杂志

Cholestasis is defined as a conjugated bilirubin level >1 mg/dL(17.1 μmol/L)if total serum bilirubin is ≤5 mg/dL(85.5 μmol/L),or conjugated bilirubin fraction >20％of total bilirubin when the total bilirubin is >5 mg/dL(85.5 μmol/L).In the recent years,the diagnosis and management of genetic cholestasis have caused considerable attention in the pediatric world,in pace with the development,maturation,and clinical application of the theories and techniques in genomics as well as molecular genetics.With a diversity of causative genes,genetic cholestasis usually demonstrates nonpathognomonic clinical manifestations.The etiology diagnosis such a disease relies on genetic tests,the treatment is often difficult,and the prognosis varies disparately,usually causing tremendous pain and burden on the affected patient and the family as well.Taking citrin deficiency,mitochondrial DNA depletion syndrome,microvi-llus inclusion disease and sodium taurocholate cotransporting polypeptide deficiency as samples,the recent advances in the diagnosis and treatment of genetic cholestasis are addressed.

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

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.