BackgroundWhole-exome sequencing (WES) has led to an exponential increase in identification of causative variants in mitochondrial disorders (MD).MethodsWe performed WES in 113 MD suspected patients from Polish paediatric reference centre, in whom routine testing failed to identify a molecular defect. WES was performed using TruSeqExome enrichment, followed by variant prioritization, validation by Sanger sequencing, and segregation with the disease phenotype in the family.ResultsLikely causative mutations were identified in 67 (59.3 %) patients; these included variants in mtDNA (6 patients) and nDNA: X-linked (9 patients), autosomal dominant (5 patients), and autosomal recessive (47 patients, 11 homozygotes). Novel variants accounted for 50.5 % (50/99) of all detected changes. In 47 patients, changes in 31 MD-related genes (ACAD9, ADCK3, AIFM1, CLPB, COX10, DLD, EARS2, FBXL4, MTATP6, MTFMT, MTND1, MTND3, MTND5, NAXE, NDUFS6, NDUFS7, NDUFV1, OPA1, PARS2, PC, PDHA1, POLG, RARS2, RRM2B, SCO2, SERAC1, SLC19A3, SLC25A12, TAZ, TMEM126B, VARS2) were identified. The ACAD9, CLPB, FBXL4, PDHA1 genes recurred more than twice suggesting higher general/ethnic prevalence. In 19 cases, variants in 18 non-MD related genes (ADAR, CACNA1A, CDKL5, CLN3, CPS1, DMD, DYSF, GBE1, GFAP, HSD17B4, MECP2, MYBPC3, PEX5, PGAP2, PIGN, PRF1, SBDS, SCN2A) were found. The percentage of positive WES results rose gradually with increasing probability of MD according to the Mitochondrial Disease Criteria (MDC) scale (from 36 to 90 % for low and high probability, respectively). The percentage of detected MD-related genes compared with non MD-related genes also grew with the increasing MD likelihood (from 20 to 97 %). Molecular diagnosis was established in 30/47 (63.8 %) neonates and in 17/28 (60.7 %) patients with basal ganglia involvement. Mutations in CLPB, SERAC1, TAZ genes were identified in neonates with 3-methylglutaconic aciduria (3-MGA) as a discriminative feature. New MD-related candidate gene (NDUFB8) is under verification.ConclusionsWe suggest WES rather than targeted NGS as the method of choice in diagnostics of MD in children, including neonates with 3-MGA aciduria, who died without determination of disease cause and with limited availability of laboratory data. There is a strong correlation between the degree of MD diagnosis by WES and MD likelihood expressed by the MDC scale.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-016-0930-9) contains supplementary material, which is available to authorized users.

A retrospective, multicenter study of 180 children with cytochrome c oxidase (COX) deficiency analyzed the clinical features, prognosis, and molecular bases of the COX deficiency. Clinical symptoms including failure to thrive, encephalopathy, hypotony, Leigh syndrome, cardiac involvement, and hepatopathy appeared in most patients early after birth or in early childhood. Two thirds of all children died. Biochemical examination revealed an isolated COX deficiency in 101 children and COX deficiency combined with disturbances of other respiratory chain complexes in 79 children. Blood and cerebrospinal fluid lactate increased in 85% and 81% of examined cases, respectively. Pathogenic mutations in mitochondrial or nuclear DNA were established in 75 patients. Mutations in surfeit locus protein 1 gene (SURF1) were found in 47 children with Leigh syndrome; 2bp deletion 845-846delCT was found in 89% of independent alleles. Mutations in a mitochondrial copper-binding protein (SCO2) gene were found in nine children with encephalomyopathy and/or cardiomyopathy; all of them were homozygotes or heterozygotes for 1541GϾA mutation. Different mitochondrial DNA (mtDNA) deletion or depletion were found in nine children, mtDNA mutation 3243AϾG in six, mtDNA mutation 8363GϾA in two children with Leigh syndrome and mtDNA mutations 8344AϾG, and 9205-9206delTA in one child each. COX deficiency represents a heterogeneous group of diseases with unfavorable prognosis. Marked prevalence of two nuclear DNA mutations (845-846delCT in the SURF1 gene and 1541GϾA in the SCO2 gene) associated with COX deficiency in a Slavonic population suggests the existence of regional differences in the genetic basis of COX deficiency.

ADP-ribosylation is a reversible posttranslational modification used to regulate protein function. ADP-ribosyltransferases transfer ADPribose from NAD þ to the target protein, and ADP-ribosylhydrolases, such as ADPRHL2, reverse the reaction. We used exome sequencing to identify five different bi-allelic pathogenic ADPRHL2 variants in 12 individuals from 8 families affected by a neurodegenerative disorder manifesting in childhood or adolescence with key clinical features including developmental delay or regression, seizures, ataxia, and axonal (sensori-)motor neuropathy. ADPRHL2 was virtually absent in available affected individuals' fibroblasts, and cell viability was reduced upon hydrogen peroxide exposure, although it was rescued by expression of wild-type ADPRHL2 mRNA as well as treatment with a PARP1 inhibitor. Our findings suggest impaired protein ribosylation as another pathway that, if disturbed, causes neurodegenerative diseases.

There is a need to replace liver biopsy with non-invasive markers that predict the degree of liver fibrosis in fatty liver disease related to obesity. Therefore, we studied four potential serum markers of liver fibrosis and compared them with histopathological findings in liver biopsy in children with non-alcoholic fatty liver disease (NAFLD). We determined fasting serum level of hyaluronic acid (HA), laminin, YKL-40 and cytokeratin-18 M30 in 52 children (age range 4-19, mean 12 years, 80 % of them were overweight or obese) with biopsy-verified NAFLD. Viral hepatitis, autoimmune and metabolic liver diseases (Wilson's disease, alpha-1-antitrypsin deficiency, cystic fibrosis) were excluded. Fibrosis stage was assessed in a blinded fashion by one pathologist according to Kleiner. Receiver operating characteristics (ROC) analysis was used to calculate the power of the assays to detect liver fibrosis (AccuROC, Canada). Liver fibrosis was diagnosed in 19 children (37 %). The levels of HA and CK18M30 were significantly higher in children with fibrosis compared to children without fibrosis (p=0.04 and 0.05 respectively). The ability of serum HA (cut-off 19.1 ng/ml, Se=84 %, Sp=55 %, PPV=52 %, NPV=86 %) and CK18M30 (cut-off 210 u/l, Se=79 %, Sp=60 %, PPV=56 %, NPV=82 %) to differentiate children with fibrosis from those without fibrosis was significant (AUC=0.672 and 0.666, respectively). The combination of both markers was superior (AUC=0.73, p=0.002). Laminin and YKL-40 levels did not allow a useful prediction. Cytokeratin-18 and hyaluronic acid are suitable serum markers predicting liver fibrosis in children with NAFLD. Studying these markers may identify patients at risk of disease progression.

1) Urgent metabolic intervention decreases mortality of LCHAD-deficient patients, but the prognosis is still uncertain. 2) Emergent metabolic reporting and service are crucial also for the survival of neonates detected by NBS. 3) The nationwide selective screening appeared efficient in LCHADD detection in the country. 4) Transient mild hyperphenylalaninaemia may occur in LCHAD-deficient newborns.