ABSTRACT
We have studied complex I (NADH-ubiquinone reductase) defects of the mitochondrial respiratory chain in 2 infants who died in the neonatal period from 2 different neurological forms of severe neonatal lactic acidosis. Specific and marked decrease in complex I activity was documented in muscle, liver, and cultured skin fibroblasts. Biochemical characterization and study of the genetic origin of this defect were performed using cultured fibroblasts. Immunodetection of 6 nuclear DNA-encoded (20, 23, 24, 30, 49, and 51 kDa) and 1 mitochondrial DNA-encoded (ND1) complex I subunits in fibroblast mitochondria revealed 2 distinct patterns. In 1 patient, complex I contained reduced amounts of the 24- and 51-kDa subunits and normal amounts of all the other investigated subunits. In the second patient, amounts of all the investigated subunits were severely decreased. The data suggest partial or extensive impairment of complex I assembly in both patients. Cell fusion experiments between 143B206 rho degrees cells, fully depleted of mitochondrial DNA, and fibroblasts from both patients led to phenotypic complementation of the complex I defects in mitochondria of the resulting cybrid cells. These results indicate that the complex I defects in the 2 reported cases are due to nuclear gene mutations.
Subject(s)
Acidosis, Lactic/genetics , Cell Nucleus/chemistry , DNA/genetics , NAD(P)H Dehydrogenase (Quinone)/genetics , Acidosis, Lactic/congenital , Acidosis, Lactic/pathology , Cells, Cultured , DNA Mutational Analysis , DNA, Complementary/genetics , DNA, Mitochondrial/genetics , Electron Transport , Fatal Outcome , Fibroblasts/enzymology , Fibroblasts/ultrastructure , Genetic Complementation Test , Genetic Heterogeneity , Humans , Hybrid Cells , Infant , Infant, Newborn , Male , Microscopy, Electron , NAD(P)H Dehydrogenase (Quinone)/deficiency , Organ Specificity , Transcription, GeneticABSTRACT
OBJECTIVE: This study was performed to identify a possible relationship between genotype and phenotype in the congenital familial long QT syndrome (cLQTS). BACKGROUND: The cLQTS, which occurs as an autosomal dominant or recessive trait, is characterized by QT-interval prolongation on the electrocardiogram and torsade de pointes arrhythmias, which may give rise to recurrent syncope or sudden cardiac death. Precipitators for cardiac events are exercise or emotion and occasionally acoustic stimuli. METHODS: The trigger for cardiac events (syncope, documented cardiac arrhythmias, sudden cardiac death) was analyzed in 11 families with a familial LQTS and a determined genotype. RESULTS: The families were subdivided in KVLQT1-related families (LQTS1, n = 5) and HERG (human ether-a-gogo-related gene)-related families (LQTS2, n = 6) based on single-strand conformation polymorphism analysis and sequencing. Whereas exercise-related cardiac events dominate the clinical picture of LQTS1 patients, auditory stimuli as a trigger for arrhythmic events were only seen in LQTS2 patients. CONCLUSIONS: Arrhythmic events triggered by auditory stimuli may differentiate LQTS2 from LQTS1 patients.
Subject(s)
Acoustic Stimulation , Cation Transport Proteins , DNA-Binding Proteins , Long QT Syndrome/diagnosis , Potassium Channels, Voltage-Gated , Potassium Channels/genetics , Trans-Activators , Adult , Aged , Aged, 80 and over , DNA/analysis , DNA Probes/chemistry , Death, Sudden, Cardiac/etiology , Disease Progression , ERG1 Potassium Channel , Electrocardiography , Ether-A-Go-Go Potassium Channels , Female , Follow-Up Studies , Genotype , Heart Rate , Humans , KCNQ Potassium Channels , KCNQ1 Potassium Channel , Long QT Syndrome/etiology , Long QT Syndrome/genetics , Male , Mutation , Phenotype , Polymorphism, Single-Stranded Conformational , Transcriptional Regulator ERGABSTRACT
The human gene for the 10-kDa flavoprotein subunit of the mitochondrial NADH:ubiquinone oxidoreductase (Complex I) was completely cloned and sequenced. The so-called NDUFV3 gene contains three exons, spanning 20 kb. The open reading frame contains a 34-codon import sequence and a 74-codon mature protein sequence. A database search revealed close homology to bovine and rat protein sequence but not to any other known protein. Northern blot analysis showed that the NDUFV3 gene is ubiquitously expressed. The NDUFV3 gene was assigned by FISH to a single location on chromosome 21q22.3 and might contribute to the Down syndrome phenotype.