Mitochondrial Respiratory Chain: Biochemical Analysis and Criterion for Deficiency in Diagnosis

Abstract

Spectrophotometric evaluation of mitochondrial respiratory chain (MRC) enzymatic complexes is the main approach to the biochemical investigation and diagnosis in oxidative phosphorylation disorders (also known as mitochondrial cytopathies). Regular dual beam spectrophotometers may be used, but we describe the protocols for double wavelength devices, allowing the analysis of complex activities from a small amount of tissue, with high sensitivity. An important concern is which tissue should be selected for analysis. Accordingly, we present the results obtained with different tissues and control values to be used. There are no standards available for the determinations and no interlaboratory quality control schemes are implemented. Additionally, different laboratories may use different protocols and comparison of results may be difficult. Currently, there is no consensus in literature for defining a criterion of an MRC deficiency to be used in biochemical diagnosis. There is statistical evidence that the most adequate criterion to define an MRC deficiency is below 40% of the mean control value normalized to citrate synthase activity.

Lethal Neonatal LTBL Associated with Biallelic EARS2 Variants: Case Report and Review of the Reported Neuroradiological Features

“…Mitochondrial OXPHOS activities (complexes I-V) were determined in muscle and liver (normalised to citrate synthase activity) as described (Grazina 2012). Cultured fibroblasts from the proband and two controls were grown in minimum essential medium (MEM) (Gibco) with 10% foetal bovine serum (FBS) (Gibco), 1Â MEM vitamins (Sigma), 1Â non-essential amino acids (Sigma), 50 U/ml penicillin, 50 mg/ml streptomycin (Sigma), 1 mM sodium pyruvate solution (Sigma), 0.05 mg/ml uridine and 2 mM L-glutamine (Sigma).…”

Identification of a novel deletion in SURF1 gene: Heterogeneity in Leigh syndrome with COX deficiency

“…Thrombophilia screening was negative. Laboratory investigation revealed increased lactate and lactate/pyruvate ratio, moderate complex IV deficiency in lymphocytes -29.7% of average control value corrected for citrate synthase (criteria according to Grazina, 2012). Five years later, in the sequence of an acute pharyngitis, this patient developed central hipoventilation lead to respiratory insufficiency with need for chronic mechanical ventilation.…”

“…Complex IV activity in lymphocytes was 20.2% of average control value corrected for citrate synthase (criteria according to Grazina, 2012). Isolated complex IV deficiency was detected in the muscle biopsy -18.4% of average control value corrected for citrate synthase (criteria according to Grazina, 2012). Investigation of SURF1 revealed a heterozygous deletion, c.-11_13del ( Fig.…”

“…1A-C). Muscle biopsy study disclosed no histology abnormalities and low complex IV activity -22.5% of average control value corrected for citrate synthase (criteria according to Grazina, 2012).…”

Genetic Variation of <b><i>MT-ND</i></b> Genes in Frontotemporal Lobar Degeneration: Biochemical Phenotype-Genotype Correlation

“…Biochemical analysis was performed by spectrophotometric evaluation of MRC complex I-IV activity in lymphocyte homogenates of 54 patients, and the results were compared with an age-matched control group, as previously described [63]. A deficiency is considered when activity is below 40% of the reference mean value normalized to citrate synthase.…”