A case of mitochondrial trifunctional protein deficiency diagnosed by acylcarnitine profile and DNA analysis in a dried blood spot of a 4-day-old boy

Clinical and molecular aspects of Japanese patients with mitochondrial trifunctional protein deficiency

Mitochondrial trifunctional protein (MTP) deficiency is a rare inherited metabolic disorder of mitochondrial fatty acid oxidation. We newly characterized three novel mutations in 2 Japanese patients with MTP deficiency, and investigated the clinical and molecular aspects of 5 Japanese patients including 3 previously reported cases. Herein, we describe the characterization of four missense mutations, R214C, H346R, R411K, and V422G, in the HADHB gene, which have been identified in Japanese patients, employing a newly developed, sensitive transient expression analysis. Co-transfection of wild-type HADHA and HADHB cDNAs in SV40-transfected fibroblasts from a MTP-deficient patient yielded sufficient enzyme activity to evaluate low-level residual enzyme activity, using two incubation temperatures of 30 degrees C and 37 degrees C. At 30 degrees C, residual enzyme activity was higher than that at 37 degrees C in V422G, R214C, and R411K. However, H346R, which was seen in the most severe case, showed no enzyme activity at both temperatures. Our results demonstrate that a defect of HADHB in MTP deficiency is rather common in Japanese patients, and the mutational spectrum is heterogeneous. The present findings showed that all missense mutations in this study were disease-causing. Although the number of patients is still limited, it is suggested that the phenotype is correlated with the genotype and a combination of two mutant alleles of the HADHB gene in MTP deficiency.

Differential inhibitory effect of long-chain acyl-CoA esters on succinate and glutamate transport into rat liver mitochondria and its possible implications for long-chain fatty acid oxidation defects

Long-chain fatty acid beta-oxidation defects are associated with a series of clinical and biochemical abnormalities, including accumulation of long-chain acyl-CoA esters which have been shown to inhibit several enzymes and transport systems that may disturb energy metabolism. Using isolated rat liver mitochondria incubated under state 3 conditions, we observed that long-chain acyl-CoA esters and their beta-oxidation intermediates inhibit ATP synthesis and oxygen consumption, both with succinate (plus rotenone) and l-glutamate as respiratory substrates. When an uncoupler (2,4-dinitrophenol) was used instead of ADP, to stimulate respiration maximally, the various CoA esters showed differential effects on the oxidation of succinate and l-glutamate, respectively. With succinate as substrate, there was a strong inhibition of oxygen consumption by palmitoyl-CoA, 2,3-unsaturated, 3-hydroxy, and 3-keto-palmitoyl-CoA, in coupled as well as uncoupled mitochondria. On the other hand, with l-glutamate as substrate, inhibition was only observed under coupled conditions. The finding that acyl-CoA esters inhibit the uncoupler-induced respiration with succinate as substrate but not with glutamate, indicates that the observed inhibitory effect is most probably at the level of the transport of succinate across the mitochondrial membrane as mediated by the mitochondrial dicarboxylate carrier. This conclusion was substantiated by mitochondrial swelling studies, which showed inhibition of succinate transport by the different CoA esters whereas no effect was observed on the phosphate/hydroxyl and glutamate/hydroxyl carriers. Furthermore, long-chain acyl-CoA esters were found to potentiate the inhibitory effect of N-butylmalonate, a known inhibitor of the dicarboxylate carrier, upon oxygen consumption driven by succinate (plus rotenone). We conclude that the inhibitory effects of long-chain acyl-CoA esters on oxidative phosphorylation are dependent on the type of substrate used with the ATP/ADP carrier and the dicarboxylate carrier as targets for inhibition.

Screening of newborns and high-risk group of children for inborn metabolic disorders using tandem mass spectrometry in South Korea: a three-year report

BACKGROUND

Mass screening using tandem mass spectrometry(MS/MS) was initiated to determine if the incidence of metabolic disorder is sufficiently high to meet the criteria for newborn screening, and whether or not early medical intervention might be beneficial to the patients.

METHODS

Newborns and children in a high-risk group were screened using MS/MS from April 2001 to March 2004. Blood spots of newborns were collected between 48 and 72 h after birth. The dried blood spots was extracted with 150 microl of methanol, and analyzed by MS/MS.

RESULTS

From April 2001 to March 2004, 79,179 newborns were screened for organic, amino and fatty acid metabolism disorders, which account for approximately 5.4% of annual births in South Korea. Twenty-eight newborns were diagnosed with one of the metabolic disorders and the collective estimated prevalence amounted to 1 in 2800 with a sensitivity of 97.67%, a specificity of 99.28%, a recall rate of 0.05%, and a positive predictive value of 6.38%. 6795 infants/children at high risk were screened and 20 were confirmed to have metabolic disorders.

CONCLUSION

The collective total prevalence of 1:2800 in newborns indicates an underestimation of the incidence of metabolic disorders prior to implementing MS/MS screening in South Korea.