Is genotyping useful for the screening of medium-chain acyl-CoA dehydrogenase deficiency in France?

Medium chain acyl-CoA dehydrogenase deficiency human genome epidemiology review

Medium chain acyl-CoA dehydrogenase (MCAD) is a tetrameric flavoprotein essential for the beta-oxidation of medium chain fatty acids. MCAD deficiency (MCADD) is an inherited error of fatty acid metabolism. The gene for MCAD is located on chromosome one (1p31). One variant of the MCAD gene, G985A, a point mutation causing a change from lysine to glutamate at position 304 (K304E) in the mature MCAD protein, has been found in 90% of the alleles in MCADD patients identified retrospectively. There is a high frequency of MCADD among people of Northern European descent, which is believed to be due to a founder effect. MCADD is inherited in an autosomal recessive manner. Of patients clinically diagnosed with MCADD, 81% who have been identified retrospectively are homozygous for K304E, and 18% are compound heterozygotes for K304E. Clinical data on the probability of clinical disease indicates that MCADD patients are at risk for the following outcomes: hypoglycemia, vomiting, lethargy, encephalopathy, respiratory arrest, hepatomegaly, seizures, apnea, cardiac arrest, coma, and sudden and unexpected death. Long-term outcomes include developmental and behavioral disability, chronic muscle weakness, failure to thrive, cerebral palsy, and attention deficit disorder (ADD). Differences in clinical disease specific to allelic variants have not been documented. Factors that may increase risk for disease onset or modify disease severity are age when the first episode occurred, fasting, and presence of infection. Acute attacks must be treated immediately with appropriate intravenous doses of glucose. For those diagnosed, long-term management of the disease includes preventing stress caused by fasting and maintaining a high-carbohydrate, reduced-fat diet, and carnitine supplementation. Hospitalization costs attributable to morbidity and mortality from MCADD are unknown; MCADD is not a diagnosis in the International Classification of Disease, 10th Revision (ICD-10) codebook. Furthermore, the penetrance of the MCAD genotypes is unknown; there appears to be a substantial number of asymptomatic MCADD individuals and some uncertainty regarding which individuals will manifest symptoms and which individuals will remain asymptomatic. Several technologies are available to detect MCADD. Diagnostic technologies include DNA-based tests for K304E mutations using the polymerase chain reaction (PCR), and the detection of abnormal metabolites in urine. Screening technologies include tandem mass spectrometry (MS/MS), which detects abnormal metabolites mostly in blood. State programs are beginning to offer screening in newborns for MCADD using MS/MS. In addition, a private company currently offers voluntary supplemental newborn screening for MCADD to birthing centers.

Population screening for the common G985 mutation causing medium-chain acyl-CoA dehydrogenase deficiency with Eu-labeled oligonucleotides and the DELFIA system

We have screened 10 171 neonatal blood spots from the Trent and West Midlands regions of the UK for the common G985 mutation to more accurately establish the incidence of medium-chain acyl coenzyme (Co)A dehydrogenase (MCAD) deficiency. We have used a technique involving PCR and Eu-labeled allele-specific oligonucleotides detected by using time-resolved fluorometry on the dissociation-enhanced fluorescence immunoassay (DELFIA) system for the detection of the G985 mutation. We have also evaluated the feasibility of neonatal screening with this technique. We identified 158 G985 heterozygotes and no G985 homozygotes. The calculated incidence of MCAD deficiency in the population studied (all mutations, assuming 90% of MCAD mutations are G985) is 1 in 13 426 (95% confidence limits 1 in 10 070–1 in 18 791). At the optimum cutoff criteria, the technique has a sensitivity of 97.5%, specificity of 99.6%, and positive predictive value of 80.2%. We conclude that this study confirms that MCAD deficiency is a common inherited metabolic disease and is a candidate for neonatal screening. The methodology used is robust and suitable for large-scale population studies such as this. The technique is also potentially suitable for screening.

A survey of the newborn populations in Belgium, Germany, Poland, Czech Republic, Hungary, Bulgaria, Spain, Turkey, and Japan for the G985 variant allele with haplotype analysis at the medium chain Acyl-CoA dehydrogenase gene locus: clinical and evolutionary consideration

Medium chain acyl-CoA dehydrogenase (MCAD) deficiency is an inborn error of fatty acid metabolism. It is one of the most frequent genetic metabolic disorders among Caucasian children. The G985 allele represented 90% of all the variant alleles of the MCAD gene in an extensive series of retrospective studies. To study the distribution of the G985 allele, newborn blood samples from the following countries were tested; 3000 from Germany (1/116). 1000 each from Belgium (1/77). Poland (1/98), Czech Republic (1/240). Hungary (1/168), Bulgaria (1/91), Spain (1/141). Turkey (1/216), and 500 from Japan (none). The frequency is shown in parentheses. The haplotype of G985 alleles in 1 homozygote and 57 heterozygote samples were then analyzed using two intragenic MCAD gene polymorphisms (Iaq1 and GT-repeat). The result indicated that only 1 of the 10 known haplotypes was associated with the G985 mutation, suggesting that G985 was derived originally from a single ancestral source. We made a compilation of the G985 frequencies in these countries and those in nine other European countries studied previously. The G985 distribution was high in the area stretching from Russia to Bulgaria in the east and in all northern countries in western and middle Europe, but low in the southern part of western and middle Europe. The incidence among ethnic Basques appeared to be low. This distribution pattern and the fact that all G985 alleles belong to a single haplotype suggest that G985 mutation occurred later than the delta F508 mutation of the CFTR, possibly in the neolithic or in a later period, and was brought into Europe by IndoEuropean-speaking people. The panEuropean distribution of the G985 allele, including Slavic countries from which patients with MCAD deficiency have rarely been detected, indicates the importance of raising the level of awareness of this disease.

Most cases of medium-chain acyl-CoA dehydrogenase deficiency escape detection in France

DNA from 414 French blood donors from the Paris area was assessed for the A985G mutation responsible for most cases of autosomal recessive medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. The mutant gene frequency averaged 1/140, predicting a frequency of mutant homozygotes of 1/19 000. Discrepancy between the numbers of expected (42 per year) and recorded cases of MCAD (6 per year) suggests that most MCAD-deficient patients escape detection in France.

The A985G mutation in the medium-chain acyl-CoA dehydrogenase gene: high prevalence in the Swiss population resident in Geneva

We have determined the frequency of the A985G mutation in the medium-chain acyl-CoA dehydrogenase (MCAD) gene in a cohort of 1142 healthy babies born in two Geneva hospitals. Among babies with at least one Swiss parent, heterozygotes were detected at a frequency of 1/52, with a 95% confidence range from 1/82 to 1/38. The high frequency of the carrier state for this mutation suggests that MCAD-deficient babies are born with a frequency of 1/10,000 in the Swiss population. This number is in sharp contrast with the low number of symptomatic MCAD-deficient patients diagnosed in this country. Thus, the fraction of homozygotes who remain asymptomatic is likely to be very high in the Swiss population, and possibly higher than in other countries of northern Europe.