Rapid, comprehensive screening of the human medium chain acyl-CoA dehydrogenase gene

Abstract

Newborn screening by tandem mass spectrometry (MS/MS) identifies patients with medium chain acyl-CoA dehydrogenase (MCAD) deficiency the most frequently observed disorder of fatty acid oxidation. Molecular genetic analysis is becoming a common tool to confirm those identified as affected by prospective screening and for carrier detection in family studies. The A985G (K304E) mutation accounts for approximately 80% of mutant alleles in MCAD deficient patients, presenting symptomatically, while greater variability of mutant alleles is observed among cases identified through prospective screening. Aside from A985G, the mutation spectrum in MCAD deficient patients is heterogeneous such that comprehensive gene analysis is required. Traditionally the MCAD gene is assayed by sequencing the entire coding region. Although effective and definitive, this approach is expensive, turn around time is slow, and is poorly amenable to a clinical service molecular genetics laboratory. Dye-binding/high-resolution thermal denaturation is a rapid and homogeneous method by which to scan a PCR product for evidence of sequence aberration. PCR is performed in capillaries in the presence of the dsDNA-binding dye LCGreen I and subsequently the DNA/dye complexes are analyzed by high-resolution thermal denaturation. DNA sequencing was limited to fragments displaying abnormal melting profiles. Of 18 specimens analyzed, 11 have a genotype consistent with MCAD deficiency and seven have a genotype consistent with carrier status. Clinical and biochemical data corroborate that the genotype results identified the affected patients and differentiates them from carriers. The entire process is homogeneous requiring no post-PCR manipulation and is completed in under 3 h.