Molecular confirmation of VLCAD deficiencies in newborns

Abstract

MOLECULAR CONFIRMATION OF VLCAD DEFICIENCIES IN NEWBORNS Megan L Landsverk, Fernando Scaglia, Lee-Jun Wong Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States Oxidation of fatty acids in the mitochondria provides the main source of energy in the brain, as well as skeletal and cardiac muscle. Acyl-CoA dehydrogenases are a group of enzymes that catalyze the initial step in the β-oxidation of fatty acids in the mitochondrial matrix. Deficiencies in acyl-CoA dehydrogenases are autosomal recessive disorders that result in a decreased ability to oxidize fatty acids, thereby leading to metabolic dysfunction. Very-long chain acyl-CoA dehydrogenase (VLCAD) targets long-chain fatty acids with a chain length of 14 to 20 carbons. VLCAD deficiency (VLCADD) can generally be group into three phenotypes: a severe, early-onset, form with a high incidence of cardiac and multiorgan failure, intermittent hypoglycemia, hepatomegaly and hypotonia; a milder childhood form usually presenting with hypoketotic hypoglycemia; and an adult myopathic form with intermittent rhabdomyolysis, muscle cramps and exercise intolerance. Early detection through newborn screening (NBS) by measuring acylcarnitines using tandem mass spectrometry has increased the number of patients identified with VLCADD, and has allowed for the identification of milder clinical phenotypes. Although, acylcarnitine profiles alone cannot confirm a diagnosis. An increase in acylcarnitine C14:1 is suggestive for VLCADD. However, normal biochemical testing on follow-up of abnormal NBS for VLCADD does not rule out the disorder since C14:1 levels tend to normalize over time. Conversely, initial elevations of C14:1 on NBS may reflect neonatal stress. Molecular identification of deleterious mutations in the ACADVL gene is necessary to confirm the diagnosis. From January 2007 to October 2009 we analyzed 175 individuals, ages 6 months and younger, presenting with abnormal NBS or clinical indications suggestive of VLCADD for mutations in ACADVL. We identified previously reported mutations as single heterozygotes in 36 (21%) individuals, double heterozygotes in nine (5%), and homozygotes in five (3%). An additional 13 (6%) individuals harbored known mutations as double heterozygotes with unclassified variants. We also identified 6 novel frameshift mutations leading to premature stop codons, 1 novel indel, 1 novel in-frame deletion, and 4 novel splice-site mutations, all heterozygous. Unclassified variants were found as single and double heterozygous in 21 (12%) and 8 (5%) individuals respectively. However, we found no known mutations or unclassified variants in the coding exons of ACADVL in 66 (38%) individuals tested for VLCADD. These results underscore the necessity of mutation analysis of the ACADVL gene when VLCADD is suspected in children under the age of 6 months based on suggestive clinical indication or positive NBS results. Poster Presentations