Test Code: 2380

Isobutyryl Co-A Dehydrogenase Deficiency: ACAD8 Gene Sequencing
Test Code: 2380
Turnaround time: 7 weeks

CONDITION DESCRIPTION

The first patient with isobutyryl Co-A dehydrogenous deficiency (IBD deficiency) was a 12-month old infant whose clinical symptoms were described in a 1998 publication [1]. This patient presented with dilated cardiomyopathy, anemia, and carnitine deficiency. An elevated C4-acylcarnitine was noted in a plasma acylcarnitine profile, but a subsequent urine organic acid analysis was normal. Treatment with oral L-carnitine supplementation led to catch- up growth and normalization of the cardiac status. It was reported that the patient remained carnitine-dependent at almost 11 years of age [2]. Twenty- one subsequent patients were all identified through newborn screening because of an isolated elevation of C4-acylcarnitine [2-5]. Twelve patients were asymptomatic at the time of reporting. One patient was noted to have muscle hypotonia and mild developmental delay at 8 months of age. Two patients were treated for speech delay at 5 years and 2 years of age, respectively, but had normal growth and development. One patient was incidentally noted at 1 year of age to have mild branch peripheral pulmonary stenosis. One patient required frequent hospitalizations due to emesis and dehydration during the first 2 years of life but was developing normally at 5 years of age. Others were lost to follow up.

The ACAD8 gene (11q25) encodes isobutyryl Co-A dehydrogenase, which catalyzes the third step of the degradation of the branched chain amino acid valine [6,7]. ACAD8 is a member of the Acyl-coenzyme A (CoA) dehydrogenases (ACADs) family of mitochondrial enzymes that catalyze the first dehydrogenation step in the beta-oxidation of fatty acyl-CoA derivatives [7]. Fatty acids provide important respiratory fuel for many tissues, including heart, skeletal muscle, brown adipose tissue, kidney, and liver, as is evident in individuals with defects in any of the ACAD family members. The mitochondrial beta-oxidation pathway is a cycle of 4 sequential reactions in which the fatty acid substrate is shortened by 2 carbon atoms with each cycle, releasing an acetyl-CoA molecule that can then be used in the tricarboxylic acid cycle or for ketogenesis.

References:
1. Roe et al. Isolated isobutyryl-CoA dehydrogenase deficiency: an unrecognized defect in human valine metabolism. Molec. Genet. Metab. 1998, 65:264-271.
2. Oglesbee et al. Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency. Genet. Med. 2007, 9: 108-116.
3. Koeberl et al. Rare disorders of metabolism with elevated butyryl- and isobutyryl-carnitine detected by tandem mass spectrometry newborn screening. Pediat. Res. 2003, 54: 219-223.
4. Sass et al. Isobutyryl-CoA dehydrogenase deficiency: isobutyrylglycinuria and ACAD8 gene mutations in two infants. J. Inherit. Metab. Dis. 2004, 27: 741-745.
5. Pedersen et al. Variations in IBD (ACAD8) in children with elevated C4-carnitine detected by tandem mass spectrometry newborn screening. Pediat. Res. 2006, 60: 315-320.
6. Nguyen et al. Identification of isobutyryl-CoA dehydrogenase and its deficiency in humans. Molec. Genet. Metab. 2002, 77: 68-79.
7. Telford et al. Isolation and characterisation of a cDNA encoding the precursor for a novel member of the acyl-CoA dehydrogenase gene family. Biochim. Biophys. Acta 1999, 1446: 371-376.

GENES
ACAD8

INDICATIONS
This test is indicated for:

  • Confirmation of a clinical/biochemical diagnosis of isobutyryl co-A dehydrogenase deficiency
  • Carrier testing in females/adults with a family history of isobutyryl co-A dehydrogenase deficiency

METHODOLOGY

PCR amplification of 11 protein-encoding exons contained in the ACAD8 gene is performed on patient genomic DNA. Direct sequencing of amplification products is performed in both the forward and reverse directions using automated fluorescence dideoxy sequencing methods. Patient gene sequences are compared to a normal reference sequence. Sequence variations are then classified as mutations, benign variants unrelated to disease, or variations of unknown clinical significance. Variants of unknown clinical significance may require further studies of the patient and/or family members. This assay does not interrogate the promoter region, deep intronic regions, or other regulatory elements. Large deletions are not detected by this analysis.

DETECTION
Clinical Sensitivity: 17/18 alleles were identified in 9 patients with IBD deficiency [2].

Analytical Sensitivity: ~99%

SPECIMEN REQUIREMENTS

Submit only 1 of the following specimen types
* Preferred specimen type: Whole Blood

Type: Whole Blood
Specimen Requirements:
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

Type: Saliva
Specimen Requirements:
OrageneTM Saliva Collection kit (available through CEN4GEN) used according to manufacturer instructions.

Specimen Collection and Shipping: Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.

SPECIAL INSTRUCTIONS
Submit copies of diagnostic biochemical test results with the sample.

RELATED TESTS
• Custom Diagnostic Mutation Analysis (test code: 6875) is available to family members if mutations are identified by sequencing.