Handbook of Genetic Counseling/Short Chain Acyl-CoA Dehydrogenase (SCAD)

Short Chain Acyl-CoA Dehydrogenase (SCAD)

General Information

 * a disorder of lipid metabolism characterized by a defect in the oxidation of short-chain fatty acids resulting in neurologic and gastrointestinal manifestations
 * SCAD is one of four enzymes in the mitochondria responsible for the breakdown of short-chain (C4-C6) fatty acids to 2-carbon fragments (acetyl-CoA) in the beta oxidation pathway
 * homozygous patients are unable to mobilize large fat stores and are thus at risk for becoming hypoglycemic when stressed (i.e., during infection or fasting) during which time the long and medium acyl-CoA dehydrogenases are unable to compensate for the lack of SCAD
 * gene map locus: 12q22-qter
 * autosomal recessive inheritance

Diagnosis

 * diagnosis is difficult because patients do not consistently excrete characteristic metabolites
 * it is necessary to collect and analyze several urine and plasma specimens in patients with neurologic abnormalities that suggest this disorder
 * deficiency of SCAD activity in leukocytes and cultured skin fibroblasts
 * prenatally, a deficiency of SCAD activity in cultured chorionic villi or amniocytes can be detected

Clinical Evaluation

 * two distinct clinical phenotypes have been identified :
 * one type observed in infants with acute acidosis and muscle weakness (generalized)
 * one type observed in middle-aged patients with chronic myopathy (localized to skeletal muscles)
 * cases with neonatal onset have a variable phenotype
 * includes metabolic acidosis, failure to thrive, developmental delay, seizures and myopathy
 * no episodes of nonketotic hypoglycemia (characteristic of medium-chain and long-chain acyl dehydrogenase deficiencies)

Infantile type

 * metabolic: neonatal acidosis, low-normal plasma total carnitine, highly esterified
 * GI: poor feeding, vomiting, failure to thrive
 * muscle: progressive skeletal muscle weakness, hypotonia
 * neurological: developmental delay
 * laboratory results: generalized SCAD deficiency, ethylmalonate urinary excretion, low normal highly esterified muscle carnitine

Adult type

 * muscle: lipid-storage myopathy
 * lab results: skeletal muscle carnitine low, deficiency of skeletal muscle mitochondrial short-chain acyl-CoA (butyryl-CoA)

Support Groups

 * James William Lazzaro Foundation
 * 4493 Liberty Road
 * South Euclid, OH 44121
 * Contact Person: Jamie Lazzaro
 * Phone: (502) 254-2209
 * Email: info@jwlsite.com
 * Website: www.jwlsite.com


 * FOD(Fatty Oxidation Disorders)Family Support Group
 * 2041 Tomahawk
 * Okemos, MI 48864
 * Contact Person: Deb Lee Gould, MEd
 * Phone: (517) 381-1940
 * Email: deb@fodsupport.org
 * Website: www.fodsupport.org