Handbook of Genetic Counseling/Medium-chain acyl-coenzyme A dehydrogenase Deficiency

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Medium-chain acyl-coenzyme A dehydrogenase Deficiency

Overview[edit]

  • Medium-chain acyl-coenzyme A dehydrogenase (MCAD) is an enzyme involved in mitochondrial fatty acid b-oxidation (FAO). Fatty acid oxidation provides energy for peripheral tissues when glycogen is depleted through hepatic ketogenesis. A defect in the MCAD enzyme causes accumulation of medium-chain fatty acids, metabolized to glycine- and carnitine-esters and dicarboxylic acids, and hypoketonia.

Genetics[edit]

  • MCAD deficiency is caused by a mutation in the ACADM gene
  • Chromosomal locus 1p31
  • 31 known disease causing mutations
  • 1 common mutation, K304E, accounts for 76% of alleles

Incidence[edit]

  • Common in Caucasians, especially with Northern European ancestry
  • Disease incidence 1:4,900 to 1:17,000
  • Carrier frequency 1:40 to 1:100
  • Less common among Hispanics
  • Rare in African-American, and Native-American populations

Diagnosis[edit]

  • Metabolic testing
  • Symptomatic individuals should have plasma acylcarnitines, plasma fatty acids, urine organic acids, and urine acylclycines analyzed and interpreted.
  • Enzymatic testing
  • MCAD enzyme activity should be measured in fibroblasts or other tissues to confirm diagnosis
  • Molecular testing
  • Molecular genetic testing by mutation analysis (for K204E) or sequence analysis of the ACADM gene can confirm diagnosis
  • Newborn screening
  • MCAD is part of the newborn screening panel in 9 states (IA, ME, MA, NC, OH, SC, SD, WI, WY).
  • Prenatal testing
  • Enzymatic or molecular testing can be performed prenatally; however, there is limited benefit to prenatal vs. newborn testing.
  • Carrier testing
  • Only molecular testing can determine carrier status.

Clinical Features[edit]

  • Typical presentation includes hypoketotic hypoglycemia, vomiting, lethargy,

seizures, and coma precipitated by prolonged fasting or common illness.

  • Hepatomegaly and acute liver disease may also be present.
  • Sudden, unexplained death may be first symptom (18%).

Natural History[edit]

  • Typically normal at birth following uneventful pregnancy
  • Most present with symptoms between 3 and 24 months in response to prolonged fasting or infection
  • Initial presentation in adulthood also possible
  • Affected individuals may lose developmental milestones or acquire aphasia or ADD as a result of acute metabolic event
  • Individuals identified as newborns typically develop normally under treatment

Inheritance[edit]

  • MCAD deficiency is an autosomal recessive disorder.

Testing[edit]

  • Enzymatic and Molecular testing can confirm diagnosis.
  • Both mutation and sequence analysis are available on a clinical basis.

Management & Treatment[edit]

  • MCAD is a highly treatable condition- good prognosis when managed
  • Avoidance of fasting is key-
  • Infants should be fed frequently
  • Toddlers should be given 2 g/kg uncooked cornstarch before bed
  • Low-fat diet and carnitine supplementation may be beneficial

Differential Diagnosis[edit]

  • Other disorders of acyl-CoA dehydrogenase (ACAD) gene family
  • Other disorders of fatty acid b-oxidation

Psychosocial Issues[edit]

  • Parental guilt over allowing too long of time between feedings which triggered onset of symptoms
  • Parental guilt over passing gene to child
  • When presenting symptom is sudden death, loss of seemingly healthy child can be devastating
  • Parent or sibling may be identified as a homozygote during carrier testing
  • Family planning- risk for future offspring/siblings of affected individual

Patient Resources[edit]

  • FOD (Fatty Oxidation Disorder) Family Support Group
805 Montrose Drive
Greensboro, NC 27410
Phone: (336) 547-8682
Email: deb@fodsupport.org
Web: www.fodsupport.org
  • Organic Acidemia Association
13210 35th Avenue North
Plymouth, MN 55441
Phone; (763) 556-1797
Email: OAANews@aol.com
Web: www.oaanews.org
  • United Mitochondrial Disease Foundation
8085 Saltsburg Road, Suite 201
Pittsburgh, PA 15239
Phone: (412) 793-8077
Email: info@umdf.org
Web: www.umdf.org

Notes[edit]

The informaiton in this outline was last updated in Feb 2003.