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Overview of Fatty Acid and Glycerol Metabolism Disorders

By Lee M. Sanders, MD, MPH

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Fatty acids are the preferred energy source for the heart and an important energy source for skeletal muscle during prolonged exertion. Also, during fasting, the bulk of the body’s energy needs must be supplied by fat metabolism. Using fat as an energy source requires catabolizing adipose tissue into free fatty acid and glycerol. The free fatty acid is metabolized in the liver and peripheral tissue via β-oxidation into acetyl CoA; the glycerol is used by the liver for triglyceride synthesis or for gluconeogenesis. Carnitine is required for long-chain fatty acid oxidation. Carnitine deficiencies can be primary or secondary. Secondary carnitine deficiency is a secondary biochemical feature of many organic acidemias and fatty acid oxidation defects.

There are a number of other disorders of fatty acid and glycerol metabolism, including those involving

Ketone Metabolism Disorders

Disease (OMIM Number)

Defective Proteins or Enzymes

Defective Gene or Genes (Chromosomal Location)

Comments

3-Hydroxy-3-methylglutaryl-CoA synthase deficiency (605911)

3-Hydroxy-3-methylglutaryl-CoA synthase

HMGCS2 (600234)

Biochemical profile: See below

Clinical features: Episodic nonketotic hypoglycemia

Treatment: Avoidance of fasting

3-Hydroxy-3-methylglutaryl-CoA lyase deficiency

Succinyl-CoA 3-oxoacid-CoA transferase deficiency (245050)

Succinyl-CoA 3-oxoacid-CoA transferase

OXCT (5p13)*

Biochemical profile: Ketonuria

Clinical features: Severe episodic ketoacidosis, vomiting, hyperventilation

Treatment: Glucose during acute episode plus judicious use of bicarbonate, high-carbohydrate diet with some restriction of protein and fat

Mitochondrial acetoacetyl-CoA thiolase deficiency (607809)

Cytoplasmic acetoacetyl-CoA thiolase deficiency (100678)

Cytoplasmic acetoacetyl-CoA thiolase

ACAT2 (6q25.3-q26)

Biochemical profile: Nonspecific

Clinical features: Intellectual disability, hypotonia

Treatment: Not established

*Gene has been identified, and molecular basis has been elucidated.

OMIM = online mendelian inheritance in man (see the OMIM database ).

Other Fat Metabolism Disorders

Disease (OMIM Number)

Defective Proteins or Enzymes

Defective Gene or Genes (Chromosomal Location)

Comments

Sjögren-Larsson syndrome (270200)

Fatty aldehyde dehydrogenase

ALDH3A2 (17p11.2)*

Biochemical profile: No readily detectable plasma or urinary abnormality

Clinical features: Ichthyosis, intellectual disability, spastic diplegia or tetraplegia, retinopathy, seizures

Treatment: Symptomatic; topical keratolytics or systemic retinoids, reduced long-chain fat and increased medium-chain triglycerides in diet

*Gene has been identified, and molecular basis has been elucidated.

OMIM = online mendelian inheritance in man (see the OMIM database ).

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