Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (72 page)

   There may be decrease of serum β-lipoprotein and cholesterol. Plasma lipids are normal in heterozygotes.

   Low serum fat-soluble vitamin (A, K, and E) levels.

   Histology: Biopsy of small intestine shows characteristic lipid vacuolization, but this is not pathognomonic (occasionally seen in celiac disease, tropical sprue, juvenile nutritional and megaloblastic anemia).

HYPOBETALIPOPROTEINEMIA

   Definition

   Hypobetalipoproteinemia is an autosomal dominant disorder with increased longevity and lower incidence of atherosclerosis.

   At least one parent will show decreased β-lipoprotein.

   Laboratory Findings

   There is a marked decrease in LDL-C and LDL-C-to-HDL-C ratio.

   Homozygous patients have decreased serum TC (<50 mg/dL) and TG and undetectable or trace amounts of chylomicrons, VLDL, and LDL.

   Heterozygotes are asymptomatic and have serum TC, LDL-C, and apo B values that are 50% of normal (consistent with codominant disorder); may also be caused by malabsorption of fats, infection, anemia, hepatic necrosis, hyperthyroidism, AMI, acute trauma.

TANGIER DISEASE

   Definition

   Tangier disease is a rare autosomal recessive disorder caused by mutations at chromosome 9q31 causing a defect in the metabolism of apo A, in which there is a marked decrease (heterozygous) or absence (homozygous) of HDL.

   Deposits of cholesterol esters in reticuloendothelial cells cause enlarged liver, spleen, and lymph nodes; enlarged orange tonsils; and small orange-brown spots in rectal mucosa. Patients may have premature CAD, mild corneal opacification, and neuropathy in homozygous type.