refers to unusually low levels of fats (lipids) in the blood. Low lipid levels may be caused by rare genetic conditions, or be a sign of another disorder such as overactive thyroid, anemia, undernutrition, cancer, chronic infection, or impaired absorption of foods from the digestive tract. Associated genetic disorders includes abetalipoproteinemia, hypobetalipoproteinemia, and chylomicron retention disease. Symptoms of the genetic or familial form of hypolipoproteinemia varies. In hypobetalipoproteinemia the low density lipoprotein (LDL) cholesterol levels are very low, yet people with this syndrome typically have no symptoms nor require treatment. Other forms result in absent or near absent LDL levels and can cause serious symptoms in infancy and early childhood. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.