FCS, also known as lipoprotein lipase deficiency (LPLD or type 1 hyperlipoproteinemia), results from homozygosity or compound heterozygosity for null mutations in one or more genes that compromise chylomicron-lipolysis and clearance, most commonly the lipoprotein lipase (LPL) gene or, less frequently, other genes directly affecting LPL activity, namely APOC2, APOA5, LMF1 and GPIHBP12. The gene discussed is LPL; the disease is familial lipoprotein lipase deficiency.