APOLIPOPROTEIN-C-II DEFICIENCY SYNDROME DUE TO APO-C-IIHAMBURG - CLINICAL AND BIOCHEMICAL FEATURES AND HPHL RESTRICTION ENZYME POLYMORPHISM

We have characterized the clinical and biochemical features of three siblings of a kindred with severe hypertriglyceridaemia due to apolipoprotein C-II (apo C-II) deficiency caused by the mutation described as apo C-II(Hamburg). The clinical syndrome is characterized by recurrent pancreatitis in two of three affected individuals, with discrete hepatosplenomegaly in all three patients and cholelithiasis in one. Eruptive xanthomas and lipemia retinalis were absent. Plasma lipoproteins were characterized by fasting chylomicronaemia, reduced low density lipoproteins (LDL) and low high density lipoproteins (HDL). The marked hypertriglyceridaemia could be corrected promptly by infusion of normal plasma. Apolipoprotein C-II (apo C-II) levels in homozygotes were very low (0.01 mg dl-1), and mean apo C-II levels in heterozygotes were lower (2.08 +/- 0.11 mg dl-1) than in normal family members (3.38 +/- 0.75 mg dl-1). Lipoprotein lipase and hepatic triglyceride lipase activities in post-heparin plasma were normal. Zonal ultracentrifugation revealed a marked increase in triglyceride-rich lipoproteins and reduced LDL and HDL. LDL consisted of two fractions with higher hydrated density of the main fraction compared with normals with a trend to normalization on a fat-free diet. The molecular defect in the apo C-II Hamburg gene has been previously identified as a donor splice site mutation in the second intron. This leads to abnormal splicing of the apo C-II Hamburg mRNA and apo C-II deficiency in plasma. The mutation causes the loss of an HphI restriction enzyme site present in the normal apo C-II gene. Digestion of polymerase chain reaction (PCR)-amplified DNA of members of the Hamburg kindred with HphI permitted the identification of non-obligate heterozygote individuals which could not be recognized by either fasting triglyceride or apo C-II plasma levels.