[Higher prevalence of familial hypercholesterolemia than expected in adult patients of four family practices in Netherlands]. / Prevalentie van familiaire hypercholesterolemie onder volwassenen in vier huisartsenpraktijken hoger dan werd aangenomen.

OBJECTIVE: To determine the prevalence of familial hypercholesterolaemia (FH). DESIGN: Patient record screening, questionnaire and if necessary, case finding. METHODS: Over the period mid-1990-mid-1992 (approximately 2.5 years) 8,800 adult individuals (age 18 years and over) in 4 general practices in Hoofddorp, the Netherlands, were screened for risk factors for coronary artery disease and invited for further analysis. Of the 3,289 selected and invited individuals 2,719 (83%) were investigated. Total cholesterol concentrations were investigated 3 times and if the mean value was above 8.0 mmol/l patients were referred to a lipid clinic to investigate the possible existence of FH. RESULTS: 114 patients were eligible for referral to a lipid clinic of whom 92 (81%) were indeed referred. Of these, 38 patients were diagnosed with FH: 23 men and 15 women, with a mean age of 47.7 years (range: 21-74). CONCLUSION: The prevalence of FH in this investigated population was at least 1:232. This is more than 1:500, the estimated number of FH patients in the Dutch population.

Apolipoprotein CII-Padova (Tyr37-->stop) as a cause of chylomicronaemia in an Italian kindred from Siculiana.

In this paper we report on the molecular defect underlying apolipoprotein CII (apoCII) deficiency in an Italian kindred. ApoCII serves as cofactor for lipoprotein lipase (LPL) in triglyceride hydrolysis of chylomicrons and very low density lipoproteins. Homozygous apoCII deficiency manifests with type I hyperlipoproteinaemia and is a rare disorder of lipoprotein metabolism. Until now, only 10 kindreds with apoCII deficiency have been published and all underlying mutations were unique. The proband was the offspring of a consanguineous mating. Sequencing of cloned DNA from the proband presented in this report showed homozygosity for a C-->A substitution at position 3002 in the apoCII gene, resulting in the introduction of a premature stop codon at residue 37 of the mature apoCII protein. Therefore, a truncated apoCII is synthesised, lacking the part of the apolipoprotein that activates LPL. This mutation has previously been described in another Italian family and is known as apoCIIPadova. We propose that apoCIIPadova is a frequent cause of apoCII deficiency in persons of Italian descent.

A compound heterozygote for lipoprotein lipase deficiency, Val69-->Leu and Gly188-->Glu: correlation between in vitro LPL activity and clinical expression.

We analyzed the molecular defects in the lipoprotein lipase gene of a patient with type I hyperlipidemia suffering from recurrent pancreatitis, indicative for lipoprotein lipase deficiency. Postheparin lipoprotein lipase activity in the patient was decreased by 70%. Direct genomic sequencing revealed compound heterozygosity for two mutation: the well-known Gly188-->Glu and a new Val69-->Leu substitution. Val69 is situated in a conserved hydrophobic region of the lipoprotein lipase protein, and the substitution with leucine gives rise to a 80% decrease in specific catalytic activity, as supported by site-directed mutagenesis experiments, followed by expression in COS-cells. The combination of both defects in the lipoprotein lipase gene was incidentally associated with severe clinical expression of disease, and triglyceride levels of more than 30 mmol/l were measured. In our patient, triglyceride levels wer usually below 10 mmol/l. We, therefore, postulate that the residual LPL activity in our patient is usually sufficient to keep the triglyceride level within bounds and expression of disease occurred only when conditions such as alcohol abuse or poor compliance to diet were present.

Homozygosity for a mutation in the lipoprotein lipase gene (Gly139-->Ser) causes chylomicronaemia in a boy of Spanish descent.

The enzyme lipoprotein lipase (LPL) plays a crucial role in triglyceride metabolism through catalysis of triglyceride-rich chylomicrons and very low density lipoproteins. Primary LPL deficiency manifests with chylomicronaemia and is caused by mutations in the LPL gene. In this paper we report a novel molecular defect (G670-->A) in exon 4 of the LPL gene, resulting in a substitution of serine for glycine at position 139 in the mature protein. We identified homozygosity for this mutation in a boy of Spanish descent. In vitro mutagenesis provided formal proof that this missense mutation completely abolishes LPL function and therefore is the cause of LPL deficiency.

Recurrent pancreatitis and chylomicronemia in an extended Dutch kindred is caused by a Gly154-->Ser substitution in lipoprotein lipase.

We report the molecular basis of familial chylomicronemia and recurrent pancreatitis in five members of a large Dutch family. All patients had normal plasma hepatic lipase and apoC-II levels, but absent lipoprotein lipase (LPL) catalytic activity and low LPL mass in postheparin plasma. The mutation in the LPL gene was characterized as a G715-->A substitution in the last nucleotide of exon 4, resulting in a substitution of Ser for Gly154. PCR amplification of exons 4 + 5 from the patients' mRNA, followed by direct sequencing, revealed normal splicing of intron 4. The mutation creates a BfaI restriction site that allows rapid screening of family members for the mutation. Reproduction of this mutation in LPL-cDNA by site-directed mutagenesis, followed by transient expression in COS-B cells, revealed production of a catalytically inactive enzyme. The Gly154-->Ser substitution appears in a conserved beta-sheet region, in close proximity to Asp156, which is part of the catalytic triad. These studies show that changes to residues close to Asp156 can have profound effects on catalytic activity of LPL.

Two naturally occurring mutations at the first and second bases of codon aspartic acid 156 in the proposed catalytic triad of human lipoprotein lipase. In vivo evidence that aspartic acid 156 is essential for catalysis.

We are studying naturally occurring mutations in the gene for lipoprotein lipase (LPL) to advance our knowledge about the structure/function relationships for this enzyme. We and others have previously described 11 mutations in human LPL gene and until now none of these directly involves any of the residues in the proposed Asp156-His241-Ser132 catalytic triad. Here we report two separate probands who are deficient in LPL activity and have three different LPL gene haplotypes, suggesting three distinct mutations. Using polymerase chain reaction cloning and DNA sequencing we have identified that proband 1 is a compound heterozygote for a G----A transition at nucleotide 721, resulting in a substitution of asparagine for aspartic acid at residue 156, and a T----A transversion, resulting in a substitution of serine for cysteine at residues 216. Proband 2 is homozygous for an A----G base change at nucleotide 722, leading to a substitution of glycine for aspartic acid at residue 156. The presence of these mutations in the patients and available family members was confirmed by restriction analysis of polymerase chain reaction-amplified DNA. In vitro site-directed mutagenesis and subsequent expression in COS cells have confirmed that all three mutations result in catalytically defective LPL. The two naturally occurring mutations, which both alter the same aspartic acid residue in the proposed Asp156-His241-Ser132 catalytic triad of human LPL, indicate that Asp156 plays a significant role in LPL catalysis. The Cys216----Ser mutation destroys a conserved disulfide bridge that is apparently critical for maintaining LPL structure and function.