Heterozygosity for lysosomal acid lipase E8SJM mutation and serum lipid concentrations.

BACKGROUND AND AIM: The complete absence of the lysosomal acid lipase (LAL) enzyme function causes Wolman's Disease that is fatal within the first six months of life. Subtotal defects cause Cholesteryl ester storage disease (CESD), an autosomal recessive disorder leading to hepatic steatosis, fibrosis, micronodular cirrhosis, combined hyperlipidemia with low HDL-cholesterol, increased risk for atherosclerosis, premature death. Since the frequency of the Exon 8 splice junction mutation (c.894 G > A, E8SJM), the CESD leading mutation, is not rare in the general population (allele frequency 0.0025), we investigated the impact of this mutation on serum lipid profile in E8SJM carriers. METHODS AND RESULTS: We collected E8SJM carriers both form genetic study-population analysis and from Outpatient Lipid Clinics and then we assessed their serum lipid profile. We found thirteen individuals heterozygote for E8SJM. Most of them were Germans, three Spanish and two Italian. We found a significant increase in total cholesterol levels in both sexes with E8SJM mutation, leading to a significant increase in LDL cholesterol in males. CONCLUSIONS: Our results show that LAL E8SJM carriers have an alteration in lipid profile with a Polygenic Hypercholesterolemia phenotype, leading to an increase in cardiovascular risk profile.

Genetic and phenotypic heterogeneity in familial lecithin: cholesterol acyltransferase (LCAT) deficiency. Six newly identified defective alleles further contribute to the structural heterogeneity in this disease.

The presence of lecithin:cholesterol acyltransferase (LCAT) deficiency in six probands from five families originating from four different countries was confirmed by the absence or near absence of LCAT activity. Also, other invariate symptoms of LCAT deficiency, a significant increase of unesterified cholesterol in plasma lipoproteins and the reduction of plasma HDL-cholesterol to levels below one-tenth of normal, were present in all probands. In the probands from two families, no mass was detectable, while in others reduced amounts of LCAT mass indicated the presence of a functionally inactive protein. Sequence analysis identified homozygous missense or nonsense mutations in four probands. Two probands from one family both were found to be compound heterozygotes for a missense mutation and for a single base insertion causing a reading frame-shift. Subsequent family analyses were carried out using mutagenic primers for carrier identification. LCAT activity and LCAT mass in 23 genotypic heterozygotes were approximately half normal and clearly distinct from those of 20 unaffected family members. In the homozygous patients no obvious relationship between residual LCAT activity and the clinical phenotype was seen. The observation that the molecular defects in LCAT deficiency are dispersed in different regions of the enzyme suggests the existence of several functionally important structural domains in this enzyme.

A unique genetic and biochemical presentation of fish-eye disease.

This paper describes a novel genetic defect which causes fish-eye disease in four homozygous probands and its biochemical presentation in 34 heterozygous siblings. The male index patient presented with premature coronary artery disease, corneal opacification, HDL deficiency, and a near total loss of plasma lecithin:cholesterol acyltransferase (LCAT) activity. Sequencing of the LCAT gene revealed homozygosity for a novel missense mutation resulting in an Asp131 - Asn (N131D) substitution. Heterozygotes showed a highly significant reduction of HDL-cholesterol and apolipoprotein A-I levels as compared with controls which was associated with a specific decrease of LpA-I:A-II particles. Functional assessment of this mutation revealed loss of specific activity of recombinant LCAT(N131D) against proteoliposomes. Unlike other mutations causing fish-eye disease, recombinant LCAT(N131D) also showed a 75% reduction in specific activity against LDL. These unique biochemical characteristics reveal the heterogeneity of phenotypic expression of LCAT gene defects within a range specified by complete loss of LCAT activity and the specific loss of activity against HDL. The impact of this mutation on HDL levels and HDL subclass distribution may be related to the premature coronary artery disease observed in the male probands.

Electrophoretic screening for human apolipoprotein C-II variants: repeated identification of apolipoprotein C-II(K19T).

Screening for apolipoprotein (apo) C-II variants in the plasma of 400 students, 600 patients of a cardiological rehabilitation center, and 1200 patients of an outpatient lipid clinic by isoelectric focusing and subsequent anti-apo C-II immunoblotting led to the identification of four individuals whose plasma samples contained an apo C-II isoform with an abnormal isoelectric point. In all cases direct sequencing of PCR-amplified DNA assessed a heterozygous A to C transversion in codon 19 of the apo C-II gene which leads to the replacement of lysine with threonine. Two of the four index patients presented with moderate hypertriglyceridemia; one suffered from severe hyperlipidemia, with triglyceride levels ranging between 180 and 1900 mg/dl, depending on dietary changes. Sequencing of this proband's lipoprotein lipase gene showed no alteration compared to the wild-type sequence. A study in his family revealed that heterozygosity for apo C-II(K19T) is not associated with differences in mean lipid and lipoprotein concentrations. In conclusion, apo C-II(K19T) occurs in Germany at a frequency of approximately 1 in 550. Although this variant is not sufficient to cause hypertriglyceridemia, it may be possible that apo C-II(K19T) cause hypertriglyceridemia in the presence of additional as yet unidentified environmental and/or genetic factors.

Molecular analysis at the Harvey Ras-1 gene in patients with long QT syndrome.

Patients with long QT syndrome (LQTS; MIM 1921500) frequently suffer from syncope and are threatened by sudden cardiac death due to ventricular arrhythmias, typically of the torsade de pointes type. Initial progress in revealing the molecular basis of the disease was made by the observation of genetic linkage of the disease locus to the Harvey Ras-1 gene (HRAS 1) on chromosome 11p15.5. More recently loci on chromosomes 3, 4, and 7 have also been found to be linked to LQTS, thus demonstrating heterogeneity in the causes for this disease. The present study performed sequence analysis on the HRAS 1 gene in patients with congenital and acquired LQTS to determine the frequency of HRAS 1 mutations in patients with this disease. In neither group were no mutations identified in the coding regions or in the splice donor and acceptor sites. Alleles characterized by a T to C transition in exon 1 and an insertion/deletion polymorphism upstream of exon 1 showed no significant difference in their frequencies between LQTS patients and normal controls. No quantitative influence of the such characterized genotypes on the QT duration was observed. These results demonstrate that structural mutations in the HRAS 1 gene are not a frequent cause of LQTS. Also, since there was no association of different alleles at the HRAS 1 locus with changes in QT duration, it appears unlikely that this gene is a major contributor to this disease.

HLA class I, II & III genes in confirmed late-onset Alzheimer's disease.

We first examined all the then known alleles (1997) at the HLA-A, B, Bw, C, DRB1, 3, 4 and 5, and DQB1 loci in 55 late-onset (>65y) AD cases and 73 elderly controls from Oxford. We found an association of HLA-B7 with late-onset AD (odds ratio = 3.1, corrected P = 0.04) that was limited to apolipoprotein E epsilon4-negative subjects (odds ratio = 5.1, corrected P = 0.005). We then studied linkages with Class III genes and, finally, we sought to replicate our HLA-B7 result in cohorts from Montreal and Nottingham. Altogether, we used 299 histopathologically confirmed cases of late-onset AD and 175 controls. Our initial, clear finding was not replicated in Montreal and Nottingham, however. We also failed to support any other previously reported association of AD with an HLA gene. Though we cannot exclude distinct linkages in different cohorts as an explanation of the conflicting results of HLA/AD studies, we conclude that there is no compelling evidence of a strong, direct association between late-onset AD and any HLA Class I or II allele.

A novel frameshift mutation in PMP22 accounts for hereditary neuropathy with liability to pressure palsies.

Peripheral myelin protein PMP22 deficiency is associated with hereditary neuropathy with liability to pressure palsies (HNPP). Most HNPP cases are caused by a 1.5-megabase deletion in chromosome 17p11.2-12, a region that contains the PMP22 gene, whereas point mutations leading to HNPP are extremely rare. We have identified a family with clinical and electrophysiologic features of HNPP,in which all affected members are heterozygous carriers of a single base insertion in codon 94. This mutation is predicted to alter the reading frame and to result in a delayed termination signal. We conclude that the functional consequences of the frameshift are equivalent to those of the PMP22 deletion allele.

PCR-based strategy for the diagnosis of hereditary neuropathy with liability to pressure palsies and Charcot-Marie-Tooth disease type 1A.

Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) are inherited peripheral neuropathies. In most cases these disorders are caused by either the duplication (in CMT1A) or the deletion (in HNPP) of a 1.5-megabase DNA fragment on chromosome 17p11.2, which contains the peripheral myelin protein 22 gene (PMP22). We developed a rapid and simple quantitative PCR assay for the detection of the CMT1A duplication or the HNPP deletion. The assay is based on the quantitative determination of the copy number of a 240-base pair DNA fragment from exon 4 of the PMP22 gene. Quantification was done on an automated fluorescence sequencer. Using this method we analyzed four families with the HNPP phenotype. In these families we identified the deletion in all affected individuals. To test the validity of the method, we compared the quantitative PCR results from 50 DNA samples, including 15 samples from individuals with HNPP, 15 samples from CMT1A patients, and 20 from normal controls, with the results obtained by Southern blot analysis. Concordant results were obtained in 49 of the 50 cases.

The replacement of arginine by cysteine at residue 151 in apolipoprotein A-I produces a phenotype similar to that of apolipoprotein A-IMilano.

Rare nonsynonymous mutations in the apolipoprotein A-I (apo A-I) gene are associated with low HDL-cholesterol levels. Despite the inverse correlation of high density lipoprotein (HDL)-cholesterol levels with the risk of coronary heart disease (CHD) in the population, reduced circulating concentrations of HDL do not necessarily predispose to premature CHD. One apo A-I defect was even reported to cause longevity. We describe a French patient who presented with very low serum HDL-cholesterol levels (10 mg/dl). Sequence analysis of the apo A-I gene identified a heterozygous mutation in the apo A-I gene which causes a cysteine for arginine replacement at residue 151. Family members with the mutation displayed 50% lower levels of plasma HDL-cholesterol and of apo A-I than unaffected members. Plasma activity of lecithin:cholesterol acyl transferase (LCAT) was significantly lower in apo A-I(R151C) heterozygotes than in controls. Furthermore, we found that as for apo A-IMilano (R173C), apo A-I(R151C) forms heterodimers with apo A-II. Moreover, HDL particles were abnormal in both lipid composition and size distribution. Despite these quantitative and qualitative differences in HDL, neither the history of the family over three generations nor the examination of the patient, gave any indication of premature occurrence of atherosclerosis or CHD. We conclude that apo A-I(R151C) causes a phenocopy of apo A-IMilano (R173C), an apo A-I variant which is assumed to cause longevity and which is considered as a potentially anti-atherogenic agent.

Molecular basis of lipoprotein lipase deficiency in two Austrian families with type I hyperlipoproteinemia.

To determine the molecular basis for type I hyperlipoproteinemia in two Austrian families, the lipoprotein lipase (LPL) gene of two patients exhibiting LPL deficiency was analyzed by Southern blotting and by direct genomic sequencing of DNA amplified by polymerase chain reaction (PCR). All exons of the LPL gene except part of the noncoding region of exon 10, all splice donor and acceptor sites, as well as 430 basepairs of the 5'-region including the promotor were sequenced. A homozygous substitution of adenine for guanine in the fifth exon at cDNA position 818 of the LPL gene was found in both patients. Our sequencing strategy largely ruled out a linkage disequilibrium of the identified nucleotide change with another defect potentially causing the clinical phenotype. The base change described abolishes a normally present AvaII restriction site allowing the identification of carriers of the mutant allele by AvaII digestion of PCR fragments of exon 5; three members of the two families were homozygous for this mutation and ten members were heterozygous. The activity of LPL in postheparin plasma was almost completely absent in homozygotes and about half normal in heterozygotes. The loss of activity was related to LPL protein structure. This mutation alters the amino acid sequence at residue 188 from Gly to Glu. The conformational preferences of the protein chain around position 188 were calculated with the use of a knowledge-based computerized method. The most probable conformation is a beta-turn formed by residues 189-192. The mutation seems to destabilize the beta-turn and/or a yet larger domain critical for substrate alignment.

Detection of missense mutations in the genes for lipoprotein lipase and hepatic triglyceride lipase in patients with dyslipidemia undergoing coronary angiography.

Coronary events have a close association with a low HDL/hypertriglyceridemia (LHDL/HTG) phenotype. As enzymes that hydrolyze triglyceride-rich lipoproteins are associated with a modulation of both HDL cholesterol and triglycerides, we have tested the hypothesis that mutations in the genes encoding lipoprotein lipase (LPL) or hepatic lipase (HTGL) may contribute to the formation of coronary atherosclerosis and, thus, of coronary heart disease (CHD). The entire coding and boundary regions of LPL and HTGL genes were analyzed by direct sequencing in 20 patients with both LHDL/HTG and diagnosed CHD. In the LPL gene six different polymorphisms were identified with same frequencies observed in the general population. In the HTGL gene, besides several polymorphisms, we identified three missense mutations: Asn37His, Val73Met, and Ser267Phe. Population screening using allele specific PCR identified Val73Met as a polymorphism while the two others were absent from 100 control individuals. One of the mutations (Ser267Phe) is known to cause HTGL deficiency and is associated with type III hyperlipoproteinemia. Since this dyslipoproteinemia meets the criteria of LHDL/HTG, it is intriguing to speculate that missense mutations in HTGL may play a role in the pathogenesis of this atherogenic phenotype.

Heterozygous hepatic lipase deficiency, due to two missense mutations R186H and L334F, in the HL gene.

Hepatic lipase (HL) is an endothelial enzyme involved in the metabolism of intermediate density lipoproteins (IDL) and high density lipoproteins (HDL) in plasma. In a Finnish pedigree consisting of 18 members belonging to three generations two missense mutations RI86H and L334F in exons 5 and 7 of the HL gene co-segregated with low post-heparin HL activity. Haplotype analysis of the HL gene in family members revealed a high degree of genetic variation and demonstrated that the two missense mutations reside on the same chromosome. In vitro site-directed mutagenesis and expression of the cDNA constructs in COS-1 cells revealed that the R186H mutation leads to a protein that is not secreted while the L334F mutation results in the production of a HL protein that is secreted but has only about 30% of wild type HL activity. Carriers of the mutated HL gene exhibited clearly reduced HL activity and mass in post-heparin plasma. Probably due to their heterozygous carrier status they had only moderate elevation of total triglycerides, IDL, and LDL-triglycerides. The LDL-particles were enriched in triglycerides and depleted of cholesterol. Also their HDL2- and HDL3-particles were enriched in triglycerides.

Roles for lipoprotein lipase in Alzheimer's disease: an association study.

Lipoprotein lipase (LPL) assists lipid transport by transferring lipids between lipoprotein particles and cells. LPL binds apolipoprotein E (apoE) lipoprotein particles and a major apoE receptor, low density lipoprotein receptor related protein (LRP). Because apoE and LRP polymorphisms alter Alzheimer's disease (AD) risk, and LPL itself is found in AD amyloid plaques, we examined whether LPL variants also affect AD risk. In case-control studies in the United States and Canada, the frequencies of two LPL alleles known to affect LPL enzymatic activity were measured in Caucasian AD or elderly normal (N) subjects. Pathologically confirmed subjects in both studies exhibited similar trends toward fewer 447Ter and more 291Ser alleles in AD. Combining results from both countries gave allele frequencies for 447Ter of 13.7% (26/190) in N and 9.4% (80/852) in AD (P = 0.10), and for 291Ser of 0.0% (0/184) in N and 1. 3% (8/636) in AD (P = 0.21). The trend appeared even greater for homozygous 447Ter subjects: 4.2% (4/95) of N vs. 1.4% (6/426) of AD (P = 0.09). These trends are consistent with a putative protective effect of 447Ter and causative effect of 291Ser on AD. Furthermore, brains of AD patients with 447Ter showed trends toward fewer plaques, tangles, and glia, and more neurons and cortical thickness than AD patients without 447Ter. Hippocampal plaques were significantly reduced. LPL might affect hippocampal function and thus dementia via its role as supplier of membrane components or antioxidants to neurons. Alternatively, LPL may play a part in plaque formation through its interaction with apoE and LRP.

Absence of mutations in peripheral myelin protein-22, myelin protein zero, and connexin 32 in autosomal recessive Dejerine-Sottas syndrome.

Motor and sensory neuropathies with the clinical features of HMSN III (Dejerine-Sottas syndrome, DSS) are etiologically related to heterozygous mutations in either peripheral myelin protein-22 (PMP22) or myelin protein zero (MPZ). Heterozygous mutations in either of these two genes are also responsible for other hereditary peripheral neuropathies (HNPP, CMT1A, CMT1B or CH). In two families DSS was related to the homozygous presence of a MPZ mutation while heterozygosity showed a much milder phenotype. It has therefore been suggested that the clinical phenotype in peripheral neuropathies is related to the mutated gene, the type of mutation and confounding effects from other sources. In this study we describe a family with recessive DSS in which mutations were absent from the PMP22, MPZ, and connexin 32 (Cx32) genes. We conclude that DSS also exists as a distinct genetic entity with autosomal recessive inheritance as originally defined by Dejerine and Sottas in 1893.

Compound heterozygosity for a known and a novel defect in the lipoprotein lipase gene (Asp250-->Asn; Ser251-->Cys) resulting in lipoprotein lipase (LPL) deficiency.

Two missense mutations in exon 6 of the LPL gene were identified on separate alleles in a Dutch patient with lipoprotein lipase (LPL) deficiency. The first mutation is a G1003-->A transition resulting in a D250N mutation, which has been shown previously to result in a catalytically defective protein in patients of French-Canadian ancestry. The second mutation, a C to G transition at nucleotide 1007, predicts a S251C residue change in the highly conserved region of LPL surrounding the loop structure the covers the catalytic triad. This mutation constitutes a novel defect among LPL gene mutations reported so far. Site-directed mutagenesis experiments provide in-vitro evidence for the complete loss of LPL activity resulting from this latter missense mutation. The G1003-->A nucleotide substitution underlying the Asp250 mutation deletes a TaqI endonuclease recognition site and the C1007-->G change that leads to the S251C alteration abolishes a HinfI recognition site. This will facilitate rapid screening for these mutations in LPL-deficient patients.

Further evidence for a synergistic association between APOE epsilon4 and BCHE-K in confirmed Alzheimer's disease.

Recent reports on a potential association between the K-variant of the gene for butyrylcholinesterase (BCHE-K) and Alzheimer's disease (AD) are discordant. An initial finding of association through a synergistic enhancement of risk of APOE epsilon4 with late-onset AD has not been confirmed by others. We have conducted a case-control study of histopathologically confirmed AD (n=135) and non-AD (n=70) cases (age of death > or =60 years), in which we have genotyped for APOE epsilon4, BCHE-K, and BCHE-A1914G, a silent polymorphism 299 bp downstream of the BCHE-K mutation. The allelic frequency of BCHE-K was 0.13 in the controls and 0.23 in the AD cases, giving a carrier odds ratio (OR(c)) of 2.1 (95% C.I. 1.1-4.1) for BCHE-K in confirmed AD. The allelic frequency for the BCHE-1914G variant was 0.19 and 0.33 in controls and AD cases, respectively (OR(c)=2.4; 95% C.I. 1.3-4.5). In an older sub-sample of 27/70 controls and 89/135 AD patients with ages of death > or =75 years, the OR(c) was increased to 4.5 (95% C.I. 1.4-15) for BCHE-K and 2.7 (95% C.I. 1.0-7.2) for BCHE-1914G carriers. The BCHE-K association with AD became even stronger in carriers of at least one APOE epsilon4 allele. Only three out of 19 controls compared with 39/81 AD cases carried BCHE-K in addition to APOE epsilon4, giving an odds ratio of confirmed AD of 5.0 (95% C.I. 1.3-19) for BCHE-K carriers within APOE epsilon4 carriers. Five out of 19 controls and 52/81 AD cases carried BCHE-1914G, giving the same odds ratio of confirmed AD of 5.0 (95% C.I. 1.6-16) for BCHE-1914G carriers within APOE epsilon4 carriers. In addition, our results suggest strong linkage disequilibrium between BCHE-K and BCHE-1914G but no major association of the sole BCHE-1914G chromosome with AD. We conclude that BCHE through its K-variant, rather than a nearby marker, is a susceptibility factor for AD and enhances the AD risk defined by APOE epsilon4 alone in an age-dependent manner.

Homozygosity for a splice junction mutation in exon 8 of the gene encoding lysosomal acid lipase in a Spanish kindred with cholesterol ester storage disease (CESD).

Deficiency of lysosomal acid lipase is expressed in two distinct recognizable phenotypes. Wolman disease represents the severe early onset form, whereas cholesterol ester storage disease is the more benign late onset type. Previous studies have indicated that compound heterozygosity consisting of a G-->A mutation at the 3'-splice junction of exon 8 (E8SJM-allele) together with a null allele of the gene encoding lysosomal acid lipase leads to cholesterol ester storage disease. We have now observed homozygosity for the G-->A splice junction mutation in a non-related Spanish kindred with the same disease. As expected, the residual activity of lysosomal acid lipase is higher in this case, suggesting that the E8SJM-allele is associated with low residual acid lipase activity. However, the phenotype of the homozygous propositus is more severe compared with the previously described case, indicating that no direct relationship exists between the genotype or residual LAL activity and the precise cholesterol or triglyceride levels in a given patient. Nevertheless, our findings provide convincing evidence that homozygosity for the E8SJM-allele causes cholesterol ester storage disease to at least the same extent as compound heterozygosity consisting of this allele and a null allele.

Dyslipidaemia in a boy with recurrent abdominal pain, hypersalivation and decreased lipoprotein lipase activity.

UNLABELLED: An 8-year-old boy with frequently recurring pancreatitis-like abdominal pain, Fredrickson type V dyslipidaemia, and significantly decreased post-heparin plasma lipoprotein lipase (LPL) activity is described. In order to exclude familial LPL deficiency, the complete LPL coding gene sequence was analysed revealing compound heterozygosity for two mutations (Asp9Asn, Ser447Ter) which are not supposed to considerably impair lipolytic enzyme activity. However, until now the combination of both these mutations in one patient has not been observed. In addition to the common symptoms of LPL deficiency, a striking feature of unknown origin was hypersalivation. Treatment including a fat-restricted diet, omega-3 fatty acids, and nicotinic acid led to long symptoms-free intervals. Symptoms recurred however when the diet was not strictly adhered to. CONCLUSION: LPL deficiency is a rare cause of abdominal pain in childhood and deserves careful treatment in order to avoid pancreatitis. The presented patients is a unique compound heterozygote for two mutations which do not abolish lipolytic activity in the homozygote state. Identification of other individuals with this genotype is necessary to understand the phenotype in our patient.

Screening for naturally occurring apolipoprotein A-I variants: apo A-I(delta K107) is associated with low HDL-cholesterol levels in men but not in women.

Isoelectric focussing (IEF) in carrier ampholyte-generated pH gradients and hybrid isoelectric focussing (HIEF) in immobilized pH gradients under nondenaturing conditions were used in parallel to screen 5,500 plasma samples for naturally occurring variants of apolipoprotein A-I (apo A-I). The following defects were identified in four unrelated subjects heterozygous for apo A-I variants: apo A-I(delta K107)(2 x), apo A-I(K107M)(1 x), and apo A-I(E41R)(1 x). The later variant is a novel finding. Family studies did not reveal any association of apo A-I(K107M) and apo A-I(E41R) with dyslipidemia, but identified several heterozygotes for apo A-I(delta K107) who had low levels of high density lipoprotein (HDL)-cholesterol. Therefore, and since the apo A-I(delta K107) is the most frequent apo A-I variant in Germany (1: 5,000) we evaluated our data and that reported from 11 families with 32 heterozygous carriers and 30 unaffected controls. This analysis revealed that apo A-I(delta K107) is associated with lower HDL-cholesterol (-30%) and higher triglycerides (+48%) in men but not in women as compared with unaffected family members as well as with controls from the Prospective Cardiovascular Münster (PROCAM) study. Moreover, 11 of 15 male apo A-I(delta K107) heterozygotes but only 2 of 17 female apo A-I(delta K107) heterozygotes had HDL-cholesterol levels below the 20th percentile of sex-matched controls from the PROCAM study. We conclude that heterozygosity for apo A-I(delta K107) decreases HDL-cholesterol and increases triglycerides in men but not in women.

Marked changes of lipid levels during puberty in a patient with lipoprotein lipase deficiency.

UNLABELLED: Clinical and biochemical characteristics of a female patient with familial lipoprotein lipase deficiency have been followed in short intervals before and during puberty. The proband is compound heterozygote for two missense mutations in the lipoprotein lipase gene. One mutation occurs in codon 250 (Asp250-->Asn), the other is in codon 410 (Glu410-->Lys). The residual lipoprotein lipase activity in the proband is less than 10% of controls. Before puberty the proband usually presented with moderate isolated hypertriglyceridaemia. During the initial phase of puberty a dramatic increase in the plasma concentration of both cholesterol and triglycerides was observed. During the second half of puberty a reduction of cholesterol but not of triglycerides was noticed. CONCLUSION: These findings show that the phenotypic expression of familial chylomicronaemia can be modified to a large extent by hormones. Furthermore they demonstrate the need for a closer clinical observation of type I patients during puberty.