Effect of sediment turbidity and color on light output measurement for Microtox Basic Solid-Phase Test

In this work, sediment samples collected from several Spanish harbours were tested with two toxicity procedures, designed for solid samples: the Microtox Basic Solid-Phase Test (BSPT) and a modified procedure of the previous test protocol (mBSPT). According to the BSPT procedure, after initial light readings, pure bacteria were exposed to sediment suspension dilutions and light production was directly measured on suspended sediments without any further manipulation. As measurements are likely to be affected by sediment turbidity and color, a variation in initial light measurement has been here suggested, in order to consider the sample effect at all time readings during the test. Firstly, when sediment suspensions at different concentrations were added to bacteria suspension, immediately the initial light output drastically decayed by more than 50% in signal difference, resulting in a false inhibition, as effect of sample turbidity/color. This effect was more evident at high EC50 values, when slightly or not toxic samples were assessed. Secondly, the comparison of the EC50 obtained with both procedures, demonstrated that the mBSPT produced higher EC50 values (less toxic) than those obtained with the standard procedure. The mBSPT procedure resulted rapid and effective and it could be applied simultaneously with BSPT, in order to better evaluate the toxicity.

Experiences against HIV/AIDS/STDS of Somalis in exile in Gothenburg, Sweden

Since 1989, the City of Göteborg Immigrant Services Administration has been making efforts to inform about HIV/AIDS. The purpose has been to ensure that even immigrant residents of the City of Göteborg (Gothenburg) have access to relevant information about HIV/AIDS. The administration's efforts have been a part of the collected efforts of Gothenburg to prevent the spreading of HIV. This paper attempts to discover and describe experiences against HIV/AIDS/STDs of Somalis in Exile in Gothenburg, Sweden. A qualitative sociological in-depth interviews with 13 individuals (6 women and 7 men) and with semi-structured and themetized emerging design was carried on. A follow up focus group interviews with 10 individuals (2 women and 8 men) was also performed. The paper reveals that the general understanding of subjects on the issues under discussion is almost the same though details may vary from one research participant to the other. They have described this through narratives. STDs and specially HIV/AIDS was perceived as something dishonourable by the subjects. The HIV/AIDS is perceived as a sin which Allah sends to punish those who have fornication or sex without marriage (Zinna). Of course, this tendency of shying off the problem leads to ignorance of how to behave, which in turn decreases the risk of perceptions and as a result may also increase the risk of being infected. As concerns protection as a preventive measure, attitudes vary. The traditionalists have argued that condom increased the possibility of promiscuity or fonication, while young and more modern people saw condom as something good. We may conclude that Somalis who have arrived in Western world and in Sweden as adults did never have a modern sexual education for themselves due to socio-cultural reasons and this has important implication for giving proper information to their children about sex organs, human sexual development and preventive measures against HIV/AIDS/STDs. These immigrant parents should be offered culturally sensitive communication and educational programmes aimed at raising their awareness about teenagers sexuality and the preventive measures against HIV/AIDS/STDs.

Ecotoxicological and chemical evaluation of phenolic compounds in industrial effluents

The aim of this paper was to evaluate the ecotoxicological response of industrial effluents containing phenolic compounds. All complex effluents collected from a chemical plant and then after both a chemical-physical and biological treatment were characterised with chemical analysis, biodegradability tests and four ecotoxicological tests (Daphnia magna, Artemia salina, Brachionus plicatilis and Vibriofisheri with Microtox). The evaluation of the chemical and ecotoxicological data was useful for predicting the effect of the raw effluent on the treatment plant and the impact of the final treated effluent on the receiving water. Besides the toxicity of the effluent from the chemical plants, the acute toxicity of its main components was also determined. The results of the tests and toxicity data from literature were transformed in Toxic Units (TUs). Effluent toxicity was under- or over-estimated by calculating the sum of the TUs of the individual components, depending on which toxicity data and test organisms were used.

Ultrastructural localization of gelsolin in lattice corneal dystrophy type I

In the light of recent studies into lattice corneal dystrophies, with particular reference to gelsolin immunoreactivity, the authors set out to determine the ultrastructural localization of gelsolin molecules in lattice corneal dystrophy type I. Immunoelectron microscopy with a monoclonal antibody against the COOH-terminal of the native gelsolin molecule (clone GS-2C4) was used to compare antigelsolin reactivity in normal and dystrophic corneas. A gelsolin-like protein was observed at the level of the rough endoplasmic reticulum in both epithelial and endothelial cells, together with mild positive staining in stromal keratocytes of normal corneas; increased keratocytic immunoreactivity with positive staining within and/or around corneal amyloid deposits was revealed in dystrophic corneas. Observed intra- and extracellular immunoreactivity suggests that amyloid deposition may induce gelsolin synthesis; this actin-related protein could be involved in the rearrangement of corneal stroma in lattice corneal dystrophy.

High prevalence of celiac sprue-like HLA-DQ genes and enteropathy in patients with the microscopic colitis syndrome

OBJECTIVE

Celiac sprue is associated with specific HLA-DQ genes (mainly DQ2). Because there are epidemiological and histopathological similarities between celiac sprue and microscopic colitis, we hypothesized that these syndrome may share an HLA genetic predisposition and pathogenesis.

METHODS

The HLA-DQ genes of 25 patients with celiac sprue, 53 patients with the microscopic colitis syndrome, and 429 normal controls were typed and compared. Serum was analyzed for antigliadin and antiendomysial antibodies. Small intestinal biopsies were analyzed for signs of histopathology.

RESULTS

HLA-DQ2 or DQ1,3 (the latter as DQ1,7,DQ1,8, or DQ1,9) were seen more frequently in both patient groups relative to controls. In patients with the microscopic colitis syndrome, serological tests for celiac sprue were weakly positive in 17%; mild inflammation of the small intestine without villous atrophy was present in 43%, and inflammation plus partial or subtotal villous atrophy was present in 27%.

CONCLUSIONS

A shared set of predisposing HLA-DQ genes account for the epidemiological overlap of celiac sprue and microscopic colitis. Mild to moderate mononuclear cell inflammation of the small intestine, often accompanied by partial or subtotal villous atrophy, is frequent in patients with the microscopic colitis syndrome. Although further studies will be necessary to determine if this enteropathy is induced by dietary gluten, we speculate that the small intestinal but not colonic histopathology in patients with microscopic colitis is caused by immunological gluten sensitivity.

Mie and debye scattering in dusty plasmas

We calculate the total field scattered by a charged sphere immersed in a plasma using a unified treatment that includes the usual Mie scattering and the scattering by the Debye cloud around the particle. This is accomplished by use of the Dyadic Green function to determine the field radiated by the electrons of the Debye cloud, which is then obtained as a series of spherical vector wave functions similar to that of the Mie field. Thus we treat the Debye-Mie field as a whole and study its properties. The main results of this study are (1) the Mie (Debye) field dominates at small (large) wavelengths and in the Rayleigh limit the Debye field is constant; (2) the total cross section has an interference term between the Debye and Mie fields, important in some regimes; (3) this term is negative for negative charge of the grain, implying a total cross section smaller than previously thought; (4) a method is proposed to determine the charge of the grain (divided by a certain suppression factor) and the Debye length of the plasma; (5) a correction to the dispersion relation of an electromagnetic wave propagating in a plasma is derived.

[Long-term clinical assessment of single-lead VDD electric stimulation]

BACKGROUND

During the last decade single lead VDD pacing has been progressively affirmed as an electrotherapy of choice in patients with advanced atrioventricular block without alterations of the sinus function. It combines the benefits of P-synchronous ventricular pacing with an easy implant procedure when compared to the conventional DDD approach. The aim of this study was to evaluate the validity of such an approach in a large population of patients, all implanted in a single center.

METHODS

From 1987 up to now, 317 patients, all affected by advanced atrioventricular block and without sinus node dysfunction, were implanted in our center with a single lead VDD pacemaker. During follow-up the persistence of a proper atrioventricular synchronization was assessed and evaluated.

RESULTS

The mean follow-up was 3.9 +/- 2.7 years/patient (range 6-138 months). The 94.6% of implanted systems maintained the normal VDD pacing function. Permanent reprogramming in VVI mode was necessary in 17 patients (5.36%); in 12 (3.78%) because of chronic atrial fibrillation and in 5 (1.63%) for loss of atrial sensing. The percentage of atrial synchronization was optimal (> 98%) and acceptable (> 95%) in 81% and 19% of patients, respectively. Episodes of paroxysmal atrial fibrillation occurred in 3 patients. Neither inhibition by myopotentials nor occurrence of sinus node disease was observed during follow-up. These results are in accordance with those reported by previous studies, performed on a smaller population or on a multicenter basis, and are comparable with the results reported for conventional DDD pacemaker.

CONCLUSIONS

Our results confirm the high reliability of the single lead VDD pacing system concerning the long-term persistence of a proper atrioventricular synchronization. Data showed above enforce our opinion that this pacing approach should be considered the treatment of choice in patients with advanced atrioventricular block and preserved sinus node function.

Chromatin condensation during Scrobicularia plana spermiogenesis: a controlled and comparative enzymatic ultracytochemical study

In Scrobicularia plana testis, a nuclear acid phosphatase (ACPase) activity was detected in mid and late spermatids with the improved Gomori-chloride procedure. Lead deposits were first observed in mid spermatids at focal points over condensed chromatin strands, increasing in density as chromatin further condensated. In late spermiogenesis, lead deposits became concentrated between chromatin aggregates, and after total DNA compaction were transfered to the nuclear periphery and then shed into the cytoplasm. The specificity of the nuclear ACPase was tested against different pH values (3.9, 7.2, 7.8, 9.0), substrates (TPP, IDP, TMP, p-NCS, ATP, GTP, AMP, ADP, AMP-PNP) and inhibitors (NaF, levamisole, Zn, vanadate, theophylline). To further specify the nature of this nuclear ACPase, other enzymes were comparatively studied at their optimal pH values and at pH 5.0: nucleoside-diphosphatase, thiamin-pyrophosphatase, inorganic trimetaphosphatase, lysosomal arylsulfatases A and B, ATPase, GTPase, 5'-nucleotidase, adenylate kinase, and adenylate cyclase. Several other controls were introduced to exclude artefactual deposits induced by lead ions and tissue molecules. The results showed that the enzyme has an optimal pH at 5.0, a high specific affinity for beta-GP, and is inhibited by NaF, which suggests that it behaves as a type B-ACPase, and all controls demonstrated the specificity of the enzymic activity. Because lead deposits were specifically and temporally associated with spermatid chromatin condensation, when DNA and RNA synthesis, histones, phosphoproteins and RNA molecules strongly decrease, it is possible to suggest that the nuclear ACPase could be associated with DNA processing during chromatin compaction or involved in the hydrolysis of 2' and 3' nucleotides resulting from nuclear RNase action during RNA degradation.

Increased stability and catalytic efficiency of yeast hexokinase upon interaction with zwitterionic micelles. Kinetics and conformational studies

The effect of ligands (glucose, ATP and Mg2+) and zwitterionic micelles of lysophosphatidylcholine (LPC) or N-hexadecyl-N,N-dimethyl-3-ammonium propanesulfonate (HPS) in the yeast hexokinase (HK) stability was studied at 35 degrees C. The thermal inactivation kinetics followed one-exponential decay. The effect of ligands on protecting the enzyme against inactivation followed the order: glucose > glucose/Mg2+ >ATP/Mg2+ approximately or approximately equal to Mg2+l approximately or approximately equal to buffer only. Both LPC and HPS micelles increased the enzyme stability only when the incubation medium contained glucose or glucose/Mg2+, suggesting that the protein conformation is a key prerequisite for the enzyme-micelle interaction to take place. This enzyme-micelle interaction resulted in an increased catalytic efficiency (with a decrease in Km for ATP and increase in Vmax as well as in changes on the tertiary (intrinsic fluorescence) structure of the yeast hexokinase.

[The long-term effects of dual-chamber stimulation in 8 patients with hypertrophic obstructive cardiomyopathy and symptoms refractory to medical therapy]

BACKGROUND

The issue of DDD pacing as a therapeutic option for patients with obstructive hypertrophic cardiomyopathy is still under debate. Moreover, some authors stress the concept of the placebo effect of electrical therapy in this particular setting.

METHODS

We retrospectively evaluated 8 symptomatic patients with obstructive hypertrophic cardiomyopathy despite medical therapy, who underwent DDD pacemaker implantation as an adjunctive therapeutic strategy. All patients were evaluated with a two-dimensional/Doppler echocardiogram at baseline, shortly after the beginning of DDD pacing and at follow-up. In 3 patients dobutamine stimulation was necessary to elicit the intraventricular gradient.

RESULTS

At follow-up (21 +/- 19 months, range 1-54 months) the peak gradient declined from 86 +/- 27 to 34 +/- 27 mmHg (55.2%). In 4 patients the peak gradient sharply declined after pacemaker implantation with active pacing and remained stable throughout the follow-up. In 2 patients we noted a continuous reduction in the peak gradient during the follow-up, while in 2 patients it returned to baseline values after 1 year and 1 month, respectively, despite an early reduction with DDD pacing. All patients experienced symptomatic amelioration throughout the follow-up. Two patients developed angina at the end of our observation together with an increase in the peak gradient.

CONCLUSIONS

We believe that DDD pacing may be considered as a practical therapeutic option for patients with obstructive hypertrophic cardiomyopathy who would otherwise be regarded as candidates for surgery.

Meta-analysis by combining p-values: simulated linkage studies

Meta-analysis has been little explored to make an overall assessment of linkage from different studies. In practice, it is likely that published linkage studies will only report p-values. We compared the performance of the widely used Fisher method for combining p-values with that of pooling raw data. More loci were consistently found by pooling raw data. In the absence of further information, combining p-values can provide an overall, but limited, assessment of different linkage studies. However, meta-analysis would be better viewed as a preliminary step toward the goal of analyzing the pooled raw data.

Meta-analysis by combining parameter estimates: simulated linkage studies

Several meta-analytic techniques have been developed for combining information from multiple studies in contexts other than linkage detection. We apply the technique of combining parameter estimates to the problem of finding disease loci in the simulated data and compare results with those obtained by reanalyzing pooled raw data. To facilitate the combination of study results, we highly recommend that parameter estimates and their standard errors be reported in published studies. If different research groups were to make original data available, progress toward disease gene location and characterization may be more quickly made.

Congenital nasolacrimal duct obstruction: therapeutic management

PURPOSE

Congenital nasolacrimal duct obstruction is a common condition, and its diagnosis must be based more on regular in-time epiphora than mattering. The purpose of this study is to better define the diagnostic criteria and therapeutic strategy.

METHODS

We have retrospectively evaluated 1563 subjects treated from 1990-1997 at the Pediatric Ophthalmological Service of Modena University Eye Clinic. The mean age at first examination was 5.7 months. According to symptoms and age, patients were treated with antibiotic therapy, office probing, or general anesthesia probing. Recovery was confirmed only after a 3-month symptom-free period.

RESULTS

More than 29% of patients recovered spontaneously or with topical antibiotic therapy. Office probing reduced the number of patients who needed a general anesthesia probing (from 62.97% from 1990-1993 to 33.61% from 1994-1997). In the period from 1994-1997, we changed the technique and especially the age of patients, obtaining a clearing of the obstruction in about 86% of cases compared with a 39% rate in the earlier period. Since 1994, in cases of general anesthesia probing, we have used a midazolam and ketamine anesthesiologic technique that has reduced risks and increased parental satisfaction and cost-effectiveness. Also, our data show that age at first attempt highly influenced probing failure rate.

CONCLUSION

If the first ophthalmologic examination is precocious and correctly timed, the possibility of curing the patient using the simplest method is increased. Better results can be obtained with cooperation among pediatricians, ophthalmologists, and anesthesiologists.

Structure, cytoskeleton, and development of the acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae)

The acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae) is relatively large and complex, consisting of an apical vesicle and two large wing-like extensions that give the spermatozoon the shape of an arrow. The wings have actin microfilaments and microtubules and are covered with a noticeable extracellular material. Actin filaments are present in the acrosome when it first appears in spermatid stages. The acrosome and the acrosomal attachment to the nucleus are more resistant than other structures to the reducing agents DTT and SDS. At the end of spermiogenesis, groups of spermatozoa juxtapose their sperm heads and become joined to form a spermatodesm encircled by an amorphous material. Treatment with the ionophore A23187 rapidly disrupted acrosomes of the free gametes, but acrosomes from spermatozoa contained in the spermatodesm were not disassembled. Packaging of sperm in a spermatodesm appears to protect the acrosome.

Testing for linkage under robust genetic models

Robust genetic models are used to assess linkage between a quantitative trait and genetic variation at a specific locus using allele-sharing data. Little is known about the relative performance of different possible significance tests under these models. Under the robust variance components model approach there are several alternatives: standard Wald and likelihood ratio tests, a quasilikelihood Wald test, and a Monte Carlo test. This paper reports on the relative performance (significance level and power) of the robust sibling pair test and the different alternatives under the robust variance components model. Simulations show that (1) for a fixed sample size of nuclear families, the variance components model approach is more powerful than the robust sibling pair approach; (2) when the number of nuclear families is at least approximately 100 and heritability at the trait locus is moderate to high (>0.20) all tests based on the variance components model are equally effective; (3) when the number of nuclear families is less than approximately 100 or heritability at the trait locus is low (<0. 20), on balance, the Monte Carlo test provides the best power and is the most valid. The different testing procedures are applied to determine which are able to detect the known association between low density lipoprotein cholesterol and the common genotypes at the locus encoding apolipoprotein E. Results from this application show that the robust sibling pair method may be more effective in practice than that indicated by simulations.

The health care reform in Italy: transition or turmoil

Health care reform in Italy is transforming its centrally planned, vertically integrated National Health Service into a market-oriented system in which public funders contract directly with individual providers. A model is envisaged in which a plurality of public and private care providers compete for contracts with capitated health agencies responsible for assuring uniform levels of services for geographically defined populations. The ultimate goal of the reform is to guarantee universal coverage and secure global spending limits while, at the same time, promoting efficiency in the delivery of care and enhancing responsiveness to consumers. The emphasis upon incentives for the individual provider which will be introduced should, however, be considered against the quest for equity in health care which was the central tenet of the 1978 reform and is yet to be attained. The fragmentation of the National Health Service into many separate, competing delivery units might well damage the ability to plan strategically for addressing the substantial inequities in health status, health care utilization, and health service availability which still exist across the country. Competition between a plurality of providers and fee-for-service payment schemes add additional concerns about unnecessary care and supplier-induced demand. It creates the need for developing rules to make competition manageable and providing sound clinical and financial information that make enforcement possible. The poor record scored in managing the contractual relationships between the LHUs and the strong private health sector suggests that massive investment in promoting managerial skills and developing appropriate clinical and financial information systems are required. Careful experimentation in implementing the reform and continuous monitoring of its impact on the health care system are, therefore, the imperatives of the next two years.

A statistically robust variance-components approach for quantitative trait linkage analysis

Previously we showed (Wang, Guerra & Cohen 1998) that a statistically robust version of the Haseman & Elston (1972) sib-pair method greatly increased power to detect linkage in the presence of outliers. In this paper we report on M-estimation to accommodate outliers in the variance-components approach to linkage analysis developed by Amos (1994). Simulations show that in the presence of outliers the robust variance-components approach provides substantially greater power, more precise estimation of heritabilities, and better false-positive rates than the original Gaussian based approach. In the absence of outliers the performance of the robust variance-components approach is similar to that of the Gaussian based approach. For illustration we apply the method to two well characterized lipoprotein systems.

Evidence for a Turner syndrome locus or loci at Xp11.2-p22.1

Turner syndrome is the complex human phenotype associated with complete or partial monosomy X. Principle features of Turner syndrome include short stature, ovarian failure, and a variety of other anatomic and physiological abnormalities, such as webbed neck, lymphedema, cardiovascular and renal anomalies, hypertension, and autoimmune thyroid disease. We studied 28 apparently nonmosaic subjects with partial deletions of Xp, in order to map loci responsible for various components of the Turner syndrome phenotype. Subjects were carefully evaluated for the presence or absence of Turner syndrome features, and their deletions were mapped by FISH with a panel of Xp markers. Using a statistical method to examine genotype/phenotype correlations, we mapped one or more Turner syndrome traits to a critical region in Xp11.2-p22.1. These traits included short stature, ovarian failure, high-arched palate, and autoimmune thyroid disease. The results are useful for genetic counseling of individuals with partial monosomy X. Study of additional subjects should refine the localization of Turner syndrome loci and provide a rational basis for exploration of candidate genes.

Statistically robust approaches for sib-pair linkage analysis

Many traits that distinguish one individual from another, such as height or weight, are clearly heritable and yet vary continuously in populations. Continuous, heritable variation in trait levels presumably reflects the segregation of multiple genes, but elucidation of the genetic architecture of quantitative traits has been limited. Haseman & Elston (1972) developed a genetically robust method (HE) for detecting linkage to quantitative trait loci using sib-pairs. The method is based on a simple linear regression of the squared sib-pairs trait difference on the proportion of alleles shared identical by descent at a marker locus. Linkage is detected by a negative slope which has been traditionally assessed by a standard t-test. Wan, Cohen & Guerra (1997) have shown that the standard t-test is robust to the violations of the stochastic assumptions underlying the test. In practice, however, the standard t-test, based on least-squares regression, is sensitive to outliers. The presence of outliers in the data can lead to false positive and false negative linkage results. Accordingly we have developed and evaluated a statistically robust procedure for the HE approach to linkage. The procedure is based on robust regression. Simulation studies show that this robust procedure has greater power than the standard t-test in the presence of outliers, and has similar power to the standard t-test in the absence of outliers. This robust procedure also shows greater power than rank-based approaches either in the absence or presence of outliers. To illustrate the methods using real data we reanalyse data from two lipoprotein systems that motivated this work.

Acute effects of soft drink intake on calcium and phosphate metabolism in immature and adult rats

OBJECTIVE

To test the acute effects of the intake of a phosphoric acid containing soft drink on acid-base balance and on calcium and phosphate metabolism.

MATERIAL AND METHODS

We studied 14 young adult male Sprague-Dawley rats aged 90 days, and 14 immature animals aged 30 days. Half of the animals in each group were randomly assigned to receive either tap water (controls), or Coca-Cola ad libitum for seven days. After this period, the rats were individually placed in metabolic cages to collect 24 hours urine, and they were exsanguinated by aortic puncture. Immediately, pH and ionized calcium were measured in whole blood. Creatinine, phosphate and total calcium were determined in the urine and plasma. Plasma levels of PTH, 1 alpha, 25 (OH)2 D3 and 25 OH D3 were measured by IRMA and RIA commercial kits.

RESULTS

The animals receiving the soft drink, both adults and immature, developed significant hypercalciuria and hyperphosphaturia. In immature animals, the plasma pH dropped from 7.45 +/- 0.04 to 7.33 +/- 0.02 (p < 0.05) but did not change in adult animals. Ionized calcium dropped significantly from 1.06 +/- 0.04 to 0.80 +/- 0.06 meq/L (p < 0.05) in immature animals but not in the adult animals. Only immature rats developed significant reduction of 1 alpha, 25 (OH)2 D3 and 25 OH D3, whereas only the adult rats developed significant hyperparathyroidism. Immature animals showed more severe derangement of calcium and phosphate metabolism related to soft drink intake.

Linkage between cholesterol 7alpha-hydroxylase and high plasma low-density lipoprotein cholesterol concentrations

Interindividual differences in plasma low-density lipoprotein cholesterol (LDL-C) levels reflect both environmental variation and genetic polymorphism, but the specific genes involved and their relative contributions to the variance in LDL-C are not known. In this study we investigated the relationship between plasma LDL-C concentrations and three genes with pivotal roles in LDL metabolism: the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and cholesterol 7alpha-hydroxylase (CYP7). Analysis of 150 nuclear families indicated statistically significant linkage between plasma LDL-C concentrations and CYP7, but not LDLR or APOB. Further sibling pair analyses using individuals with high plasma LDL-C concentrations as probands indicated that the CYP7 locus was linked to high plasma LDL-C, but not to low plasma LDL-C concentrations. This finding was replicated in an independent sample. DNA sequencing revealed two linked polymorphisms in the 5' flanking region of CYP7. The allele defined by these polymorphisms was associated with increased plasma LDL-C concentrations, both in sibling pairs and in unrelated individuals. Taken together, these findings indicate that polymorphism in CYP7 contributes to heritable variation in plasma LDL-C concentrations. Common polymorphisms in LDLR and APOB account for little of the heritable variation in plasma LDL-C concentrations in the general population.

Determinants of plasma platelet-activating factor acetylhydrolase: heritability and relationship to plasma lipoproteins

Plasma platelet-activating factor acetylhydrolase (PAF-AH) is the enzyme that inactivates PAF (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine). We determined the relative contributions of genetic and environmental factors to variation in plasma PAF-AH activity in 240 individuals from 60 nuclear families. Regression of mean-offspring PAF-AH activity on the mid-parent value indicated that 62% of the variation in plasma PAF-AH activity was heritable. Spousal values were weakly negatively correlated, indicating that familial aggregation of PAF-AH activity is due to genetic rather than to environmental factors. Among normolipidemic individuals, plasma PAF-AH activity was strongly correlated with the plasma concentration of low density lipoprotein cholesterol (LDL-C), and treatment with lovastatin resulted in proportional decreases in plasma PAF-AH activity and LDL-C concentrations. To further elucidate the relationship between PAF-AH and plasma concentrations of LDL, plasma PAF-AH activity was measured in families with well-defined, monogenic disorders of LDL metabolism. Plasma PAF-AH activity cosegregated with plasma LDL-C concentrations in familial hypercholesterolemia, but not in familial hypobetalipoproteinemia. We speculate that the rate of removal of LDL from the circulation may determine the clearance rate of PAF-AH, thereby modulating the activity of PAF-AH in blood.