Rate of evolutionary change in cranial morphology of the marsupial genus Monodelphis is constrained by the availability of additive genetic variation.

We tested the hypothesis that the rate of marsupial cranial evolution is dependent on the distribution of genetic variation in multivariate space. To do so, we carried out a genetic analysis of cranial morphological variation in laboratory strains of Monodelphis domestica and used estimates of genetic covariation to analyse the morphological diversification of the Monodelphis brevicaudata species group. We found that within-species genetic variation is concentrated in only a few axes of the morphospace and that this strong genetic covariation influenced the rate of morphological diversification of the brevicaudata group, with between-species divergence occurring fastest when occurring along the genetic line of least resistance. Accounting for the geometric distribution of genetic variation also increased our ability to detect the selective regimen underlying species diversification, with several instances of selection only being detected when genetic covariances were taken into account. Therefore, this work directly links patterns of genetic covariation among traits to macroevolutionary patterns of morphological divergence. Our findings also suggest that the limited distribution of Monodelphis species in morphospace is the result of a complex interplay between the limited dimensionality of available genetic variation and strong stabilizing selection along two major axes of genetic variation.

SPARC/osteonectin, an endogenous mechanism for targeting albumin to the blood-cerebrospinal fluid interface during brain development.

Specialized populations of choroid plexus epithelial cells have previously been shown to be responsible for the transfer of individual plasma proteins from blood to the cerebrospinal fluid (CSF), contributing to their characteristically high concentrations in CSF of the developing brain. The mechanism of this protein transfer remains elusive. Using a marsupial, Monodelphis domestica, we demonstrate that the albumin-binding protein SPARC (osteonectin/BM-40/culture-shock protein) is present in a subset of choroid plexus epithelial cells from its first appearance, throughout development, and into adulthood. The synthesis of SPARC by the lateral ventricular plexus was confirmed with real-time PCR. The expression level of SPARC was higher in plexuses of younger than older animals. Western blot analysis of the gene product confirmed the quantitative PCR results. The co-localization of SPARC and albumin shown by immunocytochemistry and its cellular location indicate that this glycoprotein may act as a recognition site for albumin. In addition, the numbers of SPARC-immunopositive cells and its expression were responsive to experimental changes of albumin concentration in the blood. It is suggested that SPARC may be one of the molecules that govern the uptake and delivery of proteins from blood to the CSF. The results also confirm that protein transfer across the blood-CSF barrier is developmentally and physiologically regulated.

Modification of protein transfer across blood/cerebrospinal fluid barrier in response to altered plasma protein composition during development.

A developmentally regulated protein-specific transfer mechanism across choroid plexus epithelial cells has previously been proposed to contribute to the characteristically high concentration of protein in cerebrospinal fluid (CSF) in the immature brain. Here we demonstrate that this mechanism is sensitive to protein variations in plasma resulting in changed numbers of transferring cells for individual proteins and altered transfer into the CSF. Pups of Monodelphis domestica at postnatal day (P)9, P65 and P110 were injected intraperitoneally with either adult Monodelphis plasma or exogenous bovine fetuin. Samples of CSF, blood and brain were collected from terminally anaesthetized animals 3-48 h later. The concentration of total protein was measured and levels of albumin, hemopexin, α-fetoprotein and bovine fetuin were estimated by western blotting. Numbers of lateral ventricular choroid plexus cells positive for total and individual plasma proteins were counted in paraffin sections of brains stained with appropriate antibodies. Following intraperitoneal injections, the content of proteins in the CSF increased at all three ages, but the concentration increased only in the CSF of older animals. The total numbers of plexus cells positive for plasma protein did not change significantly, but cells positive for individual proteins did. Fetuin was detected in all protein-positive cells, but apparently displaced α-fetoprotein and, to a lesser degree, hemopexin. The results indicate that protein transfer across the blood/CSF barrier appears to be regulated by a molecular recognition mechanism that is probably saturable but may not be as specific for individual proteins as previously suggested.

Determinants of variation in human serum paraoxonase activity.

Paraoxonase-1 (PON1) is associated with high-density lipoprotein (HDL) particles and is believed to contribute to antiatherogenic properties of HDLs. We assessed the determinants of PON1 activity variation using different substrates of the enzyme. PON1 activity in serum samples from 922 participants in the San Antonio Family Heart Study was assayed using a reliable microplate format with three substrates: paraoxon, phenyl acetate and the lactone dihydrocoumarin. There were major differences among results from the three substrates in degree of effect by various environmental and genetic factors, suggesting that knowledge of one substrate activity alone may not provide a complete sense of PON1 metabolism. Three significant demographic covariates (age, smoking status and contraceptive usage) together explained 1-6% of phenotypic variance, whereas four metabolic covariates representing lipoprotein metabolism (apoAII, apoAI, triglycerides and non-HDL cholesterol) explained 4-19%. Genes explained 65-92% of phenotypic variance and the dominant genetic effect was exerted by a locus mapping at or near the protein structural locus (PON1) on chromosome 7. Additional genes influencing PON1 activity were localized to chromosomes 3 and 14. Our study identified environmental and genetic determinants of PON1 activity that accounted for 88-97% of total phenotypic variance, suggesting that few, if any, major biological determinants are unrepresented in the models.

Genetics of variation in adiponectin in pedigreed baboons: evidence for pleiotropic effects on adipocyte volume and serum adiponectin.

To detect and localize the effects of genes influencing variation in adiponectin mRNA and protein levels, we conducted statistical genetic analyses of circulating concentrations of adiponectin and adiponectin (ADIPOQ) mRNA expression in omental adipose tissue in adult, pedigreed baboons (Papio anubis). An omental adipose tissue biopsy and blood sample were collected from 427 baboons from the colony at the Southwest Foundation for Biomedical Research, San Antonio, TX. Total RNA was isolated from adipose tissue and adiponectin mRNA levels were assayed by real-time, quantitative reverse transcriptase-PCR. Adiponectin, insulin, glucose, cholesterol, high-density lipoproteins and triglycerides were measured in fasting serum. Quantitative genetic analyses were conducted for adiponectin mRNA and serum protein using a maximum likelihood-based variance decomposition approach. A genome-wide linkage analysis was conducted using adiponectin mRNA and protein levels as phenotypes. Significant heritability was estimated for ADIPOQ mRNA levels (h2=0.19+/-0.07, P=0.01) and protein levels (h2=0.28+/-0.14, P=0.003). Genetic correlations were found between adiponectin protein and body weight (rho(G)=-0.51, P=0.03), cell volume (rho(G)=-0.73, P=0.04), serum triglycerides (rho(G)=-0.67, P=0.03), and between adiponectin mRNA and glucose (rho(G)=0.93, P<0.01). A logarithm of odds score of 2.9 was found for ADIPOQ mRNA levels on baboon chromosome 4p, which is orthologous to human 6p21. There is a significant genetic component affecting variation in the analyzed traits, and common genes may be influencing adiponectin expression, adipocyte volume, body weight and circulating triglycerides. The region on 6p21 has been linked to diabetes-related phenotypes in human studies.

Cardiac beta myosin heavy chain diversity in normal and chronically hypertensive baboons.

We have identified two distinct beta-myosin heavy chains (MHCs) present in baboon myocardium by electrophoresis in gradient pore gels and by Western blots with anti-MHC MAb. The two beta-MHCs have molecular masses of 210 and 200 kD and share several antigenic determinants including an epitope recognized by a beta-MHC-specific MAb. A fivefold increase in the level of the 200-kD beta-MHC was observed in the hypertrophied left ventricles of baboons with chronic (5.3 +/- 0.7 yr) renal hypertension. A 60% increase (P less than 0.01) in BP and a 100% increase (P less than 0.001) in left ventricular mass to body weight ratio occurred in hypertensive baboons compared with normotensive animals. The Ca2+-activated myosin ATPase activity in hypertrophied left ventricles was decreased by 35% (P less than 0.05) compared with controls. Normal levels of the 200-kD MHC were detected in the right ventricles and intraventricular septa of the hypertensive animals. These data suggest that cardiac MHCs of primates may exist in alternative molecular forms that are indistinguishable by nondenaturing gel electrophoresis and that increased concentration of a second beta-MHC is associated with ventricular hypertrophy (r = 0.55). The functional significance and mechanisms that control the concentration of beta-MHC subspecies remain to be determined.

Electrocardiographic characteristics in a population with high rates of seropositivity for Trypanosoma cruzi infection.

This study was conducted in Posse, a rural community in Goiàs, Brazil. Persons were recruited into the study through house-to-house sampling of all houses in the sampled area. Blood samples were collected for seropositivity assessments for Trypanosoma cruzi and an electrocardiogram was assessed using a portable system. The results demonstrate significant differences between seropositive and seronegative persons for electrocardiographic (ECG)-derived traits. Seropositive persons had substantially longer QRS and QT intervals than seronegative persons. The PR interval was significantly different between seropositive and seronegative persons. Conduction abnormalities were observed more frequently in seropositive than seronegative persons. Right bundle branch block, an ECG abnormality typical of Chagas disease, was observed in 15% of seropositive persons compared with less than 1% of seronegative persons. Results indicate that T. cruzi infection and subsequent Chagas disease will continue to be major health problems for the foreseeable future in this typical rural area of Brazil.

Comparative analysis of cell phenotypes in different severe clinical forms of Chagas' disease.

The understanding of the role of the immune response in the development of gastrointestinal and cardio-digestive (CD) forms of Chagas disease has received little attention. In this paper, the commitment of each leukocyte population of peripheral blood to the production of IFN-gamma, TNF-alpha, IL-12, IL-4, IL-5 and IL-10 was studied in patients with the CD form of Chagas disease. The data show that cells from patients with the CD form of the disease have distinct cytokine profiles when compared with the other clinical forms of Chagas disease and suggest that eosinophils are the major source of cytokine production in this clinical entity. The data presented in this paper demonstrate that patients with CD form can be distinguished from patients with gastrointestinal or cardiac forms of the disease by the distinct cytokine profile of peripheral blood cells.

Linkage mapping and physical localization of the major histocompatibility complex region of the marsupial Monodelphis domestica.

We used genetic linkage mapping and fluorescence in situ hybridization (FISH) to conduct the first analysis of genic organization and chromosome localization of the major histocompatibility complex (MHC) of a marsupial, the gray, short-tailed opossum Monodelphis domestica. Family based linkage analyses of two M. domestica MHC Class I genes (UA1, UG) and three MHC Class II genes (DAB, DMA, and DMB) revealed that these genes were tightly linked and positioned in the central region of linkage group 3 (LG3). This cluster of MHC genes was physically mapped to the centromeric region of chromosome 2q by FISH using a BAC clone containing the UA1 gene. An interesting finding from the linkage analyses is that sex-specific recombination rates were virtually identical within the MHC region. This stands in stark contrast to the genome-wide situation, wherein males exhibit approximately twice as much recombination as females, and could have evolutionary implications for maintaining equality between males and females in the ability to generate haplotype diversity in this region. These analyses also showed that three non-MHC genes that flank the MHC region on human chromosome 6, myelin oligodendrocyte glycoprotein (MOG), bone morphogenetic protein 6 (BMP6), and prolactin (PRL), are split among two separate linkage groups (chromosomes) in M. domestica. Comparative analysis with eight other vertebrate species suggests strong conservation of the BMP6-PRL synteny among birds and mammals, although the BMP6-PRL-MHC-ME1 synteny is not conserved.

Malignant melanoma in ultraviolet irradiated laboratory opossums: initiation in suckling young, metastasis in adults, and xenograft behavior in nude mice.

Litters of suckling young of the laboratory opossum (Monodelphis domestica) were irradiated with UV light from sunlamps with a spectral emission peak at 302 nm (UVB) to induce melanocytic nevi. Total doses of 0.87-5.0 kJ/m2 were divided equally among up to 14 exposures during the 19 days from birth. Of 358 sucklings exposed, 217 survived to weaning, and 22 (10%) possessed a nevus when shaved and examined at or after weaning. Affected animals were then exposed 3 times/week to 125 J/m2 of UVB for up to 45 weeks to promote progression to malignancy. Nevi of 8 of the 20 chronically-exposed animals progressed to malignant melanoma with metastases to lymph node(s). Cell cultures were prepared from affected nodes to confirm that pigmented nodal cells were metastatic melanomas. One established cell line (TD15L) contained highly pigmented, dendritic, malignant melanoma cells. These cells, injected s.c. as xenogeneic grafts into athymic nude mice, remained viable in the subcutis and were moderately tumorigenic in the dermis. UVR exposure of Monodelphis sucklings is a novel, effective, and proficient way of initiating melanocytic lesions for studies on susceptibility and progression to melanoma, and the cell lines derived from these melanomas will provide promising new reagents for chemotherapy and immunotherapy investigations.

Dramatic differences in lipoprotein composition among gray short-tailed opossums (Monodelphis domestica) fed a high cholesterol/saturated fat diet.

Lipoproteins of gray short-tailed opossums (Monodelphis domestica) were characterized to determine the basis of differences among individuals in response to a challenge diet enriched in saturated fat and cholesterol. Animals were selected from two phenotypic groups (high and low plasma cholesterol response to the challenge diet). Half of the animals in each group were fed basal diet (8.1% fat and 0.04% cholesterol by weight), and the remainder were fed challenge diet (17.7% fat and 0.61% cholesterol). The plasma cholesterol values of both groups fed the basal diet and of low responders fed the challenge diet were similar. In addition, both very-low-density and low-density lipoproteins (VLDL+LDLs) and high-density lipoproteins (HDLs) were similar among these groups in density and in lipid and apolipoprotein compositions. In contrast, the high responders fed the challenge diet showed a 7-fold increase in total plasma cholesterol, which was primarily a consequence of increases in the VLDL+LDL cholesterol component defined by heparin-Mn precipitation. Moreover, the VLDL+LDLs were more heterogeneous and were characterized by decreased densities. The VLDL+LDLs of the high-responding group had higher levels of apolipoprotein (apo) B and apoE than the other groups. Plasma apoB concentrations estimated by dot blotting techniques increased by 3-fold, and apoE by 44-fold in the high responding group. Understanding the factor(s) mediating responder phenotype in this new model species will expand our knowledge of the regulation of lipemic response to diet.

Effects of NIDDM on lipoprotein(a) concentration and apolipoprotein(a) size.

We investigated the effects of non-insulin-dependent diabetes mellitus (NIDDM) on lipoprotein(a) (Lp[a]) and apolipoprotein(a) (apo[a]) in a population of Mexican-Americans. In plasma samples from 536 subjects, we measured Lp(a) concentrations, and we estimated apo(a) isoform sizes following immunostaining of plasma proteins resolved using sodium dodecyl sulfate electrophoresis. We identified 81 diabetic subjects who had 108 distinct apo(a) isoform bands. We then identified 81 nondiabetic subjects from the remainder who were closely matched for apo(a) phenotype (i.e., number and size of apo(a) isoform bands). As expected, the diabetic group had higher levels of glucose and insulin (both fasted and 2 h after glucose challenge) and triglycerides, and lower levels of high-density lipoprotein (HDL) cholesterol when compared with the matching nondiabetic group. Moreover, the diabetic group also had significantly lower Lp(a) concentrations than the nondiabetic subjects (10.6 vs. 13.6 mg/dl, P = 0.045) using a paired Student's t test. To detect the effects of diabetes on apo(a) size, we identified by pedigree analysis the nondiabetic family members who possessed alleles identical to those in the diabetic group. When we compared the average sizes for each allele, we found that apo(a) isoforms averaged 4.1 kDa larger in diabetic subjects than the genetically identical apo(a) measured in nondiabetic subjects (P = 0.044, n = 36 alleles). In summary, we have detected significant effects of NIDDM both on Lp(a) concentrations and on apo(a) size.

X-linked gene expression in the Virginia opossum: differences between the paternally derived Gpd and Pgk-A loci.

Expression of X-linked glucose-6-phosphate dehydrogenase (G6PD) and phosphoglycerate kinase-A (PGK-A) in the Virginia opossum (Didelphis virginiana) was studied electrophoretically in animals from natural populations and those produced through controlled laboratory crosses. Blood from most of the wild animals exhibited a common single-banded phenotype for both enzymes. Rare variant animals, regardless of sex, exhibited single-banded phenotypes different in mobility from the common mobility class of the respective enzyme. The laboratory crosses confirmed the allelic basis for the common and rare phenotypes. Transmission of PGK-A phenotypes followed the pattern of determinate (nonrandom) inactivation of the paternally derived Pgk-A allele, and transmission of G6PD also was consistent with this pattern. A survey of tissue-specific expression of G6PD phenotypes of heterozygous females revealed, in almost all tissues, three-banded patterns skewed in favor of the allele that was expressed in blood cells. Three-banded patterns were never observed in males or in putatively homozygous females. These patterns suggest simultaneous, but unequal, expression of the maternally and paternally derived Gpd alleles within individual cells (i.e., partial paternal allele expression). The absence of such partial expression was noted in a parallel survey of females heterozygous at the Pgk-A locus. Thus, it appears that Gpd and Pgk-A are X-linked in D. virginiana and subject to preferential paternal allele inactivation, but that dosage compensation may not be complete for all paternally derived X-linked genes. The data establish the similarity between the American and Australian marsupial patterns of X-linked gene regulation and, thus, support the hypothesis that this form of dosage compensation was present in the early marsupial lineage that gave rise to these modern marsupial divisions. In addition, the data provide the first documentation of the differential expression of two X-linked genes in a single marsupial species. Because of its combination of X-linked variation, high fecundity, and short generation time, D. virginiana is a unique model for pursuing questions about marsupial gene regulation that have been difficult to approach through studies of Australian species.

Genetic analysis of liver neuraminidase isozymes in Rattus norvegicus: independent control of NEU-1 and NEU-2 phenotypes.

Two recently identified isozymes of neuraminidase in rat liver were examined for transmission patterns and linkage relationships, and for variation among inbred strains. The isozymes, designated neuraminidase-1 (NEU-1) and neuraminidase-2 (NEU-2), exhibited no electrophoretic mobility variants among the 22 inbred strains examined, but did possess striking interstrain variation in activity phenotypes on electrophoretic gels. The results of a backcross analysis involving the KGH and ACP strains revealed that NEU-1 and NEU-2 phenotypes are independently controlled, each by a single autosomal locus with additively acting alleles. The two loci are unlinked to one another, but the gene controlling NEU-1 is tightly linked to RT1, the rat major histocompatibility complex. This gene is almost certainly identical to Neu-1, a gene identified previously through its effect on "total" activity levels of liver neuraminidase as determined by fluorometric assay of tissue homogenates. NEU-2 and the gene controlling its phenotype were not detected by the fluorometric technique. We designate the genes controlling the NEU-1 and NEU-2 phenotypes as Neu-1 and Neu-2, respectively. Data from this and other studies place Neu-1 between Glo-1 and dw-3. The location of Neu-2 is unknown.

Somatic expression and autosomal inheritance of phosphoglycerate kinase B in kangaroos.

The PGK-B isozyme, currently known as PGK-2 in the mouse nomenclature, is the predominant PGK isozyme in mammalian sperm. In many species it is detectable only in sperm, in spermatogenic testes and in epididymides containing sperm. In this paper, we provide evidence that some kangaroo species express low PGK-B activity in somatic tissues, in addition to high activity in testes. Three kangaroo species, M. rufogriseus, M. robustus and M. giganteus, exhibit polymorphism of PGK-B. Breeding data support the hypothesis of autosomal co-dominant inheritance, as is the case in mice. Population data for the three polymorphisms are discussed. PGK-B is not detectable in somatic tissues or spermatogenic testis extracts of monotreme mammals, birds or lizards; it is probably restricted to therian mammals.

A quantitative trait locus on chromosome 16q influences variation in plasma HDL-C levels in Mexican Americans.

OBJECTIVE: We conducted a whole-genome, multipoint linkage screen to localize a previously reported major locus accounting for 56% to 67% of the additive genetic effects on covariate-adjusted plasma HDL cholesterol (HDL-C) levels in Mexican Americans from the San Antonio Family Heart Study (SAFHS). METHODS AND RESULTS: After using complex segregation analysis to recover the major locus in 472 SAFHS participants from 10 genotyped families, we incorporated covariates required to detect that major locus, including plasma levels of triglycerides and apolipoprotein A-I, in a maximum-likelihood-based variance-components linkage screen. Only chromosome 16 exhibited convincing evidence for a quantitative trait locus (QTL), with a peak multipoint log of the odds (LOD)=3.73 (P=0.000034). Subsequent penetrance model-based linkage analysis, incorporating genotypes at the marker locus nearest the multipoint peak (D16S518) into the segregation model, detected linkage with the previously detected major locus (LOD=2.73, P=0.000642). Initial estimates place this QTL within a 15-cM region of chromosome 16q near the structural loci for lecithin:cholesterol acyltransferase (LCAT) and cholesteryl ester transfer protein (CETP). CONCLUSIONS: A QTL influencing plasma levels of HDL-C in Mexican Americans from San Antonio maps to a region of human chromosome 16q near LCAT and CETP.

Correlated expression of atrial myosin heavy chain and regulatory light chain isoforms with pressure overload hypertrophy in the non-human primate.

OBJECTIVE: The aim was to determine the extent to which myosin heavy chain and light chain isoform transitions in atrial myocardium are coordinately regulated under pathological conditions in tissue from normal baboons, hypertensive baboons with myocardial hypertrophy, and baboons in which hypertrophy had regressed. METHODS: Quantitative distributions of myosin heavy chain (MHC) and regulatory myosin light chain (MLC2) isoforms in atrial myocardium from 35 adult baboons were determined by electrophoresis under denaturing conditions and laser densitometry. RESULTS: A significant association was observed between the ratios of MHC and MLC2 isoforms in atrial myocardium (r = 0.73, p < 0.001, n = 69). Expressions of alpha MHC and atrial MLC2 (ALC2) isoforms were correlated in atrial myocardium, as were those of beta MHC and ventricular MLC2 (VLC2) isoforms. In a subset of baboons with experimentally induced renal hypertension (n = 12) both beta MHC and VLC2 isoforms were found at higher levels in left atria than were present in normotensive baboons (p = 0.006, n = 15). Left atria from hypertensive baboons with regressed LVH contained intermediate levels of both beta MHC and VLC2 isoforms. CONCLUSIONS: There is tight coupling between the expression of myosin subunit isoforms under pathological conditions from a primate species closely related to humans. The data suggest that the synthesis of these subunits of myosin may be coordinated at the molecular level.

Development in vitro of Marsupials: a comparative review of species and a timetable of cleavage and early blastocyst stages of development in Monodelphis domestica.

The development of marsupial oocytes and embryos in vitro is reviewed. Most stages of development have been cultured successfully, usually in a complex medium with added fetal calf serum. Simpler media without added serum have been developed for fertilization and cleavage in vitro. Culture systems have been established for oocyte maturation and fertilization in the grey short-tailed opossum and for cleavage from the zygote to the early expanding unilaminar blastocyst in a number of other marsupials. Survival in vitro of the unilaminar and early bilaminar blastocyst stages is limited in all species examined. In contrast, late bilaminar, trilaminar, embryonic and fetal stages develop at rates approximating those in vivo. More stages have been cultured successfully in Sminthopsis macroura than in any other species. It has been cultured from the late bilaminar blastocyst to within 18 h of birth. Stages of cleavage and unilaminar blastocyst formation of Monodelphis domestica timed by videotaping mating animals, proceeded at similar rates in vivo and in vitro. As in other marsupials, cleavage in this opossum is characterized by a polarized conceptus. This polarity is expressed in the distribution of organelles in the zygote and the localization of secretion of the extracellular matrix material into the cleavage cavity and of the initial cell-zona attachment. Because cell-cell adhesion follows cell-zona adhesion, a unilaminar blastocyst forms without the development of an intervening morula stage.

The baboon gene for apolipoprotein A-I: characterization of a cDNA clone and identification of DNA polymorphisms for genetic studies of cholesterol metabolism.

We have isolated and sequenced a baboon apolipoprotein A-I (ApoA-I) clone from a liver cDNA library using a human cDNA hybridization probe. This baboon cDNA contains the entire ApoA-I coding region (801 bp, 267 aa), a 3' untranslated region, and a poly(A)tail. Among comparisons with apoAI sequences from other species, the baboon cDNA is most similar to that of the cynomolgus macaque (99.2% homologous) and least similar to the rat sequence (72.6% homologous). A high frequency of nonsynonymous substitutions are observed by alignment of baboon and human apoAI cDNAs, but comparisons of hydrophilicity profiles show that protein structure is conserved by substitutions of aa with similar properties. A polymorphic PstI cleavage site was identified by Southern blot analysis and subsequently mapped to the 5' end of the baboon apoAI gene. To identify effects of apoAI allelic variation on cholesterol metabolism, we used immunoblotting to compare the distributions of ApoA-I among lipoprotein size classes in baboons from each genotype under basal and atherogenic diets. We observed an increase of ApoA-I in high density lipoprotein (size class 1) particles after atherogenic diets in homozygotes for one allele, as compared to slight decreases in the other genotypes.

Characterization of the genetic elements controlling lipoprotein(a) concentrations in Mexican Americans. Evidence for at least three controlling elements linked to LPA, the locus encoding apolipoprotein(a).

Analyses of 1163 samples from the San Antonio Family Heart Study revealed several elements of genetic control of lipoprotein(a) (Lp(a)) concentrations in Mexican Americans. Apolipoprotein(a) (apo(a)) isoform size variation was inversely related to Lp(a) concentrations and explained about 22% of total phenotypic variation. Segregation analyses suggested the existence of a major gene that influenced an additional 41% of total Lp(a) variation. A G-->A polymorphism in the LPA promoter was in strong disequilibrium with apo(a) isoform size, but did not contribute a significant amount of additional information about Lp(a) variation. However, about 25% of variation in Lp(a) concentrations was influenced by additive polygenic effects, which include the effects of null phenotype alleles. Altogether, these genetic components explained 89% of Lp(a) variation, similar to heritability estimates made in several other studies. Apo(a) size variation and the major gene (explaining a total of about 62% of Lp(a) variation) were linked to each other and, as expected, to the plasminogen locus. Thus, together with the well-established null phenotype allele, these different genetic factors represent at least three distinct elements of control exerted at the LPA locus, which encodes the apo(a) protein.