Homozygosity mapping, to chromosome 11p, of the gene for familial persistent hyperinsulinemic hypoglycemia of infancy

Familial persistent hyperinsulinemic hypoglycemia of infancy (PHHI) is a rare, autosomal recessive disease of unregulated insulin secretion, defined by elevations in serum insulin despite severe hypoglycemia. We used the homozygosity gene-mapping strategy to localize this disorder to the region of chromosome 11p between markers D11S1334 and D11S899 (maximum LOD score 5.02 [theta = 0] at marker D11S926) in five consanguineous families of Saudi Arabian origin. These results extend those of a recent report that also placed PHHI on chromosome 11p, between markers D11S926 and D11S928. Comparison of the boundaries of these two overlapping regions allows the PHHI locus to be assigned to the 4-cM region between the markers D11S926 and D11S899. Identification of this gene may allow a better understanding of other disorders of glucose homeostasis, by providing insight into the regulation of insulin release.

The effect of variation in the apolipoprotein B gene on plasmid lipid and apolipoprotein B levels. I. A likelihood-based approach to cladistic analysis

A new method is described for employing family data to test for significant haplotype effects on continuously distributed variables, using likelihood-ratio tests of linear models in which haplotype effects are parameterized and familial correlations taken into account. The method is applied to the apolipoprotein B (Apo B) gene, using 5 polymorphisms (Insertion/deletion, Bsp1286I, XbaI, MspI, EcoRI) to define haplotypes in 121 French nuclear families. Eleven haplotypes were found, five of which, combined, account for over 95% of the sample. A haplotype phylogeny is proposed, and is used to define a nested set of models for testing the effects of Apo B variation on total-, low-density-lipoprotein (LDL)-, and high-density-lipoprotein (HDL)-cholesterol, triglyceride, and Apo B levels. Apo B haplotype effects account for about 10% of the genetic variance and 5% of the total variance in HDL-cholesterol and triglyceride levels. Clusters of evolutionarily-related haplotypes with similar phenotypic effects are identified for HDL-cholesterol and triglycerides. Single haplotypes with statistically significant effects are identified for cholesterol, LDL-cholesterol, and Apo B levels.

The apolipoprotein E polymorphism: a comparison of allele frequencies and effects in nine populations

Application of uniform methods for measuring the apolipoprotein (apo) E polymorphism and plasma cholesterol levels in nine populations (Tyrolean, Sudanese, Indian, Chinese, Japanese, Hungarian, Icelandic, Finnish, and Malay) revealed significant heterogeneity among them in apo E type frequencies and mean cholesterol levels. The major apo E types in all populations were E3/2 (frequency range from 7.0% in Indians to 16.9% in Malays), E3/3 (frequency range from 39.8% in Sudanese to 72.1% in Japanese), and E3/4 (frequency range from 11.3% in Japanese to 35.9% in Sudanese). Mean cholesterol levels ranged from 144.2 mg/dl in the Sudanese to 228.5 mg/dl in the Icelandics. Two-way analysis of variance of the effect of population and apo E type on cholesterol levels showed no significantly interaction effect, indicating that the effects of apo E type on cholesterol levels do not differ significantly among the populations. The overall average excess for the epsilon 2 allele was -14.12 mg/dl (range -31.63 to -8.82 mg/dl); for the epsilon 3 allele, 0.04 mg/dl (range -1.87 to 1.58 mg/dl; and for the epsilon 4 allele, 8.14 mg/dl (range -1.71 to 13.31 mg/dl). Despite the apparent heterogeneity in these values, especially for the epsilon 4 allele, comparison of the average excesses by a method of repeated sampling with random permutations revealed no significant difference in effects among populations. These data indicate that a given apo E allele acts in a relatively uniform manner in different populations despite differences in genetic background and environmental factors.

Effects of the apolipoprotein(a) size polymorphism on the lipoprotein(a) concentration in 7 ethnic groups

Apolipoprotein(a) [apo(a)] exhibits a genetic size polymorphism explaining about 40% of the variability in lipoprotein(a) [Lp(a)] concentration in Tyroleans. Lp(a) concentrations and apo(a) phenotypes were determined in 7 ethnic groups (Tyrolean, Icelandic, Hungarian, Malay, Chinese, Indian, Black Sudanese) and the effects of the apo(a) size polymorphism on Lp(a) levels were estimated in each group. Average Lp(a) concentrations were highly significantly different among these populations, with the Chinese (7.0 mg/dl) having the lowest and the Sudanese (46 mg/dl) the highest levels. Apo(a) phenotype and derived apo(a) allele frequencies were also significantly different among the populations. Apo(a) isoform effects on Lp(a) levels were not significantly different among populations. Lp(a) levels were however roughly twice as high in the same phenotypes in the Indians, and several times as high in the Sudanese, compared with Caucasians. The size variation of apo(a) explains from 0.77 (Malays) to only 0.19 (Sudanese) of the total variability in Lp(a) levels. Together these data show (I) that there is considerable heterogeneity of the Lp(a) polymorphism among populations, (II) that differences in apo(a) allele frequencies alone do not explain the differences in Lp(a) levels among populations and (III) that in some populations, e.g. Sudanese Blacks, Lp(a) levels are mainly determined by factors that are different from the apo(a) size polymorphism.