Conservation of the RB1 gene in human and primates

Mutations in the RB1 gene are associated with retinoblastoma, which has served as an important model for understanding hereditary predisposition to cancer. Despite the great scrutiny that RB1 has enjoyed as the prototypical tumor suppressor gene, it has never been the object of a comprehensive survey of sequence variation in diverse human populations and primates. Therefore, we analyzed the coding (2,787 bp) and adjacent intronic and untranslated (7,313 bp) sequences of RB1 in 137 individuals from a wide range of ethnicities, including 19 Asian Indian hereditary retinoblastoma cases, and five primate species. Aside from nine apparently disease-associated mutations, 52 variants were identified. They included six singleton, coding variants that comprised five amino acid replacements and one silent site. Nucleotide diversity of the coding region (pi=0.0763+/-1.35 x 10(-4)) was 52 times lower than that of the noncoding regions (pi=3.93+/-5.26 x 10(-4)), indicative of significant sequence conservation. The occurrence of purifying selection was corroborated by phylogeny-based maximum likelihood analysis of the RB1 sequences of human and five primates, which yielded an estimated ratio of replacement to silent substitutions (omega) of 0.095 across all lineages. RB1 displayed extensive linkage disequilibrium over 174 kb, and only four unique recombination events, two in Africa and one each in Europe and Southwest Asia, were observed. Using a parsimony approach, 15 haplotypes could be inferred. Ten were found in Africa, though only 12.4% of the 274 chromosomes screened were of African origin. In non-Africans, a single haplotype accounted for from 63 to 84% of all chromosomes, most likely the consequence of natural selection and a significant bottleneck in effective population size during the colonization of the non-African continents.     

Meconium-stained liquor during labor is associated with raised neonatal cord blood 8-iso-prostaglandin F2alpha concentration

OBJECTIVE: The purpose of this study was to compare the umbilical arterial 8-iso-prostaglandin F2alpha, concentrations between pregnancies that were complicated by moderate or thick meconium-stained liquor and those with clear liquor. STUDY DESIGN: Umbilical cord arterial blood samples were collected from 247 singleton pregnancies with either moderate or thick meconium-stained liquor at any stage of labor or clear liquor at all stages of labor for the determination of the total 8-iso-prostaglandins F2alpha concentration. RESULTS: The median total 8-iso-prostaglandins F2alpha concentration of the meconium-stained liquor group was significantly higher than that of the control group (719.2 vs 115.8 pg/mL). Among the meconium-stained liquor group, those who had a change from "clear liquor" at early labor to "moderate/ thick meconium-stained liquor" at late first stage or at delivery (late meconium-stained liquor group) had higher 8-iso-prostaglandins F2alpha concentration, compared with those who had moderate/ thick meconium-stained liquor since early labor (early meconium-stained liquor group; 959.8 vs 499.9 pg/mL). With the use of multiple regression analysis, meconium-stained liquor, duration of second stage of labor, and abnormal fetal heart tracings were independent determinants of cord blood 8-iso-prostaglandins F2alpha concentration. CONCLUSION: Moderate or thick meconium-stained liquor is an independent factor for increased oxidative stress in pregnancy.     

ABCD1 gene mutations in Chinese patients with X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy is a neurodegenerative disorder caused by mutations in the adrenoleukodystrophy (ALD) protein gene ABCD1. This study used direct sequencing of genomic polymerase chain reaction products to perform mutational analysis of ABCD1 in 34 unrelated Chinese X-linked adrenoleukodystrophy patients and 27 of their maternal relatives. Thirty-two different mutations were identified in 34 patients. Most of the mutations (62.5%, 20/32) were missense mutations, six of which are novel. One novel single nucleotide polymorphism, c.1047 C>A, was also found in three patients and their mothers, which can also be observed in 1 of 120 normal control alleles. Two synonymous mutations (p.L516L and p.V349V) appeared in two unrelated patients, and no other mutations were evident after screening the gene's 10 exons. Seventeen of the probands' mothers were found to be heterozygous for the same mutations present in their sons' ABCD1 gene. Eight of the 10 screened sisters and cousins were identified as carriers. There were no hot spot mutations in the ABCD1 gene of Chinese patients with X-linked adrenoleukodystrophy. However, over half of the mutations (19/34) were located in exon 1 and exon 6, suggesting possible hot exons. No obvious relationship between genotype and phenotype was observed.