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.     

Effects of copper on A-type potassium currents in acutely dissociated rat hippocampal CA1 neurons

The effects of copper on voltage-gated A-type potassium currents were investigated in acutely dissociated rat hippocampal CA1 neurons using the whole-cell patch-clamp technique. Extracellular application of various concentrations of copper (1-1000 microM) reversibly reduced the amplitude of voltage-gated A-type potassium currents in a dose-dependent manner with a 50% inhibitory concentration value of 130 microM. Copper (300 microM) increased the V1/2 of the activation curve and state-inactivation curve by 17.2 and 9.0 mV, respectively. Thus, copper slowed down the activation and inactivation process of voltage-gated A-type potassium currents. This study indicated that copper reversibly inhibits the hippocampal CA1 neuronal voltage-gated A-type potassium current in a dose-dependent and voltage-dependent manner, and such actions are likely involved in the regulation of the neuronal excitability and the pathophysiology of Wilson's disease.     

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.     

Rett综合征的临床特征及MeCP2的基因型与表型的关系研究

目的 总结Rett综合征(RTT)的临床特点,探讨甲基化CpG结合蛋白2(MeCP2)基因突变型与表型的关系。方法 北京大学第一医院儿科1987年以来诊断的RTT66例,每1～2年对本组患儿进行1次临床随访,并观察左旋肉碱的治疗反应。应用PCR、测序方法对39例患儿进行突变基因分析。结果 患儿3～38个月起病,59例(89％)患儿于7个月～6岁丧失手的功能,66例(100％)患儿1—5岁出现手的刻板动作,56例(85％)患儿11个月～8岁语言完全丧失,21％的患儿于2岁9个月～15岁丧失原已获得的行走能力。头围小、惊厥、呼吸节律异常、咬牙、脊柱侧凸或后凸均很常见。左旋肉碱治疗17例,8周后6例症状改善。39例进行．MeCP2基因分析者中有25例(64％)发现突变,其中2例无义突变C502T(氨基酸改变R168X)患儿均死亡,2例C397T(氨基酸改变R133C)和1例A398T(氨基酸改变R133H)突变者均保留语言。结论 RTI。特征性的表现为头围增长缓慢,手的失用与刻板动作,语言倒退,左旋肉碱可以改善部分患儿的临床症状。MeCP2基因型与表型之间有一定的相关性。     

Prenatal exposure to high level of glucocorticoids increases the susceptibility of renal proximal tubular cells to apoptosis induced by uropathogenic Escherichia coli toxins

Prenatal exposure to excessive glucocorticoids may alter the developing fetus inducing metabolic and endocrine imbalance in various organs, including the kidney. This study aimed at evaluating whether prenatal exposure to high levels of glucocorticoids adversely affects renal cell survival and predisposes to renal cell death. Pregnant rats were injected with 0.1 mg/kg dexamethasone (DEX) i.p. from day 1 of gestation. Renal proximal tubular cells (PTCs) were prepared from 20-day-old offspring in the DEX (DEX cells) and control groups (CON cells). After 4 days' culture, cells were exposed to uropathogenic Escherichia coli ARD6 toxins at concentrations known to induce apoptotic cell death. We found that cell death rate was significantly higher in DEX than in CON cells. Cells exhibited morphological and biochemical features of apoptosis. Conversely, the activity of the antioxidant enzyme catalase was significantly increased in renal cortex homogenate from 20-day-old DEX rats. The antioxidant vitamin E did not prevent apoptosis. These results indicate that prenatal exposure to high levels of glucocorticoids induces alterations in renal PTCs rendering them more sensitive to E. coli toxins via nonoxidative stress. With the increasing use of multiple doses of glucocorticoids in preterm infants, the possibility that antenatal glucocorticoids may lead to renal adverse consequences is of clinical relevance.     

46,XX sex reversal with partial duplication of chromosome arm 22q

We present a case of 46,XX sex reversal in the absence of SRY but with partial duplication of chromosome 22q. The subject had multiple congenital anomalies but nearly complete masculinization of the external genitalia. Our case along with a previous case supports the existence of a gene on chromosome 22q that can trigger testis determination in the absence of SRY. We proposed that overexpression of the SOX10 gene at 22q13 might be the cause of sex reversal. We investigated 13 additional subjects with SRY-negative 46,XX sex reversal for microduplication of chromosome arm 22q in the region of SOX10 gene, but could not find evidence for it.