Molecular prenatal diagnosis: the impact of modern technologies

Originally prenatal diagnosis was confined to the diagnosis of metabolic disorders and depended on assaying enzyme levels in amniotic fluid. With the development of recombinant DNA technology, molecular diagnosis became possible for some genetic conditions late in the 1970s. Here we briefly review the history of molecular prenatal diagnostic testing, using Duchenne muscular dystrophy as an example, and describe how over the last 30 years we have moved from offering testing to a few affected individuals using techniques, such as Southern blotting to identify deletions, to more rapid and accurate PCR-based testing which identifies the precise change in dystrophin for a greater number of families. We discuss the potential for safer, earlier prenatal genetic diagnosis using cell free fetal DNA in maternal blood before concluding by speculating on how more recent techniques, such as next generation sequencing, might further impact on the potential for molecular prenatal testing. Progress is not without its challenges, and as cytogenetics and molecular genetics begin to unite into one, we foresee the main challenge will not be in identifying the genetic change, but rather in interpreting its significance, particularly in the prenatal setting where we frequently have no phenotype on which to base interpretation. Copyright © 2010 John Wiley & Sons, Ltd.     

DNA同源性分析最终确定新疆中华根瘤菌（Sinorhizobium xinjiangensis）为一独立种

针对S.xinjiangensis分类地位的争议,从新疆再次分离获得34株快生大豆根瘤菌,在16SrDNAPCR-RFLP分析和SDS全细胞蛋白电泳分群的基础上,进行了16SrDNA全序列相似性和DNA同源性分析.所测4个菌株和S.fredii模式菌株USDA205的16SrDNA全序列有很高的相似性.而DNA同源性分析说明新分离的菌株代表与原定的S.xinjiangensis为一个DNA同源群.其模式菌株CCBAU110与S.fredii的2株参比菌株USDA194、2048之间的DNA同源性分别为31.5%和28.7%.S.fredii的模式菌株USDA205与新分离的菌株代表及原定的S.xinjiangensis的模式菌株和2个参比菌株之间的DNA同源性为20.8%～39%,远低于70%.属于种水平上的差异.按照国际细菌分类委员会以DNA同源性≥70%且△Tm≤5℃作为定种的标准,S.xinjiangensis是Sinorhizobium属中不同于S.fredii的一个独立的种.表3参20     

First-trimester prenatal diagnosis of severe alpha-thalassemia

By means of chorion biopsy together with restriction endonuclease analysis of fetal DNA, first trimester diagnoses were successfully made in 33 fetuses at risk for Bart's hydrops fetalis. Seven pregnancies with Hb H or hydrops fetalis were therapeutically terminated before 4 months of gestation. Of the 26 pregnancies intended to continue, 18 have come to term with normal deliveries; one with threatened abortion was terminated at the end of the first trimester and, seven are progresssing normally.     

Prenatal detection of fetal hemoglobin E gene from maternal plasma

In order to provide a noninvasive prenatal diagnosis of the hemoglobin E (Hb E) related disorder, we have evaluated the possibility of identifying the fetal β^E-globin gene in maternal plasma. The analysis was performed during 8 to 18 weeks of gestation using DNA extracted from 200 µL of plasma from pregnant women whose husbands carried Hb E. The β^E-globin mutation in maternal plasma was detected by a nested PCR amplification followed by the Mnl I restriction analysis. The result was compared with that of routine analysis of the CVS specimens. Among the five pregnant women examined, the fetal β^E-globin gene was identified in maternal plasma in three of them and the result was completely concordant with the conventional CVS analysis. This simple noninvasive prenatal detection of the fetal β^E-globin gene should prove useful in a prevention and control program of Hb E/β-thalassemia in countries where the β^E-globin gene is prevalent. Copyright © 2003 John Wiley & Sons, Ltd.     

Paternal expenditure is related to brood sex ratio in polygynous great reed warblers

In many polygynous animals, parents invest more heavily in individual sons than in daughters. However, it is unclear if these differences in investment are a consequence of sex differences in the demand of offspring related to sexual size dimorphism or a consequence of parental manipulation. Here, we report on parental food delivery frequency in relation to brood size and brood sex ratio in a wild population of polygynous great reed warblers Acrocephalus arundinaceus. We used the polymorphic microsatellite loci on the Z chromosome to sex chicks. We found that paternal feeding frequency (times/h per nest) increased not with brood size, but with the proportion of males in the brood, although the demand per nest was more closely related to brood size than to brood sex ratio. Additionally, the increase in rate of paternal feeding frequency in relation to the brood sex ratio was much higher than the increase in rate of nestling food demands. Maternal feeding frequency was independent of both brood size and brood sex ratio. These results strongly suggest that fathers preferentially invest in their sons. We propose that parents can afford sex-biased parental care in animals in which food provisioning is enough for all offspring to survive. Received: 22 January 1996/Accepted after revision: 30 June 1996     

Extra-pair paternity in willow ptarmigan broods: measuring costs of polygyny to males

Willow ptarmigan are one of only three monogamous grouse species in North America. However, in some populations between 5 and 20% of individuals pair polygynously. It has been suggested that monogamy may be maintained by the high cost of polygyny to males. We have used DNA fingerprinting to assess the actual reproductive success of both monogamous and polygynous adults. We determined whether or not the putative parents were the biological parents of the chicks from 38 broods. Of these clutches 30 were from monogamous matings, and 8 were from bigamous matings. Of the 207 chicks from monogamous matings 96% were within-pair offspring, compared to 67% of the 49 chicks from bigamous matings. All extra-pair offspring chicks resulted from extra-pair fertilizations (EPFs), and there were no instances of intraspecific nest parasitism. Mate guarding by monogamous males seems to be a highly effective method for maintaining genetic monogamy, as the only cases in which EPFs occurred were when the resident female left the territory for a few days or when a second female visited the territory. Our results support the notion that certainty of parentage may be one factor constraining willow ptarmigan males to be monogamous.     

Prenatal diagnosis of Fukuyama congenital muscular dystrophy

Fukuyama congenital muscular dystrophy (FCMD) is characterized by infantile hypotonia, symmetrical generalized muscle weakness, and neuronal migration disturbances that result in changes consistent with cobblestone lissencephaly with cerebral and cerebellar cortical dysplasia. FCMD is recognized as an autosomal recessive genetic defect. Genetic counselling is recommended for parents at risk of having a child with FCMD. Given the high risk and overwhelming prospect of having another child with this incurable devastating condition leads many couples to consider prenatal diagnosis. In Japanese families, haplotype analysis using microsatellite markers is available. In non-Japanese families, DNA sequence analysis is available. Both disease-causing alleles of an affected family member must be identified before prenatal testing can be performed. Copyright © 2006 John Wiley & Sons, Ltd.