Prenatal diagnosis for fetus with hemophilia A / 中华妇产科杂志

Objective To study the prenatal genetic diagnostic methods for hemophilia A fetus.Methods From 2002 to 2006,19 hemophilia A families were diagnosed either by long distance-polymerase chain reaction(LD-PCR)for factor Ⅷ intron 22 inversion or by the DNA polymorphism genetic linkage analysis of factorⅧin the Beijing Chaoyang Hospital.Results (1)Totally 19 women,with 22pregnancies received the prenatal diagnosis of fetal hemophilia A.The average week at diagnosis was 23(17-34)weeks.All the direct fetal blood sampling(DFBS)were successful.There was no fetal-loss caused by the procedures.(2)Of the 19 hemophilia A families,14 appeared to be factorⅧintron 22inversion,in which 16 prenatal diagnoses were done,10 fetuses were diagnosed as genetical hemophilia A patients,and 6 fetuses were normal.(3)Using combined polymorphism genetic linkage analysis 6 prenatal diagnoses were done,including one woman's two pregnancies,in which both her fetuses were diagnosed as genetical hemophilia A patients.(4)Factor Ⅷ levels of 16 fetuses were measured,and 6 fetuses were unmeasured either because the pregnancy weeks were lower than 20 weeks or the parents refused.Factor Ⅷlevel ranged from 0 to 198%.There were 11 fetuses whose factor Ⅷ levels were lower than 10%.Ten of them were diagnosed to be genetical hemophilia A patients,and in only one boy the factorⅧlevel was 2%,but the genetic diagnosis was normal and for one year's follow up he was doing normal.Conclusion LDPCR combined with polymorphism genetic linkage analysis enables a quick and correct detection ofhemophilia A carrier.For a carrier pregnancy.prenatal diagnosis could be done for the male fetus.Factor Ⅷ deficiency of the fetus could help make the diagnosis but the final diagnosis should be based on genetic evidence.

Detection of homozygous and heterozygous SMN deletions of spinal muscular atrophy in a single assay with multiplex ligation-dependent probe amplification / 北京大学学报(医学版)

Objective: Spinal muscular atrophy(SMA), an autosomal recessive neuromuscular degeneration of the anterior horn cells of the spinal cord and brain stem, results in one of the most common diseases with muscle fatigue and atrophy. Most SMA cases including all the types are due to the homozygous deletion of at least exon 7 within the survival motor neuron 1 (SMN-1) gene. Although a "golden standard" assay (PCR with mismatch primer followed by enzyme digestion) is very reliable for the identification of homozygous SMN-1 deletion, the carrier detection of heterozygous SMN-1 deletion remains a challenge. Methods: Some PCR-based gene dosage assays or multiplex PCR allow for the determination of the copy number of SMN-1 gene to identify heterozygous deletion, but these procedures are often time consuming and available on a limited clinical basis. Recently developed MLPA (multiplex ligation-dependent probe amplification) is an efficient procedure that can accurately analyze relative quantification to establish the copy number of the SMN gene. We performed a validation for simultaneous detection of homozygous SMN-1 deletions of SMA patients and heterozygous SMN-1 deletions of SMA carriers in a simple assay using a MLPA-SMA assay specific reagent. Results: Six out of 20 patients with SMA were found to have homozygous SMN-1 deletion, confirmed by the PCR/digestion assay. All 4 parents of the children with SMA had heterozygous SMN-1 deletion, confirmed by an independent relative quantitative analysis. Conclusion: MLPA provides a simple, rapid and accurate method of simultaneously detecting homozygous deletions and heterozygous deletions in a single assay for both SMN-1 and SMN-2 genes.

Single cell four-plex nested fluorescent PCR for hemophilia A genetic diagnosis and gender determination / 中华检验医学杂志

Objective To develop a rapid and efficient single cell PCR method for the non-invasive prenatal hemophilia A genetic diagnosis.Methods Six STR markers (DXS15,DXS9901,G6PD, DXS1073,DXS1108 and F8Civsl3) closely linked to F Ⅷ gene were examined in 118 healthy individuals and 12 hemophilia A families by muhi-plex fluorescent PCR.Three markers with the higher heterozygote rate and diagnostic rate were chosen and combined with amelogenin gene to establish the four-plex nested fluorescent PCR on single lymphocyte level.Results The single lymphocyte amplification rates of Amelogenin,DXS15,FSCivsl3 and DXSI073 were 94.3%,91.4%,100% and 100% in the normal male,and 100% ,97.1% ,97.1% and 97.1% in the normal female's respectively.The female was heterozygous in DXS1073 and DXS15.However,no allele dropout was found in both markers.Neither the false negative nor the false positive amplification was observed.Conclusion The single cell four-plex nested fluorescent PCR method established in this study is convenient and efficient,and will be hopefully employed in the clinical non-invasive prenatal genetic diagnosis for hemophilia A.

De novo mutations in sporadic deletional Duchenne muscular dystrophy (DMD) cases

Dinucleotide repeat polymorphism based genetic analysis is a powerful approach to gain insight into rare genetic events like germline mosaicism and de novo mutations. The loss of heterozygosity of polymorphic dinucleotide loci at "deletional hotspot" of dystrophin gene can provide direct evidence of carrier status in female relatives of affected DMD patients with overlapped exonic deletions. We have used 4 STR loci of the central deletional hotspot of the dystrophin gene for genetic analysis in sporadic unrelated DMD families. Twenty-nine mothers of sporadic deletional cases were analysed and their carrier status was determined. Eighteen of them showed heterozygosity in the deleted loci suggesting the occurrence of de novo mutations. In 9 cases, the carrier status was indeterminate while 2 showed germline mosaicism. Our observations reiterated the importance of STR analysis in determining the status of mothers of sporadic deletional DMD cases in order to provide proper genetic counselling.