QF-PCR Examination of Parental and Meiotic Origin of Trisomy 21 in Central and Eastern Europe

Detection of paternal origin of fetal trisomy 21 in a pregnancy with isolated ventriculomegaly but without advanced parental age

OBJECTIVE

We present detection of paternal origin of fetal trisomy 21 in a pregnancy with isolated ventriculomegaly but without advanced parental age.

CASE REPORT

A 29-year-old pregnant woman was admitted to the hospital at 18 weeks of gestation for tocolytic treatment because of irregular uterine contractions. Her husband was 30 years old. The couple had a healthy daughter. Prenatal ultrasound incidentally found isolated ventriculomegaly, and subsequent amniocentesis revealed a karyotype of 47,XX,+21 in 20/20 colonies of cultured amniocytes. The pregnancy was terminated, and the fetus manifested characteristic craniofacial appearance of Down syndrome and hyposplastic middle phalanx of the fifth finger. Postnatal polymorphic DNA marker analysis on the DNAs extracted from the cord blood and parental bloods using quantitative fluorescent polymerase chain reaction (QF-PCR) showed a paternal origin of fetal trisomy 21. The father had a karyotype of 46, XY in 40/40 blood lymphocytes.

CONCLUSION

QF-PCR is useful for rapid confirmation of prenatally detected fetal trisomy 21 and determination of paternal origin of fetal trisomy 21 especially in pregnancies with fetal structural abnormalities but without advanced parental age.

Down syndrome: parental origin, recombination, and maternal age

The aims of the present study were to assess (1) the parental origin of trisomy 21 and the stage in which nondisjunction occurs and (2) the relationship between altered genetic recombination and maternal age as risk factors for trisomy 21. The study included 102 cases with Down syndrome from the Croatian population. Genotyping analyses were performed by polymerase chain reaction using 11 short tandem repeat markers along chromosome 21q. The vast majority of trisomy 21 was of maternal origin (93%), followed by paternal (5%) and mitotic origin (2%). The frequencies of maternal meiotic I (MI) and meiotic II errors were 86% and 14%, respectively. The highest proportion of cases with zero recombination was observed among those with maternal MI derived trisomy 21. A higher proportion of telomeric exchanges were presented in cases with maternal MI errors and cases with young mothers, although these findings were not statistically significant. The present study is the first report examining parental origin and altered genetic recombination as a risk factor for trisomy 21 in a Croatian population. The results support that trisomy 21 has a universal genetic etiology across different human populations.

Chromosome 21 non-disjunction and Down syndrome birth in an Indian cohort: analysis of incidence and aetiology from family linkage data

We analysed the family linkage data obtained from short tandem repeat (STR) genotyping of 212 unrelated Indian families having a single Down syndrome (DS) baby each, in order to explore the incidence and aetiology of this human aneuploidy in our cohort. The estimated values of maternal meiotic I and meiotic II non-disjunction (NDJ) errors of chromosome 21 (Ch 21) were ~78 and ~22%, respectively. Within the paternal outcome group, about 47 and 53% were accounted for NDJ at meiosis I and meiosis II, respectively. We estimated only ~2% post-zygotic mitotic errors. The comparison of average age of conception between controls and DS-bearing mothers revealed a significant difference (P<0·001) with DS-bearing women were on an average older than controls and meiotic II non-disjoined mothers were oldest among meiotic outcome groups. Our linkage analysis suggested an overall reduction in recombination by more than 50% on meiotic I non-disjoined maternal Ch 21 with error prone to susceptible chiasma formation within the ~5·1 kbp segment near the telomeric end. We stratified meiotic I non-disjoined women in three age groups, viz. young (⩽28 years), middle (29–34 years) and old (⩾35 years) and found linear decrease in the frequency of achiasmate meiosis from the young to the old group. In contrary, a linear increase in the multiple chiasma frequency from the young to the old group was observed. Considering these results together, we propose that the risk factors for Ch 21 NDJ are of two types, one being ‘maternal age-independent’ and the other being ‘maternal age-dependent’. Moreover, a comparison of our present Indian dataset with that of other published data of ethnically different populations suggested that the genetics that underlies the NDJ of Ch 21 is probably universal irrespective of racial difference across human populations. The present study is the first population-based report on any DS cohort from the Indian subcontinent and our work will help future workers in understanding better the aetiology of this birth defect.

Prenatal detection of isochromosome 21 by QF-PCR. A comparison between FISH and traditional karyotyping

OBJECTIVE

To compare rapid aneuploidy diagnostic tests with traditional karyotyping in the prenatal detection of Down syndrome due to isochromosome 21.

METHODS

Quantitative fluorescence PCR (QF-PCR) and fluorescent in situ hybridization (FISH) for chromosomes 13, 18, 21, X and Y were performed on uncultured amniotic fluid, followed by routine karyotyping. chromosomal and microsatellite analysis of peripheral blood from parents was also carried out.

RESULTS

The QF-PCR screening showed a trisomic diallelic pattern for 5 of 6 markers spanning the long arm of chromosome 21. FISH showed 3 signals in the interphase cells for the region 21q22.13-q22 during LSI 21 probe mapping. Cultured amniotic fluid revealed an isochromosome 21 resulting in a 46,XX,i(21)(q10),+21 karyotype. Parental microsatellite analysis proved that the isochromosome was paternal in origin.

CONCLUSION

The most informative analytical tool in this case appears to be QF-PCR, although a combination of QF-PCR and karyotyping provided the most evidence.

Practical application of fluorescent quantitative PCR on Trisomy 21 in Chinese Han population

OBJECTIVE

To apply the fluorescent quantitative PCR method on the detection of Trisomy 21 by D21S11 locus and make a foundation for rapid prenatal diagnosis of Trisomy 21.

METHODS

About 409 controls (39 amniotic fluid samples and 370 peripheral blood samples) and 35 patients (4 amniotic fluid samples and 31 peripheral blood samples) with Trisomy 21 were tested using fluorescent quantitative PCR by amplification of DNA fragment on D21S11 STR locus. The results were compared with conventional cytogenetic analysis to confirm the utility of this method. And the allele frequency distributions of D21S11 STR locus were analyzed.

RESULTS

The 95% reference interval of fluorescent intensity ratios of peak heights of PCR products amplified from two alleles on D21S11 locus ranged from 0.84 to 1.42 (1.13 +/- 0.29) in heterozygous controls. About 19 out of 35 patients showed a "diallelic" pattern and their height ratio of fluorescent peaks of PCR products amplified from two alleles in patients with "diallelic" patterns were all outside of the 95% reference range of controls. The PCR products of DNA from 12 patients presented the third allele. No sample with the "monoallelic" pattern was found. Four chimeras diagnosed by cytogenetic method could not be diagnosed by this method. There were 17 and 11 alleles found in controls and patients, respectively. About 343 out of 409 controls were heterozygous and the heterozygosity was 83.86%. We did not find any significant differences in the frequency distributions of alleles on D21S11 locus between controls and patients. But there were significant differences in the frequency distributions of alleles on D21S11 locus between controls and patients. But there were significant differences in the frequency distributions of alleles on D21S11 locus among different populations.

CONCLUSIONS

The fluorescent quantitative polymerase chain reaction method was rapid, accurate, and only small amount of starting material was needed, it could be applied in rapid prenatal diagnosis of Trisomy 21. D21S11 was a good marker with high heterozygosity for the screening of Trisomy 21. And the frequency distributions of alleles on D21S11 locus were significantly related to ethnic background.