Trisomy 21 - Translocation Clinical Trial
Official title:
Trisomy of Chromosome 21 Diagnosis by High Output Sequencing of Foetal Circulating DNA in Mother Blood at First Trimester of Pregnancy.
Demonstrate that the High output shotgun sequencing of the foetal DNA in the maternal blood could allow a complete discrimination between the mothers of a trisomic fetus 21 or a DISOMIQUE foetus 21 from the first quarter of the pregnancy, and so to obtain a reliable alternative in invasive procedure.
Justification of the research :
The trisomy 21 is the most frequent cause of handicap of genetic origin with an incidence of
1.3/1 000 births which increases with the maternal age. Several strategies of antenatal
screening were developed. The High Authority of Health recently recommended to propose to
the pregnant women a 1st trimester combined screening, realized between 11+0 and 13+6 weeks
of amenorrhoea, associating measure of the NUCALE translucency and dosage in maternal serum
: PAPP-A (Pregnancy Associated Plasma Protein A) and βhCG (free β human Chorionic 1st
trimester Gonadotrophin). However, the sensibility of these screening tests is about 80 %
for 5 % of positive false. The diagnosis of aneuploidy is then established on a population
classified at high risk, by a foetal karyotype (requiring an invasive procedure : biopsy of
trophoblast or amniocentesis). A positive screening increase maternal and medical anxiety.
Furthermore, the inappropriate combination of the tests is at the origin of numerous useless
invasive procedures (national rate of amniocentesis of 11 %), at risk of foetal losses (0,5
in 1 %). This inflation of invasive procedures leads to so many losses of not affected
children as trisomic children and to a badly known maternal morbidity.
Several studies showed that 10 % of the free DNA found from the first quarter of the
pregnancy in the maternal plasma is of foetal origin and that this DNA is specific of the
foetal nuclear DNA of the current pregnancy. This opened the way of a possible not invasive
antenatal diagnosis of the foetal aneuploidy which collided during the last 10 years with
the performances limited by the isolation and by the sequencing of the foetal DNA in the
maternal plasma. A new technique of analysis by broadband sequencing of the DNA circulating
in the maternal blood for the diagnosis of the most frequent aneuploid the trisomy 21 of
which was brought back(reported). The High-output shotgun sequencing of all the DNA
circulating in the maternal blood, then the reading and the identification of all the
chromosome sequences allows to analyze the quantity of DNA resulting from the supernumerary
chromosome, without necessity of differentiating maternal and foetal DNA. On the basis of
very recent works 10, this excess of sequences resulting specifically from the chromosome 21
foetal supernumerary allows a discrimination completes between trisomy 21 and disomy 21.
However, this study analyzed only 9 cases of trisomy 21 and the sampling of maternal blood
were realized after the amniocentesis or the choriocenteses, what could artificially have
increased the quantity of circulating foetal DNA.
Objectives :
Demonstrate that the High output shotgun sequencing of the foetal DNA in the maternal blood
could allow a complete discrimination between the mothers of a trisomic fetus 21 or a
DISOMIQUE fetus 21 from the first quarter of the pregnancy, and so to obtain a reliable
alternative in invasive procedure.
Method Two public centres of antenatal screening were established to answer specifically the
recommendations of the High Authority of Health and have the capacity to make 20 000 acts of
screenings a year. All the women presenting a high risk (> 1/250) of aneuploidy and the
candidates to an invasive procedure, will see suggesting participating in the study. The
included patients will have a maternal blood sample before the invasive test. This taking
will be put in on hold in-80°C after centrifugation following the recommended protocol. At
the end of inclusion, the technic of analysis of the circulating DNA will be realized then
blind by the laboratory on all the diagnosed cases (by usual invasive examination, or at the
conclusion of the pregnancy) of trisomy 21 and on control representative of all the spectre
of the levels of risk. A study of reproducibility of the quantification of the DNA of the
chromosome 21 will be realized.
Number of subjects:
we plan to include 75 cases of trisomy 21 and 150 control cases with normal karyotype, what
allows to detect a 99,9 % sensibility and a 99,99 % specificity with a power of at least 95
%.
Duration of the study:
these objectives are practicable in two years on the basis of the number of invasive takings
realized in both center and an already realized study
Ethical Aspects: research on data and biological collection. No individual medical decision
will be taken according to the estimated test.
Perspectives:
this new technique, if it is generalizable, would allow to limit the number of procedures of
invasive diagnosis (amniocentesis and choriocentesis) which contain a significant risk of
grave maternal and fetal complications, while optimizing the capacities of this screening.
;
Observational Model: Case Control, Time Perspective: Prospective