Annual report
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Chapter in BINOCAR annual report
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BMJ paper
- BMJ paper published
- Press release
J. Morris and E. Alberman, Trends in Down's syndrome live births and antenatal diagnoses in England and Wales from 1989 to 2008: analysis of data from the National Down Syndrome Cytogenetic Register, British Medical Journal, 2009:339;b3794, doi:10.1136/bmj.b3794
Contact information
National Down Syndrome Cytogenetic Register
Wolfson Institute of Preventive Medicine
Barts and the London School of Medicine and Dentistry
Charterhouse Square
London
EC1M 6BQ
Phone: +44 (0)20 7882 6220
Fax: +44 (0)20 7882 6221
Email: ndscr
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Funding
The NDSCR is funded by the HQIP (Healthcare Quality Improvement Partnership) until 31st March 2012.
Summary
The NDSCR has accumulated over 17,000 anonymous records since the Register started in January 1989. It is now probably the largest single dataset on Down syndrome and provides an opportunity to search for possible causal factors. It also enables the study of the response of parents and clinical services to the new technologies of screening and diagnosis. Please see the Annual Reports for details.
Maternal age is the only well-recognised association of Down syndrome. Mothers below 25 have an average risk of a DS pregnancy of about 1:1600 rising to about 1:340 at 35 and 1:40 at age 43. The data we have suggests that the risk of an affected birth does not increase above this age.
Prenatal screening and diagnosis have expanded dramatically in the life of the Register. Despite this expansion, in 1999 44% of all diagnoses were at birth. Prenatal diagnosis depends on an invasive test to obtain fetal cells. Because this entails a risk of fetal loss, of 1 to 2%, it is only offered to mothers with a greater risk of having an affected child. The estimation of this risk, previously limited to high maternal age, is now much more precise with the addition of specific ultrasound and/or maternal serum findings.
Of all pregnancies with a prenatal diagnosis of trisomy 21, 94% of the parents decide to terminate the pregnancy, 5% are live born and 1% are stillbirths or neonatal deaths (1996-1999).
Family history of a reported previous affected pregnancy or close relative with a chromosome anomaly accounts for 1% of all diagnoses.
Chromosome structural variations included in the register are very similar to published data with 95% having simple trisomy for 21. In 1.1% there is mosaicism for trisomy 21, where both affected cells and another cell type (usually normal) are present. Translocation involving 21 (rearrangement of chromosome material between two chromosomes, sometimes inherited) is present in 3.1% of which 0.1% are non-Robertsonian (not usually inherited). Very rarely (0.5%) a more complicated multiple chromosome anomaly, usually lethal, is found.
Recurrence in DS is widely recognised and for those with a family history risks are adjusted upwards by about 1:100. In our records, almost certainly under-ascertained, the increased risk in non-translocation families is about 0.85% but including other chromosome anomalies rises to 1%.
Twinning occurs at a rate of about 1.2% in pregnancies in the NDSCR, of which pairs where both have trisomy 21 represent about one sixth. We cannot presume these are identical (monozygous), as one DS pair are of unlike sex.
