Down Syndrome

Introduction

Down syndrome (trisomy 21) occurs in approximately 1 in 1000 live births, making it the most common aneuploidy. It occurs in individuals who carry an extra chromosome 21 or extra chromosome 21 material, including the critical region at 21q22.3. The main features characteristic of trisomy 21 include distinctive facial features, mild to severe learning difficulties, congenital heart defects (particularly AVSD), gastrointestinal problems (such as duodenal atresia or stenosis), imperforate anus and Hirschsprung Disease. Facial features include down-slanting palperbral fissures, a flattened profile, Brushfield spots and a protruding tongue. The majority of cases are “free” trisomy 21, but in approximately 3-5% of cases the additional chromosome 21 material is the result of a derivative chromosome 21, which may be inherited from one parent who carries a balanced reciprocal translocation involving chromosome 21. Although free trisomy 21 occurs sporadically, there is an increased risk of a Down syndrome pregnancy with increasing maternal age. Trisomy 21 may also appear in a mosaic form, where normal cells are also present in the individual. These individuals may exhibit a milder phenotype, which is dependent on the extent and tissue distribution of the normal cell line.

Referral information

For prenatal referrals we accept samples from women that have a high risk (>1:150) following antenatal screening including Combined or Quadruple testing, a family history of a chromosome rearrangement predisposing to trisomy 21, a previously affected pregnancy, or ultrasound scan findings indicative of trisomy 21. For postnatal samples, we accept referrals from patients with appropriate clinical features for a diagnosis of trisomy 21 or for the confirmation of a prenatal diagnosis.

Price & reporting times

NHS referrals to this service are paid for where there is an existing specialist commissioning contract for genetic testing. In other cases please contact the lab for prices.

Test Price (£ ex VAT) TRT *
QF-PCR POA 3 cd
G-banded neonatal chromosome analysis POA 10 cd
G-banded prenatal chromosome analysis POA 14 cd
Prenatal or neonatal microarray analysis POA 14 cd

Test validation & quality assurance - information for users

The QF-PCR test is for trisomy 13, 18, 21 only and will not detect mosaicism or structural rearrangements. Rarely, testing may be uninformative or fail to give a result either due to maternal cell contamination or other factors. Maternal and paternal blood samples may be requested to help interpret results. Microarray analysis will not detected balanced rearrangements and may not detect mosaicism. Maternal cell contamination is excluded for prenatal samples prior to microarray testing by analysis of a maternal blood sample. This laboratory participates in the CEQAS quality assessment scheme for this test.

Sample requirements

Pre-natal (serum screening): amniotic fluid (minimum 10ml)/chorionic villus biopsy (CVB) (minimum 10mg) sample plus 4ml EDTA maternal blood sample

Referral guidelines

Please see our referral guidelines for more information.

OMIM Number(s) - 190685

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