Edwards syndrome is, like Down syndrome, a trisomy disorder; in this case due to the presence of one extra copy of chromosome 18. Occurrence in live births is about 1 in 7,900 (in the absence of any prenatal detection programme), and increases with increasing maternal age.
A significant proportion of fetuses with Edwards syndrome miscarry or are stillborn (36% loss rate from 2nd trimester onwards), but this fetal loss rate is comparable with that of Down syndrome (43% spontaneous loss between 11 weeks and term).
For live-born infants, Edwards syndrome is usually of far greater clinical severity than Down syndrome, having a very limited lifespan, and often with multiple congenital malformations. About 50% of infants die within the first two weeks after birth, often from central apnoea or congenital abnormality; only around 8% survive beyond one year, but with severe learning disabilities.
Growth retardation (both prenatal and postnatal) is usual; administered feeding methods are normally required.
Antenatally, increased nuchal translucency, multiple congenital abnormality, growth retardation, choroid plexus cysts and polyhydramnios may all be presenting features of Edwards syndrome. Congenital anomalies, which are usually multiple and occurring together with growth retardation, typically include a heart defect (80%-90%), and a characteristic fixed flexed positioning of the fingers, often together with some of: renal anomalies, oesophageal atresia, diaphragmatic hernia, exomphalos (abdominal wall defect), cleft lip or palate, and neural tube defect.
The head shape and facial appearance can be typical, together with a convex ‘rocker-bottom’ shape to the sole of the feet.
The outlook for survival is poor in neonates. About 50% of infants die within the first 2 weeks after birth, often from central apnoea. Around 8% survive beyond one year, but with severe learning disabilities. Median life expectancy is 14 days.
Diagnosis can be strongly suspected from the clinical features, but should always be confirmed by chromosome analysis. Before birth, there may be an abnormal maternal serum screen profile or ultrasound scan anomalies. Definitive prenatal genetic testing may be carried out.
Edwards syndrome is the result of trisomy 18 (the presence of a third copy of chromosome 18) but this can occasionally be due to translocations involving chromosome 18. The likelihood of occurrence (of simple trisomy 18, ie no translocation) increases with increasing maternal age.
Initial assessment to define any heart defect and the extent of other congenital malformation can assist clinical management decisions. Nasogastric feeding is frequently an initial requirement, perhaps changing to gastrostomy feeding beyond six months of age.
Advice to parents of a child with simple trisomy 18 (ie not associated with a translocation) is that the risk of recurrence for trisomy 18 or for the other major chromosomal abnormalities is usually very low (typically 1% unless the maternal-age dependent risk is already higher).
The definitive diagnosis in a newborn is by full karyotyping, although DNA-based techniques such as quantitative fluorescence PCR (QF-PCR) or fluorescent in-situ hybridisation (FISH) may be used simultaneously as an urgent initial way of detecting three copies of chromosome 18 material.
During pregnancy, QF-PCR and karyoptyping may be offered from a chorionic villus sample (CVS) or amniocentesis sample, where serum screen or maternal age indicate a pregnancy at increased risk, or where there are abnormalities on fetal ultrasound scan.