13th March 2024

Clinical manifestations

Down’s syndrome is associated with a number of characteristic facial features, including up-slanting palpebral fissures and epicanthic folds around the eyes, a flat nasal bridge, low-set ears, brachycephaly, and protruding tongue. Other dysmorphic features include a sandal gap between the first and second toes and transverse palmar crease. 

It affects a range of body systems, with individuals being more likely to experience gastrointestinal conditions, including duodenal atresia and coeliac disease, endocrine conditions, typically thyroid disease or type 1 diabetes mellitus.

The majority of individuals with Down’s syndrome will have some level of cognitive impairment and have a higher risk of developing dementia. 

Others with Down’s syndrome may experience haematological conditions such as polycythaemia and leukaemia and respiratory conditions, including obstructive sleep apnoea.

Cardiovascular manifestations

Around half of those with Down’s syndrome will have congenital heart disease. The most common congenital heart defect is atrioventricular septal defect. Other anomalies include ventricular septal defect, atrial septal defect, tetralogy of Fallot and patent ductus arteriosus. 

Individuals with Down’s syndrome can develop cardiac valve problems, most commonly mitral valve prolapse or aortic regurgitation.

Atrioventricular septal defect

In normal development, there is a canal connecting the atria and ventricles known as the AV canal. Typically, at 4 weeks gestation, the endocardial cushions which form the canal fuse and create the atrioventricular (AV) valves and septum. Incorrect fusion of the endocardial cushions results in an AV septal defect (AVSD) and left to right shunt. 

AVSD can be divided into complete and partial. A complete AVSD results in an ostium primum atrial septal defect (ASD), a ventricular septal defect (VSD) and a single AV valve due to complete failure of the endocardial cushions to fuse. Complete AVSD is more common than partial AVSD in Down’s syndrome. A partial AVSD is a result of incomplete fusion of the endocardial cushions and leads to an ostium primum ASD and a VSD but with separate AV valves with a cleft mitral valve. ASVD may present with the following: 

• Tachypnoea
• Tachycardia
• Pallor
• Poor feeding and weight gain