A junior doctor examines the first child of a 28 year old woman as part of a routine "baby-check" prior to discharge from hospital. The baby is 20 hours old. The doctor notices that the baby is hypotonic and also finds a systolic murmur on auscultation of the heart. After further examination by a senior paediatrician the baby's chromosomes are analysed.
The karyotype of the baby.
Q1. What is the diagnosis?
Q2. What is the most likely cardiac defect?
Trisomy 21 (Down syndrome)
Atrioventricular septal defect (AVSD)
Hypotonia is one of the most common features of Trisomy 21. Other features include a typical facial appearance (round face, relatively large/protruding tongue, epicanthic folds, upslanting palpebral fissures), brachycephaly, single transverse palmar creases, and wide sandal gap.
In this case the diagnosis was confirmed by chromosome analysis - there are three of chromosome 21.
There is an increasing risk of trisomy 21 with increasing maternal age and at age 40 the risk is approximately 1 in 110. However, most babies with Trisomy 21 are born to mothers under the age of 40. This is becuase the birth rate for mothers 40 years old or over is so low.
A congenital heart defect is present in 40% of babies with trisomy 21 - the most common is an AVSD (Atrioventricular septal defect.)
