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Trisomies
Down’s syndrome
This condition is caused by having an extra chromosome 21 leading to multiple complications
Inheritance:
– Trisomy 21 (the risk of this increases with maternal age),
– Some cases due to Robertsonian chromosome translocation (usually onto 14) – can be inherited
Risk:
The risk of Down’s syndrome increases with maternal age.
– Maternal age 20 – 1in 1500
– Maternal age 45 – 1 in 50
| Maternal Age (years) | 20 | 50 | 40 | 45 |
| Risk | 1 in 1500 | 1 in 800 | 1 in 100 | 1 in 50 |
Symptoms:
Intellectual –> Learning disability, autism, early onset Alzheimer’s disease, delayed developmental milestones
Facial –> small ears, flat face, protruding tongue, Brushfield spots in iris, oblique palpebral fissures, large tongue
Respiratory –> Repeated Respiratory Infections
Cardiac –> Most common is endocardial cushion defect (walls separating all four chambers absent)
– Ventricular septal defect (2nd most common)
– Secundum atrial septal defect
– Tetralogy of Fallot
– Patent ductus arteriosus
Gut –> Duodenal atresia, Hirschsprung’s disease
Limbs –> Big “sandal gap” between big and first toe, single palmar crease
– Short stature, Hypotonia
Endocrine –> Hypothyroidism
Reproduction –> Subfertility in both genders
Management:
No cure, managed with MDT input throughout life
Patau Syndrome
This condition is caused by having an extra chromosome 13
Inheritance:
Trisomy 13 (most common) or because each cell contains an extra partial copy of chromosome 13
Symptoms:
– Head and neck –> scalp lesions, cleft lip/palate, microcephaly
– Eyes –> Microphthalmia, cataracts, retinal detachment
– Limbs –> Polydactyly, clenched hands
– Congenital anomalies –> Heart defects, dextrocardia
– Urogenital –> abnormal genitals, renal abnormalities
Diagnosis:
Chromosomal analysis (karyotyping)
Management:
No cure available. Most (90%) of children die within the first year of life
Edwards Syndrome
This condition is caused by having an extra copy of the genetic material on 18
Inheritance:
Trisomy 18 (most common) or because each cell contains an extra partial copy of chromosome 18
Symptoms:
– Head and neck –> Prominent occiput, low-set ears, micrognathia
– Chest –> short sternum, oesophageal atresia
– Limbs –> Flexed, overlapping fingers and rocker-bottom feet
– Heart defects –> VSD, ASD, patent ductus arteriosus
Diagnosis:
Chromosomal analysis (karyotyping)
Management:
Most pregnancies affected do not result in a live birth, and 90% of children die within the first year of life
Sources
(1) Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities, Public domain, via Wikimedia Commons
