Trisomies

Trisomies are quantitative chromosomal abnormalities in which there is an extra chromosome which in turn leaves us with a total of 47 chromosomes (instead of 46).

We will be discussing 3 trisomies:

Trisomy 21 - Down’s syndrome
Trisomy 18 - Edward syndrome
Trisomy 13 - Patau syndrome

Down’s syndrome (trisomy 21)

Notes on Down’s syndrome can be found with the link below:

Down’s syndrome

Edward syndrome (trisomy 18)

Edward syndrome results from having an extra chromosome to the 18th chromosomal pair. The syndrome affects the entire body and varies in severity.

It occurs in 4/10,000 pregnancies. More than 50% of children die within the first week and only 5 to 10% survive the first year.

⚠️ Risk factors

The main risk factor is again increasing maternal age.

😷 Presentation

Antenatally:

Polyhydramnios
Small placenta
Single umbilical artery
Feta growth restriction

After birth:

Hypotonia
Marked hypoplasia of skeletal muscle and subcutaneous fat
Weak cry
Decreased response to sound

Severe learning disabilities
Facial features:

Short palpebral fissures
Small mouth and jaw - gives the face a “pinched in” appearance
Low-set ears

Head:

Microcephaly
Prominent occiput

Chest:

Short sternum
Severe congenital heart diseases - such as PDA and VSD.

Hand:

Clenched fist with the index finger overlapping the 3rd and 4th fingers

Feet:

Rocker bottom feet
Talipes (clubfeet)

Genitals and pelvis

Cryptorchidism
Narrow pelvis

Other anomalies include lung, diaphragm, gastrointestinal and renal anomalies.

🔍 Investigations:

Prenatally:

🏆 Prenatal chorionic villus sampling and/or amniocentesis with cytogenetic testing
Cytogenetic testing may be done by:

Karyotyping
Fluorescent in situ hybridization (FISH)
Chromosomal microarray analysis (CMA)

Postnatally:

Clinical suspicion may be raised based on the appearance.
🏆 Peripheral blood sample for cytogenetic testing can be done

🧰 Management

Supportive management

Patau syndrome (trisomy 13)

Patau syndrome is the syndrome resulting from an additional chromosome 13. The syndrome varies in severity, and patients usually die in the neonatal period, but supportive measurements have improved 5-year survival. Less than 10% make it past their 10th birthday.

It is rarer and found in 1.7/10,000 pregnancies.

⚠️ Risk factors

Once again, the main risk factor is increasing maternal age.

😷 Presentation

Face:

Cleft lip and palate
Microphthalmia (a small eye globe)
Coloboma of the iris - coloboma is a gap in the structure of the eye (absence) that may affect the eyelid, iris, retina, or optic nerve of one or both eyes.
Slanted palpebral fissures
Low set ears - tragus is lower than nose bridge.
Hearing loss
Loose folds of skin on the back of the neck

Small for gestational age (SGA)
Apnoeic spells
Severe learning disabilities
Holoprosencephaly - failure of the forebrain to divide normally into 2 hemispheres.
Hands: