Trisomy 18

At a glance

Chromosomal disorder characterized by a broad spectrum of variable dysmorphic features (hypoplastic mandible and maxilla) and organ malformations (atrial septal defect [ASD], ventricular septal defect [VSD], omphalocele) with extremely poor prognosis (90% of patients die before 1 year of age).

Synonyms

Edwards Syndrome; Trisomy E.

History

Chromosomal disorder described simultaneously by Edwards, Patau, and Smith teams in 1960.

Incidence

Incidence is about 1:3,000 to 8,000 live births. Two-thirds of the cases are diagnosed at the time of amniocentesis and are spontaneously aborted before delivery. It is the second most common autosomal aberration and second most common multiple malformation syndrome (after ☞Trisomy 21). Risk factors include advanced maternal age. Girls are approximately three times more often affected than boys. The prognosis after delivery is poor with a median survival of 14.5 days, and a 10% survival at 1 year. If alive at 30 days the survival to 1 year is 36%. Survival into adulthood has been described. When mosaicism occurs, patients can have a normal intelligence and a mild phenotype.

Genetic inheritance

Mostly sporadic with less than 1% risk of recurrence. Ninety percent are believed to be associated to meiotic nondisjunction (Trisomy 18 presentation). Mosaicism is suspected in 10% of the cases and because of postzygotic mitotic nondisjunction. It leads to partial clinical expression of Trisomy 18 with a longer survival rate. Translocations are very rare.

Diagnosis

The diagnosis is most often already made in utero following an amniocentesis or ultrasound examination. Otherwise a chromosome study after birth confirms the diagnosis if there is clinical suspicion based on the pattern of malformations.

Clinical aspects

More than 130 different abnormalities have been reported in the literature and so only the more common ones will be listed here. General feeble appearance. Fetal abnormalities consist mainly of polyhydramnios, small placenta with single umbilical artery, and growth deficiency. Neurologically, the patients present with mental deficiency, microcephaly, and hypertonicity. They also have a prominent occiput with a narrow bifrontal diameter. Other craniofacial anomalies consist of low-set, malformed ears, short palpebral fissures, microstomia, narrow palatal arch, and micrognathia. Numerous musculoskeletal abnormalities are present like the characteristic clenched hand with overlapping fingers, short dorsiflexed halluces, short sternum, small pelvis, and limited hip abduction. Cutaneous problems consist of redundancy, mild hirsutism of the forehead and back, and prominent cutis marmorata. A cardiac anomaly (ASD or VSD, a persistent ductus arteriosus, or coarctation of the aorta) are found in more than 90% of patients. Less frequent anomalies may include malformation or absence of the right lung, diaphragmatic muscle hypoplasia, renal malformations, and cleft lip and palate.

Precautions before anesthesia

These children are very ...