Trisomy 18 (Edwards syndrome) is a chromosomal abnormality. It is characterized growth retardation, microcephaly, microphthalmia, ocular hypertelorism, ptosis, microstomia, distinctively clenched fingers and other congenital malformations.
In utero, the patients present with heart defects, central nervous system abnormalities (such as skull anomalies and choroid plexuses cyst), weak fetal activity, small placenta, fetal distress, intrauterine growth restriction (IUGR) and excess amniotic fluid (polyhydramnios).
At birth, the baby is usually of low weight. The fists are closed with the index finger overlapping the third digit, and the fifth digit overlapping the fourth. The hips are narrow with limited capability of adduction. The feet are of typical character called rocker bottom feet (abnormal dermatoglyphics).
There are heart problems such as atrial septal defect (ASD), ventricular septal defect (VSD) and patent ductus arteriosus (PDA). Among the heart problems, ventricular septal defect (VSD) is the most common. There are also breathing difficulties and intellectual disabilities. Intestinal hernias, feeding problems and ill located anus are the common gastrointestinal manifestations.
There are also genitourinary problems such as small penis or undescended testes in case of male patient. The face is a characteristic with wide palpebral fissures, wide fontanels, elongated skull, drooping eyelids, small head, small jaw, small sternum, double toes, cleft lip and cleft palate. Microcephaly and microganathia may also be present. Ears are low set and fawn like.
There is also short neck, excessive skin folds and marked hypotonia.
Cytogenetic studies are performed to investigate the type of trisomy 18 (full trisomy 18, partial trisomy 18 or mosaic trisomy 18).
The number of platelets and neutrophils should be evaluated especially during the first week of life. Decreased platelets are the most common hematological abnormality in these patients .
Abnormal erythrocyte sedimentation rate (ESR) values may indicate infections.
Imaging studies are performed to detect cardiac abnormalities. Echocardiography may also be helpful. Abnormalities of the gastrointestinal tract are detected by barium meal swallow.
Skeletal abnormalities are evaluated by performing full body skeletal radiography.
Not much can be done to reduce mortality and morbidity in the patients of trisomy 18. The treatment is supportive. Infections are treated by the use of antibiotics. Cardiac support is provided by pharmacologically or through surgery. The patients’ parents should also be counselled and psychologically supported.
Trisomy 18 incidence increases with the increasing maternal age and there is mostly nondisjunction of maternal chromosome in meiosis phase 2. The average maternal age is 32.5 years.
With increasing maternal age, the chances of disjunction during meiosis increase. A maternal egg may have an extra pair of chromosome even before conception. After fertilization by a sperm, the egg has 47 chromosomes - two pairs of normal 23 chromosomes and one extra chromosome. These extra chromosomes lead to full trisomy 18 which manifests with full blown defects in the cardiovascular system, renal system and the central nervous system.
In some cases, partial trisomy 18 has been reported. In partial trisomy 18, the main pathology is translocation.
There is also a rare phenomenon of mosaic trisomy 18 in which some cells have an extra chromosome 18 while other cells don’t. There is marked phenotypic variation in such cases .
Trisomy 18 is the trisomy of the chromosome 18; i.e. there is an abnormally extra chromosome 18 in addition to the normal pair of chromosome 18. Trisomy 18 is also known as Edward syndrome after the scientist who described it in 1960 .
It occurs due to chromosomal disjunction during meiosis phase 2 even before conception. Females are usually more frequently affected as compared to males . Higher incidence of trisomy 18 is seen with increasing maternal age.
Most of the fetuses with this syndrome die in utero. If born, there is multisystem involvement including that of cardiac and central nervous systems. The patient usually has craniofacial and digital abnormalities. Owing to this multisystem involvement, the patients who survive suffer from high morbidity and mortality .
Trisomy 18, also called Edward syndrome occurs with increase maternal age. Most of the fetuses die in utero; those who take birth have a multiple system anomalies such as cardiac, renal, Gastro enteral, genitourinary and skeletal abnormalities.
The skeletal abnormalities are obvious when physical exam is done. There are craniofacial and digital abnormalities. Due to multiple system involvement the survival decreases with increasing age. Treatment is supportively.