Edwards Syndrome Or Trisomy 18
Trisomy 18 was described separately, both by Edwards and by Smith in 1960. Edwards syndrome is the second autosomal trisomy after Down syndrome.
The incidence of Edwards syndrome at birth is 1 / 6000-8000 of live births. Approximately 95% of the products of conception with Edwards syndrome are removed during intrauterine life, and about 80% of newborns who have Edwards syndrome are girls. One year survival rate is 5% – 10%.
In 95% of cases, Edwards syndrome is a homogeneous trisomy, mosaicism and translocations are present in small percentage. Extra chromosome 18 is responsible for the phenotypic manifestations, namely the region 18q11 – q12.
The incidence of Edwards syndrome increases with maternal age, so in about 90% of cases, the excess chromosome is of maternal origin.
The clinical presentation of Edwards Syndrome:
Edwards syndrome phenotype is characterized by:
- Head: microcephaly, narrow bifrontal diameter and prominent occiput, which gives the skull characteristic appearance of “bird head”.
- Facial presents: microphthalmia, short and horizontal palpebral fissure, hypertelorism, micrognathia, small mouth, cleft lip, cleft palate, malformed and lowset ears.
- Upper limbs: is characteristic contracture of the hand, clenched hands with the index finger overriding the middle finger and the fifth finger overriding the fourth finger.
- Foot: it has a characteristic form of rocker-bottom feet with prominent calcanei.
- Neurological manifestations: psychomotor retardation, hypertonia, myelination defects, agenesis of corpus callosum.
- Malformations of organs and systems:
- Cardiac malformations: in 90% of the cases, appear ventricular septal defect, interatrial septal defect, persistent ductus arteriosus, coarctation of the aorta;
- Pulmonary malformations: pulmonary hypoplasia with abnormal lobulation;
- Gastrointestinal malformations: omphalocele, intestinal malrotation, atresia of the esophagus, ileum atresia, anal imperforation;
- Genitourinary malformations: polycystic kidney, double ureter, unilateral renal agenesis, cryptorchidism and hypospadias in boys, labial and ovarian hypoplasia in girls.
- Edwards syndrome homogeneous or uniform trisomy in 95% of cases, the karyotype is: 47,XX+18 or 47,XY+18;
- Edwards syndrome in mosaicism or mosaic trisomy in about 5% of cases, the karyotype is: 47,XX+18 / 46,XX or 47, XY+18 / 46 XY;
- Edwards syndrome with translocation, very rare.
Prenatal diagnosis in Edwards syndrome can be established by ultrasound, which will highlight maternal polyhydroamnios, due to defective sucking and swallowing reflexes of the fetus in utero and then olighydroamnios due to renal malformations, unique umbilical artery and fetal hypotonia. To confirm the diagnosis of Edwards syndrome, karyotype is done by sampling the amniotic fluid, chorionic villi or fetal blood.
Edwards syndrome recurrence risk is 1%, but this risk increases substantially if parents are carriers of a balanced translocations. The risk of recurrence should be established for each case in accordance with structural rearrangements, and segregation mode.