Chromosomal Abnormalities

 

 

• Trisomy

  Trisomy 18

  Trisomy 13

  Treatment
   

 

 

Trisomy 18, Trisomy 13
 

Trisomy 18 and Trisomy 13 are the only two live born trisomies apart from Down’s syndrome. These trisomy disorders tend to have much more severe clinical manifestations than trisomy 21, and only rarely do affected infants survive to one year of life. Mean survival time ( MST) for Trisomy 18 is 6 days, and MST for trisomy 13 is 8.5 days. Multiple abnormalities exist in a fetus with a trisomy disorder, but there is no single anomaly that is pathognomonic for a given trisomy. Rather, there exists a characteristic constellation of clinical findings that suggest a specific diagnosis. All autosomal trisomies can present with cardiac defects, but they are more severe in trisomy 13 and 18 than in trisomy 21. Also, it is important to note that since some of these patients may be mosaics for the trisomy cell line, a variety of phenotypic expression is possible.

 

 

Trisomy 18 Syndrome

 

Trisomy 18, or Edwards Syndrome, is the second most common trisomy behind Down’s syndrome. This syndrome has an incidence of between 1 in 3000 and 1 in 8000, with a 3:1 F:M predominance. 90% of trisomy 18 is due to maternal nondysjunction, 10% due to mosaicism, and less than 1% is due to a translocation. Trisomy 18 has the following features:

1. Clenched hand, with overlap of the 2^nd and 5^th fingers, over the 3^rd and 4th

2. IUGR

3. Rocker bottom feet

4. Micrognathia, prominent occiput, micro-ophthalmia

5. Low set ears

6. Caridac defects, such as VSD, ASD and PDA

7. "Strawberry shaped" calvarium

8. Generalized muscle spasticity

9. Renal anomalies

10. Mental retardation

Trisomy 18 can be detected by karyotype with FISH analysis. The syndrome is associated with severe mental retardation, and severe failure to thrive. 50% of patients die by one week of life, and 90% of patients die by one year of life.

 

 

Trisomy 13 Syndrome

 

Trisomy 13, or Patau’s syndrome is the least common of the live-born trisomy disorders, with an incidence of 1 in 5000 to 1 in 2,000 live births, with affected males equal to affected females. 75% of trisomy 13 cases are due to maternal NDJ, 20% are due to a translocation, and 5% are due to mosaicism. The major midline dysmorphic features of trisomy 13 are due to a defect in the fusion of the midline prechordial mesoderm in the first three weeks of gestation. Trisomy 13 tends to present with more severe craniofacial and midline defects than are found in Trisomy 18 or 21. Trisomy 13 has the following clinical features:

1. Holoporsencephaly

2. Polydactly

3. Seizures

4. Deafness

5. Microcephaly

6. Midline Cleft lip

7. Midline Cleft palate

8. Abnormal ears

9. Sloping forehead

10. Omphalocele

11. Cardiac and renal anomalies

12. Mental retardation.

Trisomy 13 is also confirmed by karyotype with FISH analysis. 44% of these patients die within 1 month, and > 70% die within one year. Severe mental retardation exists in all survivors.
 
 

Treatment

There is no specific treatment, therapy or cure for a trisomy disorder. Parents should be counseled on the very short expected lifespan of the newborn with trisomy 13 or 18.