Down's Syndrome is the most common chromosomal anomaly and  most common genetic cause of moderate intellectual disability. Incidence of Down's Syndrome is 1 in 733 live births.

Risk Factor: Incidence increases with maternal age.

Mother's age                       Incidence 

25 years -                             1 in 1200 births.

30 years -                             1 in 900 births. 

40 years -                             1 in 100 births.

45 years -                             1 in 25 births.

Cause: Failure of chromosomal separation at 21st chromosome.

Clinical features :

1. Malformed teeth.

2. Scrotal tongue (rough tongue like scrotum).

3. Nuchal fold thickening (excess skin over neck area).

4. Short hands and short feet.

5. Flat occiput (back portion of skull is flat).

6. Round face.

7. Brushfield spot in the eye. 

8. Upward slanting eyes.

9. Heart defects: Eg - atrial septal defect, ventricular septal defect.

10. Gastro-intestinal anomaly: Pyloric atresia , duodenal atresia , Hirschsprung disease. 

11. Blood disorder: leukemia (Blood cancer).

12. Hands: Single palmar crease, clinodactyly (little finger is curved).

13. Foot: Sandal gap

14. Bony defects: Atlantoaxial instability (neck instability).

                               Anterior fontanel delayed closure.  

15. Delayed development. 

Antenatal screening of Down's Syndrome :

Sonography: 

1. Small weight baby 

2. Posterior part of neck swelling 

3. Heart defects: Atrial septal defect, ventricular septal defect etc.

4. Short humerus (arm bone ), Short femur (thigh bone). 

Blood tests:

1. Decreased Alpha-fetoprotein

2. Decreased Estriol

3. Increased Human Choriogonadotropin

4. Increased Inhibin

Prognosis of patients with Down's Syndrome :

 - Life expectancy of children with Down's Syndrome is reduced to 50-55 years.

- Increased risk of premature aging and risk of Alzheimer's disease. 

- Increased risk of adult deaths due to congenital heart defects, seizures and blood cancers.

- Decreased risk of solid tumors like neuroblastoma and nephroblastoma. 

- Most adults with Down's syndrome are able to perform activities of daily living but have difficulties in complex financial, legal or medical decisions.