Introduction

Synonym's: Trisomy 21:Mongol child: Mongolian idiocy

A chromosome is a rod-like structure present in the nucleus of all body cells, with the exception of the red blood cells, and which stores genetic information. Normally humans have 23 pairs of chromosomes, the unfertilized ova and each sperm carrying a set of 23 chromosomes. On fertilisation the chromosomes combine to give a total of 46 (23 pairs). A normal female has an XX pair and a normal male an XY pair.
Chromosome abnormalities give rise to specific physical features. The problem varies from a range of cognitive disabilities as well as other attributes. Out of the so many genetic abnormalities one of the most common abnormality is Down syndrome.

What is Down syndrome?
Down syndrome, a chromosomal disorder, occurs when, instead of the normal complement of 2 copies of chromosome 21, there is a whole, or sometimes part of an, additional chromosome 21.

Incidences:
Approximately 1:700 live births (Recently reported as 1:1000 or 1:1100)

Causes:

Down syndrome is caused by an error that occurs during the formation of the twenty-first chromosome. Its occurrence is sporadic and the parents are usually unaffected. The factors, which adds to the increasing incidence of this disorder are

• use of various approaches for prevention of pregnancies
• Amniotic fluid examination
• Elderly mother, though the majority of children with Down syndrome are born to younger mothers.
  

However, in a minority of cases (3-4 per cent) a mother may have a balanced translocation of chromosome 21. In these cases the condition is inheritable.

Karyo typing:
It may be of three types

1. 47 XX, +21 or 47XY, +21
2. t(14q 21q) ; t(21q 22q) ; t(21q 21q)
3. Mosiac pattern 46/47, +21

Life expectancy in children with Down syndrome

• One third of infants do not survive more then 1 year
• One half dies during the first five years of life
• Although there have been many advances in the medical care of these patients, the life expectancy of a patient with Down syndrome may be upto 50-60 years.
• Cause of death is usually cardiac complications and respiratory infections

Future risk:
The risk for future children conceived by the same couple is minimal.

Clinical features:

Early Presentations in new born:

• Apathy with feeding difficulties.
• Prolonged physiologic jaundice.
• Profound diffuse hypotonia, hyperextensibility of joints, and slowed response of neonatal reflexes are evident.
  

Generally, children with Down syndrome are maladroit, move slowly, and have an unsteady, wide-based gait. Seizures, including infantile spasms, occur in approximately 2% to 9% of patients.Some of the facial features which identify an individual as having Down syndrome include:

Other common features are:

1. Low set ears
2. Up slanting palpebral fissures
3. Low nasal bridge and dorsum
4. Abnormal and excessive facial fat distribution
5. Protruding, enlarged tongue
6. Both prenatal and postnatal growth deficiencies can exist in the Down patients.

They often exhibit a short stocky stature and also have delayed growth of the brain resulting in a reduced mental capacity. The extent to which they are intellectually deficient varies from patient to patient.