Down Syndrome (Trisomy 21; 47,XX,+21 or 47,XY,+21)

Definition

Down syndrome refers to a common genetic disorder that results in birth defects, medical problems, and some degree of mental retardation .

Causes

Down syndrome (DS) is the most frequent genetic cause of mild to moderate mental retardation. DS occurs in one out of 800 to 1,000 live births in all races and economic groups.

• Chromosomes contain the genetic makeup of your body and they occur in pairs within the body. There are 23 pairs of chromosomes. Most individuals with Down syndrome, 95%, have three (rather than the normal 2) number 21 chromosomes, Trisomy 21. This results from an error in cell division in the egg or sperm.
• The remaining 5% have either Mosaic Trisomy 21 or Translocation Trisomy 21. Where mosaicism exists (1%-2% of individuals), some cells have the extra chromosome, trisomy 21, and some have the normal count of two number 21 chromosomes. Where a translocation is found (3%-4%) part of the chromosome number 21 has broken off and reattached itself onto another chromosome. In about one third of individuals, the translocation is inherited from a parent.

In all cases, it is the extra chromosome 21 genetic material that causes problems.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

• Genetics: If either parent is a carrier of a specific type of Down syndrome (Translocation Down Syndrome), there is an increased risk of giving birth to a child with this type of Down syndrome.
• Age: The chance of having a child with Down syndrome increases after a woman reaches age 35.
• Sex: More boys than girls are born with Down syndrome.

Symptoms

Infants born with Down syndrome may have some or all of the following physical characteristics:

• Muscle hypotonia, low muscle tone
• Flat facial features, a somewhat depressed nasal bridge and a small nose
• Upward slanted eyes, small skin folds on the inner corner of the eyes
• Short neck
• Misshaped ears
• White spots on the colored part of the eye
• Single skin crease in the palm of the hand
• Excess flexibility in joints
• Heart defects
• Sight and hearing problems
• Large and protruding tongue
• Fifth finger has one flexion furrow instead of two
• Excessive space between large and second toe

The degree of medical problems and mental retardation varies. Talents, abilities, and pace of development differ. People with Down syndrome may be born with or develop:

• Vision problems
• Hearing loss
• Heart defects
• Increased incidence of acute leukemia
• Frequent ear infections and increased susceptibility to infection in general
• Gastrointestinal obstruction (imperforate anus and similar problems)
• Esophageal atresia or duodenal atresia
• One third of patients experience blocked airways during sleep
• Increased incidence of dementia in older ages
• Instability of the back bones at the top of the neck, can result in compression injury of the spinal cord
• Urinary system defects
• High blood pressure in the lungs
• Seizures
• An under-active thyroid ( hypothyroidism )
• Slow growth
• Late to sit, walk, toilet train
• Speech problems
• Obesity
• Emotional problems
• Risk that others assume that a child is more retarded than he or she is

Most of these health problems are treatable, and the majority of people born with Down syndrome today have a life expectancy of approximately 55 years.

Diagnosis

Treatment

There is no cure for Down syndrome. Some newborns may need surgery to repair serious medical problems, like heart defects. Living at home and receiving special therapy helps children with Down syndrome achieve their full potential. Most people with the condition can actively participate in the community—at schools, jobs, and various leisure activities. Some live with family, some with friends, and some independently.

Prevention

There are no guidelines for preventing Down syndrome. If you have concerns about having a child with Down syndrome, consider getting genetic counseling prior to becoming pregnant.