The human body is made of cells. All cells contain a center, called a nucleus, in which genes are stored. Genes, which carry the codes responsible for all our inherited characteristics, are grouped along rod-like structures called chromosomes. Normally, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when some or all of a person’s cells have an extra full or partial copy of chromosome 21.

The most common form of Down syndrome is known as Trisomy 21. Individuals with Trisomy 21 have 47 chromosomes instead of the usual 46 in each of their cells. The most common form of Down syndrome is known as Trisomy 21. Individuals with Trisomy 21 have 47 chromosomes instead of the usual 46 in each of their cells. The condition results from an error in cell division called non-disjunction. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.

As the embryo develops, the extra chromosome is replicated in every cell of the body. This error in cell division is responsible for 95 percent of all cases of Down syndrome. Having an extra copy of this chromosome means that each gene may be producing more protein product than normal. Cells seem to tolerate this better than having not enough protein, or having altered protein due to a mutation in the DNA sequence. The condition leads to impairments in both cognitive ability and physical growth that range from mild to moderate developmental disabilities. Through a series of screenings and tests,

Down syndrome can be detected before and after a baby is born. The only factor known to affect the probability of having a baby with Down syndrome is maternal age. That is, less than one in 1,000 pregnancies for mothers less than 30 years of age results in a baby with Down syndrome. For mothers who are 44 years of age, about 1 in 35 pregnancies results in a baby with Down syndrome. Because younger women generally have more children, about 75% – 80% of children with Down syndrome are born to younger women.

How do people get Down syndrome?

Down syndrome occurs because of an abnormality characterized by an extra copy of genetic material on all or part of the 21st chromosome. Every cell in the body contains genes that are grouped along chromosomes in the cell’s nucleus or center. There are normally 46 chromosomes in each cell, 23 inherited from your mother and 23 from your father. When some or all of a person’s cells have an extra full or partial copy of chromosome 21, the result is Down syndrome.

There are normally 46 chromosomes in each cell, 23 inherited from your mother and 23 from your father.Down syndrome is typically caused by what is called non-disjunction. If a pair of number 21 chromosomes fails to separate during the formation of an egg (or sperm), this is referred to as non-disjunction. When that egg unites with a normal sperm to form an embryo, that embryo ends up with three copies of chromosome 21 instead of the normal two. The extra chromosome is then copied in every cell of the baby’s body. Non-disjunction events seem to occur more frequently in older women. This may explain why the risk of having a baby with Down syndrome is greater among mothers age 35 and older.

What are the symptoms of Down syndrome?

Symptoms is really a misnomer. People have Down syndrome and their characteristics. Despite the variability in Down syndrome, individuals with Down syndrome have a widely recognized characteristic appearance. Typical facial features include a flattened nose, small mouth, protruding tongue, small ears, and upward slanting eyes. The inner corner of the eyes may have a rounded fold of skin (epicanthal fold). The hands are short and broad with short fingers, and may have a single palmar crease.

White spots on the colored part of the eye called Brushfield spots may be present. Babies with Down syndrome often have decreased muscle tone at birth. Normal growth and development is usually delayed and often individuals with Down syndrome don’t reach the average height or developmental milestones of unaffected individual.

How is Down syndrome treated?

No cure exists for Down syndrome. But physical therapy and/or speech therapy can help people with the disorder develop more normally. Screening for common medical problems associated with the disorder, followed by corrective surgery, can often improve quality of life. Moreover, enriched environments significantly increase their capacity to learn and lead a meaningful life.

Interesting facts about Down syndrome

• Down syndrome is really the only trisomy compatible with life. Only two other trisomies have been observed in babies born alive (trisomies 13 and 18), but babies born with these trisomies have only a 5% chance of surviving longer than one year.
• In 90% of Trisomy 21 cases, the additional chromosome comes from the mother’s egg rather than the father’s sperm.
• Down syndrome is the most common genetic disorder caused by a chromosomal abnormality. It affects 1 out of every 800 to 1,000 babies.
• Down syndrome was originally described in 1866 by John Langdon Down. It wasn’t until 1959 that a French doctor, named Jerome Lejeune, discovered it was caused by the inheritance of an extra chromosome