Down Syndrome

In most pregnancies, when the baby is conceived, the egg cell from the mother and the sperm cell from the father each contain 23 chromosomes—or half of the number of chromosomes needed to make a complete human cell. When the egg and sperm combine, the resulting embryo contains 46 total chromosomes or 23 pairs; a complete set of genetic material.

Sometimes, however, there may be more than 23 chromosomes present in either the egg or the sperm cell. When an extra chromosome is present during fertilization, this extra chromosome (known as trisomy) becomes part of the embryo’s genetic material and can lead to problems. Having an extra copy of the 21st chromosome results in Down syndrome, also called trisomy 21.

There is currently no reason to believe that prospective parents can do anything to cause or prevent Down syndrome. Doctors and researchers are unable to find a specific cause for the extra chromosome that causes Down syndrome. The only known risk factor is maternal age over 35 at the time of birth. However, more babies with Down syndrome are born to women under age 35 because more women have babies under the age of 35.

The symptoms of Down syndrome include:

• Eyes that slant upward
• Small ears that may fold over slightly at the top
• A small mouth, making the tongue appear large
• A small nose with a flattened nasal bridge
• A short neck
• Small hands with short fingers and a single crease in the palm
• Short stature
• Unusual looseness of the joints

In addition to physical appearance, having an extra 21st chromosome can also cause health problems in different parts of the body, including:

• Congenital heart disease
• Intestinal malformations and/or abdominal wall defects
• Visual impairment such as crossed eyes, nearsightedness, farsightedness or cataracts
• Hearing loss due to fluid in the ear, a nerve defect or a combination of both
• Increased risk for thyroid problems such as hyperthyroidism or hypothyroidism
• Increased risk for leukemia
• Sleep apnea
• Increased risk of colds, bronchitis and pneumonia

Additionally, Down syndrome involves some degree of intellectual disability. The severity of intellectual disability ranges from mild to moderate to severe, with most cases involving moderate intellectual disability.

Not all children with Down syndrome will have all of the physical characteristics or health problems associated with the condition. It is very difficult to determine in advance how severe the physical and intellectual effects of Down syndrome will be, and these effects vary significantly from person to person.

Diagnosis of Down Syndrome

Doctors at Riley at IU Health usually diagnose Down syndrome prenatally through genetic testing such as chorionic villus sampling or amniocentesis. It may also be detected during a fetal ultrasound, although ultrasound is not a 100 percent accurate form of diagnosis because babies with Down syndrome often look the same on ultrasound as babies without Down syndrome.

A physical examination may also reinforce suspicions of Down syndrome after birth, as babies with Down syndrome share unique physical characteristics. If Down syndrome is suspected based on prenatal test results or a physical exam, blood testing will be done after birth to confirm the diagnosis.