Heart Conditions and Diagnoses

Down Syndrome (Trisomy 21)

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What is Down syndrome?

Down syndrome, also known as Trisomy 21, is the single most common genetic pattern of malformation in man.

Most text books quote the incidence of Down syndrome to be between one in 700 to 800 live births.

In 1866, John Langdon Haydon Down described the physical features and associated medical problems that have come to be known as Down syndrome.

In the 1930s, physicians established a relationship between advanced maternal age and Down syndrome. The chromosomal, or genetic, basis of Down syndrome was not established until 1959.

Research Study

For Children and Teens 6-16 Years Old With Down Syndrome

A normal human cell contains 23 pairs of chromosomes which carry all of a person's genetic information. Due to several possible abnormal mechanisms of cell reproduction, patients with Down syndrome have an extra (third) copy of the 21st chromosome. Thus, Down syndrome is also called Trisomy 21.

Advanced maternal age is associated with a high incidence of Trisomy 21, but even women of typical child bearing age can have affected babies.

While the diagnosis may be strongly suggested by characteristic physical findings, the final diagnosis is often made only after chromosome analysis, which includes a complete count and visualization under a microscope of the chromosomes taken from cells in the blood.

A geneticist most often performs this along with a clinical evaluation.

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What are the physical characteristics of Down syndrome?

The physical characteristics of Down Syndrome in infancy typically involve low muscle tone, flat appearance of the face, upward slanting eye creases, small ears, single skin crease in the palm, extremely flexible joints, large tongue, and several others.

Physical characteristics may be very obvious, but sometimes are so subtle that the diagnosis can only be made after testing is completed. Physical findings do change as the child ages and certain features may become more or less noticeable with time.

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Non-cardiac medical problems associated with Down syndrome

While this chapter focuses on the heart problems associated with Down syndrome, some of the other medical problems seen with Trisomy 21 are:

Developmental delay -- All children with Down syndrome are delayed, although this may not be apparent until the child is beyond infancy. IQ scores range from 20 (severe mental retardation) to 85 (low normal). Overall learning abilities are usually equivalent to a 6 to 8 year old child without Down syndrome.
Gastrointestinal abnormalities -- 2 percent to 5 percent of children have complete obstruction of the small bowel known as duodenal atresia. Another 2 percent have poor movement abilities of the colon and / or rectum known as Hirschsprung disease.
Hearing loss -- Some degree of hearing loss is present in 40 percent to 75 percent of children with Down syndrome. Malformations may affect either the middle or inner ear structures. Ear infections can be a frequent, often difficult problem to treat.
Eye disorders -- 60 percent of children have eye disorders that need monitoring and treatment. Congenital cataracts (loss of transparency of the lens of the eye), glaucoma (increased pressure within the eye), strabismus (cross-eyed) and major refractory errors (far sighted or near sighted) are the common problems.
Leukemia -- Leukemia occurs in one of every 150 children with Down Syndrome. This is 20 times higher than the general population.
Thyroid disorders -- Low thyroid levels are seen in approximately 5 percent of children with Down syndrome.

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Congenital heart disease associated with Down syndrome

The overall incidence of congenital heart disease in the general population is 0.8 percent. The incidence of congenital heart disease in children with Down syndrome is up to 50 percent.

The types of heart defects in children with Down syndrome can be broken down into three broad categories:

Atrioventricular septal defects
Ventricular septal defect (VSD), atrial septal defect, or patent ductus arteriosus
Other complex heart disease

Atrioventricular septal defects (AV Canal) is greatly over-represented in these children, making up approximately 60 percent of the congenital heart disease found in Trisomy 21. For comparison, AV canals account for only 2.9 percent of the congenital heart defects in the general population.

Ventricular septal defects, atrial septal defects, and patent ductus arteriosus comprise another 20 percent of the congenital heart disease associated with Down syndrome, although these defects are much more common in the general population compared to AV canals.

Other complex congenital heart diseases including Tetralogy of Fallot and hypoplastic left heart syndrome comprise the rest of the heart disease seen in Trisomy 21.

In addition to the heart defects associated with Down Syndrome, isolated elevated blood pressure in the lungs (pulmonary hypertension) is seen with higher frequency in patients with Down syndrome. This high pressure may be related to malformation of the lung tissue, although the exact cause is not known.

The higher pressures may limit the amount of blood flow to the lungs and therefore decrease the likelihood of symptoms of congestive heart failure seen in babies with complete AV canals or large ventricular septal defects.

However, since the pulmonary hypertension can become irreversible, particularly if these large holes are not surgically corrected by a year of age, children with Down syndrome and AV canals or large ventricular septal defects are often referred for surgery earlier than a non-Down syndrome child with the same heart defect.

If the baby does have evidence of high pressures in the lungs, it may complicate postoperative management and hence prolong the recovery time.

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Signs and symptoms of children with Down syndrome and congenital heart disease

Depending on the type of heart defect, children with Down syndrome and heart disease may have a variety of symptoms.

Babies with complete AV canal defects may have signs and symptoms of congestive heart failure such as a fast respiratory rate, labored breathing, difficulty completing feedings, sweating with feedings and poor weight gain.

Children with partial AV canals can be asymptomatic because the extra blood flow to the lungs is not enough to cause symptoms of congestive heart failure.

Even babies with large ventricular septal defects as part of their heart disease who should have large amounts of extra blood flowing to their lungs may have no symptoms due to high pressures in the lungs. These babies must be watched carefully to determine the proper timing for surgery.

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Tests to diagnose congenital heart disease in babies with Trisomy 21

Most cardiologists would agree that all babies that have been diagnosed with Down syndrome should have a cardiology evaluation because of the high incidence of associated congenital heart defects.

What degree of cardiac evaluation remains controversial. A good history and physical examination should be performed by an experienced cardiologist to rule out any obvious heart defect.

Most cardiologists would perform an electrocardiogram, which can be very helpful in making the diagnosis of AV canal, even in the absence of physical findings.

Some cardiologists would be satisfied with this level of evaluation. There are those, though, who would argue that at least one echocardiogram should be performed to rule out subtle heart problems.

If the diagnosis of congenital heart disease is made, the cardiologist will follow the child with office visits on a fairly regular basis. Most patients can be watched clinically to determine if the child is having difficulty due to the heart defect.

Occasionally, a repeat electrocardiogram, chest X-ray, or echocardiogram is performed to further evaluate clinical changes. These tests are likely to be repeated before surgical repair is recommended.

Rarely, a cardiac catheterization is required for complete evaluation prior to corrective surgery, especially in patients where elevated pressures in the lungs are a concern.

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Treatment options for children with Down syndrome and congenital heart disease

Children with Down syndrome and symptoms of congestive heart failure can be initially managed medically with the use of diuretics, blood pressure medications to allow the heart to eject more blood out to the body rather than out to the lungs, and / or digoxin, a medication used to improve the pumping ability of the heart.

If the baby is having difficulty with feeding and weight gain, nasogastric tube feedings with high calorie formula or fortified breast milk can be used to help with growth.

These are all temporary solutions to allow the baby to grow while deciding if and when surgery is indicated. In general, atrial septal defects, ventricular septal defects, and AV canal defects are closed surgically if the child is demonstrating congestive heart failure that cannot be controlled with medication.

If the baby has no signs of heart failure or is controlled well with medications, the decision for surgical closure can be delayed. AV canals are usually repaired electively between 3 and 6 months of age.

Depending on the size of an atrial septal defect or a ventricular septal defect, surgery can be postponed even longer, keeping in mind the risk of developing irreversible high pressures in the lungs.

The decision must be individualized to each child's physical state as well as the family's concerns.

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Long-term prognosis of babies with Down syndrome and congenital heart disease

Overall, survival beyond one year of age is 85 percent in all children with Down syndrome. Over 50 percent of individuals with Down syndrome live to be greater than 50 years old.

Congenital heart disease is the most common cause of death in early childhood. However, as of the late 1980s, 70 percent of children with Down syndrome and congenital heart disease lived beyond their first birthday. With improved medical and surgical care, these numbers continue to improve.

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