** Just a disclaimer, my personal thoughts are in italics
Down syndrome: Excerpt from Professional Guide to Diseases (Eighth Edition)
The first disorder attributed to a chromosome aberration, Down syndrome (trisomy 21) characteristically produces mental retardation, dysmorphic facial features, and other distinctive physical abnormalities. It's commonly associated with congenital heart defects (in approximately 60% of patients) and other abnormalities.
Life expectancy for patients with Down syndrome has increased significantly because of improved treatment for related complications (heart defects, respiratory and other infections, acute leukemia). Nevertheless, up to 44% of such patients who have congenital heart defects die before age 1 year (
this should say if left untreated).
Causes and incidence
Down syndrome usually results from trisomy 21, a spontaneous chromosomal abnormality in which chromosome 21 has three copies instead of the normal two because of faulty meiosis (nondisjunction) of the ovum or, sometimes, the sperm. This results in a karyotype of 47 chromosomes instead of the normal 46. In about 4% of patients, Down syndrome results from an unbalanced translocation in which the long arm of chromosome 21 breaks and attaches to another chromosome. Most commonly, this is a robertsonian translocation and results in an increased risk of having multiple children with Down syndrome. The disorder may also be due to chromosomal mosaicism with two cell lines — one with a normal number of chromosomes (46) and one with 47 (an extra chromosome 21).
Down syndrome occurs in 1 in 660
(some references claim up 1 in 800) live births, but the incidence increases with advanced parental age, especially when the mother is age 34 or older at delivery or the father is older than age 42. At age 20, a woman has about one chance in 2,000 of having a child with Down syndrome; by age 49, she has one chance in 12. However, if a woman has had one child with Down syndrome, the risk of recurrence is 1% to 2% unless the trisomy results from translocation.
Signs and symptoms
The physical signs of Down syndrome (especially hypotonia) as well as some dysmorphic facial features and heart defects may be apparent at birth. The degree of mental retardation may not become apparent until the infant grows older. People with Down syndrome typically have craniofacial anomalies, such as slanting, almond-shaped eyes with epicanthic folds; a flat face; a protruding tongue; a small mouth and chin; a single transverse palmar crease (simian crease); small white spots (Brushfield's spots) on the iris; strabismus; a small skull; a flat bridge across the nose; slow dental development, with abnormal or absent teeth; small ears; a short neck; and cataracts.
Other physical effects may include dry, sensitive skin with decreased elasticity; umbilical hernia; short stature; short extremities, with broad, flat, and squarish hands and feet; clinodactyly (small little finger that curves inward); a wide space between the first and second toe; and abnormal fingerprints and footprints. Hypotonic limb muscles impair reflex development, posture, coordination, and balance.
Congenital heart disease (septal defects or pulmonary or aortic stenosis), duodenal atresia, megacolon, and pelvic bone abnormalities are common. The incidence of leukemia and thyroid disorders (particularly hypothyroidism) may be increased. Frequent upper respiratory infections can be a serious problem. Genitalia may be poorly developed and puberty delayed. Females may menstruate and be fertile. Males are infertile with low serum testosterone levels; many have undescended testicles.
Patients with Down syndrome may have an IQ between 30 and 70; however, social performance is usually beyond that expected for mental age. The level of intellectual function depends greatly on the environment and the amount of early stimulation received in addition to the IQ.
Diagnosis
Physical findings at birth, especially hypotonia, may suggest this diagnosis, but no physical feature is diagnostic in itself.
Confirming diagnosis
A karyotype showing the specific chromosomal abnormality provides a definitive diagnosis. Amniocentesis allows prenatal diagnosis and is recommended for pregnant women older than age 34 even if the family history is negative. Amniocentesis is also recommended for a pregnant woman of any age when either she or the father carries a translocated chromosome.
Treatment
Down syndrome has no known cure. Surgery to correct heart defects and other related congenital abnormalities and antibiotic therapy for recurrent infections have improved life expectancy considerably. Plastic surgery is occasionally done to correct the characteristic facial traits, especially the protruding tongue. Benefits beyond improved appearance may include improved speech, reduced susceptibility to dental caries, and fewer orthodontic problems later. Most patients with Down syndrome are now cared for at home and attend special education classes. As adults, some may work in a sheltered workshop or live in a group home facility.
Special considerations
Support for the parents of a child with Down syndrome is vital. By following the guidelines listed below, you can help them meet their child's physical and emotional needs.
❑ Establish a trusting relationship with the parents, and encourage communication during the difficult period soon after diagnosis. Recognize signs of grieving.
❑ Teach parents the importance of a balanced diet for the child. Stress the need for patience while feeding the child, who may have difficulty sucking and may be less demanding and seem less eager to eat than normal babies.
❑ Encourage the parents to hold and nurture their child.
❑ Emphasize the importance of adequate exercise and maximum environmental stimulation; refer the parents for early intervention as soon as the diagnosis of Down syndrome is made.
Pediatric tip
Balanced nutrition and exercise gain increased importance as the child ages. Obesity commonly becomes problematic.
Pediatric tip
All children with Down syndrome need to be checked for atlantoaxial instability before they engage in exercise or sports.
❑ Refer the parents and older siblings for genetic and psychological counseling, as appropriate, to help them evaluate future reproductive risks. Discuss options for prenatal testing.
❑ Encourage the parents to remember the emotional needs of other children in the family.
❑ Refer the parents to national or local Down syndrome organizations and support groups such as the National Down Syndrome Congress.
