Down syndrome
Incidence
1 in 800-1000 births. 1 in 200 risk at maternal age 35; 1% recurrence risk after child with trisomy 21; 10-95% risk if parental translocation.
Clinical Characteristics
Syndrome with characteristic facial appearance, upslanting palpebral fissures, single palmar creases, 5th finger clinodactyly, large space between first and second toes, hypotonia. The incidence of Down syndrome is 1 in 650 to 1 in 1000 live births and shows little variation by ethnic groups. Increasing maternal age is a significant risk factor, rising from about 1 in 2000 at age 20 years to 1 in 50 at age 40. The disorder is caused by duplicated material from the distal long arm of chromosome 21 through nondisjunction (trisomy 21) or translocation (translocation Down syndrome). The newborn with Down syndrome is often recognized because of an unusual facial appearance and low muscle tone. In some newborns, especially premature infants, facial recognition may be difficult. Characteristic minor anomalies that assist in making the diagnosis include: a central hair whorl (cowlick), flat occiput (back of the head), upslanting eyes, folds around the corner of the eye (epicanthal folds), white spots in the iris of the eye (Brushfield spots), upturned nose, extra and loose neck skin, single creases on the palms, curved fifth fingers (clinodactyly), broad space between the first and second toes, and a deep plantar crease. The tongue often protrudes, more because of low muscle tone than true enlargement. As with all syndromes, the pattern of minor and major defects in Down syndrome varies from individual to individual. None of the anomalies taken alone are specific or diagnostic for Down syndrome. When Down syndrome is suspected, a chromosome study (karyotype) will confirm or exclude the diagnosis. Neonatal liver disease is also a rare complication. Newborn jaundice, feeding problems, and narrowing of the anus that causes painful bowel movements and constipation may occur. Respiratory infections are more frequent and severe in children with Down syndrome, including chronic otitis, sinusitis, and pneumonia. Tonsillectomy and adenoidectomy are often required, but these procedures may have postoperative complications. Correctable problems such as constipation, wandering eyes (strabismus), thyroid hormone abnormalities, dental anomalies, atlantoaxial (neck spine) instability, and cryptorchidism (undescended testicles) are important not to miss. Developmental delays, learning differences, and speech problems are universal, and there is a 10% risk for behavior and psychiatric problems in older individuals with Down syndrome. Despite neuropathological changes typical of Alzheimer disease in 100% of individuals over age 35 years, symptomatic memory loss and dementia is much less frequent.
Precipitants
Old maternal age.
Provocation Tests
none
Diagnostic Procedures
When Down syndrome is suspected, a chromosome study (karyotype) will confirm or exclude the diagnosis. Prenatal diagnosis using chorionic villus biopsy or amniocentesis allows the detection of fetuses with Down syndrome by documenting the fetal karyotype. Screening of maternal serum for alpha-fetoprotein (AFP) during pregnancy is also possible, since fetuses with Down syndrome and other chromosomal abnormalities develop more slowly and result in lower AFP values in maternal serum (MSAFP values).