-IBIS-1.5.0-
tx
nervous system
Down's syndrome
diagnoses

definition and etiology

definition: An inherited autosomal condition characterized by an extra chromosome 21. Also known as "Trisomy 21", "Trisomy G" and "Mongolism".

etiology: The extra chromosome is present in 95% of the children affected. The typical occurrence is a baby born to an older mother, although random trisomic mongolism also occurs in infants of young mothers. Relatively common, the incidence is 1:700 live births: the ratio is adjusted for the mother's age at birth. In early childbirth years, the incidence is 1:2000; for mothers over 40, the ratio changes to around 1:22. The average age of mother bearing a child with Down's Syndrome is 37. The condition accounts for 1% of mental retardation.

signs and symptoms

signs and symptoms:
• Infants: usually calm, cry minimally, and have muscular hypotonicity.
• Both physical and mental developments are slowed: the mean IQ is approximately 50.

physical appearance:
• Head: Small and round, sloping forehead.
• Nose: Bridge is poorly developed or absent.
• Ears: Hung low and are round; small pinna.
• Eyes: Appear to slant upward and outward due to medial epicanthic folds; Brushfield's spots: whitish gray spots around the iris.
• Mouth: Hangs open with a large, fissured, protruding tongue.
• Hands: Exhibit one palmar crease ("simian crease"); are small and broad; fingers curve inward from hypoplastic or absent middle phalanges (clinodactyly); and have typical dermatoglyphics.
• Feet: Large space between 1st and 2nd toes, with typical dermatoglyphics.
• Brain: Subnormal weight; simple convolutional folds.

lab findings:
• X-rays: Show decreased acetabular and iliac angles.
• (+) Chromosomal analysis: Available from amniocentesis aspiration or buccal scrapings.

course and prognosis

The child born with Trisomy 21 has a decreased life span. The death rate is especially high in the first years of the child's life, from heart disease, respiratory infections, and acute leukemia. Although today, even severe cardiac birth defects may be corrected early in the child's life, death still usually occurs in the 4th or 5th decade because of an accelerated rate of aging and/or the development of a premature form of Alzheimer's cerebral degeneration.

However, most people with Down's are happy, able to work in protected environments, and delight in simple pleasures which most people take for granted.

differential diagnosis

• Cretinism (hypothyroidism of childhood)
• Other gene variants: translocations and mosaics.


footnotes