DOWN SYNDROME

Down syndrome

Down syndrome

Introduction

Down syndrome is a chromosomal disorder that affects more than 350,000 U.S. citizens. Down syndrome ranks second to fragile X syndrome as the most frequent genetic cause of mental retardation. Although recognized by Edouard Seguin, a French physician and educator, as early as 1846, the first written description of the disorder was published in 1866 by John Langdon Down, a British physician from whom the syndrome derives its name (Braunschweig, et al, 2004). Jerome LeJeune, a French geneticist, and his colleagues established the genetic basis of Down syndrome in 1959.

What is Down syndrome?

Down syndrome is the common name for a genetic anomaly, trisomy-21-nondisjunction of the 21st chromosome during meiosis, resulting in a zygote carrying an extra 21st chromosome. Down syndrome occurs in one out of every 600 to 800 live births, making it by far the most common form of chromosomal nondisjunction in the living human population (Braunschweig, et al, 2004).

Down syndrome is estimated to occur in 1 in 1,000 live births. The syndrome can be diagnosed prenatally through chromosomal analysis derived from either chorionic villus sampling or amniocentesis. Boys outnumber girls 1.3 to 1.0, and the disorder occurs in all racial and ethnic groups. Down syndrome is predominantly (95% of cases) due to trisomy of chromosome 21, involving a nondisjunction or failure of the two chromosomes of pair 21 to separate during meiosis prior to ovulation (Braunschweig, et al, 2004). Five percent of Down syndrome cases result from translocation in which part of chromosome 21 attaches to another chromosome or from mosaicism due to an error in cell division soon after conception. Increased maternal age is related to both nondisjunction and mosaicism. Down syndrome is incurable. The only current preventive strategy is termination of pregnancy, an option that appears to be increasingly utilized.

Physical and Medical Aspects

Susan (2008) mentions affected individuals share to varying degrees a set of physical characteristics. The most common features of Down syndrome include a flattened face with a recessed bridge of the nose; upward slanting eyes with epicanthal folds; small ears and mouth; large tongue; short, broad hands and feet; stubby fingers; broad neck; stocky appearance; and loose skin folds at the nape of the neck. Down syndrome has a large number of associated medical problems including congenital gastrointestinal and cardiac abnormalities, eye problems, low muscle tone, and mild to moderate conductive hearing loss secondary to chronic middle ear infections. Infants and young children with Down syndrome are also at greater risk for acute leukemia than the general population.

High rates of hypothyroidism have also been linked to Down syndrome, using normative values from the general population. Lower thyroid functioning values for people with Down syndrome may reflect the susceptibility of adults with Down syndrome to experience “premature aging” (Susan, 2008) and not thyroid disorder. Despite increased truncal obesity among people with Down syndrome, traditional risk factors for type II diabetes and cardiac disease, including hypertension, elevated lipids, and elevated glucose, are less than those reported by the general ...