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Down's Syndrome Prader-Willi Syndrome Cerebral Palsy

Down's Syndrome

M Collins and A Laverty, Muckamore Abbey Hospital, Antrim, UK

© 2005 Elsevier Ltd. All rights reserved.

Down's syndrome, named after John Langdon Down, is the most widely recognized chromosomal disorder found in humans and falls into a category of chromosomal disruptions known as trisomies; hence the other term for the condition, trisomy 21. People with Down's syndrome vary widely in their abilities, but the syndrome is the most common genetic cause of learning disability. The syndrome is characterized by abnormalities of both structure and function, some of which may be amenable to nutritional intervention.

More than 90% of Down's syndrome individuals have a total of 47 chromosomes in cells instead of the usual 46. The remaining cases are mainly either translocations, where there is a rearrangement of fragments of chromosomes, or mosaics, in whom there are both normal and trisomic cells (i.e., mosaic trisomy 21). There is a relationship between the frequency of Down's syndrome births and age, with both very young mothers and older mothers having a higher incidence of the syndrome. It has been suggested that nutrition may be implicated in the nondisjunction of the chromosomes. The additional chromosomal material in Down's syndrome usually comes from the mother, but it can come from the father, and one study reported that the maternal age relationship had been found associated with paternal origin of the additional chromosome. This observation may be indicative of hormonal changes in the older mother that reduce the likelihood of spontaneous abortion in an abnormal pregnancy.

The incidence of Down's syndrome is approximately 1 in 600-1000 live births. Prevalence is rising as life expectancy has improved in recent years with advancing medical knowledge and higher standards of care, but concurrently there is a declining incidence of live births in industrialized countries due to prenatal diagnostic screening and abortion.

Physical defects common in Down's syndrome include congenital anomalies of the gastrointestinal tract, which occur in approximately 12% of infants with Down's syndrome. Most of these anomalies require the neonate to be operated on immediately to allow nutrition. Congenital heart disease occurs in approximately 40% of infants with Down's syndrome. Children with congenital heart disease may present with failure to thrive, but after surgical repair of heart defects these children usually improve. Immune dysfunction, increased susceptibility to leukemia, and premature aging with Alzheimer-like changes in the brain are major features of the syndrome.

Thyroid dysfunction is more common in people with Down's syndrome, with the incidence increasing as they get older. Hypothyroidism is most frequently reported, but hyperthyroidism can also occur. Correction of thyroid function is essential to allow normal learning processes to take place and to aid weight control.

There are many biochemical anomalies associated with the syndrome, mainly quantitative rather than qualitative. It is presumed that the overexpression of genes on chromosome 21 contributes to both the structural and the functional pathology. Overdose effects of the genes already mapped to chromosome

Table 1 Nutritional complications of Down's syndrome

Physical

Problems with muscle tone, oral health and

dentition, chewing, and swallowing

Metabolic

Anomalies in carbohydrate protein and lipid

metabolism

Increased demands on antioxidant defence

system and methylation pathways

Increased incidence of diabetes, coeliac

disease, obesity, and thyroid disorders

Behavioral

Food consumption and exercise choices

21 are thought to alter pathways controlling the production of monocarbons, purines, pyrimidines, tubulins, and myelin.

The nutritional complications associated with Down's syndrome are summarized in Table 1.

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