Down Syndrome: A Gift Of God?

in medicine, biology

"Every child is created special, with awesome purpose and amazing potential." Sarah Palin's ‘letter from God’ refers to Trig Palin's Down syndrome.  Down syndrome is the most common single cause of human birth defects.

Down syndrome is a genetic condition due to the presence of an additional copy of a chromosome. Chromosomes are thread like structures located inside the nucleus of cells, packaged with DNA. Human cells have 23 pairs of chromosomes. However, individuals with Down syndrome have an extra copy of chromosome 21, in full or part, in their cells. Down syndrome is also called trisomy 21, meaning three chromosome 21 copies. The extra chromosome causes problems with the way the body and brain develop.

Sarah Palin was not the first to rescind prenatal elimination of Down syndrome fetuses.  The man who discovered the cause of Down syndrome, Dr Jerome Lejeune, maintained that a cure should be the focus, not rejection of the Down syndrome fetus. In 1959 Lejeune was the first to discover that Down syndrome resulted from an extra chromosome, which was later identified as chromosome 21.

down syndrome trisomy 21Lejeune did not get a Nobel Prize for this discovery.  According to Neri and Opitz, "the Nobel Prize never come immediately after the discovery for which it is awarded, giving Lejeune sufficient time to make many enemies within the scientific establishment."  They added: " (he) was an outspoken critic of prenatal diagnosis as a means to prevent the birth of Down syndrome children, in contrast to the prevailing view."  Lejeune's focus was to find a cure for Down syndrome based on a metabolic intervention.

The risk for many aneuploidies (euploid, when chromosome number is normal) increases with maternal age. According to the National Institute of Child Health and Human Development, the chance of having a baby with Down syndrome increases as a woman gets older-from about 1 in 1,250 for a woman who gets pregnant at age 25, to about 1 in 100 for a woman who gets pregnant at age 40.  Prenatal screening can identify fetuses with trisomy 21.

  trisomy 21 down syndrome  

The above Figure illustrates the 23 pairs of chromosomes and the extra chromosome 21 seen in trisomy 21.  Autosomes are chromosomes other than the sex chromosomes. Females will have two X chromosomes and males have one X and one Y chromosome. These are called sex chromosomes. Trisomy results in 47 chromosomes. Image: National Library of Medicine. 

There is a general cognitive impairment in individuals with Down syndrome due to deficits in learning, memory and language. Not all individuals with Down syndrome show the same phenotype.  This variation is believed to be due to genetic and epigenetic variations, and environmental factors. By middle age (around 40 years) most of them develop plaques and tangles characteristic of Alzheimer disease. They also have disproportionately smaller volumes of frontal and temporal areas in cerebellum.

About a half of children with Down syndrome are born with heart problems and severe heart problems may lead to early death.

Recent advances in medical treatment and social inclusion have significantly increased the life expectancy of people with Down syndrome. Though premature aging is a characteristic of Down syndrome, individuals with Down syndrome are living longer than ever before. In 1929, the life span of those with Down syndrome was only nine years, where as, they now live well beyond 50 years.   

A quick search of the public database of the NIH (National Institutes of Health, USA) funded grants show that over 220 studies are currently funded to investigate clinical and basic science aspects related to Down syndrome.  Influential people like Sarah Palin must be able to attract additional private funding for further studies on this debilitating disease, so that a cure can be found faster.

Source References:
Down syndrome: comments and reflections on the 50th anniversary of Lejeune's discovery.Neri G, Opitz JM. Am J Med Genet A. 2009;149A(12):2647-54. PMID:19921741.

Down syndrome--recent progress and future prospects. Wiseman FK, Alford KA, Tybulewicz VL, Fisher EM. Hum Mol Genet. 2009 Apr 15;18(R1):R75-83. PMID:19297404.

Down syndrome: from understanding the neurobiology to therapy. Gardiner K, Herault Y, Lott IT, Antonarakis SE, Reeves RH, Dierssen M. J Neurosci. 2010;30:14943-5.PMID:21068296.

Molecular basis of pharmacotherapies for cognition in Down syndrome. Gardiner KJ.Trends Pharmacol Sci. 2010;31:66-73. Epub 2009 Dec 4.PMID:19963286.

 

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