A Look at Human Genetics: Down Syndrome

People from all races have children with Down syndrome. Socioeconomic status has no impact on the frequency of the incidence of this disorder. More than 400,000 people in the United States have Down syndrome, and live with the impact it creates on their lives. While no one knows why it occurs, the risk of having a child with this condition is greater with advanced maternal age. However, most children with Down syndrome are actually born to women under 35, probably because more women of this age actually have babies.

Down syndrome, or Trisomy 21, is a genetic disorder affecting approximately 1 in 800 births. Physical features specific to the disorder as well many different health related problems are likely to occur with Down syndrome. Congenital heart conditions are common, as is low muscle tone. Many children have problems with digestion as well. Vision problems are also typical. A variety of developmental delays are characteristic of Down syndrome, with many children being served in special education environments. Cognitive impairments seem to occur across the board, however, the severity varies greatly. Most have mild to moderate cognitive delays. With a closer look at human genetics, Down syndrome being the focus, we will see how this disorder occurs.

When a woman conceives, both mother and father typically contribute 23 chromosomes each, adding up to 46 total chromosomes. In Down syndrome, a child inherits an extra chromosome, with a total of 47 chromosomes. The extra chromosome occurs in chromosome 21. This is usually caused by something known as nondisjunction. When a number 21 chromosome does not separate during the egg or sperm cell formation, it is called a nondisjunction. When this malformed egg or sperm meets a normal egg or sperm and an embryo is formed, there will be 3 number 21 chromosomes. When this happens, Down syndrome is the result. Having an extra chromosome means that more protein than normal is present in the genes. This possibly contributes to the symptoms caused by certain genes on the 21st. chromosome.

Carriers of Down syndrome can sometimes be the result of something caused Robertsonian translocation. This is when the arm of the number 21 chromosome breaks off and joins another chromosome at the center. The baby will not have Down syndrome symptoms, but may have a child with the disorder as a result of this occurrence.

As we see with a look at human genetics, Down syndrome spontaneously occurs without any known cause. The result of trisomy 21 is a variety of differences, symptoms, and challenges, but people with Down syndrome are more like others than not, and this is what we should remember when working with these children as teachers.

1. National Association for Down Syndrome: http://www.nads.org/pages_new/facts.html

2. Kids Health: http://kidshealth.org/parent/medical/genetic/down_syndrome.html#

3. Genetics Science Learning Center: http://learn.genetics.utah.edu/content/disorders/whataregd/down/