Someone who has an extra chromosome has 47 total chromosomes instead of the typical 46, or 23 from each parent. This results in a condition known as trisomy. Trisomy is associated with mental retardation and often death, depending on which chromosome has malfunctioned.
Trisomy which occurs on the 13th or 18th chromosomes results in severe mental retardation. Babies born with this condition generally die from medical complications within days, and sometimes sooner. The vast majority of chromosomal disorders happen in early pregnancy and cause the fetus to abort itself, resulting in a miscarriage. Therefore, most babies who have an extra chromosome die.
In one condition, however, children can live and even have productive lives if treatment and special education and attention is given. Babies born with trisomy 21, or an extra chromosome 21, have a condition known as Down Syndrome. Although children with Down Syndrome do suffer form some level of mental retardation, the majority of them are high-functioning.
Children with Down Syndrome generally have a distinctive physical appearance, with smaller heads than normal and eyes that are rounded at the ends instead of pointed. They may also have lack of muscle tone, small ears and mouths, and wide hands with short fingers. The mental capabilities of these children vary widely, but most can live productive lives if the proper interventions are taken early.
A mother is more likely to have a child with an extra chromosome as she gets older. This could be because her eggs are aging and are more likely to have chromosomal defects than those of a younger woman. There is no known prevention for Down Syndrome, although diagnostic testing can be performed during pregnancy to determine if an unborn child has the condition. These are not always accurate, as most babies with abnormal tests do not have Down Syndrome.
Aside from physical characteristics and mental differences in children born with an extra chromosome, serious health conditions can often occur. These can include vision problems, intestinal blockages, heart problems including an enlarged heart, constipation, sleep apnea, and hypothyroidism. Many of these things can be successfully treated, although severe heart conditions may require surgery to correct.
Diagnosis for Down Syndrome can generally be made based on blood test results which test for an extra chromosome 21. Suspicion of Down syndrome will generally occur right at birth though when the doctor notices the typical physical characteristics common with trisomy 21. The infant will be checked for additional health problems once a diagnosis has been made.