List of Genetic Syndromes Caused by Abnormal Chromosome Numbers
Anomalies occur because of abnormalities in the structure and numbers of chromosomes. When one chromosome in a given pair is missing, it is called a monosomy. One example is Turner syndrome. A trisomy occurs when an additional chromosome appears in the genetic make-up of an individual. Examples are Down syndrome, Patau syndrome, Klinefelter syndrome and Edward's syndrome.
Down syndrome, also referred to as trisomy 21, is the most common chromosomal disorder. It affects approximately 1 in every 800 live births. Babies with Down syndrome have an extra number 21 chromosome. It usually presents as a lifelong mental disability, along with delays in growth and development. The distinct appearance of an affected person includes flat facial features, small head, upward-slanting eyes, large protruding tongue and oddly shaped ears.
Patau syndrome is a rare chromosomal anomaly resulting from the presence of another chromosome number 13. It is the common cause of miscarriage in the early stage of pregnancy, yet there are infants that are able to survive after birth. Affected children usually present with organ defects, physical malformations and mental retardation.
Edward’s syndrome, or trisomy 18, is a chromosomal disorder where there is an extra copy of chromosome number 18. Infants with trisomy 18 have low birth weight, microcephaly or small size of head, smaller mouth and jaw, overlapping fingers and congenital heart problems. Most infants with this condition rarely live past the first year of life.
Klinefelter syndrome is a chromosomal abnormality where male children get an additional X chromosome. Symptoms of the syndrome usually vary with age. Babies with Klinefelter syndrome have difficulty sitting, crawling and walking, as their muscles are weak. As the child gets older, his testosterone level becomes abnormally low, thus he appears less masculine and his sex characteristics are often underdeveloped compared to other boys of his age.
Turner syndrome, a monosomy, affects females and usually occurs because one of her X chromosomes is missing. Females with this disorder are usually appear short with webbed neck and low-set ears. Their sexual characteristics are often affected, thus they do not experience puberty at the same time as most girls. Their ovaries also do not develop properly and this often results in infertility.