A List of Genetic Syndromes Caused by Abnormal Chromosome Numbers

Page content

Cells are the basic units of life. When grouped together they form the tissues and organs inside the body. Cells normally contain 23 pairs of chromosomes, or a total of 46 chromosomes each. Chromosomes are inherited from both parents, of which 22 pairs are autosomes and one pair is composed of sex chromosomes. Sex chromosomes determine the gender of the child. Females have two X chromosomes and males contain an XY. The mother always contributes one X, and from the father either an X or Y.

Chromosomes are also made up of genes. Genes are important in the production of proteins which are vital for normal growth and development. Once any of these genes or chromosomes is missing or duplicated, the production of proteins will also change. It will either produce too little or too much which often result in the abnormal growth and development of an individual. Genetic disorders are usually inherited from either one of the parents or from both of them. Some genetic mutations however, can occur randomly and affect individuals without any history of the disorder in the family. Some environmental factors can also promote genetic mutations as well.

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

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’s Syndrome

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

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

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

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.


Learn.Genetics: What are Genetic Disorders?

MedicineNet.com: Genetic Disease