Pediatric Chromosomal Anomalies
A chromosomal anomaly is a change to a child’s genetic material or DNA, which alters the baby's development before birth. This can include extra, missing or irregular chromosomes.
DNA is the building block of life and responsible for everything in your body, including eye color, organ development, height, facial features and motor development. A chromosomal anomaly is a congenital (present at birth) disorder that causes irregularities in the DNA makeup, such as extra or missing chromosomes. These anomalies are also known as chromosomal disorders or mutations.
Anomalies occur while a baby is developing in their mother's womb, and an error takes place during cell division. Typically, a child has 23 pairs of chromosomes, or a total of 46 chromosomes, in each cell. Children normally receive 23 pairs from the egg and 23 pairs from the sperm.
There are several types of chromosomal anomalies, including numerical and structure anomalies.
Numerical abnormalities occur when there is either a missing chromosome (monosomy) from a pair, or a child has more than two chromosomes of a pair (trisomy). The following are examples and some of the characteristics related to the disorder.
- Down syndrome or trisomy 21 – occurs when there is an extra full or partial 21st chromosome and alters mental development, as well as characteristic facial appearance and poor muscle tone (hypotonia).
- Edward's syndrome or trisomy 18 – occurs when there is an extra 18th chromosome, and causes organs and physical features to develop abnormally.
- Klinefelter's syndrome or XXY – occurs when there is an additional X chromosome in males, which impacts the testosterone hormone.
- Turner syndrome – occurs when there is a single X chromosome in females, which impacts the estrogen hormone.
Structural abnormalities include missing sections or duplications of chromosomes. Transfers (translocations) occur when sections move to another chromosome. Inversions occur when a chromosome breaks off and reattaches upside down. Rings will form when a chromosome section breaks off and forms a separate circle with or without the loss of material. The following are examples and some of the characteristics related to the disorder.
- Cri du chat syndrome or 5p minus syndrome – partial deletion of the short arm of the 5th chromosome, which impacts head size and birth weight.
- Jacobsen syndrome or 11q deletion disorder – loss of genetic materials from the 11th chromosome, resulting in distinct facial features and developmental delays.
- Pallister Killian syndrome – duplication of the 12th chromosome, resulting in intellectual disabilities, seizures and poor muscle tone (hypotonia).
Some of the possible causes of a chromosomal anomaly include:
- Environmental factors — substances like toxic chemicals or types of radiation may play a role, but there hasn’t been conclusive evidence that proves a specific environmental trigger will cause anomalies.
- Maternal age — older women are at higher risk of having children with an abnormality
- Meiosis mistake (an error in the mother or father’s reproductive organs that causes an egg or sperm to have less than 23 pairs).
- Mitosis error — when a problem occurs during cell division. In normal division, mitosis duplicates the original cell, but an abnormality occurs when two cells are instead created during the duplication process.
Symptoms depend on the type of chromosomal anomaly, and can include the following:
- Abnormally-shaped head
- Below average height
- Cleft lip (openings in the lip or mouth)
- Defects of the heart, intestines, kidneys, lungs and stomach
- Distinctive facial features (widely spaced eyes, small and low ears, drooping eyelids, flattened facial profile, short neck or upward-angled eyes)
- Learning disabilities
- Little to no body hair
- Low birth weight
- Mental and physical impairments
- Reduced muscle mass