Congenital chromosomal anomalies

What are congenital chromosomal anomalies?

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.

What are the different types of congenital chromosomal anomalies?

There are several types of chromosomal anomalies, including numerical and structure anomalies.

Numerical anomalies

This 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 - This 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 or hypotonia.

• Edward's syndrome or trisomy 18 - This occurs when there is an extra 18th chromosome, and causes organs and physical features to develop abnormally.

• Klinefelter's syndrome or XXY - This occurs when there is an additional X chromosome in males, which impacts the testosterone hormone.

• Turner syndrome - This occurs when there is a single X chromosome in females, which impacts the estrogen hormone.

Structural abnormalities

This 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).

What are the signs and symptoms of congenital chromosomal anomalies?

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)

• Infertility

• Learning disabilities

• Little to no body hair

• Low birth weight

• Mental and physical impairments

• Defects of the heart, intestines, kidneys, lungs and stomach

• Reduced muscle mass

• Distinctive facial features (widely spaced eyes, small and low ears, drooping eyelids, flattened facial profile, short neck or upward-angled eyes)

What are the causes of congenital chromosomal anomalies?

Some of the possible causes of a chromosomal anomaly include:

• 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.

• 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.

• 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.