A chromosome rearrangement is the rearrangement of genetic material between or within the same chromosome. Some people with certain chromosome rearrangements may be at increased risk to have pregnancy losses, stillbirths, and children with chromosome abnormalities such as Down syndrome.
Your family’s health history is a major factor in determining the likelihood of you, or of someone in your family having a chromosome rearrangement. By using AccessDNA's family history tool, you will be taking an essential step towards learning your risk of having a chromosome rearrangment. Click below to use the tool or scroll down to read more about chromosome translocations and inversions.
What is a Chromosome Rearrangement?
A chromosome rearrangement is the rearrangement of genetic material within the same chromosome (called a chromosome inversion) or between chromosomes (called a chromosome translocation). Chromosome rearrangements can be detected by analyzing the structure and banding patterns of the chromosomes, which is called a chromosome analysis (or karyotype).
What is a Chromosome Translocation?
A chromosome translocation is a chromosome abnormality caused by the rearrangement of genetic material between different numbered (also called non-homologous) chromosomes.
Chromosome translocations can be characterized as balanced or unbalanced.
- A balanced translocation involves an apparently even exchange of genetic material resulting in no loss or gain of total genetic information. A balanced translocation does not typically result in physical and/or mental abnormalities.
- An unbalanced translocation involves an uneven exchange of genetic material resulting in a gain or loss of total genetic information. An unbalanced translocation is more likely to result in physical and/or mental abnormalities.
There are two main types of translocations: reciprocal and Robertsonian.
- Reciprocal translocations typically involve an exchange of genetic material between non-homologous chromosomes and are found in about 1 in 600 newborns.
- Robertsonian translocations involve the fusion of acrocentric chromosomes near the centromere with the loss of the p (short) arm. Acrocentric autosomal chromosomes include chromosomes 13, 14, 15, 21, and 22. The chromosome analysis of a person with a balanced Robertsonian translocation would reveal 45 chromosomes since two of the chromosomes have fused together. The most common Robertsonian translocation is found is about 1 in 1300 people and involves chromosomes 13 and 14.
Although people with balanced chromosome translocations do not usually have mental and/or physical abnormalities, they may be at increased risk to have pregnancy losses, stillbirths, and children with chromosome abnormalities. For example, people who carry a balanced Robertsonian translocation involving chromosome 21 have a higher chance to have a child with Down syndrome.
What is a Chromosome Inversion?
A chromosome inversion is a chromosome abnormality caused when a segment of genetic material is broken away from the chromosome, inverted from end to end, and re-inserted into the chromosome at the same breakage sites.
Chromosome inversions can be characterized as balanced or unbalanced.
- A balanced inversion involves no net gain or loss of total genetic information. A balanced inversion does not typically result in physical and/or mental abnormalities. However, in some cases, gene disruptions at the breakage site can cause genetic conditions.
- An unbalanced inversion involves a gain or loss of total genetic information. A unbalanced inversion almost always results in physical and/or mental abnormalities.
There are two type of inversions: paracentric and pericentric.
- Paracentric inversions do not include the centromere and both breaks occur in one arm of the chromosome.
- Pericentric inversions include the centromere and there is a break point in each arm.
Although people with balanced inversions do not usually have mental and/or physical abnormalities, they may be at increased risk to have pregnancy losses, stillbirths, and children with chromosome abnormalities. For example, people with balanced paracentric inversions have a higher risk to have non-viable pregnancies (pregnancies that miscarry).