What Is Robertsonian Translocation?

Written by Lilianna Hogan
Medically Reviewed by Dan Brennan, MD on February 16, 2024
3 min read

Abnormalities in the structure of chromosomes within someone’s genetic makeup are called structural chromosomal abnormalities.

Robertsonian translocations are very rare structural chromosomal abnormalities — with only about one in 900 people having them. Translocations like this happen on their own and are out of our medical control.

If the Robertsonian translocation is passed along to a child, it may cause a type of Down syndrome. There is also a risk of having a baby with Patau syndrome, a rare genetic condition that causes serious birth defects. ‌

Chromosomes are the microscopic building blocks of our genetic makeup. They tell your body all of the information it needs to know in order to take shape and function properly.

Humans normally have 46 chromosomes — 23 from the mother and 23 from the father. Each chromosome has a short and a long arm.

Chromosomes 13, 14, 15, 21, and 22 have a very short arm, which doesn’t contain any unique genetic material, and are called acrocentric chromosomes.

In a translocation, two of these five chromosomes break at the short arm.  The broken acrocentric chromosomes then fuse together so that these chromosomes now have two long arms but no short arms. While the short arms on these chromosomes aren’t functional, the short arms on the remaining acrocentric chromosomes can be of service.

Because the other acrocentric chromosomes lend only their short arms, there are no health problems that come from Robertsonian translocations. Still, a Robertsonian translocation carrier will only have 45 chromosomes, not 46. 

You may either inherit a Robertsonian translocation from your parents or get it over time. So, you can also pass it along to your child. 

There are two kinds of Robertsonian translocations:

  • Balanced Robertsonian translocation — If a person has this kind of Robertsonian translocation, they’re called a Robertsonian translocation carrier. These carriers live healthy, long lives. They may not even know they have this translocation, and they may pass it down from generation to generation without anyone knowing. 
  • Unbalanced Robertsonian translocation — This translocation may be discovered only after a baby is born. In many babies with an unbalanced Robertsonian translocation, parents have normal chromosomes — the baby gets the condition when it’s growing in the womb. In very few babies with this condition, one parent may be a Robertsonian translocation carrier. 

The main medical concern for people who have a Robertsonian translocation is that they may pass along extra genetic material to their children. But, your child won’t always inherit your translocation.

The inheritance of a Robertsonian translocation from you to your child can work out in three ways:

  • Your child may receive none of the chromosomes involved in the Robertsonian translocation from either parent. This will result in a healthy child with no genetic abnormalities.
  • Your child may receive a set of chromosomes with Robertsonian translocations and a set of normal chromosomes from one parent and then a set of normal chromosomes from the other parent. Then, your child will have extra genes. This can lead to a disability like translocation Down syndrome in your child. But, the kind and severity of the disability depend on exactly which chromosomes the child has inherited.
  • Your child may receive one copy of the translocated chromosomes and one set of regular chromosomes. Though your child may not get a disability, they’ll be a Robertsonian translocation carrier.

A woman with a Robertsonian translocation has a high risk of miscarriage or having a child with a disability. But, the miscarriage risk is pretty low in Robertsonian translocation carriers.

Some men with a Robertsonian translocation have lowered sperm count — or a lessened ability to produce sperm.

Most people might not even know that they have a Robertsonian translocation until they have a baby born with extra genetic material. However, there are tests that both you and your partner can take to get a better idea of the risk your child might have of having a disability.

This test is usually recommended to people who have been known to have chromosome translocations in their family or to people who are at risk of having chromosomal irregularity.

The test will be a simple blood test — where your blood is drawn and the chromosomes in your blood cells are seen under a microscope. Your healthcare provider checks to see if your chromosomes are regular or not.