Diagnosis of Ring 18

There are several different reasons that a healthcare provider might suspect that there is an underlying chromosome change present. Some of the more common reasons include:

 • Child missing developmental milestones

 • Birth defects 

• Health problems

• Minor differences in facial features 

• A family history of a chromosome condition 

On rare occasions, ring 18 may be detected before a baby is born. However, it is usually diagnosed during infancy or childhood. There are two tests that are commonly performed to identify ring 18. Both of these tests are usually performed on a blood sample. 

Routine Chromosome Analysis

 In this test, white blood cells are grown in the lab. The chromosomes are stained and examined under a microscope by a qualified cytogeneticist. This individual is trained in recognizing extra, missing, and rearranged pieces of chromosomes. Results from a chromosome analysis will tell us the number of chromosomes, whether the person is a male or a female, and which bands of the chromosome are involved in the change. The chromosome result of a person with ring 18 might look something like this:

 46,XY,r(18) 

This result tells us that the person is a male and that one of the chromosome 18’s has formed a ring. 

Although this tells us that a ring is present, it does not give us information about which genes on chromosome 18 are actually missing. For a more precise determination of the missing parts of the chromosome, a different technology is required. 

Microarray Analysis
A microarray analysis is similar to a routine chromosome analysis in that it can tell us if there are extra or missing pieces of a chromosome. However, microarrays can detect chromosome deletions and duplications that are too small to be visible under a microscope. Therefore, it is a much more precise test than a routine chromosome analysis. A microarray result can tell us with great specificity which genes are included in the deletion.

Although microarrays are very useful in determining exactly what is missing and what is extra, they cannot determine some other types of chromosome changes. Microarrays cannot detect chromosome changes that do not involve extra or missing chromosome material. For example, they cannot detect certain chromosome rearrangements, such as balanced translocations or inversions. Therefore, both tests may be ordered to fully describe the underlying genetic change.