Here, we will talk about genes on 18p that have been linked to specific health concerns. It is important to have an understanding of basic genetic concepts. You can read about genes and chromosomes here.

Of the 67 genes on 18p, the very large majority do not have an impact when deleted. As of this writing, six genes on 18p have an unknown effect when deleted. There are a handful of genes that we know are associated with significant health concerns. Families and physicians are able to keep track of the latest information about the genes on chromosome 18 through the Gene Dosage map. If you have a concern for one of the conditions described here, it is important to speak with your healthcare provider.

TGIF1: Holoprosencephaly
This gene is located in chromosome band 18p11.31. About 10% of individuals who are missing TGIF have a particular kind of brain malformation called holoprosencephaly. In people with holoprosencephaly, the brain did not divide into two separate halves during early embryonic development. There is a wide range of severity of holoprosencephaly. In some cases, this condition is severe, and the pregnancy does not survive to delivery, or the baby dies shortly after birth. Other people with holoprosencephaly may have milder forms. For example, an MRI may show that their brain has minor changes, such as a missing corpus callosum (the connection between the two halves of the brain). There may be changes in the facial features as well, such as a cleft lip and or a single incisor (front tooth) located at the midline of the mouth.

GNAL: Dystonia
This gene can be found in chromosome band 18p11.21. Individuals with deletions that include this gene are more likely to develop a neurologic condition called dystonia. Dystonia is an involuntary contraction of muscles. Because the muscles cannot relax, people with dystonia may have twisting, repetitive movements or changes in their posture. This condition is most often identified in the teens or early adulthood. At this point in time, we do not know how likely it is that someone missing this gene will develop dystonia. As research advances, we hope to better understand the likelihood of developing dystonia in individuals missing this gene.

SMCHD1: Facioscapulohumeral muscular dystrophy type 2 (FSHD2)
This gene is located in chromosome band 18p11.32. People who are missing one copy of this gene and also have some genetic changes present on chromosome 4 have an increased possibility of having FSHD2. FSHD2 is a type of muscular dystrophy. It causes weakness in several areas of the body, including the face, the shoulders, the upper arms, and the upper legs. However, the grand majority of people with 18p- do not have FSHD, as additional genetic changes are also required to develop features of this condition.

In addition to the genes listed above, there are a number of genes that are currently under investigation.  You can learn about them here.