Cowden syndrome is part of a group of conditions called PTEN hamartoma tumor syndrome (PHTS). It is usually caused by a harmful variant—sometimes called a mutation—in one copy of the PTEN gene. The PTEN gene helps regulate cell growth. When it does not work properly, certain cells may grow or form growths more readily. Many of these growths are benign, but the change also raises the chance of developing some cancers.

Cowden syndrome is usually inherited in an autosomal dominant pattern. A person has two copies of most genes, one from each parent. If a person has a harmful PTEN variant in one copy, each of their children has a 50% chance of inheriting that variant. The chance is the same for each pregnancy, and the variant can be passed on by people of any sex.
Sometimes the variant is not inherited from either parent. It can arise for the first time in the affected person; this is called a de novo variant. In that situation, the person may be the first in the family known to have Cowden syndrome. A de novo result does not mean the person did anything to cause it.

An inherited PTEN variant can affect people in the same family differently. One relative may have noticeable skin or mouth growths, while another may have few obvious features. The age when features appear and the types of health problems can also vary. So, a relative who seems healthy may still carry the family variant.

When a harmful inherited variant is found in one person, relatives may be offered genetic counseling and targeted testing for that specific variant. This can help identify who may benefit from screening and who did not inherit the family variant. A genetic counselor or clinical geneticist can explain what a test result means, discuss possible implications for relatives, and help plan next steps.
Cowden syndrome is one condition within the broader PHTS group. People with a harmful inherited PTEN variant can have overlapping features, and their clinical label may depend on their particular symptoms and medical history. In practice, care is guided by the person’s PTEN result, health features, and family history.