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TBC1D20 gene

Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

TBC1D20 gene

The TBC1D20 gene provides instructions for making a protein that regulates cellular processes by controlling the activity of specific GTPase proteins.

Normal Function

The TBC1D20 gene provides instructions for making a protein that helps regulate the activity of other proteins called GTPases, which control a variety of functions in cells. Often referred to as molecular switches, GTPases can be turned on and off. They are turned on (active) when they are attached (bound) to a molecule called GTP and are turned off (inactive) when they are bound to another molecule called GDP.

The TBC1D20 protein turns off a GTPase known as RAB18 by stimulating a reaction that turns the attached GTP into GDP. When active, RAB18 is involved in a process called vesicle trafficking, which moves proteins and other molecules within cells in sac-like structures called vesicles. RAB18 regulates the movement of substances between compartments in cells and the storage and release of fats (lipids) by structures called lipid droplets. The protein also appears to play a role in a process called autophagy, which helps clear unneeded materials from cells. RAB18 is important for the organization of a cell structure called the endoplasmic reticulum, which is involved in protein processing and transport.

The TBC1D20 protein is also thought to inactivate another GTPase called RAB1. RAB1 is important for maintaining the structure of a cell compartment called the Golgi apparatus, in which newly produced proteins are modified so they can carry out their functions. The TBC1D20 protein also appears to play a role in the copying (replication) of viruses in infected cells.

Health Conditions Related to Genetic Changes

RAB18 deficiency

At least five mutations in the TBC1D20 gene have been found to cause Warburg micro syndrome, which is the most severe of the disorders caused by RAB18 deficiency. Warburg micro syndrome is characterized by multiple eye abnormalities, vision impairment, severe intellectual disability, and a reduction of the hormones that direct sexual development (hypogonadotropic hypogonadism).

The TBC1D20 gene mutations that cause Warburg micro syndrome eliminate the function of the TBC1D20 protein. Researchers suspect that loss of this protein's function disrupts the normal control of RAB18 activity. It is unclear, though, how the resulting changes in RAB18 activity might lead to eye problems, brain abnormalities, and other features of Warburg micro syndrome.

Coloboma

MedlinePlus Genetics provides information about Coloboma.

Other Names for This Gene

  • C20orf140
  • dJ852M4.2
  • WARBM4

Frequently Asked Questions

RAB18 deficiency is a rare genetic disorder that can affect multiple body systems. Common symptoms include neurological issues such as developmental delay, intellectual disability, and sometimes seizures. Individuals may also experience eye abnormalities, skin problems, and issues related to lipid metabolism, as the RAB18 protein is involved in fat storage and release.
Diagnosis of RAB18 deficiency typically involves a combination of clinical evaluation of symptoms and genetic testing. Genetic testing looks for specific mutations in the TBC1D20 gene. Imaging studies, such as brain MRI, and metabolic tests may also be performed to assess the extent of the condition and rule out other disorders.
Currently, there is no specific cure for RAB18 deficiency. Treatment focuses on managing symptoms and providing supportive care. This may include therapies for developmental delays, anti-seizure medications if epilepsy is present, and ophthalmological care for eye issues. A multidisciplinary team approach involving neurologists, geneticists, and other specialists is often recommended.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.