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BUB1B gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

BUB1B gene

The BUB1B gene provides instructions for making the BUBR1 protein, which is critical for ensuring chromosomes are correctly separated during cell division.

Normal Function

The BUB1B gene provides instructions for making a protein called BUBR1, which is important for proper chromosome separation during cell division. Before cells divide, they must copy all of their chromosomes. The copied DNA from each chromosome is arranged into two identical structures, called sister chromatids, which are attached to one another during the early stages of cell division. The sets of chromosomes align within the cell, with each chromatid attached to a structure called a spindle microtubule; when all chromatids are correctly attached, the spindle microtubule pulls the two halves of the chromatid pair to opposite sides of the cell. The cell then divides in two such that each new cell contains one complete set of chromosomes.

The BUBR1 protein helps ensure that each sister chromatid is attached to a spindle microtubule. If any chromatids remain unattached, the protein prevents cell division.

Health Conditions Related to Genetic Changes

Mosaic variegated aneuploidy syndrome

More than a dozen mutations in the BUB1B gene have been found to cause mosaic variegated aneuploidy (MVA) syndrome type 1. This condition is characterized by cells with abnormal numbers of chromosomes, a situation known as aneuploidy. Affected individuals grow slowly and have an unusually small head size (microcephaly) and an increased risk of developing cancer in childhood.

MVA syndrome type 1 occurs when both copies of the BUB1B gene have mutations. These mutations reduce the amount of BUBR1 protein in cells or impair the protein's ability to function. A shortage of functioning BUBR1 protein leads to errors in the distribution of chromatids during cell division. Without BUBR1 protein, cell division can proceed, even if all the chromatids are not attached to spindle microtubules. Unattached chromatids are not positioned correctly for separation, and the resulting cells have abnormal numbers of chromosomes.

Research suggests that impairment of the process that delays cell division until the correct time underlies the increased risk of cancer in MVA syndrome. Researchers speculate that the abnormal cells undergo self-destruction (apoptosis), and the signs and symptoms of MVA syndrome may be due to the loss of cells from various tissues during early development.

Other disorders

Mutations in the BUB1B gene can also cause a related problem with chromosomes called premature chromatid separation trait. Although individuals with this trait have chromosome abnormalities that indicate trouble with normal chromosome separation during cell division, affected individuals usually have no health problems related to the trait. This trait occurs in individuals with a genetic change in one of the two copies of the BUB1B gene.

Frequently Asked Questions

Diagnosis begins with cytogenetic testing via blood karyotyping or skin fibroblast analysis, which reveals multiple different aneuploidies (mosaic gains and losses of entire chromosomes, such as monosomies and trisomies) in at least 25 percent of dividing cells. Definitive molecular confirmation is achieved by sequencing the BUB1B gene to identify biallelic pathogenic variants.
Because BUB1B mutations causing mosaic variegated aneuploidy (MVA) syndrome carry a high early risk for embryonal tumors, surveillance protocols typically include frequent abdominal ultrasounds (every 3 months up to age 7 to 8) to screen for Wilms tumor, complete physical examinations to identify rhabdomyosarcomas, and periodic clinical checks for hematologic malignancies.
Children with BUB1B-related MVA frequently face profound prenatal and postnatal growth retardation, microcephaly, distinct facial features, intellectual disability, and congenital heart defects. Early intervention with physical, speech, and occupational therapies is critical, as is routine endocrine and nutritional support to address severe failure to thrive.
The BUB1B gene encodes BUBR1, a crucial checkpoint protein that monitors whether chromosomes are properly attached to the mitotic spindle before a cell divides. A deficiency in functioning BUBR1 allows cells with unattached or misaligned chromosomes to proceed prematurely through mitosis, resulting in daughter cells with random, unpredictable numbers of extra or missing chromosomes.
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.

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