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Diseases

Genetic and Rare Diseases Information Center (GARD)

Bardet-Biedl syndrome


Other Names for this Disease
  • BBS
  • Biedl-Bardet Syndrome
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Your Question

What about siblings of people with Bardet-Biedl syndrome?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

How is Bardet-Biedl syndrome inherited?

Bardet-Biedl syndrome (BBS) has an autosomal recessive pattern of inheritance.[1] People with this syndrome have pathogenic variants (mutations) in both copies of a gene associated with Bardet-Biedl syndrome. These people typically have unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier, and a 25% chance to not have the condition and not be a carrier (i.e. have 2 normal copies of the gene). An affected individual's full siblings who do not have Bardet-Biedl syndrome have approximately a 66 % (2/3) chance of being a carrier for the condition. Autosomal recessive disorders are typically not seen in every generation of an affected family. [1]

Some cases of Bardet-Biedl syndrome appear to require the presence of at least three mutations for the symptoms to show (), which is known as triallelic inheritance,[1] in which mutations in more than one gene are involved in a condition. In these cases, in addition to inheriting a single mutation of the same gene from each parent, like in a recessive trait, a child also needs at least one more mutation of another gene to have the syndrome.

However, in practical terms,  these families are fewer than 10% of all families with BBS.[1] Therefore, the inheritance is considered to be autosomal recessive in most cases. 
Last updated: 7/18/2016

References
Other Names for this Disease
  • BBS
  • Biedl-Bardet Syndrome
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.