Bardet-Biedl syndrome

BBS has an autosomal recessive pattern of inheritance.^[1] This means that to have the syndrome, a person must have a mutation in both copies of the responsible gene in each cell. People with BBS inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically do not have any signs or symptoms (they are unaffected). When 2 carriers of an autosomal recessive condition have children, each child has a:

• 25% chance to be affected
• 50% chance to be an unaffected carrier like each parent
• 25% chance to be unaffected and not a carrier

Some cases of BBS (fewer than 10%) appear to require the presence of at least three mutations for a person to have features of the condition. This is known as triallelic inheritance.^[1] In these cases, in addition to inheriting a mutation in the same gene from each parent, a child also needs to have at least one more mutation in another gene to be affected.