Bardet–Biedl syndrome (BBS)
Bardet–Biedl (pronounced BAR–day BEED–el) syndrome, also known as BBS, is a rare genetic disorder of obesity that has a wide range of symptoms, including early–onset obesity and insatiable hunger. Other symptoms may include progressive vision impairment, extra toes or fingers, learning disabilities, kidney problems, and delayed puberty.
What causes BBS?
BBS is caused by variants variants Genetic variants may result in serious health problems or be “silent” with no negative health effects. , or changes, in genes genes Our body’s instruction manual that informs how our bodies grow, develop, and function. It is through our genes that traits are passed down from parent to offspring. located on the MC4R pathway MC4R Pathway The MC4R pathway is one of the pathways that regulates weight and appetite in the brain. that affect signals signals Chemicals and proteins that the body and brain use to communicate and direct processes in the body. between the brain and body. In someone with BBS, signals that control hunger don't reach the brain. This means an individual doesn't get the message that the body has had enough to eat, even after a meal. Learn more about insatiable hunger >
You may hear people refer to BBS as a ciliopathy, a disease of the cilia. Scientists are learning more each day about the genes that cause BBS and the impact they have on cilia.
“He went from 10 to 20 pounds in a month, I think. We were just amazed. When we put a bottle in his mouth, it would be gone.”
What are the signs and symptoms of BBS?
It's important to know that the signs and symptoms of BBS can vary from person to person. The severity of symptoms can also differ greatly. This can make it hard for doctors to diagnose. Signs and symptoms of BBS may include:
- Severe, early–onset obesity (often apparent by age 1)
- Insatiable hunger (hyperphagia)
- Progressive vision impairment/loss
- Extra toes or fingers (polydactyly)
- Kidney problems
- Delayed puberty in adolescence
- Learning disabilities
How is BBS inherited?
BBS is inherited from both parents. Each parent is a “carrier,” meaning they have one gene copy with the variant and one gene copy without the variant. An individual with BBS has two copies of the genetic variant that causes BBS, one from each parent.
How is BBS diagnosed?
BBS is diagnosed by a doctor based on an individual showing specific characteristics. The Beales Diagnostic Criteria, developed by Dr. Philip Beales, outlines primary and secondary characteristics of BBS. To get a clinical BBS diagnosis, an individual should have four of the primary characteristics listed below, or three primary characteristics and at least two secondary characteristics. BBS symptoms can appear over time, so it may take a while to get a clinical diagnosis. A doctor may use genetic testing to confirm a diagnosis or to identify which BBS gene is the cause.
- Visual impairment caused by retinal abnormalities (rod-cone dystrophy)
- Extra fingers or toes (polydactyly)
- Learning disabilities
- Lack of hormones hormone Chemical messengers made in the endocrine glands that control body functions. that normally stimulate the testes (hypogonadism in males)
- Kidney malformations and/or malfunctions (renal abnormalities)
- Speech disorder/delay
- Abnormalities of the eye (strabismus strabismus A condition in which the eyes don't look in exactly the same direction at the same time. , cataracts cataracts A condition in which the lens of the eye becomes progressively cloudy, resulting in blurred vision. , astigmatism astigmatism A common condition where the front surface of the eye has an irregular curve, causing blurred vision. )
- Short or fused fingers or toes (brachydactyly brachydactyly A shortening of the fingers and toes due to unusually short bones. , syndactyly syndactyly A condition wherein two or more digits are fused together. )
- Developmental delay
- Large urine output or great thirst caused by rare renal disease (polyuria polyuria A condition where the body urinates more than usual and passes excessive or abnormally large amounts of urine each time you urinate. , polydipsia polydipsia Abnormally great thirst as a symptom of disease (such as diabetes) or psychological disturbance. )
- Balance or coordination problems (ataxia)
- Mild muscle spasms (spasticity)
- Dental differences (small teeth, small lower jaw, short teeth)
- Heart abnormalities (left ventricular hypertrophy, congenital heart disease)
- Liver disease (hepatic fibrosis)
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Learn from the growing community of people living with rare genetic disorders of obesity