Bardet-Biedl syndrome (BBS) is a rare genetic condition that is often diagnosed in infancy or early childhood. BBS can be hard to diagnose, but genetic testing can help confirm it.

Bardet-Biedl syndrome (BBS) is a rare inherited condition that predominantly affects the retina. The retina is a layer of light-sensitive cells at the back of your eye that helps you see. People who are born with this condition gradually lose their vision.

BBS also affects other parts of the body. It can cause extra fingers and toes, obesity, and learning disabilities. Often, the diagnosis is made during infancy or early childhood.

Because this condition involves so many parts of the body, a team of specialists is necessary to treat it. While there is no cure for BBS, lifestyle strategies and medications can help manage the symptoms and prevent complications.

Doctors may first suspect BBS if a child is born with extra fingers, extra toes, or both. Healthcare professionals refer to the presence of extra digits as polydactyly. According to the National Organization for Rare Disorders, polydactyly is present in about 70% of people who have BBS.

Night blindness is another symptom that often leads to a BBS diagnosis. Cone-rod dystrophy (the loss of rods and cones in the eyes) makes it hard to see in the dark. Children with BBS gradually lose their peripheral (side) vision and central vision.

Some people with BBS may become legally blind. BBS can damage the retina in a similar way to a condition called retinitis pigmentosa.

Although most babies with BBS are born at a typical weight, they may gain weight quickly during the first year of life, particularly in their belly and chest. Weight gain can lead to health problems such as type 2 diabetes, metabolic syndrome, and heart disease.

Other symptoms of BBS include:

  • learning disabilities
  • webbed fingers and toes
  • below-average height
  • kidney disease
  • liver disease
  • arrhythmias (irregular heart rhythms)
  • reduced sense of smell
  • underdeveloped genitals, such as a small penis or undescended testicles in males and an underdeveloped uterus and fallopian tubes in females

The symptoms of BBS overlap with those of other conditions. These similarities can make the condition challenging to diagnose.

Before genetic testing was widely available, the average age at diagnosis was 9 years old. Vision loss often led doctors to suspect this condition. Now that genetic testing is more common, the average age at diagnosis has decreased to 6 years.

To receive a BBS diagnosis, a child must have at least four major clinical signs or three major clinical signs and two minor clinical signs.

Major clinical signs include:

  • retinal cone-rod dystrophy
  • central obesity (above-average fat deposits in the trunk and belly)
  • an extra finger or toe
  • learning disabilities
  • underdeveloped genitals or sexual organs (testes or ovaries) that make few to no sex hormones (hypogonadism)
  • kidney disease

Minor clinical signs include:

  • problems with coordination and speech
  • decreased or lost sense of smell
  • a heart defect or valve problem
  • missing teeth or too many teeth that are crowded
  • inflammatory bowel disease
  • digestive issues caused by rare conditions such as Hirschsprung disease
  • type 2 diabetes
  • metabolic syndrome
  • reduced production of thyroid hormone (subclinical hypothyroidism)
  • polycystic ovary syndrome

Genetic testing can sometimes help confirm the diagnosis. Some people with BBS have mutations (changes) to the BBS1 or BBS10 gene. These genes code for a protein your body needs to make cilia, which are hair-like projections that stick out from the surface of cells and help with cell movement and signaling.

BBS is rare. The number of people who are living with this condition varies in different parts of the world.

In North America and Europe, between 1 in 120,000 and 1 in 160,000 people have BBS. The condition is more common in some places, including Kuwait and the Newfoundland region of Canada, because marriages between members of the same family may happen more often in those places.

It can be hard to find doctors who specialize in BBS. The condition is so rare that very few doctors have treated it. You might be able to ask your child’s pediatrician for a referral to a specialist or check with an organization such as the Bardet Biedl Syndrome Foundation.

To manage the condition, people with BBS may need treatment from multiple specialists, such as the following:

  • primary care doctor
  • eye doctor
  • hepatologist (liver specialist)
  • nephrologist (kidney specialist)
  • endocrinologist (hormone specialist)
  • dietitian
  • geneticist
  • speech and language therapist

Managing BBS requires many visits to doctors for tests and follow-up care.

BBS has no cure. Treatment aims to manage symptoms and prevent complications from conditions such as diabetes, kidney damage, metabolic syndrome, and eye damage. Weight management — through diet and sometimes medication — is an important part of treatment.

BBS is a rare condition that’s typically diagnosed in infancy or early childhood. It causes vision loss, weight gain in the trunk and belly, and other complications.

Doctors diagnose BBS based on its symptoms. Genetic testing can help doctors confirm the diagnosis.

Because BBS affects so many parts of the body, treatment from many specialists is necessary to manage it. While BBS isn’t curable, treatments are available to relieve the symptoms and prevent complications.