Bardet-Biedl syndrome is a rare genetic condition that may be difficult to diagnose, but genetic testing can help confirm it. Visual challenges, localized obesity, and extra digits in hands or feet are common signs.

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 BBS mostly experience visual impairment.

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

To reach a diagnosis, a doctor may explore different signs and symptoms that could initially indicate BBS. Some may already be obvious to a parent or guardian, and others may require testing or waiting for a child to be able to communicate.

Doctors may initially consider BBS if a child is born with extra fingers, toes, or both. This is formally known as polydactyly. According to the National Organization for Rare Disorders, polydactyly is present in about 70% of people who have BBS.

Cone-rod dystrophy (the loss of rods and cones in the eyes) is also common in BBS and makes it hard to see in the dark. So, night blindness is another symptom that may lead to a BBS diagnosis.

Additionally, children with BBS gradually lose peripheral (side) and central vision, so a doctor may look for signs that the little one has reduced vision during the day, too.

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

Other symptoms of BBS may 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 or an underdeveloped uterus and fallopian tubes

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.

BBS symptoms overlap with those of other conditions, making diagnosis challenging.

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 old.

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

Major clinical signs include:

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

Minor clinical signs include:

  • challenges 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 challenges related to 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 at an earlier age. Some people with BBS have mutations (changes) to the BBS1 or BBS10 gene. These genes are linked to a protein that 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.

After receiving a diagnosis, the next step is to coordinate the necessary care. Because the condition is so rare, not many doctors have experience diagnosing or treating BBS. But a pediatrician may be a good source of referrals to a specialist.

Organizations like the Bardet-Biedl Syndrome Foundation may also help with more information and doctor referrals. The National Organization for Rare Disorders (NORD) also offers multiple resources for families and caregivers, including patient assistance programs.

Depending on the symptoms and age, some of the specialists that may be needed to treat BBS include:

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

Managing BBS may require multiple visits to doctors for tests and follow-up care.

Treatment for BBS can help manage symptoms and prevent complications, such as diabetes, kidney damage, metabolic syndrome, and vision loss. Weight management — through diet and sometimes medication — may also become an important part of BBS management.

BBS is a rare condition that doctors typically diagnose in infancy or early childhood. Symptoms may include partial vision loss, quick weight gain in the trunk and belly, and extra toes and fingers.

Doctors diagnose BBS based on its symptoms. Genetic testing can help 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.