What is Bardet-Biedl Syndrome (BBS)?

Bardet-Biedl Syndrome (BBS) is a rare inherited genetic condition that affects multiple parts of the body. It belongs to a group of disorders called ciliopathies, which are caused by problems with hair-like structures in our cells called cilia. These structures are important for the communication and function of cells.

 BBS is passed down in an autosomal recessive pattern, meaning a child must inherit one affected gene from each parent to develop the condition. So far, researchers have identified more than 26 genes linked to BBS. Symptoms and severity can vary widely from person to person – even within the same family.

 How common is BBS?

BBS is considered a very rare disease

-         About 1 in 160 000 people are affected in Switzerland.

-         Higher rates (about 1 in 13 500 to 1 in 17 500) have been reported in Kuwait and Newfoundland, where close-relative marriages are more common.

-         The exact prevalence in Taiwan is currently unknown.

 What are the common symptoms?

The symptoms of BBS can affect many organs and systems. Doctors often group then into primary (major) and secondary (additional) features to help with diagnosis. In 2024, European Reference Networks updated the diagnostic criteria to better reflect different age groups and genetic findings.

Primary Features

1. Vision Problems

Vision issues are one of the most common features of BBS

-         Affects more than 90% of patients

-         Usually begin between 5 to 12 years of age

-         Early signs: difficulty seeing at night

-         May progress to narrowed vision (tunnel vision) and vision loss

Other possible eye problems include sensitivity to light, cataracts and refractive errors (myopia, hyperopia, astigmatism)

 2. Obesity

Many children with BBS develop weight gain early in life

-         About 90% of children over age 5 are affected

-         Often continues into adulthood

This may increase the risk of:

-         Diabetes mellitus

-         High cholesterol

-         High blood pressure

 3. Extra Fingers or Toes (Polydactyly)

-         Around 60-80% of children with BBS are born with extra fingers or toes

 4. Developmental and Learning Difficulties

Children with BBS may experience:

-         Learning difficulties and delayed development (about 60%)

-         Behavioral challenges

-         Autism spectrum features

-         Reduced or absent sense of smell

 5. Reproductive System Differences

-         Boys: may have underdeveloped genitalia or undescended testes

-         Girls: may have structural differences such as hydrometrocolpos or vaginal atresia.

 6. Kidney problems

Kidney involvement is common and can be serious.

-         Occurs in more than 50% of patients

-         May include structural abnormalities or reduce kidney function

-         Some patients may develop chronic kidney disease (CKD over time)

Secondary Features

Some individuals can also have:

-         Developmental delay

-         Congenital heart disease

-         Dental problems

-         Hormonal or metabolic conditions (such as diabetes)

-         Liver involvement (fibrosis)

 Treatment and Long-term Care

There is currently no cure for BBS. However, early diagnosis and proper care can make a significant difference.

Recommended care includes:

-         Early developmental support (screening for developmental delays)

-         Speech and occupational therapy

-         Regular eye examinations

-         Kidney function monitoring

-         Hormonal and metabolic evaluations

-         Genetic counseling for families

Care is best provided by a multidisciplinary medical team, including specialists in ophthalmology, pediatric nephrology and endocrinology.

 Support and Resources

Families can access additional support through organizations such as the Taiwan Foundation for Rare Diseases, which provides information, resources and patient support services.

 A Message for Patient and Families