Bardet-Biedl syndrome (BBS)

Bardet-Biedl syndrome (BBS)

Overview

Bardet-Biedl (BAR-day, BEE-dul) syndrome, also called BBS, is a rare condition caused by changes in genes. BBS can affect almost any part of the body. Starting in early childhood, extra weight gain and vision loss can happen. People with BBS also can have issues that include kidney conditions, changes in sex organ development, and extra fingers or toes. The condition can affect speaking, learning, thinking and memory.

There is no cure for Bardet-Biedl syndrome, but early diagnosis and treatment for conditions related to BBS can ease symptoms, lessen complications and help with a better quality of life. Because BBS can affect many body systems, different specialists may be needed to manage care.

Symptoms

Symptoms of Bardet-Biedl syndrome develop slowly. The symptoms usually are noticed during the first 10 years of life, but sometimes later. Symptoms and when they begin can vary greatly among people with BBS. Some people may have only a few mild symptoms. Others may have many or more severe symptoms.

Symptoms that occur more often may include:

Having extra weight, starting in early childhood.

Poor eyesight, leading to vision loss.

Changes with how the kidneys develop and work.

Low hormone levels that cause changes in sex organ development, delayed puberty and changes in sexual function.

Extra fingers or toes, called polydactyly (pol-e-DAK-tuh-lee).

Changes that affect speaking, learning, thinking and memory.

Other symptoms may include:

Changes with the brain and nerves that may cause seizures or affect speech, walking, balance and coordination.

Changes that affect mood and behavior.

Medical conditions such as diabetes, high cholesterol, high blood pressure, sleep apnea and liver disease.

Changes related to thyroid hormone.

Digestive system conditions, such as inflammatory bowel disease or celiac disease.

Not being able to smell, a condition called anosmia.

Eye conditions, such as the eyes not focusing together, called strabismus, and clouding of the eye lens, called a cataract.

Needing to urinate often during the day and night.

Developmental symptoms may include:

Delays in growth and development.

Short height and short fingers or toes. Sometimes two fingers or toes are attached by extra skin called webbing.

Heart conditions present at birth.

Dental conditions, including small, short teeth and a small lower jaw.

Causes

Changes in certain genes can cause Bardet-Biedl syndrome. These changes might be new or passed down from parents to children. Many different gene changes can result in BBS. Even though a lot has been learned about the genes linked with the condition, it's not fully understood how changed genes cause specific symptoms. Sometimes, healthcare professionals diagnose BBS based on symptoms because they can't find changes in genes.

BBS may be inherited in an autosomal recessive way. This means that each parent passes on one changed gene to the child.

Risk factors

Parents can pass down to their children the changes in genes that cause Bardet-Biedl syndrome.

Complications

Complications of Bardet-Biedl syndrome can include:

Extra weight gain. Most people with BBS have extra body weight by the time they are 3 to 5 years old. This continues into adulthood. The extra body weight can affect health and limit the ability to do daily activities.

Long-term kidney disease and loss of kidney function. Changes in how the kidneys develop and function can cause long-term kidney conditions. Extra body weight and diabetes raise the risk of developing kidney disease. Some people develop end-stage renal disease, which results in the kidneys not being able to filter waste and toxic substances from the body and get rid of them in urine.

Vision loss and blindness. Rods and cones are the cells in the eye that are important for sight. These light-sensitive cells, called photoreceptors, are on the tissue at the back of the eye. This tissue is called the retina. With BBS, these rods and cones are slowly destroyed over time, a condition called retinal degeneration. Vision loss occurs in almost all people with BBS and often starts in early childhood. The first symptom may be trouble seeing in low light. Low vision, but not total blindness, usually happens around 15 years of age.

Hormone imbalances. Changes in hormone balance can affect growth and development. Changes in development of the sex organs before birth, including the testicles and ovaries, can affect the hormones that cause puberty.

Other health conditions. Having BBS can raise the risk of other medical conditions, such as diabetes, high blood pressure, high cholesterol, fatty liver disease, poor coordination and obstructive sleep apnea.

Learning disabilities. Speaking, learning, thinking and memory can be affected and can impact daily functioning and independence.

Behavioral issues and mental health conditions. Autism spectrum disorder is common. Other conditions can include depression, obsessive-compulsive disorder, anxiety, hyperactivity and behavior challenges.

Diagnosis

Bardet-Biedl syndrome is a very rare condition. Symptoms begin over time and may include many that can happen in other genetic conditions. Because of this, BBS may not be diagnosed right away.

To diagnose BBS, your child's healthcare professional does a physical exam, checks weight and blood pressure, and talks with you about symptoms and your family history. Because many symptoms of BBS can be found in other medical conditions, genetic testing is helpful in confirming the diagnosis.

Genetic testing looks for gene changes known to cause BBS. Sometimes the genetic test doesn't show a difference in genes, so the diagnosis is based on symptoms.

For genetic testing, a sample of DNA is examined in the lab. One of these methods is used to get the sample:

Cheek swab. A cotton swab is rubbed inside the cheek to get a cell sample.

Saliva collection. Saliva is spit into a collection tube.

Blood test. A sample of blood is taken from a vein in the arm.

A genetic counselor talks with you about the results of genetic testing. A counselor also can offer information on the risk of BBS for future children. Testing other family members may be suggested.

Diagnosis may involve other lab tests to check hormone levels, liver and kidney function, blood sugar, and cholesterol. Your child may have exams of the eyes and teeth. Your child also may have imaging tests to check the heart, lungs, digestive system, brain, kidneys and sex organs.

Sometimes a healthcare professional suspects BBS before birth based on ultrasound images of the baby that show kidney changes and extra fingers or toes. Talking with a specialist in medical genetics can help to confirm the diagnosis.

Treatment

Treatment for conditions related to BBS can ease symptoms, lessen complications and help make quality of life better. But there is no treatment for the changed genes that cause Bardet-Biedl syndrome.

Because BBS can affect almost any part of the body, different specialists may be needed. A Bardet-Biedl syndrome multispecialty center provides this expertise and experience in one place.

Depending on your child's needs, your care team may include specialists in:

Eye conditions, called ophthalmology.

Hormone conditions, called endocrinology.

Medical genetics.

Nutrition and weight management.

Kidney conditions, called nephrology.

Digestive system conditions, called gastroenterology.

Urinary system and reproductive system conditions. These may include specialists in urology and gynecology.

Dental conditions.

Your care team also may include specialists in:

Children who have complex conditions related to development and behavior, called developmental pediatrics.

Mental health and behavior.

Weight management

Constant hunger and an urge to eat that's hard to control can be linked with BBS. This can be challenging when trying to manage eating every day. Your care team can help you create a plan for managing weight that works for your child and your family. Your plan may include nutrition guidance, strategies for encouraging healthy eating and physical activity, recommendations for managing challenging behaviors, and medicine.

A dietitian with expertise in BBS can help create a food plan that considers your child's calorie needs and other health conditions such as kidney conditions, diabetes and high blood pressure. The dietitian also can offer suggestions for meal planning, meal portions and meal schedules. The dietitian can suggest home tips to help control access to extra food.

Setmelanotide (Imcivree) is approved by the U.S. Food and Drug Administration for weight management in people with BBS who are overweight and age 2 and older. The medicine causes weight loss and may help lessen constant hunger and the urge to eat.

Setmelanotide is given as a shot once a day. The most common side effects can include darker skin color, irritation at the spot where the shot was given, upset stomach and headache, among others.

Other medicines

Other medicines may be needed, depending on other health conditions. For example, medicines can treat diabetes and low thyroid. Hormone therapy can help with growth and sexual development.

Therapies

Starting therapy early can help with muscle strength, coordination and speech delays. Therapies can include physical therapy, occupational therapy, and speech and language therapy. Behavioral therapy and mental health treatments might be recommended based on needs and goals.

Vision aids

There is currently no treatment for vision loss. Glasses can help with some early vision changes. Low vision aids, such as magnifiers, large print formats and high-resolution images, can help with low vision. Communication devices or assistive technology, such as audio description devices, text-to-speech programs and smart speakers, can help people with blindness. Learning braille, using a white cane for mobility and getting help from a service animal are options too.

Surgery

Surgery may be done for:

Extra fingers or toes. Surgery can remove extra fingers or toes or separate fingers or toes.

Changes in development that happen before birth. Surgery can help with changes that affect heart development. Surgery also may be done for differences with sex organs and urinary tract changes that happened before birth.

Kidney failure. Kidney transplant may be an option for some people when the kidneys no longer work.

Cataracts. If an eye lens becomes cloudy, a condition called a cataract, the lens can be replaced with a lens implant.

Ongoing care

Regular, ongoing medical visits are an important part of lifelong care. At each visit, the healthcare professional does a physical exam and checks blood pressure and weight. The medical team does blood tests or other tests to check the liver, kidneys, blood sugar and hormone levels. Regular eye exams and dental care are important too.

Type of Doctor department :  A medical geneticist