Bardet-Biedl Syndrome: Symptoms & Treatment | GetWellGo

Bardet-Biedl syndrome (BBS) is a genetically inherited disease that influences several systems of the body. It is also part of a group of diseases known as ciliopathies due to its root cause having to do with the cellular organelles known as cilia that play a role in communication and motility in various cell types.

Bardet-Biedl Syndrome Symptoms

The signs of Bardet-Biedl syndrome (BBS) may be extremely variable from one person to another, even in the same family. But there are certain essential features that frequently occur, together with secondary ones that can occur as well.

Primary (Core) Symptoms:

These are generally necessary for diagnosis:

Rod-cone dystrophy

• Progressive loss of vision due to retinal degeneration
• Night blindness (frequently in early childhood)
• Tunnel vision, with blindness in adult life

Polydactyly

• Extra fingers or toes (generally on the outer edge of hands or feet)

Obesity

• Onset is early childhood    
• Most frequent type is central obesity

Difficulty in learning

• Mild to moderate intellectual impairment
• Speech delay and poor coordination are frequent

Male hypogonadism

• Underdeveloped genitalia and delayed onset of puberty

Abnormalities of the kidneys

• Structural or functional abnormalities
• Risk of chronic kidney disease or failure

Secondary Symptoms:

These can validate the diagnosis if primary symptoms are encountered:

• Speech and language delay
• Behavioral issues (e.g., emotional immaturity, poor interpersonal skills)
• Developmental delay (motor skills, coordination)
• Dental anomalies (crowded teeth, missing teeth, defects in enamel)
• Anosmia (deficiency or impaired sense of smell)
• Type 2 diabetes mellitus
• Hypertension (increased blood pressure)
• Heart anomalies (e.g., congenital heart defects)
• Hearing loss
• Liver anomalies
• Poor balance and coordination

Bardet-Biedl Syndrome Treatment

Bardet-Biedl Syndrome (BBS) is treated symptomatically and supportively since there is no cure at present. Management involves a multidisciplinary team to monitor and treat the affected systems.

Key Areas of Treatment and Management:

Vision Care

• Routine eye examinations (by an ophthalmologist)
• Low-vision devices: magnifiers, Braille materials, screen readers
• Orientation and mobility training
• Note: Retinitis pigmentosa is progressive and not reversible at present

Weight Management

• Nutritional guidance
• Exercise programs
• Behavioral therapy for eating habits
• In other instances, anti-obesity drugs or bariatric surgery might be indicated

Kidney Monitoring and Treatment

• Routine kidney function tests
• Ultrasound scans for structural defects
• Early treatment of high blood pressure
• Nephrology follow-up to avoid progression to kidney failure

Hormonal and Genital Problems

• Hormone replacement therapy (particularly in men with hypogonadism)
• Urological or reproductive referral as necessary

Learning and Behavioral Support

• Early intervention programs
• Individualized education plans
• Speech therapy, occupational therapy, and physical therapy
• Psychological counselling for behavioural or emotional difficulties

Treatment of Other Health Problems

• Diabetes: monitoring of blood sugar, diet, medications
• Hypertension: routine monitoring, medications
• Dental care: orthodontic care and oral hygiene
• Hearing aids if hearing loss exists

Bardet-Biedl Syndrome Diagnosis

Bardet-Biedl syndrome is diagnosed on the basis of a combination of clinical findings and genetic analysis. Due to wide variability in symptoms, particularly in early childhood, diagnosis is difficult and delayed.

Clinical Diagnostic Criteria

Diagnosis can be suspected clinically when an individual presents with a distinctive combination of features.

Major (Primary) Features:

• Rod-cone dystrophy (retinitis pigmentosa)
• Polydactyly (extra digits or toes)
• Obesity (in early childhood)
• Learning disability or developmental delay
• Hypogonadism in males
• Renal abnormalities

Minor (Secondary) Features:

• Speech disorder or delay
• Behavioral defects
• Dental defects
• Diabetes mellitus
• Anosmia (smell loss)
• Congenital heart disease
• Hearing loss
• Liver fibrosis

Diagnosis is made when:

≥4 primary features, or

3 primary + 2 secondary features

Genetic Testing

• Genetic confirmation is by finding mutations in one of the established BBS genes (more than 20 genes identified, including BBS1, BBS10, etc.).
• Next-generation sequencing (NGS) or whole exome sequencing is most frequently utilized
• Confirms the diagnosis and assists with family planning
• BBS is inherited in an autosomal recessive fashion

Other Tests (to complement diagnosis):

• Eye examination (ERG, funduscopy): for retinitis pigmentosa
• Kidney function tests and renal ultrasound
• CT or MRI scan (kidneys and brain, if necessary)
• Hormonal levels (such as testosterone in males)
• Developmental and intelligence tests
• Tests of hearing
• Cardiac examination

Bardet-Biedl Syndrome Causes

Bardet-Biedl syndrome (BBS) is a genetic disorder resulting from mutations in certain genes that impair the function of cilia—microscopic hair-like appendages on cells that play a significant part in cellular signaling and upkeep.

BBS is usually passed on in an autosomal recessive pattern, so both parents must have a mutated version of the gene for a child to be born with the condition. A child will only be affected with BBS if they receive a mutated gene from both parents.

Genetic Causes:

• Mutations in BBS genes
• Autosomal Recessive Inheritance

Environmental Factors:

• There is no conclusive evidence to propose that environmental reasons (such as lifestyle or diet) lead to Bardet-Biedl syndrome.
• Certain components of the syndrome (e.g., obesity) are, however, possibly modified by environmental causes, although the causative genetic mechanism remains unchanged.

Bardet-Biedl Syndrome Genetic Testing

Genetic testing is essential for the diagnosis confirmation of Bardet-Biedl syndrome (BBS), particularly when clinical features are in accordance with the disorder but are not conclusive. It is useful not only in diagnosis but also in genetic counselling for families, establishing the mode of inheritance, and identifying the particular gene mutations involved.

Types of Genetic Testing for BBS:

Targeted Genetic Testing

• Applied when a particular mutation is suspected due to the clinical presentation (for example, if a family has a known history of a particular BBS gene mutation).
• Screens for mutations in one or more of the established BBS genes.
• Typically screens for BBS1, BBS10, and other BBS-related genes.

Next-Generation Sequencing (NGS)

• NGS panels for BBS will typically screen multiple genes at once, including all established BBS-related genes.
• This test is very sensitive and effective, with the ability to identify rare or unknown mutations.
• Exome sequencing (sequencing all of the protein-coding genes in the genome) is a more general test that can be performed if targeted testing is not conclusive.

Whole Genome Sequencing (WGS)

• A more extensive test that sequences the whole genome (all genes, regulatory regions, etc.).
• This is not typically utilized but can be useful to detect mutations that may not be detected by NGS or targeted sequencing.

Gene Panels

• Ciliopathy-specific panels, including BBS and other associated conditions (e.g., Meckel-Gruber syndrome, Joubert syndrome).
• These panels screen for mutations in all cilia-related genes.

Bardet-Biedl Syndrome Prognosis

The prognosis in Bardet-Biedl syndrome (BBS) is highly variable across patients and depends on the intensity of symptoms, whether there is involvement of certain organs, and the age of diagnosis and treatment. As BBS is a multisystem, progressive disease, the prognosis will generally be based on the aggregate effects of a number of health issues that have occurred over a lifetime.

Most Important Points in Prognosis in BBS:

Vision Impairment:

• Retinitis pigmentosa is a characteristic feature, causing progressive loss of vision.
• Night blindness typically first presents as the initial symptom, followed by visual field constriction (tunnel vision).
• The majority of individuals with BBS will become legally blind by adulthood.
• Vision loss may be variable, and some individuals may maintain some useful vision into old age.
• Low vision devices and assistive technology can be used to compensate for vision loss.

Kidney Function:

• Most people with BBS have renal abnormalities, ranging from mild to severe.
• Chronic kidney disease is prevalent and may result in kidney failure in some people.
• Kidney function must be monitored regularly, and early treatment of kidney-related complications (e.g., hypertension) can enhance long-term outcomes.

Obesity:

• Obesity usually starts in childhood and is a major health issue.
• This may result in comorbidities like diabetes, cardiovascular disease, and joint issues.
• Weight management by diet, exercise, and in some cases medical treatment is essential to enhance long-term health results.

Developmental and Intellectual Disabilities:

• Most people with BBS have mild to moderate developmental delay and learning disabilities.
• These are typically treatable with early intervention, special education, and therapy.
• Intellectual disability severity varies, and some people become relatively independent in adulthood, while others require more assistance.

Endocrine and Reproductive Health:

• Hypogonadism (underdeveloped sex organs) is prevalent, especially in men.
• Early detection of hormonal imbalance can result in proper treatments, including hormone replacement therapy, to enhance quality of life.
• Fertility can be compromised, especially in men, but most people with BBS can bear children, although fertility options may have to be sought.

Life Expectancy:

• Life expectancy in patients with Bardet-Biedl syndrome may be normal or slightly diminished, depending on the degree of kidney disease and cardiac involvement.
• Early treatment and meticulous management of complications can enhance quality of life and prolong life expectancy.

Bardet-Biedl Syndrome Kidney Disease

Kidney (renal) anomalies are among the principal characteristics of Bardet-Biedl Syndrome (BBS) and largely determine the prognosis of the disorder. They can be structural, functional, or both. In some cases, in individuals with kidney disease, this can result in chronic kidney disease (CKD) or end-stage renal disease (ESRD) and require dialysis or transplant.

Epidemiology of Kidney Involvement in BBS:

Structural Abnormalities:

• Dysplastic or abnormal kidneys
• Cystic kidneys (renal cysts)
• Renal hypoplasia (underdeveloped kidneys)
• Hydronephrosis (urine accumulation causing swelling)
• Duplex kidneys or other urinary tract malformations

Functional Abnormalities:

• Impaired kidney filtration (low glomerular filtration rate or GFR)
• Proteinuria (presence of protein in the urine)
• Tubular dysfunction (abnormalities in salt and water management)

Bardet-Biedl Syndrome Obesity

Obesity is one of the defining characteristics of Bardet-Biedl Syndrome and tends to occur in early childhood, usually in the first 3 years of life. In contrast to typical obesity, obesity that is associated with genetic and hormonal disturbances in the syndrome is harder to treat using conventional weight reduction measures alone.

Why Obesity Exists in BBS

BBS impairs primary cilia function — small sensory organelles on cells that play a role in signaling pathways, such as those that govern hunger, metabolism, and energy balance. Brain regions like the hypothalamus, where the dysfunction of these cilia leads to:

• Altered satiety signaling (patients remain hungry after eating)
• Decreased resting metabolic rate
• Disrupted fat storage and insulin resistance

BBS gene mutations interfere with essential pathways, such as the leptin pathway, which controls hunger and energy expenditure.

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