Bardet-Biedl Syndrome – Understanding the Disease
The Rare Disease Odyssey
BBS is part of what is known as the “rare disease odyssey”. It has been determined that on average, it takes five to seven years to come up with the right diagnosis. During this time, patients probably see anywhere between six and eight different doctors and receive an average of four different alternative diagnoses.
BBS is a Ciliopathy
BBS is part of a recently described disease category called ciliopathies that together affect up to 1 in 700 individuals spread across at least 35 diseases. Ciliopathies share a common etiology arising from dysfunction of cilia, finger-like appendages projecting from the apical surface of most cells in the body.
Cilia are ubiquitous throughout the animal kingdom and come in two broad types – motile and non-motile (primary), which are most abundant and important for cellular signaling. Primary cilia are essential components of many cell types and we are increasing our understanding of their function. Common overlapping phenotypes include defective sensory, renal, neurocognitive, and endocrine/metabolic components.
The Impact of BBS
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Developmental Delay/Learning Difficulties
Speech and motor skill deficits, impaired social skills, behavioral issues, and learning difficulties are all common in patients and can persist into adulthood.
Rod Cone Dystrophy
Night vision difficulties arise by mid-childhood, followed by blind spots in the periphery of vision. Most patients are legally blind by mid-teens due to progressions in central vision loss.
Patients can have a reduced sense of smell or inability to smell anything.
A majority of patients experience dental anomalies due to abnormal tooth development, with thin enamel covering, dental crowding and small roots. Many also have a high-arched palate.
These range from an underactive thyroid to insufficient sex hormones, such as low testosterone or oestrogens.
Congenital Heart Disease
Patients are occasionally born with congenital heart anomalies (ASD, VSD) or acquire thickening of the heart’s muscular walls (LVH).
From our own natural history data we see that a quarter of patients develop Type 2 diabetes mellitus at some point in their life.
Structural renal and urinary tract anomalies, cysts and renal dysfunction affect roughly 50-80% of patients.
Patients suffer from genital and urinary abnormalities. Males show undescended testis with small penis and infertility. Females have ovaries, uterus fallopian tubes and vagina affected.
Weight gain is quickly evident in the first two years of life and becomes a life-long problem, driven by excessive eating.
Patients are often born with extra fingers or toes, or digit variations such as shorter, mildly webbed or fused digits.