This article explains about a genetic condition called Bardet-Biedl Syndrome. This syndrome affects multiple vital organs in the body, especially the eyes. It also affects the renal function resulting in some potentially serious complications. In this article, we will discuss about some of the symptoms, causes, and treatment of Bardet-Biedl Syndrome.
How Is Bardet-Biedl Syndrome (BBS) Defined?
- Genetic Disorder- Bardet-Biedl syndrome is a genetic multisystem pathological condition, which is characterized by deterioration of cells which receive light stimuli.1
- Extra Rudimentary Growth- These cells are called as cone and rod cells. This syndrome is also characterized by presence of an extra finger adjoining the pinky finger or an extra toe adjoining the fifth toe.
- Fat Distribution- In Bardet-Biedl syndrome, there is inappropriate distribution of fat in the chest and abdomen, a phenomenon called truncal obesity.
- Urogenital Embryonic Defects- Embryonic abnormal hypoplastic growth of the urogenital organs triggered by genetic mutation results in abnormal vagina, uterus, fallopian tube and gonads. There is also presence of renal abnormalities. Kidney dysfunction in Bardet-Biedl Disease often leads to potential life threatening complications.
- Abnormal Vision- Bardet-Biedl Syndrome affects primarily the eyes and hence progression of this disease results in potential blindness.
Causes of Bardet-Biedl Syndrome (BBS)
- Bardet-Biedl syndrome is caused from gene mutations in about 14 different genes.
- The genes are called as BBS genes. The BBS genes play an important role in cell structure named cilia.2
- Cilia are minute finger-like projections, which stick out from surface of numerous types of cells.
- Cilia are extremely important in that they are required for sensory perceptions like vision, smell, and hearing. BBS genes produce proteins, which facilitate maintenance of cilia.
- Mutations in these BBS genes cause dysfunctions in the proper functioning of cilia resulting in abnormalities in sensory perception.
- Many researchers are of the belief that this dysfunction of cilia causes most of features seen in Bardet-Biedl syndrome.
Symptoms of Bardet-Biedl Syndrome (BBS)
- Skeletal System-
- Polydactyl- Extra toe or finger
- Syndactyl- Webbing fingers and toes
- Growth retardation
- Eyes- Abnormal photoreceptor and neuron function causes following symptoms3–
- Poor Vision
- Cardiovascular System
- Cardiomyopathy– Thickening of wall of heart septum and chambers.
- Urogenital System
- Central Nervous system
- Mental Retardation
- Autistic Behavior
- Sensory System Abnormality- Patient unable to differentiate changes in temperature and pressure sensation
- Anosmia– Unable to smell or extra-sensitive smell
Diagnosis for Bardet-Biedl Syndrome (BBS)
- Examination- Diagnosis of Bardet-Biedl Syndrome is generally made depending on clinical features experienced by the affected individual.
- Metabolic Screening- However metabolic screening to include checking renal functions and cardiovascular risk factors is also performed.
- Radiological Studies- MRI studies are also conducted to confirm the diagnosis.
- Genetic Study- In some instances, genotyping is done to differentiate between Bardet-Biedl syndrome and other genetic conditions.
Treatment for Bardet-Biedl Syndrome (BBS)
- At present, there is no specific treatment for genetic disorder and definitive cure for Bardet-Biedl Syndrome.
- Poor Vision- Visual symptoms are treated with prescription glasses and frequent eye examination. As the diseases progresses, there is deterioration of vision and hence visual aids are helpful.
- Kidney Disease- Frequent urine examination is performed to evaluate kidney function once the diagnosis is established. Prognosis for people with Bardet-Biedl Syndrome who experience renal failure is extremely poor.
- Endocrinal Disorder- Such as diabetes (high blood sugar) is treated with oral anti-sugar medication or insulin.
- Metabolic Disorder- Hyperlipidemia and obesity is monitored and treated with diet control.
- Urogenital System Abnormalities- Vaginal or uterine anatomical abnormalities are treated with surgery if necessary. Hypogonadism is treated with androgen or sexual hormone.
- Skeletal Abnormalities- Polydactyl or Syndactyl are treated with surgery.
- Autism or Cognitive Behavioral Abnormalities- Psychological central nervous system diseases are treated with medications and psychotherapy.
Prognosis for Bardet-Biedl Syndrome (BBS)
- Prognosis is worst when kidney is involved and diagnosis is end-stage renal disease (ESRD). Patient may need kidney dialysis or kidney transplant.
- Vision restrictions may result in prescription glasses or blindness.
- Comprehensive molecular diagnosis of Bardet-Biedl syndrome by high-throughput targeted exome sequencing.
Xing DJ1, Zhang HX2, Huang N1, Wu KC1, Huang XF1, Huang F1, Tong Y3, Pang CP4, Qu J5, Jin ZB1.
PLoS One. 2014 Mar 7;9(3):e90599. doi: 10.1371/journal.pone.0090599. eCollection 2014.
- Novel homozygous mutations in the genes ARL6 and BBS10 underlying Bardet-Biedl syndrome.
Khan S1, Ullah I, Irfanullah, Touseef M, Basit S, Khan MN, Ahmad W.
Gene. 2013 Feb 15;515(1):84-8.
- Bardet-Biedl syndrome.
Keith CG., Aust J Ophthalmol. 1984 May;12(2):143-8.
- The importance of renal impairment in the natural history of Bardet-Biedl syndrome.
O’Dea D1, Parfrey PS, Harnett JD, Hefferton D, Cramer BC, Green J.
Am J Kidney Dis. 1996 Jun;27(6):776-83.