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Bardet-Biedl syndrome (BBS) is named after Georges Louis Bardet, a French physician (born 1885) and after Artur Biedl, a Hungarian pathologist and endocrinologist (born 1869). It is a genetically heterogeneous autosomal recessive condition. 14 BBS genes have been identified to date. The underlying pathophysiology involves a complex interaction between genetic factors and ciliary dysfunction. When major dysfunction of the renal tubule cilia is involved, renal failure is a predominant feature and a leading cause of of BBS mortality.
Bardet-Biedl syndrome (BBS) is a familial condition.
- The prevalence in most of North America and Europe is 1 in 140,000 to 1 in 160,000 newborns.
- Bedouins and the Arab population of Kuwait have an incidence of 1:13,500.
- A high incidence (1:17,500) is also found in Newfoundland.
- Ratio of male:female is approximately 1.3:1.
Although it had been originally thought to be a recessive disorder, it has been demonstrated that some forms of BBS require recessive mutations in 1 of the 6 loci, plus an additional mutation in a second locus. This has been called 'tri-allelic inheritance', or 'recessive inheritance with a modifier of penetrance'.
Fourteen forms have been identified with differing phenotypes:
- There are only subtle differences among BBS families with BBS1, BBS2, or BBS4 forms. The most obvious feature is that affected offspring in the BBS1 category are taller than their parents. Affected subjects in the BBS2 and BBS4 groups were found to be significantly shorter than their parents.
- BBS3 patients have polydactyly limited to the lower limbs, average IQ and obesity reversible by calorie restriction and/or exercise.
- In a reported case series of BBS5, no patients had polydactyly but all had brachydactyly and/or syndactyly. All had severe visual impairment with retinal macular changes and there was hypogonadism in the two males examined.
NB: Laurence-Moon-Biedl syndrome and Laurence-Moon-Biedl-Bardet syndrome are no longer considered valid terms, because the patients of Laurence and Moon had paraplegia, but no polydactyly and obesity, which are the main characteristics of BBS.
Laurence-Moon syndrome is a separate entity.
- Growth restriction.
- Poor visual acuity and blindness.
- Rod-cone dystrophy (sometimes called atypical retinitis pigmentosa), myopia, strabismus and cataracts.
- Polydactyly, syndactyly or brachydactyly.
- Hypertrophy of interventricular septum and left ventricle and dilated cardiomyopathy.
- Hepatic fibrosis, central obesity and diabetes mellitus.
- Hypogonadism, renal failure, urogenital sinuses, ectopic urethra, uterus duplex, septate vagina and hypoplasia of the uterus, ovaries and Fallopian tubes
- Hippocampal dysgenesis with accompanying neuropsychiatric symptoms such as obsessive-compulsive disorder, slow thought processes and attention difficulties.
- Laurence-Moon syndrome (where affected individuals have a spastic paraparesis but no polydactyly).
- Cohen's syndrome (a genetic disorder involving developmental delay, intellectual disability, microcephaly, progressive myopia and retinal dystrophy).
- Alström's syndrome (a genetic condition featuring paediatric cone-rod dystrophy, obesity, deafness).
- McKusick-Kaufman syndrome (a genetic disorder involving polydactyly, congenital heart disease and fluid in the pelvis).
- Diagnosis is usually made on the basis of the clinical features. However, in view of the sequelae, metabolic screening including renal function and cardiovascular risk factors should be performed.
- MRI shows distinct abnormalities and may be necessary in cases of doubt.
- Genotyping may be required to differentiate Bardet-Biedl syndrome (BBS) from other rare genetic disorders.
There are no specific treatments for the characteristics associated with Bardet-Biedl syndrome (BBS).
- As vision worsens, individuals will benefit from the use of low-vision aids and orientation as well as from mobility training.
- To manage the complications of renal disease, every individual with the disorder should be examined by a renal physician.
- Metabolic consequences such as diabetes and hyperlipidaemia may need to be addressed.
- Diet, exercise and behavioural therapies may be needed to manage obesity.
- Excision of accessory digits may be necessary to improve function and facilitate the fitting of footwear.
Prognosis is very poor where renal failure occurs.
Genetic counselling and preconception genotyping of family members may be worthwhile.
Further reading & references
- RP Fighting Blindness
- Telander DG et al: Retinitis Pigmentosa, Medscape, Mar 2013
- Aksoy A, Karaguzel G, Akbulut U, et al; Two sisters with Bardet-Biedl syndrome: brain abnormalities and unusual facial Turk J Pediatr. 2011 Jul-Aug;53(4):460-3.
- Putoux A, Attie-Bitach T, Martinovic J, et al; Phenotypic variability of Bardet-Biedl syndrome: focusing on the kidney. Pediatr Nephrol. 2012 Jan;27(1):7-15. Epub 2011 Jan 19.
- Bardet-Biedl Syndrome, Online Mendelian Inheritance in Man (OMIM).
- Pereiro I, Valverde D, Pineiro-Gallego T, et al; New mutations in BBS genes in small consanguineous families with Bardet-Biedl Mol Vis. 2010 Feb 1;16:137-43.
- Karaman A; Bardet-Biedl syndrome: a case report. Dermatol Online J. 2008 Jan 15;14(1):9.
- Kugler M; Laurence-Moon-Bardet-Biedl Syndrome, Rare Diseases, About.com, 2007
- Mihai CM, Marshall JD, Stoicescu RM; Bardet-Biedl syndrome with end-stage kidney disease in a four-year-old Romanian J Med Case Reports. 2011 Aug 15;5:378.
- Falk MJ, Wang H, Traboulsi EI; Cohen Syndrome
- Aliferis K, Helle S, Gyapay G, et al; Differentiating Alstrom from Bardet-Biedl syndrome (BBS) using systematic Ophthalmic Genet. 2011 Oct 17.
- Schaefer E, Durand M, Stoetzel C, et al; Molecular diagnosis reveals genetic heterogeneity for the overlapping MKKS and Eur J Med Genet. 2011 Mar-Apr;54(2):157-60. Epub 2010 Oct 29.
- Imhoff O, Marion V, Stoetzel C, et al; Bardet-Biedl syndrome: a study of the renal and cardiovascular phenotypes in a Clin J Am Soc Nephrol. 2011 Jan;6(1):22-9. Epub 2010 Sep 28.
- Keppler-Noreuil KM, Blumhorst C, Sapp JC, et al; Brain tissue- and region-specific abnormalities on volumetric MRI scans in 21 BMC Med Genet. 2011 Jul 27;12:101.
- Waters A et al; Bardet-Biedl Syndrome, Gene Reviews, 2011.
- Sapp JC, Nishimura D, Johnston JJ, et al; Recurrence risks for Bardet-Biedl syndrome: Implications of locus heterogeneity. Genet Med. 2010 Oct;12(10):623-7.
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Dr Hayley Willacy
Dr Laurence Knott
Dr Hannah Gronow