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Bardet-biedl syndrome 21(BBS21)

MedGen UID:
1374358
Concept ID:
C4319932
Disease or Syndrome
Synonyms: BARDET-BIEDL SYNDROME 21; BBS21
 
Gene (location): CFAP418 (8q22.1)
 
Monarch Initiative: MONDO:0044308
OMIM®: 617406

Definition

BBS21 is an autosomal recessive ciliopathy characterized by obesity, postaxial polydactyly, retinal degeneration, and mild cognitive impairment (Heon et al., 2016; Khan et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900). [from OMIM]

Clinical features

From HPO
Horseshoe kidney
MedGen UID:
65140
Concept ID:
C0221353
Congenital Abnormality
A connection of the right and left kidney by an isthmus of functioning renal parenchyma or fibrous tissue that crosses the midline.
Postaxial hand polydactyly
MedGen UID:
609221
Concept ID:
C0431904
Congenital Abnormality
Supernumerary digits located at the ulnar side of the hand (that is, on the side with the fifth finger).
Obesity
MedGen UID:
18127
Concept ID:
C0028754
Disease or Syndrome
Accumulation of substantial excess body fat.
Overweight
MedGen UID:
105424
Concept ID:
C0497406
Finding
Increased body weight with a body mass index of 25-29.9 kg per square meter.
Delayed speech and language development
MedGen UID:
105318
Concept ID:
C0454644
Finding
A degree of language development that is significantly below the norm for a child of a specified age.
Elevated circulating hepatic transaminase concentration
MedGen UID:
338525
Concept ID:
C1848701
Finding
Elevations of the levels of SGOT and SGPT in the serum. SGOT (serum glutamic oxaloacetic transaminase) and SGPT (serum glutamic pyruvic transaminase) are transaminases primarily found in the liver and heart and are released into the bloodstream as the result of liver or heart damage. SGOT and SGPT are used clinically mainly as markers of liver damage.
Partial congenital absence of teeth
MedGen UID:
43794
Concept ID:
C0020608
Congenital Abnormality
Tooth agenesis in some form is a common human anomaly that affects approximately 20% of the population. Although tooth agenesis is associated with numerous syndromes, several case reports describe nonsyndromic forms that are either sporadic or familial in nature, as reviewed by Gorlin et al. (1990). The incidence of familial tooth agenesis varies with each class of teeth. Most commonly affected are third molars (wisdom teeth), followed by either upper lateral incisors or lower second premolars; agenesis involving first and second molars is very rare. Also see 114600 and 302400. Selective tooth agenesis without associated systemic disorders has sometimes been divided into 2 types: oligodontia, defined as agenesis of 6 or more permanent teeth, and hypodontia, defined as agenesis of less than 6 teeth. The number in both cases does not include absence of third molars (wisdom teeth). Faulty use of the terms, however, have confounded their use. The term 'partial anodontia' is obsolete (Salinas, 1978). Genetic Heterogeneity of Selective Tooth Agenesis Other forms of selective tooth agenesis include STHAG2 (602639), mapped to chromosome 16q12; STHAG3 (604625), caused by mutation in the PAX9 gene (167416) on chromosome 14q12; STHAG4 (150400), caused by mutation in the WNT10A gene (606268) on chromosome 2q35; STHAG5 (610926), mapped to chromosome 10q11; STHAG7 (616724), caused by mutation in the LRP6 gene (603507) on chromosome 12p13; STHAG8 (617073), caused by mutation in the WNT10B gene (601906) on chromosome 12q13; STHAG9 (617275), caused by mutation in the GREM2 gene (608832) on chromosome 1q43; STHAG10 (620173), caused by mutation in the TSPEAR gene (612920) on chromosome 21q22; and STHAGX1 (313500), caused by mutation in the EDA gene (300451) on chromosome Xq13. A type of selective tooth agenesis that was formerly designated STHAG6 has been incorporated into the dental anomalies and short stature syndrome (DASS; 601216). Of 34 unrelated patients with nonsyndromic tooth agenesis, van den Boogaard et al. (2012) found that 56% (19 patients) had mutations in the WNT10A gene (STHAG4), whereas only 3% and 9% had mutations in the MSX1 (STHAG1) and PAX9 (STHAG3) genes, respectively. The authors concluded that WNT10A is a major gene in the etiology of isolated hypodontia. Genotype-Phenotype Correlations Yu et al. (2016) observed that the most frequently missing permanent teeth in WNT10B-associated oligodontia were the lateral incisors (83.3%), whereas premolars were missing only 51.4% of the time, which they noted was a pattern 'clearly different' from the oligodontia patterns resulting from WNT10A mutations. They also stated that the selective pattern in WNT10B mutants was different from that associated with mutations in other genes, such as MSX1, in which second premolars are missing, and PAX9, in which there is agenesis of molars.
Abnormality of the dentition
MedGen UID:
78084
Concept ID:
C0262444
Finding
Any abnormality of the teeth.
Myopia
MedGen UID:
44558
Concept ID:
C0027092
Disease or Syndrome
Nearsightedness, also known as myopia, is an eye condition that causes blurry distance vision. People who are nearsighted have more trouble seeing things that are far away (such as when driving) than things that are close up (such as when reading or using a computer). If it is not treated with corrective lenses or surgery, nearsightedness can lead to squinting, eyestrain, headaches, and significant visual impairment.\n\nNearsightedness usually begins in childhood or adolescence. It tends to worsen with age until adulthood, when it may stop getting worse (stabilize). In some people, nearsightedness improves in later adulthood.\n\nFor normal vision, light passes through the clear cornea at the front of the eye and is focused by the lens onto the surface of the retina, which is the lining of the back of the eye that contains light-sensing cells. People who are nearsighted typically have eyeballs that are too long from front to back. As a result, light entering the eye is focused too far forward, in front of the retina instead of on its surface. It is this change that causes distant objects to appear blurry. The longer the eyeball is, the farther forward light rays will be focused and the more severely nearsighted a person will be.\n\nNearsightedness is measured by how powerful a lens must be to correct it. The standard unit of lens power is called a diopter. Negative (minus) powered lenses are used to correct nearsightedness. The more severe a person's nearsightedness, the larger the number of diopters required for correction. In an individual with nearsightedness, one eye may be more nearsighted than the other.\n\nEye doctors often refer to nearsightedness less than -5 or -6 diopters as "common myopia." Nearsightedness of -6 diopters or more is commonly called "high myopia." This distinction is important because high myopia increases a person's risk of developing other eye problems that can lead to permanent vision loss or blindness. These problems include tearing and detachment of the retina, clouding of the lens (cataract), and an eye disease called glaucoma that is usually related to increased pressure within the eye. The risk of these other eye problems increases with the severity of the nearsightedness. The term "pathological myopia" is used to describe cases in which high myopia leads to tissue damage within the eye.
Constriction of peripheral visual field
MedGen UID:
68613
Concept ID:
C0235095
Finding
An absolute or relative decrease in retinal sensitivity extending from edge (periphery) of the visual field in a concentric pattern. The visual field is the area that is perceived simultaneously by a fixating eye.
Blindness
MedGen UID:
99138
Concept ID:
C0456909
Disease or Syndrome
Blindness is the condition of lacking visual perception defined as a profound reduction in visual perception. On the 6m visual acuity scale, blindness is defined as less than 3/60. On the 20ft visual acuity scale, blindness is defined as less than 20/400. On the decimal visual acuity scale, blindness is defined as less than 0.05. Blindness is typically characterized by a visual field of no greater than 10 degrees in radius around central fixation.
Retinal atrophy
MedGen UID:
101075
Concept ID:
C0521694
Disease or Syndrome
Well-demarcated area(s) of partial or complete depigmentation in the fundus, reflecting atrophy of the retinal pigment epithelium with associated retinal photoreceptor loss.
Foveal hypoplasia
MedGen UID:
393047
Concept ID:
C2673946
Finding
Underdevelopment of the fovea centralis.
Retinal thinning
MedGen UID:
762617
Concept ID:
C3549703
Finding
Reduced anteroposterior thickness of the retina. This phenotype can be appreciated by retinal optical coherence tomography (OCT).
Reduced amplitude of dark-adapted bright flash electroretinogram a-wave
MedGen UID:
892805
Concept ID:
C4072973
Finding
An abnormal reduction in the amplitude of the a-wave.
Hyperautofluorescent macular lesion
MedGen UID:
893119
Concept ID:
C4073101
Finding
Increased amount of autofluorescence in the macula as ascertained by fundus autofluorescence imaging.
Cone-rod dystrophy
MedGen UID:
896366
Concept ID:
C4085590
Disease or Syndrome
The first signs and symptoms of cone-rod dystrophy, which often occur in childhood, are usually decreased sharpness of vision (visual acuity) and increased sensitivity to light (photophobia). These features are typically followed by impaired color vision (dyschromatopsia), blind spots (scotomas) in the center of the visual field, and partial side (peripheral) vision loss. Over time, affected individuals develop night blindness and a worsening of their peripheral vision, which can limit independent mobility. Decreasing visual acuity makes reading increasingly difficult and most affected individuals are legally blind by mid-adulthood. As the condition progresses, individuals may develop involuntary eye movements (nystagmus).\n\nThere are more than 30 types of cone-rod dystrophy, which are distinguished by their genetic cause and their pattern of inheritance: autosomal recessive, autosomal dominant, and X-linked. Additionally, cone-rod dystrophy can occur alone without any other signs and symptoms or it can occur as part of a syndrome that affects multiple parts of the body.\n\nCone-rod dystrophy is a group of related eye disorders that causes vision loss, which becomes more severe over time. These disorders affect the retina, which is the layer of light-sensitive tissue at the back of the eye. In people with cone-rod dystrophy, vision loss occurs as the light-sensing cells of the retina gradually deteriorate.
Rod-cone dystrophy
MedGen UID:
1632921
Concept ID:
C4551714
Disease or Syndrome
An inherited retinal disease subtype in which the rod photoreceptors appear to be more severely affected than the cone photoreceptors. Typical presentation is with nyctalopia (due to rod dysfunction) followed by loss of mid-peripheral field of vision, which gradually extends and leaves many patients with a small central island of vision due to the preservation of macular cones.

Professional guidelines

PubMed

Deng L, Liu Y, Yuan M, Meng M, Yang Y, Sun L
Clin Chim Acta 2022 Mar 1;528:16-28. Epub 2022 Jan 20 doi: 10.1016/j.cca.2022.01.012. PMID: 35065907
Tang X, Liu C, Liu X, Chen J, Fan X, Liu J, Ma D, Cao G, Chen Z, Xu D, Zhu Y, Jiang X, Cheng L, Wu Y, Hou L, Li Y, Shao X, Zheng S, Zhang A, Zheng B, Jian S, Rong Z, Su Q, Gao X, Rao J, Shen Q, Xu H; Chinese Children Genetic Kidney Disease Database (CCGKDD); “Internet Plus” Nephrology Alliance of the National Center for Children’s Care
J Med Genet 2022 Feb;59(2):147-154. Epub 2020 Dec 15 doi: 10.1136/jmedgenet-2020-107184. PMID: 33323469
Kiess W, Reich A, Müller G, Meyer K, Galler A, Bennek J, Kratzsch J
Int J Obes Relat Metab Disord 2001 May;25 Suppl 1:S75-9. doi: 10.1038/sj.ijo.0801704. PMID: 11466594

Recent clinical studies

Therapy

Habek D, Franicevic D, Stanojevic M
J Pediatr Adolesc Gynecol 2008 Feb;21(1):31-2. doi: 10.1016/j.jpag.2007.08.001. PMID: 18312798
Fulton AB, Hansen RM, Glynn RJ
Arch Ophthalmol 1993 Nov;111(11):1500-6. doi: 10.1001/archopht.1993.01090110066026. PMID: 8240105

Prognosis

Cai M, Guo C, Wang X, Lin M, Xu S, Huang H, Lin N, Xu L
Exp Biol Med (Maywood) 2023 May;248(10):858-865. Epub 2023 May 19 doi: 10.1177/15353702231164933. PMID: 37208928Free PMC Article
Deng L, Liu Y, Yuan M, Meng M, Yang Y, Sun L
Clin Chim Acta 2022 Mar 1;528:16-28. Epub 2022 Jan 20 doi: 10.1016/j.cca.2022.01.012. PMID: 35065907
Atmış B, Karabay-Bayazıt A, Melek E, Bişgin A, Anarat A
Turk J Pediatr 2019;61(2):186-192. doi: 10.24953/turkjped.2019.02.006. PMID: 31951329
Álvarez-Satta M, Castro-Sánchez S, Pousada G, Valverde D
J Cell Mol Med 2017 Oct;21(10):2268-2275. Epub 2017 May 13 doi: 10.1111/jcmm.13147. PMID: 28502102Free PMC Article
Haws RM, Joshi A, Shah SA, Alkandari O, Turman MA
Pediatr Nephrol 2016 Nov;31(11):2153-61. Epub 2016 Jun 1 doi: 10.1007/s00467-016-3415-4. PMID: 27245600

Clinical prediction guides

Forsythe E, Mallya UG, Yang M, Huber C, Cala ML, Greatsinger A, Hagopian E, Pomeroy J, Haqq AM
Orphanet J Rare Dis 2023 Jul 7;18(1):181. doi: 10.1186/s13023-023-02692-8. PMID: 37415214Free PMC Article
Nasser F, Kohl S, Kurtenbach A, Kempf M, Biskup S, Zuleger T, Haack TB, Weisschuh N, Stingl K, Zrenner E
Genes (Basel) 2022 Jul 8;13(7) doi: 10.3390/genes13071218. PMID: 35886001Free PMC Article
Parameswarappa DC, Das AV, Thakur PS, Takkar B, Multani PK, Padhy SK, Doctor MB, Agarwal K, Jalali S
Indian J Ophthalmol 2022 Jul;70(7):2533-2538. doi: 10.4103/ijo.IJO_2268_21. PMID: 35791150Free PMC Article
Tang X, Liu C, Liu X, Chen J, Fan X, Liu J, Ma D, Cao G, Chen Z, Xu D, Zhu Y, Jiang X, Cheng L, Wu Y, Hou L, Li Y, Shao X, Zheng S, Zhang A, Zheng B, Jian S, Rong Z, Su Q, Gao X, Rao J, Shen Q, Xu H; Chinese Children Genetic Kidney Disease Database (CCGKDD); “Internet Plus” Nephrology Alliance of the National Center for Children’s Care
J Med Genet 2022 Feb;59(2):147-154. Epub 2020 Dec 15 doi: 10.1136/jmedgenet-2020-107184. PMID: 33323469
Forsythe E, Beales PL
Eur J Hum Genet 2013 Jan;21(1):8-13. Epub 2012 Jun 20 doi: 10.1038/ejhg.2012.115. PMID: 22713813Free PMC Article

Recent systematic reviews

Deng L, Liu Y, Yuan M, Meng M, Yang Y, Sun L
Clin Chim Acta 2022 Mar 1;528:16-28. Epub 2022 Jan 20 doi: 10.1016/j.cca.2022.01.012. PMID: 35065907

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