MedGen

Bardet-Biedl syndrome is an autosomal recessive and genetically heterogeneous ciliopathy characterized by retinitis pigmentosa, obesity, kidney dysfunction, polydactyly, behavioral dysfunction, and hypogonadism (summary by Beales et al., 1999). Eight proteins implicated in the disorder assemble to form the BBSome, a stable complex involved in signaling receptor trafficking to and from cilia (summary by Scheidecker et al., 2014). Genetic Heterogeneity of Bardet-Biedl Syndrome BBS2 (615981) is caused by mutation in a gene on 16q13 (606151); BBS3 (600151), by mutation in the ARL6 gene on 3q11 (608845); BBS4 (615982), by mutation in a gene on 15q22 (600374); BBS5 (615983), by mutation in a gene on 2q31 (603650); BBS6 (605231), by mutation in the MKKS gene on 20p12 (604896); BBS7 (615984), by mutation in a gene on 4q27 (607590); BBS8 (615985), by mutation in the TTC8 gene on 14q32 (608132); BBS9 (615986), by mutation in a gene on 7p14 (607968); BBS10 (615987), by mutation in a gene on 12q21 (610148); BBS11 (615988), by mutation in the TRIM32 gene on 9q33 (602290); BBS12 (615989), by mutation in a gene on 4q27 (610683); BBS13 (615990), by mutation in the MKS1 gene (609883) on 17q23; BBS14 (615991), by mutation in the CEP290 gene (610142) on 12q21, BBS15 (615992), by mutation in the WDPCP gene (613580) on 2p15; BBS16 (615993), by mutation in the SDCCAG8 gene (613524) on 1q43; BBS17 (615994), by mutation in the LZTFL1 gene (606568) on 3p21; BBS18 (615995), by mutation in the BBIP1 gene (613605) on 10q25; BBS19 (615996), by mutation in the IFT27 gene (615870) on 22q12; BBS20 (619471), by mutation in the IFT172 gene (607386) on 9p21; BBS21 (617406), by mutation in the CFAP418 gene (614477) on 8q22; and BBS22 (617119), by mutation in the IFT74 gene (608040) on 9p21. The CCDC28B gene (610162) modifies the expression of BBS phenotypes in patients who have mutations in other genes. Mutations in MKS1, MKS3 (TMEM67; 609884), and C2ORF86 also modify the expression of BBS phenotypes in patients who have mutations in other genes. Although BBS had originally been thought to be a recessive disorder, Katsanis et al. (2001) demonstrated that clinical manifestation of some forms of Bardet-Biedl syndrome requires recessive mutations in 1 of the 6 loci plus an additional mutation in a second locus. While Katsanis et al. (2001) called this 'triallelic inheritance,' Burghes et al. (2001) suggested the term 'recessive inheritance with a modifier of penetrance.' Mykytyn et al. (2002) found no evidence of involvement of the common BBS1 mutation in triallelic inheritance. However, Fan et al. (2004) found heterozygosity in a mutation of the BBS3 gene (608845.0002) as an apparent modifier of the expression of homozygosity of the met390-to-arg mutation in the BBS1 gene (209901.0001). Allelic disorders include nonsyndromic forms of retinitis pigmentosa: RP51 (613464), caused by TTC8 mutation, and RP55 (613575), caused by ARL6 mutation. [from OMIM]

BBS2 is an autosomal recessive ciliopathy characterized by retinal degeneration, polydactyly, renal disease, hypogonadism, obesity, dysmorphic features, and variable degrees of cognitive impairment (Innes et al., 2010). Mutation in the BBS2 gene is the third most frequent cause of BBS, accounting for approximately 8% of cases (Zaghloul and Katsanis, 2009). For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900). [from OMIM]

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500). [from OMIM]

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PROM1 gene. [from MONDO]

Cone-rod dystrophy (CORD) characteristically leads to early impairment of vision. An initial loss of color vision and of visual acuity is followed by nyctalopia (night blindness) and loss of peripheral visual fields. In extreme cases, these progressive symptoms are accompanied by widespread, advancing retinal pigmentation and chorioretinal atrophy of the central and peripheral retina (Moore, 1992). In many families, perhaps a majority, central and peripheral chorioretinal atrophy is not found (Tzekov, 1998). Genetic Heterogeneity of Autosomal Cone-Rod Dystrophy There are several other autosomal forms of CORD for which the molecular basis is known. CORD3 (604116) is caused by mutation in the ABCA4 gene (601691) on chromosome 1p22. CORD5 (600977) is caused by mutation in the PITPNM3 gene (608921) on chromosome 17p13. CORD6 (601777) is caused by mutation in the GUCY2D gene (600179) on chromosome 17p13.1. CORD9 (612775) is caused by mutation in the ADAM9 gene (602713) on chromosome 8p11. CORD10 (610283) is caused by mutation in the SEMA4A gene (607292) on chromosome 1q22. CORD11 (610381) is caused by mutation in the RAXL1 gene (610362) on chromosome 19p13. CORD12 (612657) is caused by mutation in the PROM1 gene (604365) on chromosome 4p15. CORD13 (608194) is caused by mutation in the RPGRIP1 gene (605446) on chromosome 14q11. CORD14 (see 602093) is caused by mutation in the GUCA1A gene (600364) on chromosome 6p21. CORD15 (613660) is caused by mutation in the CDHR1 gene (609502) on chromosome 10q23. CORD16 (614500) is caused by mutation in the C8ORF37 gene (614477) on chromosome 8q22. CORD18 (615374) is caused by mutation in the RAB28 gene (612994) on chromosome 4p15. CORD19 (615860) is caused by mutation in the TTLL5 gene (612268) on chromosome 14q24. CORD20 (615973) is caused by mutation in the POC1B gene (614784) on chromosome 12q21. CORD21 (616502) is caused by mutation in the DRAM2 gene (613360) on chromosome 1p13. CORD22 (619531) is caused by mutation in the TLCD3B gene (615175) on chromosome 16p11. CORD23 (see 613428) is caused by mutation in the C2ORF71 gene (PCARE; 613425) on chromosome 2p23. CORD24 (620342) is caused by mutation in the UNC119 gene (604011) on chromosome 17q11. A diagnosis of CORD was made in an individual with a mutation in the AIPL1 gene (604392.0004) on chromosome 17p13.1, as well as in an individual with a mutation in the UNC119 gene (604011.0001) on chromosome 17q11.2. Other mapped loci for autosomal CORD include CORD1 (600624) on chromosome 18q21.1-q21.3; CORD7 (603649) on chromosome 6q14; CORD8 (605549) on chromosome 1q12-q24; and CORD17 (615163) on chromosome 10q26. For a discussion of X-linked forms of cone-rod dystrophy, see CORDX1 (304020). [from OMIM]

Any retinitis pigmentosa in which the cause of the disease is a mutation in the CNGB1 gene. [from MONDO]

Retinitis pigmentosa-43 (RP43) is characterized by night blindness in the first decade of life, with progressive loss of peripheral visual fields and reduction in visual acuity. Examination reveals typical features of RP, including waxy pallor of optic disc, attenuated retinal vessels, and bone-spicule pigment in midperipheral retina. Macular edema and/or atrophy has been observed in some patients. Electroretinographic responses are markedly reduced or absent (summary by Huang et al., 1995 and Corton et al., 2010). [from OMIM]

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).

There 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.

Cone-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. [from MedlinePlus Genetics]

Cone-rod dystrophy-3 (CORD3) is an autosomal recessive, clinically heterogeneous retinal disorder with typical findings of reduced visual acuity, impairment of the central visual field, color vision deficits, and fundoscopic evidence of maculopathy, with no or few midperipheral retinal pigment deposits. Cone degeneration appears early in life with a central involvement of the retina, followed by a degeneration of rods several years later (summary by Klevering et al., 2002 and Ducroq et al., 2002). Both cone and rod a- and b-wave electroretinogram (ERG) amplitudes are reduced (Fishman et al., 2003). For a general phenotypic description and a discussion of genetic heterogeneity of cone-rod dystrophy, see 120970. [from OMIM]

Any retinitis pigmentosa in which the cause of the disease is a mutation in the ZNF513 gene. [from MONDO]

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PRPF6 gene. [from MONDO]

Retinitis pigmentosa-49 (RP49) is characterized by onset of night blindness in childhood, followed by progressive loss of visual fields and reduced visual acuity. Typical fundus features are present, including pale optic disc, attenuated vasculature, and pigment deposits in the midperiphery (Zhang et al., 2004; Katagiri et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000. [from OMIM]

Cone-rod dystrophy-10 (CORD10) is characterized by progressive loss of visual acuity and color vision, followed by night blindness and loss of peripheral vision. Patients may experience photophobia and epiphora in bright light (Abid et al., 2006). Mutation in SEMA4A can also cause a form of retinitis pigmentosa (RP35; 610282). For a general phenotypic description and a discussion of genetic heterogeneity of cone-rod dystrophy, see 120970. [from OMIM]

Lowry-Wood syndrome (LWS) is characterized by multiple epiphyseal dysplasia and microcephaly. Patients exhibit intrauterine growth retardation and short stature, as well as developmental delay and intellectual disability. Retinal degeneration has been reported in some patients (Farach et al., 2018; Shelihan et al., 2018). Microcephalic osteodysplastic primordial dwarfism type I (MOPD1; 210710) and Roifman syndrome (RFMN; 616651), the features of which overlap with those of Lowry-Wood syndrome, are also caused by biallelic mutation in the RNU4ATAC gene. [from OMIM]

Neurodegeneration with ataxia and late-onset optic atrophy (NDAXOA) is an autosomal dominant disorder with somewhat variable manifestations. Most affected individuals present in mid-adulthood with slowly progressive cerebellar and gait ataxia, optic atrophy, and myopathy or myalgia. Some patients may have a childhood history of neurologic features, including limited extraocular movements. Additional features can include cardiomyopathy, psychiatric disturbances, and peripheral sensory impairment (summary by Taylor et al., 1996 and Courage et al., 2017). [from OMIM]

Retinitis pigmentosa-87 with choroidal involvement (RP87) is characterized by a slowly progressive visual disturbance, including night blindness and reduced central and peripheral vision, accompanied by extensive choroid/retinal atrophy that mimics certain aspects of choroideremia. Disease severity and age of onset are variable, and some carriers are unaffected (Hull et al., 2016; Li et al., 2019). For a discussion of genetic heterogeneity of RP, see 268000. [from OMIM]

Rod-cone dystrophy, sensorineural deafness, and Fanconi-type renal dysfunction (RCDFRD) is characterized by onset of hearing impairment and reduced vision within the first 5 years of life. Renal dysfunction results in rickets-like skeletal changes, and death may occur in childhood or young adulthood due to renal failure (Beighton et al., 1993). [from OMIM]

Retinitis pigmentosa with or without skeletal anomalies (RPSKA) is characterized by retinal degeneration, brachydactyly, craniofacial abnormalities, short stature, and neurologic defects. Night blindness occurs around 10 years of age, followed by restriction of visual fields. Brachydactyly affects primarily the distal phalanges. Craniofacial abnormalities include frontal bossing, downslanting palpebral fissures, large columella, hypoplastic nares, micrognathia, and large low-set ears (summary by Xu et al., 2017). [from OMIM]

Any retinitis pigmentosa in which the cause of the disease is a mutation in the AGBL5 gene. [from MONDO]

Hypotaurinemic retinal degeneration and cardiomyopathy (HTRDC) is an autosomal recessive disorder characterized by low plasma taurine, childhood-onset progressive retinal degeneration, and cardiomyopathy (Ansar et al., 2020). [from OMIM]