Choroideremia (CHM) is characterized by progressive chorioretinal degeneration in affected males and milder signs in heterozygous (carrier) females. Typically, symptoms in affected males evolve from night blindness to peripheral visual field loss, with central vision preserved until late in life. Although carrier females are generally asymptomatic, signs of chorioretinal degeneration can be reliably observed with fundus autofluorescence imaging, and – after age 25 years – with careful fundus examination.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the RP1 gene.

Cohen syndrome is characterized by failure to thrive in infancy and childhood; truncal obesity in the teen years; early-onset hypotonia and developmental delays; microcephaly developing during the first year of life; moderate to profound psychomotor retardation; progressive retinochoroidal dystrophy and high myopia; neutropenia in many with recurrent infections and aphthous ulcers in some; a cheerful disposition; joint hypermobility; and characteristic facial features.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the FAM161A gene.

Retinitis pigmentosa-17 (RP17) is characterized by relatively mild disease, with decreased visual acuity, visual field constriction, nyctalopia, and slow progression. Many affected individuals have preserved central vision and acuity until the sixth or seventh decades of life (de Bruijn et al., 2020). For a phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the NRL gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the SNRNP200 gene.

A retinitis pigmentosa that has material basis in variation in the chromosome region 1p21.3-p13.3.

Posterior column ataxia with retinitis pigmentosa (AXPC1) is an autosomal recessive neurologic disorder characterized by childhood-onset retinitis pigmentosa and later onset of gait ataxia due to sensory loss (summary by Ishiura et al., 2011).

Early-onset neurodegeneration in the human retina can lead to Leber congenital amaurosis (LCA), the most severe human form of inherited photoreceptor-neuron degeneration resulting in congenital blindness, with an incidence of approximately 1 in 80,000 (summary by Koenekoop et al., 2012). NMNAT1 mutations have been observed to cause severe and rapidly progressive macular degeneration, leading to severe central atrophy with an appearance of congenital macular coloboma in the neonatal period, as well as an unusual early-onset atrophy of the optic nerve (Perrault et al., 2012). Some patients present with later onset and milder phenotype than typical LCA (Kumaran et al., 2021). For a general discussion of the phenotypic and genetic heterogeneity in Leber congenital amaurosis, see LCA1 (204000).

Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of retinal dystrophies characterized by a progressive degeneration of photoreceptors, eventually resulting in severe visual impairment. For a discussion of genetic heterogeneity of RP, see 268000.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the TULP1 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the CRB1 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PRPF8 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the FSCN2 gene.

Newfoundland rod-cone dystrophy (NFRCD) is a severe retinal dystrophy in which night blindness is present from infancy. Progressive loss of peripheral, central, and color vision begins in childhood and results in severe visual loss by the second to fourth decade of life (Eichers et al., 2002).

X-linked retinitis pigmentosa (XLRP) is a severe form of inherited retinal degeneration that primarily affects the rod photoreceptors (Demirci et al., 2002). It typically causes an early-onset night blindness and loss of peripheral vision, often causing patients to become legally blind by the age of 30 to 40 years. In RP3, affected males have a severe phenotype, and carrier females show a wide spectrum of clinical features ranging from completely asymptomatic to severe RP (Jin et al., 2007). Mutation in the RPGR gene is believed to account for approximately 70% of XLRP (Vervoort et al., 2000). For a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

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.

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).

Autosomal recessive congenital stationary night blindness is a disorder of the retina, which is the specialized tissue at the back of the eye that detects light and color. People with this condition typically have difficulty seeing and distinguishing objects in low light (night blindness). For example, they may not be able to identify road signs at night or see stars in the night sky. They also often have other vision problems, including loss of sharpness (reduced acuity), nearsightedness (myopia), involuntary movements of the eyes (nystagmus), and eyes that do not look in the same direction (strabismus).\n\nThe vision problems associated with this condition are congenital, which means they are present from birth. They tend to remain stable (stationary) over time.

BBS9 is an autosomal recessive disorder characterized by obesity, polydactyly, renal anomalies, retinopathy, and mental retardation (Abu-Safieh et al., 2012). For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).

Any retinitis pigmentosa in which the cause of the disease is a mutation in the EYS gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PRCD gene.

Any congenital stationary night blindness in which the cause of the disease is a mutation in the RHO gene.

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.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the ABCA4 gene.

A retinitis pigmentosa that is characterized pigmentary retinal degeneration with onset in the teens leading to blindness in the sixth ans seventh decades of life.

Retinitis pigmentosa-10 (RP10) is characterized in most patients by early onset and rapid progression of ocular symptoms, beginning with night blindness in childhood, followed by visual field constriction. Some patients experience an eventual reduction in visual acuity. Funduscopy shows typical changes of RP, including optic disc pallor, retinal vascular attenuation, and bone-spicule pattern of pigmentary deposits in the retinal midperiphery. Electroretinography demonstrates equal reduction in rod and cone responses (Jordan et al., 1993; Bowne et al., 2002; Bowne et al., 2006). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Autosomal dominant retinitis pigmentosa (ADRP) is characterized by a typical fundus appearance, narrowed retinal vessels, and changes in the electrophysiological responses of the eye. Early signs are night blindness and constriction of the visual fields with a variable ages of onset (summary by Jay et al., 1992).

Pigmented paravenous chorioretinal atrophy is a stationary disease of the ocular fundus in which bone corpuscle pigmentation is seen in a paravenous distribution. Patients are usually asymptomatic; diagnosis is based on the characteristic fundus appearance. Most cases have been reported in males (summary by Traboulsi and Maumenee, 1986).

Microphthalmia-retinitis pigmentosa-foveoschisis-optic disc drusen syndrome is a rare, genetic, non-syndromic developmental defect of the eye disorder characterized by the association of posterior microphthalmia, retinal dystrophy compatible with retinitis pigmentosa, localized foveal schisis and optic disc drusen. Patients present high hyperopia, usually adult-onset progressive nyctalopia and reduced visual acuity, and, on occasion, acute-angle glaucoma.

BBS13 is an autosomal recessive ciliopathy with features of obesity, polydactyly, and retinitis pigmentosa (Leitch et al., 2008; Xing et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).

At least 20 genetic types of Leber congenital amaurosis have been described. The types are distinguished by their genetic cause, patterns of vision loss, and related eye abnormalities.\n\nLeber congenital amaurosis, also known as LCA, is an eye disorder that is present from birth (congenital). This condition primarily affects the retina, which is the specialized tissue at the back of the eye that detects light and color. People with this disorder typically have severe visual impairment beginning at birth or shortly afterward. The visual impairment tends to be severe and may worsen over time.\n\nLeber congenital amaurosis is also associated with other vision problems, including an increased sensitivity to light (photophobia), involuntary movements of the eyes (nystagmus), and extreme farsightedness (hyperopia). The pupils, which usually expand and contract in response to the amount of light entering the eye, do not react normally to light. Instead, they expand and contract more slowly than normal, or they may not respond to light at all.\n\nA specific behavior called Franceschetti's oculo-digital sign is characteristic of Leber congenital amaurosis. This sign consists of affected individuals poking, pressing, and rubbing their eyes with a knuckle or finger. Poking their eyes often results in the sensation of flashes of light called phosphenes. Researchers suspect that this behavior may contribute to deep-set eyes in affected children.\n\nIn very rare cases, delayed development and intellectual disability have been reported in people with the features of Leber congenital amaurosis. Because of the visual loss, affected children may become isolated. Providing children with opportunities to play, hear, touch, understand and other early educational interventions may prevent developmental delays in children with Leber congenital amaurosis.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PROM1 gene.

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.

Retinitis pigmentosa-54 (RP54) is characterized by typical signs of RP, including poor night vision and peripheral field loss, retinal bone spicule-type pigment deposits, pale optic discs, and markedly reduced or extinguished responses on electroretinography. Atypical features that have been observed include early degeneration of the cone photoreceptor system with macular abnormalities, and ring scotoma on the visual field (Collin et al., 2010). Patients may exhibit an early-onset form of cone-rod dystrophy (CORD23), with central vision loss and ring scotoma around the fovea that progresses to marked chorioretinal atrophy in the macular area (Serra et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000. For a general phenotypic description and discussion of genetic heterogeneity of cone-rod dystrophy, see CORD2 (120970).

Any retinitis pigmentosa in which the cause of the disease is a mutation in the TTC8 gene.

Retinitis pigmentosa-56 (RP56) is an early-onset form of RP with progressive visual-field loss and deterioration of visual acuity (Bandah-Rozenfeld et al., 2010). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PDE6G gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the ZNF513 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the RHO gene.

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.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the CNGB1 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PDE6B gene.

Retinitis pigmentosa-39 (RP39) is characterized by the typical features of RP, including constriction of visual fields and reduced vision, with the fundus showing bone-spicule pigment deposition and attenuation of retinal vessels (Kaiserman et al., 2007; Jung et al., 2023). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa (RP), see 268000.

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).

Any retinitis pigmentosa in which the cause of the disease is a mutation in the PRPF6 gene.

Retinitis pigmentosa-61 (RP61) is an autosomal recessive photoreceptor degenerative disorder initially characterized by impairment of night vision and midperipheral visual field loss. Bone spicule pigmentation in the retinal periphery is present, and loss of rod function is detected by electroretinography (ERG) (Khan et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa (RP), see 268000.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the MAK gene.

Cone-rod dystrophy (CORD) and retinitis pigmentosa (RP) are clinically and genetically overlapping heterogeneous retinal dystrophies. RP is characterized initially by rod photoreceptor dysfunction, giving rise to night blindness, which is followed by progressive rod and cone photoreceptor dystrophy, resulting in midperipheral vision loss, tunnel vision, and sometimes blindness. In contrast to RP, CORD is characterized by a primary loss of cone photoreceptors and subsequent or simultaneous loss of rod photoreceptors. The disease in most cases becomes apparent during primary-school years, and symptoms include photoaversion, decrease in visual acuity with or without nystagmus, color vision defects, and decreased sensitivity of the central visual field. Because rods are also involved, night blindness and peripheral vision loss can occur. The diagnosis of CORD is mainly based on electroretinogram (ERG) recordings, in which cone responses are more severely reduced than, or equally as reduced as rod responses (summary by Estrada-Cuzcano et al., 2012).

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).

Jalili syndrome is an autosomal recessive disorder consisting of cone-rod dystrophy and amelogenesis imperfecta. Significant visual impairment with nystagmus and photophobia is present from infancy or early childhood and progresses with age. Enamel of primary and secondary dentitions is grossly abnormal and prone to rapid posteruptive failure, in part reflecting hypomineralization (summary by Parry et al., 2009).

Bardet-Biedl syndrome-17 (BBS17) is an autosomal recessive ciliopathy characterized by retinitis pigmentosa, cognitive impairment, obesity, renal dysfunction, and hypogenitalism. Polydactyly, most often postaxial, is also a primary feature of BBS; in BBS17, mesoaxial polydactyly, with fused or Y-shaped metacarpals, is a distinct manifestation (Deffert et al., 2007; Schaefer et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of Bardet-Biedl syndrome, see BBS1 (209900).

Any retinitis pigmentosa in which the cause of the disease is a mutation in the RBP3 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the SLC7A14 gene.

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.\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\nThe 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).

A rare genetic syndromic rod-cone dystrophy disorder with characteristics of psychomotor developmental delay from early childhood, intellectual disability, short stature, mild facial dysmorphism (e.g. upslanted palpebral fissures, hypoplastic alae nasi, malar hypoplasia, attached earlobes), excessive dental spacing and malocclusion, juvenile cataract and ophthalmologic findings of atypical retinitis pigmentosa (i.e. salt-and-pepper retinopathy, attenuated retinal arterioles, generalised rod-cone dysfunction, mottled macula, peripapillary sparing of retinal pigment epithelium).

Any retinitis pigmentosa in which the cause of the disease is a mutation in the HGSNAT gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the ZNF408 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the REEP6 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the POMGNT1 gene.

Any retinitis pigmentosa in which the cause of the disease is a mutation in the AGBL5 gene.

TRNT1 deficiency encompasses what was first thought to be two separate disorders, a severe disorder called sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay (SIFD) and a milder disorder called retinitis pigmentosa with erythrocytic microcytosis (RPEM), each named for its most common features. SIFD begins in infancy, and affected individuals usually do not survive past childhood. RPEM, on the other hand, is recognized in early adulthood, and the microcytosis usually does not cause any health problems. However, it has since been recognized that some individuals have a combination of features that fall between these two ends of the severity spectrum. All of these cases are now considered part of TRNT1 deficiency.\n\nFeatures that occur less commonly in people with TRNT1 deficiency include hearing loss caused by abnormalities of the inner ear (sensorineural hearing loss), recurrent seizures (epilepsy), and problems with the kidneys or heart.\n\nNeurological problems are also frequent in TRNT1 deficiency. Many affected individuals have delayed development of speech and motor skills, such as sitting, standing, and walking, and some have low muscle tone (hypotonia).\n\nEye abnormalities, often involving the light-sensing tissue at the back of the eye (the retina), can occur in people with TRNT1 deficiency. Some of these individuals have a condition called retinitis pigmentosa, in which the light-sensing cells of the retina gradually deteriorate. Eye problems in TRNT1 deficiency can lead to vision loss.\n\nIn addition, many individuals with TRNT1 deficiency have recurrent fevers that are not caused by an infection. These fever episodes are often one of the earliest recognized symptoms of TRNT1 deficiency, usually beginning in infancy. The fever episodes are typically accompanied by poor feeding, vomiting, and diarrhea, and can lead to hospitalization. In many affected individuals, the episodes occur regularly, arising approximately every 2 to 4 weeks and lasting 5 to 7 days, although the frequency can decrease with age.\n\nMany people with TRNT1 deficiency have an immune system disorder (immunodeficiency) that can lead to recurrent bacterial infections. Repeated infections can cause life-threatening damage to internal organs. The immunodeficiency is characterized by low numbers of immune system cells called B cells, which normally help fight infections by producing immune proteins called antibodies (or immunoglobulins). These proteins target foreign invaders such as bacteria and viruses and mark them for destruction. In many individuals with TRNT1 deficiency, the amount of immunoglobulins is also low (hypogammaglobulinemia).\n\nA common feature of TRNT1 deficiency is a blood condition called sideroblastic anemia, which is characterized by a shortage of red blood cells (anemia). In TRNT1 deficiency, the red blood cells that are present are unusually small (erythrocytic microcytosis). In addition, developing red blood cells in the bone marrow (erythroblasts) can have an abnormal buildup of iron that appears as a ring of blue staining in the cell after treatment in the lab with certain dyes. These abnormal cells are called ring sideroblasts.\n\nTRNT1 deficiency is a condition that affects many body systems. Its signs and symptoms can involve blood cells, the immune system, the eyes, and the nervous system. The severity of the signs and symptoms vary widely.

An atypical form of Usher syndrome, here designated type IV (USH4), is an autosomal recessive disorder characterized by late onset of retinitis pigmentosa and usually late-onset of progressive sensorineural hearing loss without vestibular involvement (summary by Khateb et al., 2018). For a discussion of genetic heterogeneity of Usher syndrome, see 276900.

Retinitis pigmentosa-83 (RP83) is characterized by onset of night blindness in the first decade of life, with decreased central vision in the second decade of life in association with retinal degeneration. The retinal dystrophy is associated with cataract, and macular edema has also been reported in some patients (Holtan et al., 2019).

Intellectual developmental disorder and retinitis pigmentosa (IDDRP) is characterized by mild to moderate intellectual disability and typical features of RP. Patients experience reduced night vision, constriction of visual fields, and reduced visual acuity; optic disc pallor, attenuated retinal blood vessels, and bone-spicule pigmentation are seen on funduscopy. Attention-deficit/hyperactivity disorder is observed in some patients (Tatour et al., 2017).

Retinitis pigmentosa-86 (RP86) is characterized by night blindness followed by progressive narrowing of visual fields and decline in visual acuity, with typical findings of RP on fundus examination, including attenuated retinal vessels, waxy pallor of the optic disc, and bone spicule-like pigmentation (de Bruijn et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

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.

Retinitis pigmentosa-88 (RP88) is characterized by night blindness and constriction of peripheral visual fields, with mildly reduced visual acuity. Examination shows typical findings of RP, including attenuated retinal vessels, pale optic discs, and pigment deposits in the peripheral retinal pigment epithelium (Zobor et al., 2018; Hu et al., 2019; Albarry et al., 2019). For a discussion of genetic heterogeneity of RP, see 268000.

Liberfarb syndrome is a progressive disorder involving connective tissue, bone, retina, ear, and brain. Patients exhibit severe short stature and scoliosis with thoracic kyphosis and lumbar hyperlordosis. Severe joint laxity results in dislocations of elbows, hips, and knees. Eye findings are consistent with early-onset retinal degeneration, and there is moderate to severe early-onset hearing loss. Microcephaly is apparent by school age, and patients exhibit developmental delay and intellectual deficits (Peter et al., 2019). Clinical variability has been observed, with some patients presenting differences in the severity and location of skeletal dysplasia involvement as well as variation in other features of the syndrome (Girisha et al., 2019; Zhao et al., 2019).

Retinitis pigmentosa-90 (RP90) is characterized by early-onset night blindness, within the first decade of life. Patients exhibit other typical features of RP, including retinal vessel attenuation, optic disc pallor, and retinal pigment epithelium (RPE) atrophy and pigmentation abnormalities. Macular pseudocoloboma and cystoid macular edema have also been observed (Pierrache et al., 2017). For a discussion of genetic heterogeneity of RP, see 268000.

Retinitis pigmentosa-95 (RP95) is characterized by pale optic discs, attenuation of retinal vessels, and atrophy of the retinal pigment epithelium with bone-spicule pigmentation. Patients experience night blindness, and visual fields are restricted to approximately 10 degrees, with visual acuity ranging from normal to hand movement only. Age at onset of symptoms varies from childhood to the fifth decade of life (Van de Sompele et al., 2019). For a general phenotypic description and a discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.

Retinitis pigmentosa-96 (RP96) is characterized by difficulty with night vision and progressive visual field constriction beginning as early as the third decade of life, but most patients retain good visual acuity into the seventh decade. Funduscopy shows the typical features of RP, including bone-spicule pigmentation, attenuation of retinal vasculature, optic disc pallor, and cystic macular edema. Unlike patients with biallelic mutations in the SAG gene, they do not show the golden sheen of the fundus that is typical of Oguchi disease (Sullivan et al., 2017). For a general phenotypic description and discussion of genetic heterogeneity of retinitis pigmentosa, see 268000.