<unk>  may be: (1) non-syndromic, that is, it occurs alone, without any other clinical findings, (2) syndromic, with other neurosensory disorders, developmental abnormalities, or complex clinical findings, or (3) secondary to other systemic diseases. *<unk>  combined with deafness (congenital or progressive) is called Usher syndrome. * Alport's syndrome is associated with<unk>  and an abnormal glomerular-basement membrane leading to nephrotic syndrome. It is inherited as X-linked dominant. *<unk>  combined with ophthalmoplegia, dysphagia, ataxia, and cardiac conduction defects is seen in the mitochondrial DNA disorder Kearns–Sayre syndrome (also known as Ragged Red Fiber Myopathy) *<unk>  combined with retardation, peripheral neuropathy, acanthotic (spiked) RBCs, ataxia, steatorrhea, and absence of VLDL is seen in abetalipoproteinemia. *<unk>  is seen clinically in association with several other rare genetic disorders (including muscular dystrophy and chronic granulomatous disease) as part of McLeod syndrome. This is an X-linked recessive phenotype characterized by a complete absence of XK cell surface proteins, and therefore markedly reduced expression of all Kell red blood cell antigens. For transfusion purposes, these patients are considered completely incompatible with all normal and K0/K0 donors. *<unk>  associated with hypogonadism, and developmental delay with an autosomal recessive inheritance pattern is seen with Bardet–Biedl syndrome Other conditions include neurosyphilis, toxoplasmosis and Refsum's disease. Genetics<unk>  <unk>  is one of the most common forms of inherited retinal degeneration. There are multiple genes that code for proteins needed in the visual pathway, when mutated, they can cause the<unk>  phenotype. Inheritance patterns of<unk>  have been identified as autosomal dominant, autosomal recessive, X-linked, and maternally (mitochondrially) acquired, and are dependent on the specific<unk>  gene mutations present in the parental generation. (Of note, Autosomal Dominant<unk>  Type 11 (PRPF-31) can be inherited as a genotype only, because of incomplete penetrance, thus coded for in the DNA but, does not manifest the disease as a phenotype.) In 1989, a mutation of the gene for rhodopsin, a pigment that plays an essential part in the visual transduction cascade enabling vision in low-light conditions, was identified. The rhodopsin gene encodes a principal protein of photoreceptor outer segments. Mutations in this gene most commonly presents as missense mutations or misfolding of the rhodopsin protein, and most frequently follow autosomal dominant inheritance patterns. Since the discovery of the rhodopsin gene, more than 100 RHO mutations have been identified, accounting for 15% of all types of retinal degeneration, and approximately 25% of autosomal dominant forms of<unk> . Over 100 mutations have been reported to date in the opsin gene associated with the<unk>  since the Pro23His mutation in the intradiscal domain of the protein was first reported in 1990. These mutations are found throughout the opsin gene and are distributed along the three domains of the protein (the intradiscal, transmembrane, and cytoplasmic domains). One of the main biochemical causes of<unk>  in the case of rhodopsin mutations is protein misfolding, and the disruption of molecular chaperones. It was found that the mutation of codon 23 in the rhodopsin gene, in which proline is changed to histidine, accounts for the largest fraction of rhodopsin mutations in the United States. Several other studies have reported various codon mutations associated with<unk> , including Thr58Arg, Pro347Leu, Pro347Ser, as well as deletion of Ile-255. In 2000, a rare mutation in codon 23 was reported causing autosomal dominant<unk> , in which proline changed to alanine. However, this study showed that the retinal dystrophy associated with this mutation was characteristically mild in presentation and course. Furthermore, there was greater preservation in electroretinography amplitudes than the more prevalent Pro23His mutation. Autosomal recessive inheritance patterns of<unk>  have been identified in at least 45 genes. This means that two unaffected individuals who are carriers of the same<unk> -inducing gene mutation in diallelic form can produce offspring with the<unk>  phenotype. A mutation on the USH2A gene is known to cause 10-15% of a syndromic form of<unk>  known as Usher's Syndrome when inherited in an autosomal recessive fashion. Mutations in four pre-mRNA splicing factors are known to cause autosomal dominant<unk> . These are PRPF3 (human PRPF3 is HPRPF3; also PRP3), PRPF8, PRPF31 and PAP1. These factors are ubiquitously expressed and it is proposed that defects in a ubiquitous factor (a protein expressed everywhere) should only cause disease in the retina because the retinal photoreceptor cells have a far greater requirement for protein processing (rhodopsin) than any other cell type. The somatic, or X-linked inheritance patterns of<unk>  are currently identified with the mutations of six genes, the most common occurring at specific loci in the<unk> GR and<unk> 2 genes. Types include: OMIM Gene Type<unk> Y<unk>  Y-linked<unk> 1<unk> -1<unk> 2<unk> -2<unk> GR<unk> -3 PRPH2<unk> -7<unk> 9<unk> -9 IMPDH1<unk> -10 PRPF31 Inheritance can be either phenotypic or genotypic.<unk> -11 Autosomal Dominant CRB1<unk> -12, autosomal recessive PRPF8<unk> -13 TULP1<unk> -14 CA4<unk> -17 HPRPF3<unk> -18 ABCA4<unk> -19 EYS<unk> -25 CERKL<unk> -26 FSCN2<unk> -30 TOPORS<unk> -31 SNRNP200<unk>  33 SEMA4A<unk> -35 PRCD<unk> -36 NR2E3<unk> -37 MERTK<unk> -38 USH2A<unk> -39 PROM1<unk> -41 KLHL7<unk> -42 CNGB1<unk> -45 BEST1<unk> -50 TTC8<unk>  51 C2orf71<unk>  54 ARL6<unk>  55 ZNF513<unk>  58 DHDDS<unk>  59 BEST1<unk> , concentric PRPH2<unk> , digenic LRAT<unk> , juvenile SPATA7<unk> , juvenile, autosomal recessive CRX<unk> , late-onset dominant<unk> GR<unk> , X-linked, and sinorespiratory infections, with or without deafness
Retinitis pigmentosa
Far-sightedness
Photic retinopathy
Chloroquine retinopathy
Corneal dystrophy
Sickle cell retinopathy
Ocular melanosis
Diabetic retinopathy