User talk:Matveevt

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Article is below
It needs work before it can go live. Specifically references need to be correctly formatted. Let me know if you have any questions.

Best Doc James  (talk · contribs · email) 02:07, 24 December 2017 (UTC)

Bietti’s Crystalline Dystrophy (BCD) is a rare autosomal recessive condition associated with retinal degeneration and characterized by the presence of numerous crystalline retinal and corneal deposits, gradual atrophy of the retinal pigment epithelium (RPE), and choriocapillaris loss (Battu et al., 2016; Ayata et al., 2008; Bietti, 1937). Retinal degeneration and sclerosis of the vessels of the choroid eventually lead to partial loss of visual field in the third and fourth decade of life, as well as night blindness (Ayata et al., 2008). Disease progression results in focal hypertrophy and hyperplasia (Kaiser-Kupfer et al., 1994), and culminates in legal blindness typically in the fifth or sixth decade of life.

'''Background ''' Recent reports describe age-related differences in disease presentation. While fundus examination reveals macular concentration of crystalline deposits in both younger and older patients, substantial atrophy of the choriocapillaris is evident in the latter, accompanied by fewer crystals in the macula. In younger adults, macular crystalline deposits were more extensive and usually concomitant to marked intraretinal pigmentation (Battu et al., 2016). Full field Electroretinogram (ERG) used to measure retinal response to photic stimulation is extinguished or subnormal in most patients, suggesting a profound decline of retinal health (Battu et al., 2016). Early efforts to characterize BCD suggest that it affects a small proportion of patients affected by non-syndromic retinitis pigmentosa (RP); as the condition progresses, pronounced choriocapillary atrophy and abnormalities in the retinal pigment epithelium at the posterior pole are apparent, sparing the macular island until later stages of the disease. Sclerosis of ciliary and choroidal arteries is typically also present (Matafasi et al., 2004). Of note, while RP and BCD are believed to be distinct conditions, there two share common symptoms; those include worsening night vision and visual field constriction. Despite symptom similarity, recent reports have demonstrated reduced subfoveal choroidal thickness and outer choroidal vascular area in BCD patients in comparison to a subgroup of RP patients with mutations in the EYS gene (Miyata et al., 2017). BCD also shares symptomatology with macular degeneration, mostly due to the development of scotomas, which obstruct vision and restrict the visual field (Gheorghe et al., 2015). Early reports of BCD discuss the presence of a “glare,” a likely consequence of deposits in the cornea (Rodger, 1973).

Prevalence
While Bietti’s Crystalline Dystrophy is regarded as a rare condition, it is possible that its prevalence estimates are affected by misdiagnosis. Studies suggest that one in ten people diagnosed with autosomal recessive retinitis pigmentosa are also diagnosed wit BCD (Matafasi et al., 2004). The estimated worldwide prevalence of retinitis pigmentosa is about one in four thousand, with autosomal recessive retinitis pigmentosa accounting for over half of the cases (Hartong et al., 2006). It has thus been suggested that the prevalence of BCD approximates one in sixty-seven thousand, amounting to nearly five thousand cases in the United States (Okialda et al., 2012). BCD is more commonly diagnosed in people of East Asian descent and in those of Lebanese and Mexican background (Hu et al., 1983; Lin et al., 2005). A diagnosis of BCD in patients of European descent typically accompanies presentation with retinitis pigmentosa (Matafasi et al., 2004).

Signs and symptoms
Although the characteristic features of Bietti’s Crystalline Dystrophy are described above, the rare presentation of the disorder and the heterogeneity of its etiology limit the opportunity to obtain a clinical picture from a robust patient population. Most accounts of BCD come from case reports and reflect the varied presentation of symptoms over time. Yet, there appears to be sufficient evidence to enable a distinction between early, intermediate, and late stages of BCD (Yuzawa et al., 1986); it should nevertheless be noted that age of onset, early symptoms, and progression of the condition can vary substantially from patient to patient, perhaps posing a challenge to proper diagnostics (Saatci et al., 2014). Early stages of Bietti’s Crystalline Dystrophy are characterized by the presence of yellowish-white polygonal crystals at the posterior pole and the periphery. Crystals are fewer at the posterior pole during the intermediate stage of the disease but are apparent surrounding the area of central atrophy and up to the equator (Staatci et al., 2014). Crystalline deposits are minimal in the advanced stage of the disease, marked by nearly complete chorioretinal atrophy. Macular function gradually worsens as BCD progresses, and in rare cases, visual acuity is drastically affected (Padhi et al., 2011). Typically by the 6th decade of life, patients will present with significant deterioration of vision and, eventually, legal blindness.

Cause
As mentioned briefly previously, BCD is a rare condition with an autosomal recessive pattern of inheritance. Early attempts to identify the genetic etiology of BCD report that a mutation in the CYP4V2 gene is associated with the development of the disorder (Li et al., 2004). Epidemiological accounts as well as diverse presentation and disease progression, however, reveal the etiological heterogeneity of BCD. Indeed, later work has identified other rare mutations related to developing BCD and associated with gradual loss of night vision, loss of visual acuity (with some asymmetry between the eyes at baseline), progressive constriction of the visual field, pronounced pericentral loss of visual sensitivity, and ultimately the development and enlargement of scotomas (Lockhart et al., 2017). Remarkably, Lockhart and colleagues report that the rate of macular degeneration is comparable between the two eyes regardless of the fact that one eye might lag behind the other, that is—it is common that macular degeneration does not begin to develop in both eyes at the same time, but eventually its degree becomes similar in both eyes. Of etiological significance is the novel suggestion that inflammatory processes could play a role in the progression of BCD, and that anti-inflammatory therapies could thus be beneficial to a subpopulation of patients. Further efforts to identify etiologically relevant mutations describe homozygous, compound heterozygous, and single heterozygous mutations on CYP4V2. The range of mutations was related to a somewhat diverse symptom presentation, including the characteristic BCD phenotype described above, as well as choroidal neovascularization, and abnormalities in other parts of the body, such as changes in the terminals of fingers and toes (Yin et al., 2016).

Treatment
The clinical presentation of Bietti’s Crystalline Dystrophy (findings from diagnostic testing and electrophysiology) are commonly present in other disorders of vision involving retinal degeneration. Retinitis pigmentosa and related conditions share certain clinical features with BCD (such as night blindness, constriction of the visual field due to photoreceptor death, specifically rods) are likely to contribute to a misdiagnosis (therefore under-diagnosing of BCD). Crystalline deposits in the retina—a primary symptom of BCD, manifest in cystinosis, hyperoxaluria types 1 and 2, Sjögren-Larsson syndrome, or can be a consequence of prolonged drug consumption or drug toxicity. Improvement in diagnostic tools since the early 2000s has made possible the more accurate and early diagnosis of Bietti’s Crystalline Dystrophy. Unfortunately, while diagnostic accuracy has improved, currently no treatment exists for those affected by the disorder. Patients are often referred to low vision specialists and advised to utilize low vision aids to help lessen the impact of vision loss (Okialda et al., 2012). Images obtained from BCD patients are available at the end of this article (Ayata et al., 2008).

Research
The intractable nature of Bietti’s Crystalline Dystrophy has led to repeated efforts to establish analogs of the condition in animal models in the hopes of making possible a deeper insight into the causal mechanisms governing the development of disease and to test pharmacotherapies to prevent its progression. Among the models most successful in recapitulating the main features of BCD is the Cyp4v3 knockout mouse model, with Cyp4v3 representing the urine ortholog to CYP4V2. This model offers a viable route to characterizing causal components of BCD, as well as assess the efficacy of therapeutic interventions for this devastating condition (Lockhart et al., 2014). Existing therapies include anti-vascular endothelial growth factor therapy which has had minimal success in preventing disease progression, and injections of intravitreal ranibizumab, which preserves visual acuity in a small proportion of patients (Hua et al., 2015; Nachiappan et al., 2012). Recently, computational models of the disorder have been employed to better predict its course (Lockhart et al., 2014). Immunotherapies and the use of anti-inflammatories have also been proposed as a possible intervention aimed at alleviating symptoms associated with Bietti’s Crystalline Dystrophy. To date, the development and testing of pharmacotherapies to address the disorder are in the nascent stages. Combined with genetic testing and continuing improvements in diagnostic tools, there is some hope that BCD will be detected sooner, and its course-influenced more effectively in the near future.