Vargas Mauricio, Mitchell Amanda, Yang Paul, Weleber Richard
Ophthalmic Genetics Service Casey Eye Institute Oregon Health Sciences University Portland, Oregon
Genetic Counselor, Casey Eye Institute Oregon Health Sciences University Portland, Oregon
Bietti crystalline dystrophy (BCD) is a chorioretinal degeneration characterized by the presence of yellow-white crystals and/or complex lipid deposits in the retina and (to a variable degree) the cornea. Progressive atrophy and degeneration of the retinal pigment epithelium (RPE) / choroid lead to symptoms similar to those of other forms of retinal degeneration that fall under the category of retinitis pigmentosa and allied disorders, namely: reduced visual acuity, poor night vision, abnormal retinal electrophysiology, visual field loss, and often impaired color vision. Marked asymmetry between eyes is not uncommon. Onset is typically during the second to third decade of life, but ranges from the early teenage years to beyond the third decade. With time, loss of peripheral visual field, central acuity, or both result in legal blindness in most if not all affected individuals.
DIAGNOSIS/TESTING: The diagnosis of BCD is based on the finding of numerous small, glistening yellow-white retinal crystals associated with atrophy of the RPE, pigment clumps, and sclerosis of the choroidal vessels; variable crystalline deposits in the corneal limbus; varying degrees of rod and cone dysfunction on electroretinography; visual field defects; and reflective dots visualized by spectral domain optical coherence tomography. Identification of biallelic pathogenic variants in by molecular genetic testing can confirm the diagnosis if clinical features are inconclusive.
Referral to low-vision specialists and organizations/professionals trained to work with the visually impaired. Periodic ophthalmologic examination to monitor disease progression and periodic visual field testing particularly as it relates to determination of driving eligibility and eligibility for government programs and/or disability.
BCD is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk relatives and prenatal testing for a pregnancy at increased risk are possible if the pathogenic variants in the family are known.
贝氏结晶状营养不良（BCD）是一种脉络膜视网膜变性疾病，其特征是视网膜以及（程度不一）角膜中存在黄白色晶体和/或复合脂质沉积。视网膜色素上皮（RPE）/脉络膜的进行性萎缩和变性会导致出现与色素性视网膜炎及相关疾病范畴内的其他形式视网膜变性相似的症状，即：视力下降、夜视力差、视网膜电生理异常、视野缺损，且常伴有色觉障碍。双眼明显不对称的情况并不少见。发病通常在人生的第二个至第三个十年，但范围从青少年早期到第三个十年之后。随着时间推移，大多数（如果不是全部）受影响个体的周边视野丧失、中心视力丧失或两者皆有，会导致法定失明。
诊断/检测：BCD的诊断基于发现大量小的、闪闪发光的黄白色视网膜晶体，伴有RPE萎缩、色素团块和脉络膜血管硬化；角膜缘有可变的晶体沉积；视网膜电图显示不同程度的视杆和视锥功能障碍；视野缺损；以及光谱域光学相干断层扫描可见的反射点。如果临床特征不明确，通过分子基因检测鉴定双等位基因致病变异可确诊。
转诊至低视力专家以及接受过与视障人士合作培训的组织/专业人员。定期进行眼科检查以监测疾病进展，并定期进行视野测试，特别是与确定驾驶资格以及参与政府项目和/或残疾资格相关的测试。
BCD以常染色体隐性方式遗传。在受孕时，受影响个体的每个同胞有25%的几率受到影响，50%的几率为无症状携带者，25%的几率不受影响且不是携带者。如果家族中的致病变异已知，则有可能对有风险的亲属进行携带者检测，并对风险增加的妊娠进行产前检测。
