Clinical Guidance

A study of 125 individuals of Chinese ancestry with BCD showed that individuals who were compound heterozygous for the most common pathogenic variant had an earlier age of onset than those who did not have this pathogenic variant . Individuals homozygous for also tended to have a younger age of onset than individuals with other pathogenic variants, although not to a statistically significant degree. Another study of 18 individuals of Chinese descent with BCD showed that those who were homozygous for or compound heterozygous for variants and had more severe disease based on electrophysiologic testing; namely, lower EOG Arden indices and higher likelihood of a nonrecordable scotopic ffERG and 30-Hz flicker ERG when compared with individuals with pathogenic variants in the coding region.

Source: GeneReviews — "Bietti Crystalline Dystrophy"

Diagnostic Criteria

The diagnosis of BCD, a chorioretinal degeneration, is based on the clinical findings of the typical crystalline deposits in the cornea and retina. BCD is one of few ocular diseases for which the diagnosis can be made with a high degree of confidence by careful examination alone.

Suggestive Findings

Bietti crystalline dystrophy should be suspected in individuals with the following clinical, electrophysiology, and optical coherence tomography (OCT) findings.

Clinical Findings

Vision impairment. Onset of impairment is typically during the second or third decade of life; however, age of onset, presenting symptoms, and disease severity vary widely. Vison impairment is progressive. Marked asymmetry between eyes is common.

Source: GeneReviews — "Bietti Crystalline Dystrophy"

Differential Diagnosis

Retinitis pigmentosa. The clinical symptoms and findings on visual field testing and electrophysiologic studies in Bietti crystalline dystrophy (BCD) are similar to those of other forms of retinal degeneration that fall under the category of retinitis pigmentosa and allied disorders. Crystalline deposits in the retina may be associated with the following:

• Primary hyperoxaluria type 1 and primary hyperoxaluria type 2

• Cystinosis, particularly the more benign adolescent presentation

• Sjgren-Larsson syndrome (OMIM 270200)

• Drug toxicity (e.g., tamoxifen, the anesthetic methoxyflurane, the oral tanning agent canthaxanthine)

• Drug abuse (talc retinopathy)

Source: GeneReviews — "Bietti Crystalline Dystrophy"

Management Guidelines

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs of an individual diagnosed with Bietti crystalline dystrophy (BCD), the evaluations summarized in this section (if not performed as part of the evaluation that led to the diagnosis) are recommended:

• Fundoscopic examination

• Full-field electroretinogram (ffERG) to establish a baseline

• Visual field testing (perimetry) to evaluate the degree of visual field constriction or presence of scotomas and to establish a baseline

• Optical coherence tomography to evaluate for complications such as choroidal neovascularization (CNV) or macular hole formation

• Consultation with a clinical geneticist and/or genetic counselor

Treatment of Manifestations

No specific treatment for BCD currently exists; however, affected individuals should be referred to services specific to those with vision impairment:

• Low-vision specialists can prescribe low-vision aids/devices to optimize remaining vision.

• State services for the blind or organizations/professionals trained to work with the visually impaired provide access to services related to employment, education, and counseling regarding the psychosocial adaptation to visual loss.

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Source: GeneReviews — "Bietti Crystalline Dystrophy"

Surveillance Guidelines

Ophthalmologic examination is recommended every one to two years to monitor disease progression. Examination should include visual field testing particularly as it relates to determination of driving eligibility and eligibility for government programs and/or disability. Affected individuals should be aware of the possibility of CNV and the option of self-monitoring using an Amsler grid under direction of their primary care ophthalmologist.

Source: GeneReviews — "Bietti Crystalline Dystrophy"