Bietti's Crystalline Dystrophy

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 by Victoria Chang, MD on March 29, 2020.


Bietti's Crystalline Dystrophy
Bietti crystalline dystrophy.
Glistening crystalline-like lesions at posterior pole of retina in patient with Bietti crystalline dystrophy. Fundus also shows atrophic-like changes of RPE and patchy atrophic change of choriocapillaris vessels. Clumping of retinal pigment is also apparent. © 2019 American Academy of Ophthalmology [1]


Disease Entity

2018 ICD-10 Code: H35.53: Other dystrophies primarily affecting the sensory retina

Disease

Bietti’s Crystalline Dystrophy (BCD), is a rare autosomal recessive ocular disease that involves yellow-white crystalline lipid deposits in the retina and sometimes cornea, degeneration of the retinal pigment epithelium (RPE) and sclerosis of the choroidal vessels. Progression of the disease ultimately results in reduced visual acuity, night blindness, visual field loss, and impaired color vision. Onset of the disease can occur from early teenage years to third decade of life, but can also occur beyond the third decade. As the disease progresses, decreases in peripheral acuity, central acuity or both ultimately results in legal blindness in most patients.

BCD was first described by Italian Ophthalmologist Dr. G.B. Bietti in 1937.[2] There have been around 100 reported cases documented in the literature (OMIM 210370).

Genetics

The mode of inheritance for BCD is autosomal recessive. BCD involves the pathologic variant of the CYP4V2 gene.[3]

Risk Factors

Asians, especially those of Chinese ethnicities, have been found to have a relatively higher incidence of BCD.[4]

Pathophysiology

The pathophysiology of BCD is still unclear. However, biallelic pathologic variations in CYP4V2 have been implicated in the disease. CYP4V2 enzyme has been shown to play a role in fatty acid and steroid metabolism. Dysfunctional lipid metabolism could result in complex lipid retinal or corneal deposits in crystalline form.[5] In patients with BCD, lipid inclusions are found systemically, suggesting possible dysfunctional lipid metabolism elsewhere as well.[6]

Diagnosis

Diagnosis of BCD is based on ophthalmic evaluation of numerous small glistening yellow-white retinal crystalline deposits in the retinal with or without crystalline deposits in the cornea, RPE atrophy, and choroidal vessels sclerosis.[7] The corneal crystals are usually isolated in the subepithelial and anterior stroma of the peripheral cornea.[8] CYP4V2 is only moderately expressed in the cornea and the conjunctiva; thus, ocular surface findings are not required for diagnosis.[9] Diagnostic tools include electroretinography for evaluating degree of rod and cone dysfunction, humphrey visual field test for visual field deficits, spectral domain OCT for identifying reflective dots, in vivo confocal microscopy, and specular microscopy.[10]

If clinical features are equivocal, the disease can be confirmed by the identification of pathologic variants in CYP4V2 by molecular genetic testing.[11]

Image 1: Shiny, yellow-white crystalline deposits present in posterior pole of right eye retina.[12]

Clinical presentation

Typically patients with BCD begin noticing symptoms between the second and third decades of life. Patients experience a progressive reduction in visual acuity, nyctalopia, and visual field loss. Occasionally, color vision may also be impaired. Visual deficits can progress at different rates in each eye, and the severity and rate of progression varies widely among affected individuals. Over time patients, particularly in the fifth or sixth decade, can have legal blindness.

Differential Diagnosis

The differential diagnosis for BCD includes other diseases that involve crystalline deposits in the retina such as:

Image 2: Ciliary body viewed with electron transmission micrograph. Arrow points to melanosome lipid-complex inclusions found in pigmented ciliary epithelium.[7]

Management

Currently, there are no evidence based surgical treatments or medical treatment specific to BCD available in the existing literature.

Standard of care for BCD patients include follow-up with an ophthalmologist for a yearly exam to monitor disease and to watch for macular hole, edema, or atrophy and choroidal neovascularization.

Standard of care for BCD patients with vision impairment include referral to low vision specialists or state services for the blind.

Genetic testing is available for those that have immediate family diagnosed with BCD in order to identify abnormal CYP4V2 genes. Genetic counseling is offered for those with diagnosed BCD or BCD carriers for family planning, whereas prenatal testing for BCD is possible but controversial.[10]

Prognosis

There is no known cure for this disease. As a result, loss of peripheral visual field and visual acuity can result in legal blindness in patients with the disease.

Conclusion

Bietti’s Crystalline Dystrophy (BCD) is a rare retinal dystrophy that is characterized by deposition of yellow-white crystals in the retina and sometimes the cornea, degeneration of the retina, and sclerosis of the choroidal vessels that results in the progressive loss of peripheral visual acuity and night blindness. There is currently no specific treatment for BCD. However, early diagnosis and referral to low-vision specialists can help with management of patients with the disease.

References

  1. American Academy of Ophthalmology. Bietti crystalline dystrophy. https://www.aao.org/image/bietti-crystalline-dystrophy Accessed September 19, 2019.
  2. Bietti G. Ueber familiaeres Vorkommen von 'Retinitis punctata albescens' (verbunden mit 'Dystrophia marginalis cristallinea corneae'), Glitzern des Glaskoerpers und anderen degenerativen Augenveraenderungen. Klin Monatsbl Augenheilkd. 99: 737-757, 1937.
  3. Lin J, Nishiguchi KM, Nakamura M, Dryja TP, Berson EL, Miyake Y. Recessive mutations in the CYP4V2 gene in East Asian and Middle Eastern patients with Bietti crystalline corneoretinal dystrophy. J Med Genet. 2005;42(6):e38.
  4. Kaiser-Kupfer MI, Chan CC, Markello TC, Crawford MA, Caruso RC, Csaky KG, Guo J. Clinical biochemical and pathological correlations in Bietti’s crystalline dystrophy. Am J OphthalmoI 1994; 118: 569–582.
  5. Lee J, Jiao X, Hejtmancik JF, et al. The metabolism of fatty acids in human Bietti crystalline dystrophy. Invest Ophthalmol Vis Sci. 2001;42(8):1707-14.
  6. Wilson DJ, Weleber RG, Klein ML, Welch RB, Green WR. Bietti's crystalline dystrophy. A clinicopathologic correlative study. Arch Ophthalmol. 1989;107(2):213-21.
  7. 7.0 7.1 Furusato E, Cameron JD, Chan CC. Evolution of Cellular Inclusions in Bietti's Crystalline Dystrophy. Ophthalmol Eye Dis. 2010;2010(2):9-15.
  8. Krachmer J, Mannis M, Holland E: CORNEA, 4th ed.Elsevier Mosby, 2017, 251-264.
  9. Garcia-Garcia GP, Martinez-Rubio M, Moya-Moya MA, Perez-Santonja JJ, Escribano J. Current perspectives in Bietti crystalline dystrophy. Clin Ophthalmol 2019;13:1379-99.
  10. 10.0 10.1 Vargas M, Mitchell A, Yang P, Weleber R. Bietti Crystalline Dystrophy. GeneReviews. 2012.
  11. Xiao X, Mai G, Li S, Guo X, Zhang Q. Identification of CYP4V2 mutation in 21 families and overview of mutation spectrum in Bietti crystalline corneoretinal dystrophy. Biochem Biophys Res Commun. 2011;409(2):181-6.
  12. Mansour AM, Uwaydat SH, Chan CC. Long-term follow-up in Bietti crystalline dystrophy. Eur J Ophthalmol. 2007;17(4):680-2.
  1. Jiao X, Munier FL, Iwata F, et al. Genetic linkage of Bietti crystallin corneoretinal dystrophy to chromosome 4q35. Am J Hum Genet. 2000;67(5):1309-13.
  2. Mamatha G, Umashankar V, Kasinathan N, et al. Molecular screening of the CYP4V2 gene in Bietti crystalline dystrophy that is associated with choroidal neovascularization. Mol Vis. 2011;17:1970-7.
  3. Mataftsi A, Zografos L, Millá E, Secrétan M, Munier FL. Bietti's crystalline corneoretinal dystrophy: a cross-sectional study. Retina (Philadelphia, Pa). 2004;24(3):416-26.
  4. O’Neill M, McKusick V. #210370 Bietti Crystalline Corneoretinal Dystrophy; BCD. OMIM. 2015
  5. Sahu DK, Rawoof AB. Bietti's crystalline dystrophy. Indian J Ophthalmol. 2002;50(4):330-2.