Bietti's crystalline dystrophy (BCD) is a rare
autosomal recessive
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
named after G. B. Bietti.
BCD is a rare disease and appears to be more common in people with Asian ancestry.
Presentation
Symptoms of BCD include:
* Crystals in the
cornea (the clear covering of the eye)
* Yellow, shiny deposits on the
retina
* Progressive
atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations (which can destroy the gene to build up the organ), poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply t ...
of the retina, choriocapillaries and
choroid
The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye, and contains connective tissues, and lies between the retina and the sclera. The human choroid is thickest at the far extreme rear ...
(the back layers of the eye). This tends to lead to progressive
night blindness
Nyctalopia (; ), also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition ( ...
and visual field constriction.
Genetics
BCD is inherited in an autosomal recessive manner.
[ This means the defective gene responsible for the disorder is located on an ]autosome
An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...
, and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.
BCD is associated with mutations in the ''CYP4V2
Cytochrome P450 4V2 is a protein that in humans is encoded by the ''CYP4V2'' gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''b ...
'' gene.[
The nematode ]C. elegans
''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (r ...
has a duplicated gene (cyp31A2 and cyp31A3) that are orthologous of the human gene.
These genes code for cytochrome P450s involved in fatty acid synthesis.[ ]
Diagnosis
Treatment
At this time, there is no treatment for BCD. Genetic studies are being conducted to find treatments for patients with BCD.
References
External links
*
{{Eye pathology
Autosomal recessive disorders
Rare diseases
Disorders of choroid and retina