Persistent Hyperplastic Primary Vitreous
Patient Information
Characteristics
Background and History
This condition has been recognized as a cause of blindness for many decades but few families have been reported.
Clinical Correlations
The posterior chamber of the eye contains the retina (the tissue that responds to light) and is filled with a transparent jelly-like substance called the vitreous humor. Diseases of the vitreous are uncommon but, as in the case of persistent hyperplastic vitreous (PHPV) described here, can have severe vision consequences. Normally during embryonic life certain developing components in the vitreous such as blood vessels regress leaving it transparent. When that process is interrupted the vitreous becomes a dense, opaque, and vascularized tissue that prevents light from reaching the retina. This usually is present at birth in only one eye and is seldom familial.
The eyeball may be abnormally small (microphthalmia) and the lens can be opaque (cataract). Some eyes develop glaucoma and retinal detachments. Vision is often completely absent. No abnormalities in other parts of the body have been associated.
Genetics
Inheritance
In most instances, there is no family history of PHPV. However, a six-generation family has been reported in which multiple individuals with this disorder were found in a pattern consistent with autosomal recessive inheritance. Further, the distribution of mutations in a specific gene suggested the same pattern of inheritance. The presence of this mutation in both parents (with normal eyes) would give them a risk of having on average one out of four children with PHPV.
In another family, PHPV was present in 3 generation in a pattern consistent with autosomal dominant inheritance. No gene mutation in this pedigree was reported but in this case children of an affected parent would have a 50% risk of developing PHPV.
Pedigree
Autosomal dominant
Autosomal dominant disorders require only one mutation for the disease to be expressed. Since an affected parent has two chromosomes, only one of which has the mutant gene, parents can expect that half (50%) of their children will receive that one and inherit the disease. It is common for individuals that inherit the mutation, however, to not have evidence of the disease (nonpenetrance).
Autosomal dominant inheritance leads to a vertical pattern of transmission
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
The diagnosis is usually made at birth by an ophthalmologist. It is usually inoperable and the loss of vision is permanent. Lifespan is normal and the vitreous scarring does not spread to the other eye. Therefore, if only one eye has PHPV, most individuals are able to see normally with the other eye.
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