Albinism is a group of inherited conditions in which there is little or no pigment in eyes, skin and or hair. It results from inherited genes that do not synthesize adequate amounts of the pigment MELANIN. The cells in skin make a protein called melanin that gives skin color and protects it from harmful rays in sunshine. The lack of pigment in the eyes causes visual problems and people with albinism are abnormally sensitive to sunlight due to this lack of this pigment. Albinism affects all races and is found in one person in every 17,000 births. (4 )
A parent who has a child with albinism must carry the gene for albinism. For most types of albinism both parents must carry the gene. The parents will have normal hair and eye color for their ethnic background but still carry the gene for albinism. However, when both parents carry the gene but neither has albinism, they have a one in four chance that each pregnancy will bear a baby with albinism This type of inheritance is known as AUTOSMAL RECESSIVE INHERITANCE.
There are at least six different genes that may result in albinisim depending on the position where the biochemical block of the melanin occurs. If all these defects in melanin synthesis are inherited as autosmal recessive traits then it is possible for two persons with albinism to produce normal offspring. For instance, two individuals such as a pair who are homozygous recessive for different defects in the melanin synthesis may produce normal offspring because they have albinisim for different reasons.
There are many types of albinism and DNA studies have shown numerous types of changes in the genes of those with albinism. A test has recently been developed to identify individuals who carry the gene for TY-NEG ALBINISM and for other types of albinism in which the tyrosinase enzyme does not function. This test uses a blood sample to identify the gene for the tyrosinase enzyme.
To test for Ty-Positive albinism a hair-bulb incubation test is conducted in which single hairs with the bulb intact are plucked from head of individuals and incubated in a solution of tyrosine. If the hair bulb is found to contain tyrosinase it means pigment developed and the individual with albinism is said to be tyrosinase-postivive. If the hair bulb did not contain tyrosinase, no pigment developed and the individual with albinism would be called tyrosinase-negative.
Ty-neg or similar albinism can also be identified in a fetus by testing for this enzyme from fluid drawn through the process of amniocentesis.
Ty-Negative or Type 1A albinism results from the absence of an enzyme called tyrosinase which helps the body to change the amino acid tyrosine into pigment. No melanin pigmentation is provided. The individual expresses difficulty with vision.
When two individuals with albinism have children it would be expected that all their children will have albinisim. This usually is the case, but occasionally two parents with albinism will have a normally pigmented child.
This is possible if the parents have albinism for different reasons. that is because they have a lack of different enzymes In this case the father has the enzyme lacked by the mother and the mother has the enzyme lacked by the father. The father could pass on to a child the gene for the enzyme he had and the mother could pass the gene for the enzyme she had with the results that the child would have both needed enzymes and so would be normally pigmented
For some types of ocular albinism, called X-linked ocular albinism, the explanation above does not apply. The gene for X-Linked ocular albinism is located on the X chromosome. Males have one X chromosome and one Y chromosome. Females have two X chromosomes. X-linked ocular albinism is found almost exclusively in males.
Mothers pass the gene to their sons. For a mother who carries the gene, there is one in two chance of one of her sons having X-linked ocular albinism.
Ocular albinism is a type of albinism which involves primarily the eye but may include lighter hair and skin colors. It is often caused by lack of the enzyme tyrosinase. The pattern of inheritance is X-linked or autosomal recessive.
II CONGENITAL CATARACTS
Cataracts are a partial or complete opacity in the crystalline lens of the eye. When cataracts are present the lens becomes more and more opaque which results in progressively impaired vision The removal of the cloudy lens may restore vision.
Len opacities may be present from birth or may develop soon after. An individual’s acuity may be near normal or may be very impaired. Glare tends to be a problem and outdoor vision may be blurred or hazy. Contrast is reduced. Nystagmus (rapid movement of the eyes) and strabismus (deviation of the gaze from their normal straight position) may present problems. Field of vision is normal. The progression and severity may vary. The pupil will appear white when the cataract is total. Individuals with a central lens opacity will have trouble in bright light.
The only treatment is surgery to remove the affected lens. After their removal The patient is fitted with corrective lenses or contacts to compensate for the loss of the lens. A significant and permanent increase in visual acuity usually is the result of treatment.
Aphakic individuals (lens removed) may have corrected visual acuity of approximate 20/70. They may no longer have power of accommodation
(the ability to adjust from far to near vision.) Corrective lenses for near vision, bifocal lenses or with contacts lenses may be helpful. Reading lens or hand magnifiers will help with reading. For distance viewing a telescopic device may be necessary.
Congenital cataracts are usually transmitted as a dominant trait. For instance, juvenile cataracts are determined by a dominant gene. The trait never skips a generation, that is, no child has cataracts unless one of the parents has cataracts. However, sex-linked and recessive transmission are also possible.
III. RETINITIS PIGMENTOSA
Retinitis Pigmentosa is usually a recessive trait, but it may be an autosomal dominant or sex-linked.
Retinitis Pigmentosa is a hereditary degeneration of the retina in which the retinal rods, cones, and nuclear layers are slowly destroyed. The onset of this disease is usually seen in the teenage years. It is more common in males. The disease is almost always bilateral.
Loss of peripheral vision and night blindness are the first problems. As the disease progresses the field of vision contracts until only a tiny central area of vision remains. It is a disease that progresses slowly. Some retention of some central field is present for some individuals.
Because visual fields continue to become smaller until only time central vision remains there is often difficulty in mobility. A cane or guide dog may become necessary.
Students experience difficulty in reading because they can see only words, not phrases. Braille usually becomes a needed skill as more and more vision is lost.
No treatment is available at this time so genetic counseling is important.
IV. GLAUCOMA (Open angle)
Autosonal recessive trait
Glaucoma is a disease of the eye in which an abnormally high intraocular pressure is present. In this condition the aqueous outflow is defective because the drainage channels are clogged due to the high intraocular pressure. This increase in pressure causes pathologic changes in optic disc and defects in visual field.
Glaucoma may be primary, secondary or congenital and is a major cause of visual impairments and blindness in adults. Infantile glaucoma is present at birth to three years. Congenital cataracts are usually bilateral. This disorder is more common in boys.
When left untreated it results in severe visual loss or blindness because pressure stretches the cornea and it swells. Tissue damage causes the peripheral vision to fade and abnormal blind spots develop. In latter stages the central vision is lost.
The drug pilocarpine or other miotic medications are used to constrict the pupil and help to facilitate aqueous flow. Such mediations help stop the progress of glaucoma by keeping the pressure under control.
In some cases, surgery to the tissue blocking anterior chamber helps reduce the tension and is required. When there is no treatment the eye will continue to stretch and may rupture.