Albinism, Ocular Type 1
Patient Information
Characteristics
Background and History
It is unknown for how long people have recognized individuals with decreased pigmentation, often called albinos. We now know of a number of gene mutations that cause a variety of disorders in which the skin and hair are pale or even white. In these disorders, the pigmentation in the eyes is also affected, most noticeably in the iris which is usually pale blue. However, the gene mutations also affect an important layer beneath the retina, known as the retinal pigment epithelium, visible when an eye doctor looks into the eye.
Clinical Correlations
Ocular albinism is a disorder in which the decrease in pigmentation affects only the eye. The iris is pale blue and often has defects that allow light to shine through. The pigmentary layer of the retina is also lacking normal pigmentation so that the retina is highly transparent. More seriously, in ocular albinism as in other forms of albinism, the central portion of the retina is not formed normally and the nerves connecting the eye to the brain are incorrectly routed. Together these result in decreased vision and loss of depth perception in most people. Abnormal sensitivity to light and nystagmus (dancing eyes) are often seen as well.
No other health problems are associated with this disorder.
Genetics
Inheritance
This is an X-linked recessive condition in which in general only males have the complete clinical picture. It is not uncommon for females who carry the mutation in one of their X-chromosomes to have some features such as abnormal pigmentation in the iris and retina although vision is seldom affected. Such females will usually pass the abnormal X chromosome to half their children so that half of their sons will have ocular albinism and half of their daughters will be carriers like themselves. Males with ocular albinism will not have children with the same disorder but half of their daughters would be expected to be carriers with one abnormal X-chromosome.
Pedigree
X-linked recessive, father affected
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked recessive, carrier mother
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
Diagnosis and Prognosis
Ocular albinism cannot be diagnosed by simple inspection alone. Light blue eyes may suggest the diagnosis in families in which the disorder is known to occur, but blue eyes are not uncommon in the general population. The presence of ‘dancing eyes’ and decreased vision are also suggestive of this condition but only your eye doctor can make the precise diagnosis.
No treatment is available for this pigmentary disorder.
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