Coloboma, Microphthalmia, Albinism, and Deafness
Patient Information
Characteristics
Background and History
This condition has so far been reported in two families and the full description of the clinical features is not yet available. It results from two mutations in the same gene.
Clinical Correlations
The most striking feature is the lack of pigmentation in hair, skin, and eyes. Both reported patients had severe hearing loss at birth with small eyes and relatively prominent skulls. The cornea (windshield) is small and often is covered by scar tissue. One individual at least had cataracts and the eyes are incompletely formed resulting in colobomas (lack of fusion of embryonic tissues). The optic nerves are small. X-rays may show abnormalities of bone growth (osteopetrosis). The external ears may be rotated posteriorly and one patient was said to have a low muscle tone (hypotonia).
Genetics
Inheritance
This seems to be an autosomal recessive condition based on the two studied patients. The 4 parents, who also had some clinical features (such as hearing loss and decreased pigmentation), contributed two different mutations to each of the affected offspring. The risk of additional affected children for each of the the two sets of parents is 25%.
Pedigree
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
Neurologists, orthopedists, pediatricians, audiologists and ophthalmologists should collaborate on the diagnosis and care of this complex syndrome. However, gene testing is necessary for confirmation.
The fair skin and lack of hair pigmentation is evident at birth. Evidence of decreased hearing requires confirmation by hearing tests. X-rays can document bony changes. A full ophthalmological examination should reveal the eye abnormalities although these are not diagnostic for the condition.
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