Isolated coloboma can follow all possible patterns of single gene inheritance, namely autosomal dominant, autosomal recessive and X-linked.In one family, however, coloboma will follow only one pattern. For instance, in case of an autosomal dominant pattern, a person with coloboma would have a 50/50 chance of passing on the coloboma to each of his or her offspring. In families with a single case of coloboma, it is not possible to say what pattern of inheritance is involved; therefore it is not possible to give an exact recurrence risk number. The recurrence risk of coloboma computed from averaging data across many families (empiric risk) is about 10 percent. This is an imperfect number, as it mixes information from families where this risk may be close to 0 percent with information from families where the actual risk may be 25 percent or even 50 percent.
The topic of inheritance of coloboma is complicated by several factors:
- Sometimes a person who is at risk for developing coloboma may not develop the condition, or it may be so minor that it goes unnoticed. This may appear in the family history as an inconsistent, non-interpretable pattern of inheritance.
- Knowing the pattern of inheritance of coloboma in a family does not give information on how severely an at-risk person will be affected (e.g., how good their visual acuity will be).
- There may be more than one gene involved in being at risk for coloboma, which makes predicting inheritance even more difficult.
For coloboma due to a known syndrome, such as CHARGE syndrome, inheritance is based on what is known about that particular syndrome. However, it is rarely, if ever, possible to say whether coloboma will be a feature of the syndrome in a person inheriting the genetic background responsible for this syndrome.
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