How is Alkaptonuria inherited?
Alkaptonuria is inherited in an autosomal recessive manner. This means that both copies of the gene have to have changes for the person to show signs and symptoms of the disease. If only one copy of the gene has a change, the person is a carrier for Alkaptonuria and does not have the condition.
- Introne WJ, Perry MB, Troendle J, Tsilou E, Kayser MA, Suwannarat P, O'Brien KE, Bryant J, Sachdev V, Reynolds JC, Moylan E, Bernardini I, Gahl WA. A 3-year randomized therapeutic trial of nitisinone in alkaptonuria. Mol Genet Metab. 2011;103:307?14.
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What does it mean to have a "variant" in the gene for Alkaptonuria?
A variant is a change in the DNA sequence that is different that what is considered to be "normal." A pathogenic variant is one that has been found to cause disease. The HGD gene currently has over 130 pathogenic variants identified. If you have two known pathogenic variants, this is consistent with a diagnosis of Alkaptonuria. Having one is associated with being an unaffected carrier. Occasionally genetic testing might find a variant that has not been previously seen, and this will be classifed as a "variant of unknown significance" (VUS). When a VUS is found it is not certain if this change is part of normal human genetic variation or if it is a change that will cause Alkaptonuria. Because the diagnosis of Alkaptonuria is based on clinical findings, a person who is identified to have a variant of unknown significance should base their medical management on the presence or absence of the clinical findings of Alkaptonuria.