A pseudodeficiency allele or pseudodeficiency mutation is a mutation that alters the protein product or changes the gene's expression, but without causing disease.
For example, in the lysosomal storage diseases, patients with a pseudodeficiency allele show greatly reduced enzyme activity, yet they remain clinically healthy.
In medical genetics, a false positive result occurs in an enzyme assay test when test results are positive, but disease or morbidity is not present.
One possible cause of false positive results is a pseudodeficiency allele.
[1] For some genetic diseases, especially those that have low penetrance or are easily treatable, carrier screening may be of questionable value when pseudodeficiency alleles are present at high frequency.