Objective: To describe two cases of 5α - reductase deficiency and the identification of a novel frameshift mutation in this sibling pair. Design: Case report. Setting: An adolescent clinic at a university hospital. Patient(s): A 14- year- old girl and her younger sister, who presented with primary amenorrhea, deepening of the voice, and clitoromegaly. Intervention(s): Deoxyribonucleic acid was extracted from peripheral blood, and 8 exons of the androgen receptor gene and 5 exons of the steroid 5α - reductase type 2 gene (encoded by SRD5A2 gene)- were amplified by polymerase chain reaction and subjected to sequence analyses. Main Outcome Measure(s): Genetic diagnosis of 5α - reductase deficiency. Result(s): There was no evidence of a genetic abnormality in the 8 screened exons of the androgen receptor gene, but exon 4 of the SRD5A2 gene showed a novel homozygous deletion of the thymine at nucleotide position c.655 (c.655delT), leading to a frameshift mutation predicted to result in an abnormally long protein with an extended termination signal. Conclusion(s): The molecular characterization of the mutation can be a relevant tool for a correct diagnosis of 5α - reductase deficiency.
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