A new deletion of the 5 alpha-reductase type 2 gene in a Turkish family with 5 alpha-reductase deficiency.

UNLABELLED: The molecular basis for male pseudohermaphroditism produced by the 5 alpha-reductase deficiency is becoming increasingly understood.

OBJECTIVE

We have performed biochemical and molecular analyses of the 5 alpha-reductase type 2 gene in a Turkish family with a 5 alpha-reductase deficiency.

PATIENT: A 46,XY prepubertal Turkish patient with female phenotype showing clitoral hypertrophy, high plasma testosterone and dihydrotestosterone, and normally differentiated and developed testosterone-dependent internal genitalia.

MEASUREMENTS: 5 alpha-Reductase activity, measured by the conversion of 3H-T into 5 alpha-reduced compounds, was determined from cultured genital skin fibroblasts by both intact monolayer assay and cell-free extracts at various pH values. The five exons of the 5 alpha-reductase type 2 gene were sequenced after enzymatic amplification (PCR) of the patient's genomic DNA. Labelled PCR of the consanguineous parents' DNA was submitted to electrophoresis on a sequencing gel.

RESULTS

A marked decrease in the transformation of T into 5 alpha-reduced compounds by intact cells and a diminished 5 alpha-reductase activity at acidic pH by sonicated cell extracts strongly suggested a 5 alpha-reductase type 2 deficiency. Molecular analysis of the 5 alpha-reductase type-2 gene showed a trinucleotide deletion straddling codons 156 and 157, responsible for a methionine residue deletion at position 157 of the protein. The parents' DNA contained both normal and deleted alleles.

CONCLUSIONS

This is the third deletion described in the 5 alpha-reductase type 2 gene. The deleted methionine 157 is conserved in both types 1 and 2 of human and rat 5 alpha-reductase, which suggests its crucial role in the functioning of the enzyme. This gene rearrangement was thus clearly responsible for the reduced 5 alpha-reductase activity and abnormal genital development in this patient.