Undervirilization in XY newborns may hide a 5α‐reductase deficiency: report of three new SRD5A2 gene mutations

The observation of ambiguous genitalia in the newborn signals a medical, surgical and psychological emergency. The most crucial decision will be the choice of sex assignment. Rapid and precise diagnosis is thus essential. In XY newborns with normal/high plasma testosterone (T), partial androgen insensitivity syndrome (PAIS) is usually the first diagnosis evoked, which implies an androgen receptor (AR) defect. The diagnosis of steroid‐5‐alpha‐reductase deficiency is rarely considered by the paediatrician. We report three new SRD5A2 gene mutations in four newborns from France, Morocco and Turkey. The newborns presented with ambiguous genitalia and normal plasma T values and the initial diagnosis\PAIS. In all four cases, normal sequences of the complete AR gene excluded this diagnosis and raised the hypothesis of 5α‐reductase deficiency. The entire coding region (5 exons) of the SRD5A2 gene was assessed by PCR and direct sequencing analysis. For patient 1, we identified a new homozygous 2bp deletion in exon 1 (c.122_123delAG). Patient 2 had a known homozygous mutation, p.G115D, in exon 2. New compound heterozygous mutations in exon 4 (p.A215V) and exon 5 (p.X255Q) were found in patient 3. Patient 4 presented a new substitution in exon 1 (p.S14R) associated with a known polymorphism (p.V89L). Our data confirm our previous experience and clearly demonstrate that a 5‐α reductase defect should be considered in all XY newborns with ambiguous genitalia and normal plasma T secretion, whatever their geographic area or ethnic group; moreover, this defect was not linked to specific phenotype. Early molecular diagnosis is indispensable for the crucial decision of the newborn's sex of rearing.