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.