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Background/Aims: P450c17 deficiency is an uncommon steroidogenic disorder that typically presents as a sexually infantile adolescent phenotypic female with hypertension and hypokalemia. Although cortisol synthesis is impaired, elevated corticosterone and deoxycorticosterone ordinarily prevent adrenal insufficiency. Thus, diagnosis prior to puberty is rare. We report novel clinical features of an infant with complete P450c17 deficiency due to two novel mutations in CYP17A1. Methods: A 10-week-old, 46,XY phenotypic female presented with hypotension, developed hypokalemic hypertension post-resuscitation, then hyperkalemic hyponatremia upon weaning salt supplements. All CYP17A1 exons of the proband and parents were PCR-amplified and sequenced. Cosyntropin, GnRH agonist, and hCG tests were performed. Results: Sequencing demonstrated compound heterozygosity for two novel CYP17A1 mutations, C327dupT and C362G>A (W121X), both generating premature stop codons in exon 2 and predicting non-functional enzymes. Plasma corticosterone was very elevated, deoxycorticosterone normal, cortisol detectable, and aldosterone low-normal at baseline. Responses to cosyntropin of corticosterone and progesterone were elevated, deoxycorticosterone and aldosterone normal, cortisol subnormal, and 17α-hydroxycorticosteroid intermediates undetectable. GnRH agonist/hCG testing showed no androgenic response. Conclusion: This is the first report of P450c17 deficiency presenting in a 46,XY female infant with hypotensive shock, a state exacerbated by the atypical absence of deoxycorticosterone elevation. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]