The overall incidence of all differences of sex development (DSD) has been estimated at 1.7%, but this includes conditions that usually do not present with atypical genitalia at birth, such as Turner syndrome, Klinefelter syndrome, and complete androgen insensitivity syndrome.[3]Blackless M, Charuvastra A, Derryck A, et al. How sexually dimorphic are we?: review and synthesis. Am J Hum Biol. 2000 Mar;12(2):151-166.
http://www.ncbi.nlm.nih.gov/pubmed/11534012?tool=bestpractice.com
The prevalence of atypical genitalia at birth may be up to 1 in 300 births; however specialist input is required in about in 1 in 3000 births and sex assignment is delayed in 1 in 11,000 births.[4]Ahmed SF, Dobbie R, Finlayson AR, et al. Prevalence of hypospadias and other genital anomalies among singleton births, 1988-1997, in Scotland. Arch Dis Child Fetal Neonatal Ed. 2004 Mar;89(2):F149-51.
https://www.doi.org/10.1136/adc.2002.024034
http://www.ncbi.nlm.nih.gov/pubmed/14977900?tool=bestpractice.com
[5]Rodie ME, Ali SR, Jayasena A, et al. A nationwide study of the prevalence and initial management of atypical genitalia in the newborn in Scotland. Sex Dev. 2022;16(1):11-8.
https://www.doi.org/10.1159/000517327
http://www.ncbi.nlm.nih.gov/pubmed/34352789?tool=bestpractice.com
In boys with atypical genitalia, chromosomal abnormalities have been reported to be present in approximately 3% of those with isolated cryptorchidism, 7% with hypospadias, and 13% of those with cryptorchidism and hypospadias.[6]Moreno-Garcia M, Miranda EB. Chromosomal anomalies in cryptorchidism and hypospadias. J Urol. 2002 Nov;168(5):2170-2; discussion 2172.
https://www.doi.org/10.1097/01.ju.0000029562.62482.74
http://www.ncbi.nlm.nih.gov/pubmed/12394752?tool=bestpractice.com
[7]Ahmed SF, Achermann J, Alderson J, et al. Society for Endocrinology UK Guidance on the initial evaluation of a suspected difference or disorder of sex development (Revised 2021). Clin Endocrinol (Oxf). 2021 Dec;95(6):818-40.
https://www.doi.org/10.1111/cen.14528
http://www.ncbi.nlm.nih.gov/pubmed/34031907?tool=bestpractice.com
The incidence of 46,XY DSD is estimated at 1 in 20,000 live male births.[8]Morel Y, Rey R, Teinturier C, et al. Aetiological diagnosis of male sex ambiguity: a collaborative study. Eur J Pediatr. 2002 Jan;161(1):49-59.
http://www.ncbi.nlm.nih.gov/pubmed/11808880?tool=bestpractice.com
In one review of gonadal developmental disorders among patients with atypical genitalia or delayed puberty, 52% of patients had 46,XY DSD, 35% had 46,XX DSD, and 14% had a disorder of gonadal development.[9]Siklar Z, Berberoglu M, Adiyaman P, et al. Disorders of gonadal development: a broad clinical, cytogenetic and histopathologic spectrum. Pediatr Endocrinol Rev. 2007 Mar;4(3):210-7.
http://www.ncbi.nlm.nih.gov/pubmed/17551482?tool=bestpractice.com
Overall, in 46,XY DSD patients with no clear abnormality of steroidogenesis, a genetic diagnosis is made in less than 50% of patients.[7]Ahmed SF, Achermann J, Alderson J, et al. Society for Endocrinology UK Guidance on the initial evaluation of a suspected difference or disorder of sex development (Revised 2021). Clin Endocrinol (Oxf). 2021 Dec;95(6):818-40.
https://www.doi.org/10.1111/cen.14528
http://www.ncbi.nlm.nih.gov/pubmed/34031907?tool=bestpractice.com
This contrasts with 46,XX DSD, where classic congenital adrenal hyperplasia accounts for over 95% of cases.