With the determination of an XY karyotype and normal SRY, the differential diagnosis of 46,XY DSD is made with endocrinological measurements of T/DHT ratios (which indicate 5αR2 activity) and precise anatomical imaging since 5αR2D can be difficult to distinguish from other causes of 46,XY DSD (e.g., partial androgen insensitivity syndrome and 17β- hydroxysteroid dehydrogenase type 3 enzyme deficiencies).The measurement of the serum DHT concentration is challenging since the concentrations are low and DHT has a high level of cross-reactivity. A high level of assay specificity is required to measure concentrations of DHT since serum T levels are generally 10 fold higher than DHT in young males. Endocrinological tests for T/DHT ratios can be difficult to interpret since the normal ratio level varies according to age and severity of 5αR2 activity impairment. Affected young males of at least pubertal age with normal serum T levels demonstrate elevated T/DHT levels (normal T, lower than normal DHT). Stimulation with human chorionic gonadotropin (hCG) (alternatively, testosterone enanthate) is required in prepubertal children (with stimulation and samples taken over several days) to increase serum testosterone levels for measurement. Interpreting T/DHT ratios in male newborns is especially challenging due to neonatal testosterone surge and higher than normal 5a-reductase type 1 activity. SRD5A2 gene analysis is recommended for diagnosis in newborns. Broadly, 5αR2D is diagnosed with T/DHT ratios greater than 18 while ratios greater than 30 have been observed in severely affected individuals.
The majority of SRD5A2 mutations are missense mutations but small deletions, splice junction mutations, and gross deletions were also observed. Mutations result in a spectrum of activity effects ranging from destabilizing 5αR2 to complete loss of activity.SRD5A2 mutations are inherited in an autosomal recessive pattern. Homozygous defects are more common than compound heterozygous ones. A phenotype-genotype correlation is not known to exist for many of the most common mutations, and affected males with the same 5αR2 mutations have variable phenotypes suggesting other interacting genetic factors that determine phenotype. Diagnosis
Diagnosis is usually made between birth and puberty. Pseudovaginal perineoscrotal hypospadias presenting with female appearing genitalia and pubertal virilization is the classical syndrome attributed to 5αR2D, but modern diagnostic methods can diagnose the deficiency shortly after birth and recognize the broad spectrum of presentation.The initial diagnosis of 46,XY DSD is indicated by overt genital abnormality. The objective clinical evaluation of dysmorphic features to diagnose 46,XY DSD for apparent female genitalia include: enlarged clitoris, posterior labial fusion, and inguinal/labial mass. For apparent male genitalia:  nonpalpable testes, micropenis, isolated perineal hypospadias, or mild hypospadias with undescended testis. Family history and prenatal history are also taken into account in evaluation. Karyotyping and SRY gene analysis on samples from peripheral leukocytes will exclude sex chromosome abnormalities.