Dihydrotestosterone and Its Relationship to Testosterone in Infancy and Childhood*

A cross-sectional and longitudinal study of the change in dihydrotestosterone (DHT) and testosterone (T) serum concentration was undertaken in infants from birth to 18 months to elucidate the differences in the concentration of DHT and T in male and female infants. In addition, changes in DHT, T, and the T:DHT ratio were studied in males from infancy to adulthood. Both DHT and T in cord blood were significantly higher in male than in female infants (P < 0.005 and P = 0.01, respectively). Postnatally, in male infants, there was a parallel rise in DHT and T to pubertal levels, resulting in a constant T: DHT ratio (mean ± sd, 4.9 ± 2.7). After hCG stimulation, the T: DHT ratio was similar in this age group (mean ± sd, 5.3 ± 1.7). Both DHT and T decreased sharply at age 6 months in young male infants. The T:DHT ratio rose significantly (P < 0.001) in late puberty (mean ± sd, 10 ± 1.9). The T:DHT ratio after hCG stimulation in older male infants and prepubertal boys (mean ± sd, 11 ± 4.4) with varying conditions was similar to the basal T:DHT ratio in late pubertal males. The T:DHT ratio after hCG stimulation in a prepubertal genetic male with 5α-reductase deficiency was clearly elevated (>27). In two genetic male neonates with ambiguous genitalia whose T concentration (168 and 180 ng/dl) reached the same peak observed in normal newborns, the diagnosis of 5α-reductase deficiency was excluded by the normal T:DHT ratio (3.0–4.0) in both the baseline and hCG stimulated state. DHT and T were low or undetectable in female infants. The following conclusions were reached. 1) T and DHT levels in cord blood are higher in males than in females. The presence of DHT suggests that there is active fetal peripheral metabolism of T to DHT. 2) In males, DHT and T rise in parallel, resulting in a constant T:DHT ratio in early infancy. There is a significant rise in the T:DHT ratio in late puberty. 3) In young male infants whose T and DHT are normally high, the T:DHT ratio may exclude 5α-reductase deficiency, while in older infants and prepubertal males, hCG stimulation is necessary to assess the T:DHT ratio.