Fig.1: Examples of primary and secondary causes of male hypogonadism. Klinefelter’s syndrome results from the 46,XXY karyotypic abnormality present in approximately 1 in 500 male births. The example of Kallmann’s syndrome is rare isolated deficiency of GnRH, resulting in hypogonadotropic hypogonadism associated with olfactory lobe dysgenesis and anosmia. FSH, follicle-stimulating hormone; GnRH, gonadotropin-releasing hormone; LH, luteinizing hormone; T, testosterone.

Fig. 2: Regulation of testicular function. Note that the single decapeptide gonadotropin-releasing hormone (GnRH) stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Pulsatile GnRH is required. Chronic exposure downregulates the GnRH receptor and causes impaired FSH and LH release, the mechanism whereby pharmacologic GnRH agonists result in chemical castration. Prolactin excess also results in impaired GnRH pulse generator function and hypogonadotropic hypogonadism. Feedback inhibition of LH secretion is a sex steroid–mediated event, whereas FSH secretion has dual feedback regulation involving inhibition by sex steroids and the Sertoli cell product inhibin. Accordingly, a monotropic elevation of the FSH level (normal LH and testosterone levels) may result from deficient Sertoli cell–spermatogenic function. CNS, central nervous system.

Author: Stephen Kemp, MD, PhD, Professor, Department of Pediatrics, Section of Pediatric Endocrinology, University of Arkansas and Arkansas Children’s Hospital

Introduction

Hypogonadism manifests differently in males and in females before and after the onset of puberty. If onset is in prepubertal males and testosterone replacement is not instituted, the individual has features of eunuchoidism, which include sparse body hair, poor development of skeletal muscles, and delay in epiphyseal closure, resulting in long arms and legs. When hypogonadism occurs in postpubertal males, lack of energy and decreased sexual function are the usual concerns. In females with hypogonadism before puberty, failure to progress through puberty or primary amenorrhea is the most common presenting feature. When hypogonadism occurs in postpubertal females, secondary amenorrhea is the usual concern.

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Images Source (1 and 2): Cleveland Clinic