Anti-Müllerian Hormone

Anti-Müllerian Hormone (AMH) is a glycoprotein hormone belonging to the transforming growth factor-beta (TGF-β) superfamily. It is primarily produced by the granulosa cells of ovarian follicles in females and by Sertoli cells of the testes in males during fetal development. AMH plays a crucial role in sexual differentiation, reproductive physiology, and folliculogenesis.

Biological Role and Function

Embryonic Sexual Differentiation

During male embryonic development, AMH is secreted by Sertoli cells of the fetal testes. Its primary function at this stage is to induce the regression of the Müllerian ducts, which are the precursors of the female reproductive tract (fallopian tubes, uterus, and upper part of the vagina). This regression is essential to the development of male internal genitalia, preventing the formation of female reproductive structures.

In females, AMH is produced at low levels during fetal life and early childhood, with no role in Müllerian duct regression, allowing the development of female internal genital organs.

Regulation of Folliculogenesis in Females

Postnatally, AMH is expressed by granulosa cells of preantral and small antral ovarian follicles. It regulates folliculogenesis by inhibiting the initial recruitment of primordial follicles and decreasing the sensitivity of growing follicles to follicle-stimulating hormone (FSH). This modulation prevents premature depletion of the ovarian follicle pool and aids in the selection of dominant follicles for ovulation.

AMH levels reflect the size of the growing follicle pool, making it a marker of ovarian reserve and reproductive potential.

Production and Secretion

Source in Females

AMH is secreted by granulosa cells starting from the primary follicle stage and continues through the small antral follicle stages. Production ceases once follicles reach the large antral stage or become dominant, resulting in a decrease of AMH secretion as follicles mature. AMH serum levels remain relatively stable throughout the menstrual cycle, providing a consistent indicator of ovarian function.

Source in Males

In males, Sertoli cells secrete AMH during fetal life and early childhood, peaking during infancy and declining at puberty as testosterone production increases. After puberty, AMH levels are significantly reduced but detectable.

Clinical Applications

Assessment of Ovarian Reserve

AMH is widely used as a biomarker to evaluate ovarian reserve in women, which reflects the quantity of remaining follicles within the ovaries. Measurement of serum AMH is valuable in fertility assessments, predicting response to ovarian stimulation in assisted reproductive technologies (ART), and diagnosing conditions that affect ovarian function such as primary ovarian insufficiency or polycystic ovary syndrome (PCOS).

Diagnosis of Disorders of Sexual Development (DSD)

AMH measurement aids in differentiating causes of ambiguous genitalia and gonadal dysgenesis in infants and children. In males with suspected gonadal dysgenesis, low or absent AMH levels suggest Sertoli cell dysfunction or absence. In females, elevated AMH may be associated with PCOS.

Monitoring Gonadal Function

AMH levels serve as an indicator of gonadal function after chemotherapy, radiation, or surgical interventions that may affect fertility. It is also useful in monitoring ovarian reserve over time in women undergoing fertility preservation.

Laboratory Measurement and Interpretation

Assay Methods

Serum AMH is measured using immunoassays, including enzyme-linked immunosorbent assays (ELISA) and automated chemiluminescent platforms. Standardization of assays is important for accurate and reproducible results, as variability exists among different commercial kits.

Reference Ranges

AMH levels vary according to age, sex, and physiological status:

• In females, AMH peaks during reproductive years and declines with age, becoming undetectable after menopause.
• In males, AMH is high during infancy and early childhood, decreasing after puberty.

Interpretation of AMH levels must consider the clinical context, assay used, and patient demographics.

Molecular Structure and Signaling

AMH is a dimeric glycoprotein composed of two identical subunits linked by disulfide bonds. It is synthesized as a precursor protein that undergoes proteolytic cleavage to generate the biologically active C-terminal fragment.

AMH exerts its effects by binding to a specific receptor complex on target cells, consisting of the type II AMH receptor (AMHR2) and type I receptors (ALK2, ALK3, or ALK6). Binding activates intracellular SMAD signaling pathways, modulating gene expression to induce Müllerian duct regression or regulate follicular development.

Summary of Key Characteristics

Summary of Clinical Relevance

• Fertility assessment: AMH measurement provides insight into the ovarian follicle pool and reproductive lifespan.
• PCOS diagnosis: Elevated AMH correlates with increased antral follicle count in PCOS.
• Gonadal function monitoring: Useful after gonadotoxic treatments or in gonadal dysgenesis.
• Pediatric endocrinology: Helps evaluate testicular function in male infants and children.

In conclusion, Anti-Müllerian Hormone is a critical regulator of sexual differentiation and reproductive function, serving as a valuable biomarker in clinical endocrinology and reproductive medicine. Its measurement and understanding provide essential information for the diagnosis and management of various reproductive and developmental conditions.