Neonatal Testosterone Surge Identified as Initial Trigger for Rare Muscle Wasting Disease in Men

Nagoya University researchers find that neonatal testosterone spikes trigger SBMA. Early gene-silencing therapy may prevent adult muscle wasting and tremors.

By: AXL Media

Published: Mar 28, 2026, 5:46 AM EDT

Source: Information for this report was sourced from Nagoya University

The Biological Catalyst of Early Onset Neurological Decay

A groundbreaking study from the Nagoya University Graduate School of Medicine has identified the exact developmental window when Spinal and Bulbar Muscular Atrophy, or SBMA, begins its destructive process. According to lead author Tomoki Hirunagi, a natural burst of testosterone occurring immediately after birth acts as the primary trigger for this rare inherited condition. This hormonal surge, which lasts approximately six months in human males, activates a mutant protein that overstimulates the motor neurons responsible for muscle control. While patients typically do not exhibit visible muscle weakness or tremors until their thirties or forties, this research confirms that the foundation for adult disability is laid during the very first days of life.

Mechanisms of Protein Accumulation in the Neonatal Phase

The pathology of SBMA is rooted in the behavior of the mutant androgen receptor protein, which requires the presence of testosterone to enter the nucleus of a nerve cell. The research team confirmed that in male subjects possessing the SBMA mutation, this protein begins accumulating in the nuclei of motor neurons within the first twenty four hours of life. This process was notably absent in female subjects with the same mutation, providing definitive evidence that the neonatal testosterone surge is the essential driver of the disease. This early accumulation leads to a cascade of cellular dysfunction, specifically targeting the nerve cells that bridge the gap between the spinal cord and the muscular system.

Synaptic Overactivity and the Role of Glutamate Receptors

During the critical first week of development, researchers observed that genes responsible for nerve cell activation were pathologically overactive. According to the findings, glutamate receptors within the SBMA subjects showed abnormal levels of stimulation, causing motor neurons to fire excessively. To validate these animal models, the scientists grew motor neurons in a laboratory setting using cells from human SBMA patients. The results mirrored the mouse studies, suggesting that the human disease process follows an identical pattern of early synaptic dysregulation. This overactivation acts as a precursor to the eventual breakdown and death of these vital nerve cells in adulthood.