Neonatal Testosterone Spike Identified as Early Trigger for Rare Spinal and Bulbar Muscular Atrophy

Nagoya University researchers find that neonatal testosterone spikes trigger SBMA. Learn how early gene-silencing drugs could prevent motor neuron decay.

By: AXL Media

Published: Mar 27, 2026, 9:55 AM EDT

Source: Information for this report was sourced from Nagoya University

Uncovering the Origins of Early Motor Neuron Decay

Spinal and Bulbar Muscular Atrophy, or SBMA, is a progressive genetic disorder that primarily causes muscle wasting and weakness in men. While clinical diagnosis typically occurs around age 40, new research from Nagoya University suggests the biological foundations of the disease are laid just days after birth. Investigators identified that a mutant androgen receptor protein becomes toxic when exposed to testosterone, leading to the overactivation and eventual collapse of the motor neurons that control muscle movement.

The Role of Neonatal Mini-Puberty in Disease Activation

The study focuses on a brief biological window known as the neonatal testosterone surge, which occurs in all newborn males. In humans, this period of "mini-puberty" lasts approximately six months, during which testosterone levels rise naturally. According to lead author Tomoki Hirunagi, this surge acts as the primary catalyst, driving the accumulation of mutant proteins into the nuclei of motor neurons within the first day of life. Female mice carrying the same mutation showed no such accumulation, confirming that testosterone is the essential trigger for the pathology.

Identifying Pathological Overactivity in Nerve Cells

The research team observed that during the first week of life, genes responsible for nerve cell activation—specifically glutamate receptors—became abnormally overactive in SBMA subjects. This cellular "hyperexcitability" was not limited to animal models; similar patterns of overactivity were found in motor neurons grown in laboratories from the cells of human SBMA patients. This discovery suggests that the disease process in humans likely follows the same early developmental timeline observed in the laboratory.