More than hypomyelination in Pol-III disorder.

Area of Science:

• Neurology
• Genetics
• Pathology

Background:

• 4H syndrome (hypomyelination, hypodontia, hypogonadotropic hypogonadism) is a rare leukodystrophy linked to polymerase III (Pol-III) gene mutations.
• The clinical spectrum and underlying pathophysiology of Pol-III-related leukodystrophies remain incompletely understood.
• Neuropathologic data for 4H syndrome are scarce, hindering a comprehensive understanding of its disease mechanisms.

Observation:

• This study presents detailed clinical, neuroradiologic, and neuropathologic findings of a patient with 4H syndrome and confirmed POLR3A mutations.
• Neuropathologic examination revealed significant oligodendrocyte loss, severe myelin loss, and moderate axonal loss in white matter.
• Distinct features included patchy preservation of white matter, mild glial activation, and a macrophage reaction potentially indicating an immune response.

Findings:

• The neuropathology of 4H syndrome is characterized by heterogeneous white matter abnormalities, extending beyond simple hypomyelination.
• Significant neuroaxonal and glial pathology, including cortical laminar astrogliosis and mineralization, were observed.
• The findings highlight the complex nature of this leukodystrophy, with implications for understanding its pathogenesis.

Implications:

• Neuropathologic findings challenge the uniform hypomyelinating pattern suggested by MRI, revealing a more complex disease process.
• The observed macrophage reaction suggests a potential immunologic component in the pathophysiology of 4H syndrome.
• This detailed neuropathologic analysis provides crucial insights into the heterogeneous nature of Pol-III-related leukodystrophies and their impact on brain tissue.