A 6-year-old boy with a diagnosis of 'dyskinetic cerebral palsy' has worsening involuntary movements despite standard therapies. His parents mention that two maternal uncles both had 'cerebral palsy' and died of respiratory complications in their 20s; his mother and maternal aunts are unaffected, and no affected females are known in the family. MRI shows progressive white matter abnormalities. This family history pattern most strongly suggests: