X-linked Tremor, sometimes called shaking puppy syndrome, is a neurological disorder of the central nervous system, caused by a lack of the insulating myelin sheath covering the axons of the nerves. This can lead to premature death. Signs in males include severe tremors in the body, head, and limbs, worsening with activity and appearing to improve during rest, difficulties standing, moving, and eating - later progressing to seizures. Pups are smaller in size than their unaffected littermates. Age of onset form 2 weeks. The life expectancy of affected dogs is not normally beyond 3-4 months. Females carriers of the disorder may have mild tremors during puppyhood that resolve by 4-6 weeks of age.