Pelizaeus-Merzbacher-like disease type 1

Pelizaeus-Merzbacher-like disease type 1 is an inherited condition involving the brain and spinal cord (central nervous system). This disease is one of a group of genetic disorders called leukodystrophies. Leukodystrophies are abnormalities of the nervous system's white matter, which consists of nerve fibers covered by a fatty substance called myelin. Myelin insulates nerve fibers and promotes the rapid transmission of nerve impulses. In particular, Pelizaeus-Merzbacher-like disease type 1 involves hypomyelination, which means that the nervous system has a reduced ability to form myelin. The signs and symptoms of this condition are very similar to another leukodystrophy called Pelizaeus-Merzbacher disease, but the two disorders have different genetic causes.

Beginning in the first few months of life, infants with Pelizaeus-Merzbacher-like disease type 1 typically experience weak muscle tone (hypotonia), involuntary movements of the eyes (nystagmus), and delayed development of speech and motor skills, such as sitting or grasping objects. As children with Pelizaeus-Merzbacher-like disease type 1 get older, hypotonia changes to muscle stiffness (spasticity).

During childhood, individuals with Pelizaeus-Merzbacher-like disease type 1 develop problems with movement and balance (ataxia), difficulty with movements that involve judging distance or scale (dysmetria), tremors that occur mainly during movement (intention tremors), and head and neck tremors (titubation). People with this condition have an inability to perform quick, alternating movements (dysdiadochokinesia), such as quickly tapping different fingers. Some develop involuntary tensing of the muscles (dystonia) and jerking (choreiform) movements. Many people with Pelizaeus-Merzbacher-like disease type 1 develop skeletal issues such as an abnormal curvature of the spine (scoliosis) and require wheelchair assistance from childhood.

Muscle abnormalities can lead to difficulty swallowing and problems producing speech (expressive language), but affected individuals can understand speech (receptive language). Most individuals with Pelizaeus-Merzbacher-like disease type 1 have normal intelligence. Rarely, hearing loss, optic atrophy, and recurrent seizures (epilepsy) can occur.