A 9 year old boy is brought in after tripping and falling onto the sidewalk. His parents mention that he started walking at the age of 18 months, and that he has always been clumsy when walking and running. He trips and falls over very frequently, and has difficulty getting up from the floor afterwards. His performance in school is above average. His medical and family histories are unremarkable.
In both lower limbs, there is a marked reduction in the conduction velocities of both sensory and motor nerves, with evidence of denervation of the distal muscles.
Appearance: clear WBC: 3/mm3 (0 - 5) Protein: 0.2 g/dl (0.15 - 0.4) Glucose: 80 mg/dl Random blood glucose: 100mg/dl
The biopsy shows a mild loss of myelinated axons. Prominent onion bulb formations are evident upon both light microscopy and ultrastructural examination.
There is duplication of the peripheral myelin protein-22 (PMP22) gene on chromosome 17.