CMT Type 1 (CMT1) is defined as an autosomal dominant demyelinating form of CMT. CMT1 accounts for about 55 percent of all cases of CMT.
What causes CMT1
CMT1 is caused by a variety of gene mutations. The gene that is mutated determines the subtype of CMT1 that a person has. Mutations that can cause type 1 include:
- CMT1A, CMT1E – Peripheral myelin protein 22 (PMP22)
- CMT1B – Myelin protein zero (MPZ/P0)
- CMT1C – Lipopolysaccharide-induced tumor necrosis factor-alpha factor (LITAF/SIMPLE)
- CMT1D – Early growth response 2 (EGR2/Krox20)
- CMT1F – Neurofilament light polypeptide (NEFL)
- CMT1G – Peripheral myelin protein 2 (PMP2)
- CMT1H – fibulin 5 gene (FBLN5)
- CMT1I – polymerase III, RNA, subunit B gene (POLR3B)
- CMT1J – inositol 1,4,5-trisphosphate receptor, type 3 (ITPR3)
What are the Symptoms of CMT1
Affected patients may experience:
- weakness, atrophy, and sensory loss in the distal legs followed by the distal arms
- foot deformities and areflexia (absence of neurological reflexes such as knee jerk reaction) are sometimes present
There is considerable variability in the degree of neurological deficits within families, and even between identical twins, indicating that other factors modulate disease severity. Examinations of sensory and motor function worsen gradually. Atypical presentations are reported, including cranial nerve involvement, proximal weakness, diaphragmatic weakness, calf hypertrophy, and cramps.
When do symptoms of CMT1 start?
The age of onset of CMT1 varies. Onset can appear anywhere from infancy to later decades of life (40, 50, etc.). Patients usually have first symptoms between the first and second decades of life. Other clinical manifestations may appear later.
