Can Be Homozygous or Can Be Compound Heterozygous
CMT4B3 is caused by autosomal recessive mutations in the SBF1 gene. CMT4B3 tends to be a fairly severe type of CMT.
CMT4B3 symptom onset usually occurs by the time the CMTer is 10 years old. A CMTer who has CMT4B3 usually experiences a rapidly progressive disease causing distal and proximal weakness and atrophy in the lower and upper limbs. Wheelchair dependency usually occurs by around 40 years old.
Significant cognitive impairment and microcephaly have been reported in CMT4B3, with some having a reported IQ of ~50. Some CMTers with CMT4B3 might also experience loss of hand function.