Charcot Marie tooth disease is a hereditary neuropathy characterized by both sensory and motor involvement instead of being one. The disease was first discovered by two scientists Charcot and Marie which was later thoroughly described by Tooth, hence the name. Unlike the separate sensory and motor neuropathies, CMT disease consists of both sensory and motor neuropathies together which is a differentiating feature from other neuropathies, hence also known by the name of hereditary sensory and motor neuropathy(HSMN). Charcot Marie tooth disease mainly has been classified into 4 different types known as CMT 1, 2, 3 and 4, although various other types have been discovered lately and are incorporated in the classification.
It is a disorder consisting of defect of myelin in CMT disease types 1, 3 and 4 whereas CMT disease type 2 belongs to axonal neuropathies. CMT disease type 1 suffers from defective myelin which easily breaks off and leaves the nerves unmyelinated. CMT disease type 3 and 4 are more severe forms of CMT disease type 1 and also differs in the pattern of inheritance. CMT 2 is related to the axonal dysfunction due to the neuronal disintegration and Wallerian degeneration of the nerve fibers causing peripheral neuropathies but follows a similar pattern of inheritance like that of CMT disease type 1.
Is Charcot Marie Tooth Disease Dominant Or Recessive?
These vary upon differences in the inherited genes and their presentation. The pattern of inheritance is usually autosomal in all four types. These are further divided into various subtypes which belong to either autosomal dominant or recessive inheritance patterns. In the majority of the cases, CMT 1 and 2 are autosomal dominant disease whereas CMT 3 and 4 are usually autosomal recessive in inheritance. A few subtypes of CMT 1 are also autosomal recessive and even X linked but most common subtype follows the autosomal dominant pattern.
The gene associated with CMT disease type 1 and type 3 is PMP 22 gene. CMT disease type 2 is associated with ATP1A1 gene and CMT type 4 is associated with the PRPS1 gene. CMT disease type 3 is also known as Dejerine sottas disease and CMT disease type 4 is also known by the name of refsum syndrome.
In the data compilation of various studies, the prevalence has been found between 10 to 30 with the maximum number of cases belonging to CMT disease type 1. It is a rather common disease in comparison to the other neurological conditions found in the patients and presentation of the disease comes to the symptomatic stage in first decade itself. There is no male or female preponderance seen with equal distribution among them. Racial and ethnic factors have not been specified for any of the types of Charcot Marie tooth disease. Even after the presentation of the disease occurs in the early part of life but the patient can cope with it for the entire life. It is because the CMT disease is slowly progressive in nature and only in few cases is found to be rapidly progressive in the age group of >50 years.
Charcot Marie tooth disease follows an autosomal pattern in the most number of cases which can be dominant or recessive depending upon the type of CMT disease. Since the CMT disease type 1 and 2 are the most common among all, it follows an autosomal dominant pattern of inheritance. A few cases of X linked inheritance has also been reported. The autosomal dominant pattern ensures the disease is found in nearly every generation if one or both of the parents are affected whereas autosomal recessive inheritance is seen in only 25% of the children whose both parents are carriers. If one parent is affected in autosomal recessive type of inheritance then the chances of involvement of children increases.
Due to the slow involvement of the nerves, although the signs and symptoms come at a very early age but take a lifetime to progress which in turn increases the morbidity and decreases the quality of life.