Paula and Bobby
Parents of Lillie
Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1
What is Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1?
Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1 is a rare disease. It is also known as Charcot-marie-tooth Disease, Autosomal Recessive, With Focally Folded Myelin Sheaths, Autosomal Recessive, Type 4b1 Charcot-marie-tooth Disease, Type 4b; Cmt4b Charcot-marie-tooth Neuropathy, Type 4b1 CMT4B Hered. motor and sensory neuropathy - type II AR (CMT4B).
Clinically this is very similar to HMSN type I AR. Onset is between a year and 18 months and some patients are off their feet in early adulthood. In one report (Sabatelli et al., 1994) cranial nerves became involved later in the course of the illness (including vocal cord paralysis). A few cases have a congenital onset, and one of these had a diaphragmatic paralysis (Tyson et al., 1997). Claw hands and chest deformities have also been reported (Nouioua et al., 2011). It differs from HMSN type 1 AR only in that the latter shows on nerve biopsy, classic, basal lamina, onion bulbs whereas the entity here shows excessive myelin outfolding (redundant loops and folds). Both are recessive. There is one family with dominant inheritance (Umehara et al., (1993). This family has now been shown to have a mutation in the MPZ (myelin protein zero) gene (Nakagawa et al., 1999). Other patients with CMT 1B, with focally folded myelin, had MPZ mutations (Fabrizi et al., 2000, Kochanski et al., 2004).
The recessive condition has now been mapped to 11q23 (Bolino et al., 1996), but there is evidence of heterogeneity (Gambardella et al., 1998). An inbred Saudi family also mapped to 11q23 (Salih et al., 2000). A second locus at 11p15, was reported in a Tunisian family by Ben Othmane et al., (1999) but another Tuniaian family did not map to either locus. The gene (MTMR2) at 11q22 has now been charactarized and encodes the myotubularin- related protein-2 (Bolino et al., 2000). The lack of the MTMR2 protein may result in constitutive phosphorylation with overgrowth of myelin (Bolino et al., 2000). Two novel mutations in the 5' end of the gene were reported by Houlden et al., (2001) in two families and a further novel mutation by Nelis et al., (2002). Mutations in the MTMR2 gene account for the majority of AR neuropathies with focally folded myelin.
* This information is courtesy of the L M D.
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What gene changes cause Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1?
The syndrome is inherited in the following inheritance pattern/s:
Autosomal Recessive - Autosomal recessive inheritance means an affected individual receives one copy of a mutated gene from each of their parents, giving them two copies of a mutated gene. Parents, who carry only one copy of the gene mutation will not generally show any symptoms but have a 25% chance of passing the copies of the gene mutations onto each of their children.
Autosomal Dominant - In the case of autosomal dominant inheritance, just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.
In some cases, a genetic syndrome may be the result of a de-novo mutation and the first case in a family. In this case, this is a new gene mutation that occurs during the reproductive process.
OMIM Number - 601382 (please check the OMIM page for updated information)
The syndrome can be caused by mutations in the following gene/s location/s:
MTMR2 - 11q21
What are the main symptoms of Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1?
The typical symptoms of the syndrome are:
Scoliosis, Proximal muscle weakness, Talipes equinovarus, Autosomal recessive inheritance, Irregular myelin loops, Distal amyotrophy, Abnormal auditory evoked potentials, Distal sensory impairment, Distal muscle weakness, Decreased motor nerve conduction velocity, Motor delay, Facial palsy
How does someone get tested for Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1?
The initial testing for Charcot-Marie-Tooth Disease, Type 4B1; CMT4B1 can begin with facial genetic analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the type of genetic testing needed. A consultation with a genetic counselor and then a geneticist will follow.
Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.
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