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Re: Jan!

Here's an article about the F413C mutation:

F413C
It appears to be one of those rare mutations that can be inherited either way. So you would want to take precautions with anesthesia for family members with that mutation even if they don't have symptoms.

Here is an article about the other one:

R894X

and another about Northern Finland:

R894X

This mutation is also considered both recessive and dominant.

Hope that's helpful!

Jan

Type of Myotonia: Thomsen's

Country: USA

Re: Jan!

M.T.I

For all practical purposes, you would be considered to have Becker MC, however, as Jan said, those mutations fall into the recessive/dominant overlapping range, causing symptoms by themselves in a small number of individuals. The reason for this isn't know but there have been a few proposed theories, which I can tell you if you are interested.

F413C is a fairly common MC causing mutation (and one of the one's I have). It produces skeletal muscle chloride ion channels (think little doors in the muscle cell wall that let chloride into the cell) that function almost, but not quite normally. The primary way it is thought to cause myotonia is via something called an defective endoplasmic reticulum transport mechanism. In simple terms, this means that the "doors" are hard to transport from the interior of the cell, where they are made, to the wall of the cell, where they are to be "installed". So this might result in a cell with not enough chloride "doors", and when chloride can't get into the cell fast enough to stop the contraction, myotonia ensues. As best I understand it anyway.

R894X is a mutation, which, like F413C is a common MC causing mutation, particularly in the German population. It is thought to produce "doors" that aren't stable, which probably limits the cell's ability to shunt in chloride and thus, causes myotonia.



Type of Myotonia: Becker

Country: USA

Re: Jan!

M.T.I

Did you have both CLCN1 and SCN4a genes sequenced?

If you Google ""scn4a" PAM"; low on the first page of
results you should find a title reading:
"GP 102 SCN4A mutations in Finland".

This is an article abstract relating to CLCN1 R894X and
SCN4A R1460Q defects occuring together.

Sweden and Finland have the highest incedences of
defects in both of these genes so it would seem that
this population is most likely to defects in
them together.

Type of Myotonia: SCN4a PAM

Country: US