Mutations in the MTM1 gene cause X-linked recessive myotubular myopathy (XLMTM; 
MIM310400). Myotubularin, the implicated protein, is a phosphoinositide 
phosphatase that belongs to a large protein family conserved through evolution 
that also includes the antiphosphatase Sbfl and the protein hMTMR2 mutated in 
Charcot-Marie-Tooth type 4B. Myotubularin is detectable in a variety of cell 
lines by immunoprecipitation followed by Western blotting. We screened 29 
independant patients with XLMTM phenotype and four with centronuclear myopathy. 
87% (21/24) of patients with known MTM1 mutations showed abnormal myotubularin 
levels, including some with missense mutations. Moreover, myotubularin was also 
undetectable in a patient for whom no mutation could be identified by SSCP 
screening. The centronuclear cases investigated have a normal level of protein, 
suggesting that the centronuclear form is not the result of a decrease in 
myotubularin level. Thus, immunoprecipitation of myotubularin from cultured 
cells represents a rapid and helpful method for classifying those cases where no 
mutation was found. On the other hand, the amount of expression may be of 
diagnostic value for disease course in patients with a mutation.