We analyzed in yeast S. cerevisiae the expression of four missense mutations in MTM1, two affecting the PPIn interaction PH-GRAM domain (MTM1V49F and MTM1R69C), one the protein-protein interaction domain RID (MTM1N180K) and one the phosphatase catalytic domain (MTM1R421Q), leading respectively to severe, mild or severe (depending on the family), very mild, and severe XLCNM forms (Figure 1A) [3], [5], [6], [22]. Here, MTM1 is linked to X-linked myotubular myopathy.