X-linked myotubular myopathy in a family with three adult survivors.

We describe a family with an extremely mild form of X-linked myotubular myopathy. Three affected males survived to adulthood with sufficient muscle strength to enable them to carry out normal daily activities. The mildness of the myopathy in this family is highlighted by the following: no neonatal or infant mortality resulting from the myopathy; one affected male who did not have neonatal asphyxia and had normal early motor milestones - this affected male was able to increase his muscle bulk and strength to normal by weightlifting; and a 55-year-old male who still lives an independent life. DNA sequencing identified a novel missense mutation - G469A (E157K) - in exon 7 of the MTM1 gene in this family. To our knowledge, this is the third X-linked myotubular myopathy family, with multiple adult survivors, to be reported in the literature.