The human neuromuscular diseases X-linked myotubular myopathy and 
Charcot-Marie-Tooth disease type 4B are caused by mutations in myotubularin 
family proteins. The myotubularins are a unique subfamily of protein tyrosine 
phosphatases that utilize inositol phospholipids, rather than phosphoproteins, 
as substrates. Recent structural studies, including the first crystal structure 
of a myotubularin family protein, have defined the structural features that are 
characteristic of the family and revealed the molecular basis of their unique 
substrate specificity. Interestingly, the myotubularin family contains a 
subgroup of proteins that are catalytically inactive. Recent biochemical studies 
have established that the inactive myotubularins function as adaptors for the 
active members and play an important regulatory role within the family.