TK2 and hyperinsulinemic hypoglycemia, familial, 4: The clinical features and results of the diagnostic tests described in our series show a homogeneous phenotypic pattern in late-onset TK2 deficiency consisting of progressive proximal limb, axial neck flexor and facial muscle weakness frequently associated with ptosis, ophthalmoparesis and bulbar weakness, along with an early and severe, although unrecognized, respiratory involvement.