Cognitive outcome of patients with classic infantile Pompe disease receiving enzyme therapy. [Response]

Author response to an Editor's note concerning cognitive function:

Our study confirmed Spiridigliozzi et al.'s findings of normal or mildly delayed IQ scores in children with classic infantile Pompe disease treated with ERT. This is important because ERT cannot cross the blood–brain barrier. The longest follow-up reported by Spiridigliozzi et al. was 9 years and 11 months; ours was 12 years and 3 months.
Although Spiridigliozzi et al. found a correlation between cognitive and motor development, test limitations prevented them from determining whether lower cognition was caused by motor disabilities or weak cognition. Our more suitable nonmotor intelligence tests of 2 tetraplegic teenagers revealed the influence of severe motor disabilities on developmental scores. These teenagers previously had the lowest possible mental development scores during their first 4 years, but now scored normal or mildly delayed.
Similar to the findings of Spiridigliozzi et al., we also found delayed processing speed. Conceivably, these delays are explained by white matter changes like those on the MRIs we reported.
Although mild delays may develop over time, infantile Pompe disease differs substantially from other lysosomal storage diseases where progressive storage in the CNS and profound mental retardation occur at an early age.