pompe disease is characterized by a deficiency of the glycogen - degrading lysosomal enzyme , acid alpha - glucosidase ( gaa ) , . in classic infantile - onset pompe disease ( iopd ) ,
glycogen deposition in cardiac , skeletal , and respiratory muscles causes severe cardiomyopathy , hypotonia , and respiratory failure , leading to death by 1  year of age if not treated . in those with onset during childhood or adulthood ( late - onset pompe disease [ lopd ] ) ,
glycogen deposition is mainly in skeletal and respiratory muscles , causing progressive limb - girdle myopathy and respiratory insufficiency , .
enzyme replacement therapy ( ert ) with recombinant human gaa ( alglucosidase alfa ) has been shown to improve walking distance and stabilize pulmonary function in lopd patients , , and to improve survival and motor outcomes in classic iopd patients .
studies have examined the effect of individual mutations in the gaa gene and other genetic factors ,   with one gene of interest encoding angiotensin converting enzyme ( ace ) .
ace catalyzes the conversion of angiotensin i to the active form , angiotensin ii ( a potent vasoconstrictor ) , and degrades bradykinin ( a potent vasodilator ) .
half of the variation in human ace activity is attributable to an insertion / deletion ( i / d ) marker allele in intron 16 of the ace gene , , , .
an insertion ( i allele ) of an alu repeat results in lower ace activity , whereas the absence of the insertion ( or deletion , d allele ) results in higher activity .
the ace i / d polymorphism has been linked to physical performance and exercise duration , and it has been reported that the i allele is associated with a predominance of slow - twitch muscle fibers ( type i ) and the d allele with fast - twitch muscle fibers ( type ii ) , . taken together , it has been hypothesized that differences in muscle - fiber type and vasodynamics may impact the skeletal muscle response to ert .
the d / d genotype in 14 lopd patients was found to be associated with higher serum creatine kinase levels at diagnosis , earlier onset of disease , and the presence of muscle pain . in a larger cohort of pompe patients ( n  =  85 ) , individuals with the d / d ace genotype presented with an earlier onset of disease and muscle pain , confirming the previous observation .
the relationship between ace genotype and clinical parameters in a cohort of lopd patients who received biweekly infusions of alglucosidase alfa for >  2  years also was reported .
notably , i / i genotype patients had significantly greater muscle mass measured by quantitative magnetic resonance imaging ( mri ) .
muscle strength and endurance variations demonstrated a similar trend , with the i / d genotype resulting in intermediate outcomes between i / i and d / d ; however , these differences were not statistically significant .
we tested the hypothesis that ace genotype was a contributing factor to disease progression and clinical response to ert in the pompe disease late - onset treatment study ( lots ) .
lots , a randomized , double - blind , placebo - controlled trial involving 90 lopd patients , evaluated the safety and efficacy of biweekly infusions ( 20  mg / kg ) of alglucosidase alfa compared to placebo for 78  weeks in juvenile and adult lopd patients .
only patients who completed   26  weeks of the study were included in this analysis ( n  =  58 alglucosidase alfa - treated ; n  =  30 placebo - treated )
. the i / d allele status of a 287 base - pair alu repeat in intron 16 of the ace gene was determined by polymerase chain reaction ( pcr ) analysis using methods described previously   with slight modifications ( 2  u platinum taq polymerase , 1   platinum taq pcr buffer - mg , 3  mm mgcl2 , 0.25  mm dntp mix , and 0.5  mm of the forward and reverse primers ) .
one - way anova analysis was used to evaluate correlations between ace genotype ( i / i , i / d , and d / d ) and baseline pompe disease characteristics .
student 's t - test was conducted to compare alglucosidase alfa treatment and placebo within each ace genotype .
at baseline , patients with the d / d genotype did not present with earlier onset of disease ( mean age at first symptoms : 27.4    12.7  years vs. 28.5    11.5 [ i / d ] and 28.6    14.4 [ i / i ] ) , longer duration of disease at trial entry ( mean duration since symptom onset : 18.3    10.2  years vs. 17.6    11.6 [ i / d ] and 20.4    9.9 [ i / i ] ) , or more severe disease as measured by 6-minute walk test ( 6mwt ) ( mean : 343.0    144.4  m vs. 339.2    125.6 [ i / d ] and 293.1    147.4 [ i / i ] ) , or percent predicted forced vital capacity ( fvc ) ( mean : 53.3    15.4% vs. 56.2    15.6 [ i / d ] and 52.4    12.5 [ i / i ] ) .
, lots patients with the d / d genotype appeared less responsive to alglucosidase alfa treatment than patients with the i / i or i / d genotypes ( fig .
patients with the i / d and i / i genotype who received ert showed significantly greater improvements in fvc ( mean change : 1.516 [ p  =  0.028 ] and 4.8 [ p  =  0.007 ] , respectively ) compared to d / d patients ( mean change :   1.412 ) receiving treatment ( fig .
similarly , the mean increase in the 6mwt was significantly higher in i / d patients on ert ( mean change : 40.16 [ p  =  0.022 ] ) compared to the d / d group ( mean change :   1.412 ) , with a trend for an improved response in patients with the i / i genotype ( mean change : 32 ) ( fig .
1c presents the change from baseline in patients treated with alglucosidase alfa and also illustrates a trend toward lower responsiveness to alglucosidase alfa in d / d genotype patients .
importantly , while the mean changes in fvc and 6mwt do not appear to indicate an overall response to alglucosidase alfa within the d / d genotype group , it is important to note that a variable response to ert was observed , and several patients demonstrated gains in the 6mwt and fvc with this genotype ( fig .
the d / d genotype was not associated with increases in peak igg titers , sustained antibody titers , or inhibitory antibodies ( data not shown ) , indicating that the correlation between ace genotype and response to ert is not associated with an immune response to alglucosidase alfa .
our finding that lopd patients with the ace d / d genotype demonstrate a reduced response to alglucosidase alfa relative to those with i / i or i / d genotypes is consistent with earlier findings .
we also demonstrated the presence of this association regardless of baseline disease severity and anti - gaa igg antibody levels .
however , unlike patients in earlier studies , , lots patients with the d / d genotype did not present with an earlier onset of disease or a longer duration of disease at study entry .
our results suggest that the ace i / d polymorphism may influence the response to alglucosidase alfa treatment independent of the patient 's disease severity at treatment initiation .
these findings raise pertinent questions about the mechanisms by which the ace genotype influences the muscle response to alglucosidase alfa treatment .
does the d / d genotype result in increased vasoconstriction , and therefore less enzyme delivery to skeletal muscle ?
do patients with the d / d genotype have an increase in type ii muscles fibers ( fast - twitch , anaerobic , glycogen - rich ) that decreases their response to treatment ?
type i muscles fibers ( slow - twitch , aerobic , mitochondria - rich ) have an increased capillary density , which has been correlated with increased glycogen clearance after ert in a mouse model of pompe disease . on the other hand ,
type ii muscle fibers exhibit increased autophagic pathology in pompe mice , which may be responsible for the mis - targeting of ert within the muscle fiber .
finally , it is important to note that individual patient responses to alglucosidase alfa were variable across the three ace genotypes , and many patients with the d / d genotype demonstrated improvements in the functional assessments evaluated .
this supports the concept that an individualized treatment approach and careful follow - up are warranted for pompe disease patients receiving ert . in conclusion ,
pompe disease patients with the ace d / d genotype appeared to show a decreased response to alglucosidase alfa , although the mechanism underlying this observation is not yet known .
continued genotyping of pompe disease patients for the ace polymorphism and further investigation of therapeutic response are warranted .
all authors are employees of sanofi , and the study was funded by sanofi genzyme .
 correlations between angiotensin - converting enzyme ( ace ) genotype ( i / i , i / d , d / d ) , disease severity at baseline and response to enzyme replacement therapy ( ert ) were assessed in the pompe disease late - onset treatment study ( lots ) . 
 no correlations were observed between ace genotype and disease severity at baseline . 
 however , d / d patients appeared to have a reduced response to alglucosidase alfa treatment than i / i or i / d patients , suggesting that ace polymorphisms may influence the response to alglucosidase alfa treatment and warrants further investigation . 
Introduction
Materials and methods
Results
Discussion
Conflict of interest