Angiotensin-converting enzyme gene polymorphism and respiratory muscle function in infants

Angiotensin-converting enzyme (ACE) gene contains a polymorphism consisting of either the presence (I) or absence (D) of a 287-bp fragment. Recent studies have suggested that the I-allele may be associated with superior exercise endurance; respiratory muscle function may be similarly influenced. The pressure-time index of inspiratory muscles (PTImus) is a measure of the load-capacity ratio of the inspiratory muscles. The objective of this study was to determine whether infants homozygous for the I-allele have lower PTImus compared to infants homozygous for the D-allele or heterozygous I/D.

One hundred thirty-two infants were studied. ACE genotyping was performed by polymerase chain reaction amplification, using DNA from peripheral blood. PTImus was calculated as (Pi(mean)/Pi(max)) × (T(i)/T(tot)), where Pi(mean) was the mean inspiratory pressure estimated from airway pressure, generated 100 ms after an occlusion (P(0.1)), Pi(max) was the maximum inspiratory pressure and T(i)/T(tot) was the ratio of the inspiratory time to the total respiratory cycle time. Pi(max) was the largest pressure generated during brief airway occlusions performed at the end of a spontaneous crying effort.

Infants with I/I genotype had significantly lower PTImus than infants with either D/D or I/D genotypes (P = 0.000007). ACE genotype was significantly related (P = 0.005) to PTImus measurements, independent of other factors that may affect respiratory muscle function.

These results suggest that an association of ACE genotypes with PTImus measurements may exist in infants.