Background:
If it was possible to assay biomarkers of neuroplasticity it might facilitate clinical management of deaf implanted children by identifying those among them who are at risk of speech and language rehabilitation failure. MMP9 is a proteinase involved in neuroplasticity underlying different clinical conditions in human.

Material and methods:
This was a longitudinal, prospective cohort study of 61 congenitally deaf children who underwent cochlear implantation. We investigated the genetic variants of matrix metalloproteinase 9 (MMP9) and plasma levels of MMP-9 that have been implicated in neuroplasticity after cochlear implantation. Auditory development was assessed by using the LittlEARS Questionnaire (LEAQ) at three follow-up points and the plasma level of MMP-9 was measured at implantation.

Results:
There was a significant negative correlation between MMP-9 plasma level at implantation and LEAQ score at 18 months follow-up (p < 0.05). Two clusters of good and poor CI performers could be isolated based on this correlation. The prevalence of genetic variants of MMP9 – rs3918242, rs20544, and rs2234681 – in the good performers cluster was different to their prevalence in the poor performers cluster.

Conclusions:
The study showed that children born deaf who have an MMP-9 plasma level of less than 150 ng/ml at cochlear implantation have a reasonable chance of attaining a high LEAQ score after 18 months of speech and language rehabilitation. It appears that MMP-9 plasma level at cochlear implantation is a promising prognostic marker for CI outcome.