Hierarchical clustering of miRNA in testicular tissue samples. Testicular tissue samples were clustered according to the expression profile of 173 two-fold differentially expressed miRNAs between 3 NOA patients and 2 controls. All samples were properly assigned to the correct class. The key color bar indicates that miRNA expression levels increased from green to red color compared to controls (dark color indicates the expression level is close to that of controls). N: controls; A: NOA patients.