ADA and Global developmental delay: Hearing threshold of these ADA–/– mice (n = 5) at 31–35 days old were still increased at both 8 and 16 kHz (66.3 ± 13.6 and 58.5 ± 18.5 dB, respectively) compared to ADA+/– littermates controls, indicating that the hearing abnormalities were not due to a developmental delay.