Demographical and clinical findings
The study involved a total of 17 patients were diagnosed with GA-1 and 20 healthy individuals between 2017 and 2018 years. The main clinical features of the patients are summarized in Table 1. GA-1 patients were created with the age ranged 6-27 years (mean; 15,1±9,2). Of those, 7 (%42,2) were male (mean aged;15,8±8,7) and 10 (%58,8) were female (mean aged; 16,1± 9,8) . On the other hand, the age at symptom onset ranged from 0.13 to 10 years (mean 2,69 ± 6,63), and the age at diagnosis ranged from 0,13 to 12,66 years (mean 4,54 ± 6,62). The consanguinity level was 82,32 % (n = 14), and there was no statistically difference between consanguinity and the onset of disease (p = 0.279). On the other hand, 14 (82,32% ) missense, 3 (17,68 %) deletions variants type of mutation and 12 (70,58% ) homozygous, 3(17,64%) heterozygous, 2 (11,76% ) compound heterozygous mutation were detected among the patients. Unfortunately, case 17 died at age 19 but until her death, she would come to the clinical check-ups.
Pure tone hearing thresholds of the study group were higher (worse) than the control group’s hearing levels and the difference was statistically significant (p < 0.05; Figure 1). Their mean and standard deviation (SD) thresholds at 0.25, 0.5, 1, 2, 4, 6 and 8 kHz were 15±3,13; 15,37±3,50; 16,62±3,84; 17,12±5,19; 18,12±5,18; 21,87±6,31 and 24,12±6,26 dB HL. PTA results showed that a total of 23.53 % (n=4) of the individuals in the study group had normal hearing levels and 77.47 % (n=13) had mild sensorineural hearing loss. The hearing levels of the control group were within normal limits. Also, no difference was detected between left and right ears.
There was no statistically significant difference between the left and right ear in DPOAE amplitudes (p > 0,05). DPOAE amplitudes of the study group were less than the control group in all octave frequencies (1, 1.5, 2, 3, 4 , 6, and 8 kHz), and there was a statistically significant difference for 2 and 3 kHz on the right ear (p= 0.027, p=0.020), while for 1, 2 and 3 kHz (p=0.034, p=0.036, p=0.041) on the left ear (p < 0.05; Table 2).
Contralateral Suppression of DPOAE
We observed that the contralateral suppression values of the study group were below 1 dB which is considered as suppression amount (Prasher, Ryan, & Luxon, 1994; Yilmaz, Sennaroglu, Sennaroglu, & Köse, 2007). Contralateral suppression values of the study group were less than the control group for both ears at all frequencies (p<0,05; Table 3).
Auditory Brainstem Response (ABR)
There is a significant difference observed in the ABR findings of the mean absolute latencies of wave I, III, V, and interpeak latencies of I–III and I–V when compared for statistical analysis in each group (p<0,05).
ABR threshold results comparison of the GA-1 group: Absolute latencies of wave I, III and V were found to be significantly delayed at 30, 50, and 70 dB nHL in cases of GA-1 compared to the control group (p<0,05). While wave I and III could not be obtained for the study group at the 30 dB nHL tone, the absolute latency of wave V was longer (8±0.4 ms) in both ears compared to the control group (p<0.05).
The absolute latency values of the wave I and III in the study group was shorter than the control group at 50 dB nHL tone (I= 2.4±0.4 and III=4.4±0.5 ms , p<0,05).) while there was not any significant difference in the absolute latency values between the groups for the wave V (p>0,05).
The absolute latency values of the wave I and III in the study group was significantly shorter than the control group at 70 dB nHL tone (I= 1.8±0.3 and III=4.0±0.3 ms ,p<0,05). There was not any significant difference in the absolute latency values between the groups for the wave V (p>0,05).
While there was not a significant difference in the absolute latency values between the groups for wave I at 90 dB nHL tone (p>0,05), the absolute latency values of the wave III and V in the study group was significantly longer than the control group for both ears (III=4.1±0.3and V=5.9±0.3ms, p<0,05).
I-III, III-V, and I-V waveinterpeak latency values of all the participants, regardless of their age and gender, at 90 dB nHL tone were presented in Figure 2. While I-III and I-V wave mean interpeak latency values of the study group were longer compared to the control group, III-V wave mean interpeak latency value was shorter (p<0,05).