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. 2021 Jan 24;12(2):151.
doi: 10.3390/genes12020151.

Peripheral Anomalies in USH2A Cause Central Auditory Anomalies in a Mouse Model of Usher Syndrome and CAPD

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Peripheral Anomalies in USH2A Cause Central Auditory Anomalies in a Mouse Model of Usher Syndrome and CAPD

Peter A Perrino et al. Genes (Basel). .

Abstract

Central auditory processing disorder (CAPD) is associated with difficulties hearing and processing acoustic information, as well as subsequent impacts on the development of higher-order cognitive processes (i.e., attention and language). Yet CAPD also lacks clear and consistent diagnostic criteria, with widespread clinical disagreement on this matter. As such, identification of biological markers for CAPD would be useful. A recent genome association study identified a potential CAPD risk gene, USH2A. In a homozygous state, this gene is associated with Usher syndrome type 2 (USH2), a recessive disorder resulting in bilateral, high-frequency hearing loss due to atypical cochlear hair cell development. However, children with heterozygous USH2A mutations have also been found to show unexpected low-frequency hearing loss and reduced early vocabulary, contradicting assumptions that the heterozygous (carrier) state is "phenotype free". Parallel evidence has confirmed that heterozygous Ush2a mutations in a transgenic mouse model also cause low-frequency hearing loss (Perrino et al., 2020). Importantly, these auditory processing anomalies were still evident after covariance for hearing loss, suggesting a CAPD profile. Since usherin anomalies occur in the peripheral cochlea and not central auditory structures, these findings point to upstream developmental feedback effects of peripheral sensory loss on high-level processing characteristic of CAPD. In this study, we aimed to expand upon the mouse behavioral battery used in Perrino et al. (2020) by evaluating central auditory brain structures, including the superior olivary complex (SOC) and medial geniculate nucleus (MGN), in heterozygous and homozygous Ush2a mice. We found that heterozygous Ush2a mice had significantly larger SOC volumes while homozygous Ush2a had significantly smaller SOC volumes. Heterozygous mutations did not affect the MGN; however, homozygous Ush2a mutations resulted in a significant shift towards more smaller neurons. These findings suggest that alterations in cochlear development due to USH2A variation can secondarily impact the development of brain regions important for auditory processing ability.

Keywords: USH2A; Usher syndrome type 2; central auditory processing disorder; medial geniculate nucleus; superior olivary complex.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Stereological Measurements. Visual representation of the superior olivary complex (SOC) (A) and medial geniculate nucleus (MGN) (B) taken at 2.5× magnification to determine volume of brain region. (C) The Optical Fractionator probe of Stereo Investigator was used to determine neuron population. Arrow 1 indicates a neuron that was counted due to the presence of a clearly defined nucleolus, while Arrow 2 indicates a cell that was not counted. (D) The Nucleator probe was used to determine neuron size (area). Optical Fractionator and Nucleator probes were used at 100× magnification.
Figure 2
Figure 2
Histological assessment in SOC. (A) Volumetric analysis of left, right and total (left + right) SOC. Heterozygous Ush2a mutations increased the volume of the right SOC while homozygous Ush2a mutations reduced the volume of the right SOC. (B,C) There were no significant genotype differences in neuron population (B) or average neuron area (C). * p < 0.05.
Figure 3
Figure 3
Histological assessment in MGN. (AC) There were no significant genotype differences when evaluating volume (A), neuron population (B) or neuron area (C). (D) Comparison of cumulative percent distribution of neuronal cell size (area) revealed a significant shift towards fewer larger neurons and more smaller neurons in the right MGN in Ush2a homozygous (KO) mice.

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