Materials and Methods Animals and breeding To determine the proportion of inheritance for the German waltzing guinea pigs, heterozygous (gw/+) pairs were mated (figure 1). The homozygous animals (gw/gw) were characterized by their waltzing behavior while the heterozygotes could not be distinguished from normal animals. ABR and noise exposure Thirty animals (14 males and 16 females) of the 39 offspring from the original (gw/+) breeding couples were exposed to a free-field noise with a bandwidth 800 Hz centered at 4 kHz at a level of 110 dB SPL for six hours. Frequency specific ABR hearing thresholds were recorded at 2, 4, 6.3 and 12.5 kHz before noise exposure as well as at 24 hours, one week and four weeks after the noise exposure. After ABR measurements the animals were sent back to the animal facility for breeding, mated with a homozygous partner to determine genotype (figure 1). If any offspring from the litter was waltzing, thus confirmed as a (gw/gw) the exposed parent could be classified as (gw/+). If no animal of the offspring within the litter was waltzing, the exposed animal was bred for up to three times. If there were no waltzing animal in the litter, the exposed animal was considered as normal (+/+). After the animals were grouped by the phenotype of their offspring the ABR data from the different time points were analyzed and compared between animal groups (i.e. (gw/+, and (+/+)). Reduced susceptibility to noise in carriers of German waltzing guinea pig Åsa Skjönsberg 1, 2, 3, Paula Mannström 3 and Mats Ulfendahl 3 1 Karolinska Institutet, Dept. of CLINTEC, Sect. Of Audiology, 2 Karolinska University Hospital, Dept. Of hearing and Balance, 3 Center for hearing and Communication research Karolinska Institutet Åsa Skjönsberg, PhD, audiologist Dept. Of Clinical Science, Intervention and Technology Section of Audiology Phone , Fax: Table 1. The outcome of the breeding, the distribution of gender and number of individuals in all groups. The distribution of the genotype was very close to the expected ( %) as well was the distribution between gender (approx. 50%) Homozygous gw/gw Heterozygous gw/+ Normal +/+ Females3134 Males5112 Unknown100 Total9 (23 %)24 (62 %)6 (15 %) Acknowledgements The Swedish Research Council The Foundation Tysta skolan The Petrus and Augusta Hedlund Foundation The Stinger Foundation Ongoing studies At the present we are studying the impact of environmental factors and the genetic background in a human twin material Results Figure 3 Threshold shifts 24 hours after noise exposure. The gw/+ animals (n= 24) was statistically significant less affected of the noise trauma at 4, 8, and 12.5 kHz (p< 0.05) compared to +/+ animals (n= 6). Figure 4 Threshold shifts 4 weeks after noise exposure. The gw/+ animals (n= 24) was statistically significant less affected by the noise at 2, and 12,5 kHz (p< 0.05) compared to +/+ animals (n= 6). gw/+ +/+ gw/gw gw/+gw/gw gw/+ gw/w gw/+ gw/gw +/+ Conclusions The heterozygous animals of the German waltzing guinea pig seems to have some genetic protection mechanisms against noise trauma compared to littermates and other control animals. Introduction The German waltzing guinea pig strain originates from Bayreuth, Germany where they spontaneously arose in a breeding facility in Two normal-behaving animals delivered a litter consisting of five animals, where two progenies showed a characteristic circling behavior. The two waltzing animals were interbred, resulting in two litters, each consisting two waltzing animals. The aim of present study was to further investigate if the altered susceptibility to acoustic trauma in the heterozygous animals of the German waltzing guinea pig strain was to be found in their genetic background. Figure 1 Breeding pattern. Breading couples consisting of only (gw/+) animals were used. This allows offspring of all three possible outcomes i.e. (gw/gw) (gw/+) and (+/+) Figure 2 Hearing thresholds before noise exposure. There was no statistically significant difference between gw/+ animals (n=24) and +/+ animals (n=6) before noise exposure at any of the frequencies measured.