PROJECT SUMMARY Congenital central hypoventilation syndrome (CCHS) is an autonomic and respiratory disorder caused by mutations in the paired-like homeobox transcription factor gene, PHOX2B. CCHS patients have severe episodes of hypoventilation, especially during sleep, that likely reflect reduced arousal and ventilatory responses to high CO2. In CCHS, PHOX2B mutations commonly include polyalanine repeat mutations (PARMs), with increasing severity associated with more extensive expansions, along with other loss-of-function gene variants that yield particularly dire clinical presentations including various accompanying dysautonomia. The neuropathology associated with CCHS-causing mutations in humans has not been delineated. In mice, Phox2b is expressed in several brain-stem neurons that may be relevant for various clinical features of CCHS. However, the respiratory chemosensory neurons of the retrotrapezoid nucleus (RTN) are thought to be particularly important for the alveolar hypoventilation and loss CO2-dependent reflexes, the two cardinal signs of CCHS, because they are intrinsically CO2-sensitive, contribute to breathing and waking reflexes activated by hypoventilation, and they are uniquely eliminated in mouse genetic models of CCHS. The transcriptional role of Phox2b in RTN neurons, and how it contributes to respiratory regulation by those neurons has not been determined. This proposal examines gene regulatory functions of wild type and polyalanine mutants of Phox2b in RTN neurons, and the relevance of Phox2b-regulated genes for RTN function in respiratory control.