A genetic defect that causes a severe immune deficiency in humans may also produce balance disorders, according to a new study. The study examined a specialized strain of Jackson Laboratory mice with a mutation that eliminates the production a protein called p22phox. Disruption of this protein causes a form of chronic granulomatous disease (CGD) — a severe immune deficiency — in humans. The researchers found that mice without p22phox develop an immune deficiency that mimics human CGD. They also discovered that the gene defect produces a severe balance disorder in the mice caused by loss of gravity-sensing crystals in the inner ear.