Bradypneic, a new mutation in mice causing slow breathing, runting, and early death

A new recessive mutation, bradypneic (bd), causes variable weight retardation beginning as early as 3 to 5 days. Severely affected mice die within the first 2 weeks; less severely affected mice may survive to weaning or to adulthood and may be fertile. Bradypneic mice tested at 3 weeks or older breathed at half the normal rate, but breathing was deeper and O2 consumption per unit of body surface was normal. No obstruction was found in the nasal passages, pharynx, trachea, or bronchi. The lungs were somewhat emphysematous and, probably in consequence, the right atrium was enlarged. The only other pathological conditions found were dilation of some of the distal tubules of the kidney and large amounts of gas in the stomach and intestines. The investigation did not reveal the cause of the breathing defect, but it is possible that the breathing defect is responsible for the emphysema, intestinal gas, small size, and early death. Extensive linkage tests have not yet revealed the chromosomal location of bd.