This minor histocompatibility 3 (H3e) congenic strain is also carrying the closely linked pallid mutation (Bloc1s6pa) as well as the black and tan allele of nonagouti also residing on Chromosome 2. Histocompatibility 3 is one of several loci isolated and identified by Dr. George Snell and co-workers. Histocompatibility gene differences were identified by generating congenic resistant strains and testing for resistance to transplantable tumors. Homozygous pallid mice have pink eyes, a diluted coat color and their viability is slightly reduced. Some homozygotes have slightly abnormal behavior, with abnormal postural responses and head tilting due to the absence of otoliths in the sacculus and utriculus in many but not all mutant mice. The effect of pallid on behavior and otolith morphology appears to be a result of manganese deficiency. Homozygotes display defective mucopolysaccharide synthesis in the otolith matrix and a slower rate of transport of manganese, L-dopa, and L-tryptophane in the brain. Homozygotes have elevated basal and testosterone-induced levels of the kidney lysosomal enzymes b-glucuronidase, b-galactosidase, and a-mannosidase, accompanied by lowered enzyme excretion in the urine. Pallid mice have a deficiency in serum a1-antitrypsin and have been proposed as a model of genetic a1-antitrypsin deficiency. Lung lesions similar to those seen in human emphysema are found in these mice, and are attributed, like human hereditary emphysema, to a decreased capacity to inhibit serum elastase although liver a1-antitrypsin activity is normal. Pallid mice have prolonged bleeding time due to a platelet storage pool deficiency (SPD) characterized by a normal platelet number but a deficiency in the number of platelet dense granules and in the serotonin, ATP, and ADP content of the granules. Two other mouse coat color mutants, muted (Bloc1s5mu) and mocha (Ap3d1mh), present a similar concatenation of pigment, otolith, and platelet SPD abnormalities, which also occur in human Hermansky-Pudlak syndrome.
