Gross examination of internal organs also showed that the mutants' thymi were consistently inconspicuous and were very small for their age, whereas those of their littermates were very prominent in size (Figure 2G). This difference was evident as early as P3. Quite frequently mutant thymi in P12–P17 mutant mice also contained black deposits within the tissue (unpublished data). Mutant mice were also examined for any skeletal abnormalities by preparing skeletal specimens of P16–P17 mice stained with Alizarin red. No differences between the normal and KA mutant mice in the mandibular bone can be detected, but the mutant mice lacked or had underdeveloped set of maxillary incisors and molars (Figure 2H). We detected no other major skeletal abnormalities.