Maltese dilution, as this mutation was originally called, is an old mutation of the mouse fancy. The blue-gray color of the hair produced by this mutation in nonagouti (a/a) mice is caused by clumping of the melanin pigment into a few large masses (J:12958). The melanocytes are misshapen, with fewer and thinner dendritic processes than wild-type melanocytes, and melanin granules are largely clumped around the nucleus (J:12970). Incorporation of tyrosine into melanin proceeds at a normal rate (J:12173), and the fine structure of the melanin granules is normal (J:5346). Cultured primary melanocytes from dilute homozygotes are normal in morphology but display clustering of melanosomes (J:37976).

Griscelli disease (Chediak-Higashi-like syndrome, OMIM 214450) is a human autosomal recessive disorder whose symptoms include pigment dilution, immunodeficiency, and acute lethal lymphocyte and macrophage activation. Melanocyte malformation is characteristic of the pigment abnormality. The immunological abnormality includes absence of cutaneous hypersensitivity and impaired function of natural-killer cells. Griscelli disease resembles the dilute-lethal mouse mutant, except for the neurological disorder in the mouse. The locus for Griscelli disease colocalizes with the locus for myosin Va, which is mutated in at least some Griscelli patients. Griscelli disease is thus the homolog of mouse Maltese dilution (J:41253).