Alder anomaly (also known as Alder-Reilly anomaly) is characterized by large azurophilic granules that stain dark-purple and are seen throughout the leukocyte cytoplasm, even covering the nucleus. The inclusions (granules) are seen in the cytoplasm of almost all mature leukocytes i.e., granulocytes, lymphocytes, and monocytes. This distinguishes Alder anomaly inclusions from toxic granulation, which is only observed in neutrophils. Another feature that distinguishes Alder anomaly from toxic changes is the lack of cytoplasmic vacuoles of toxic origin in the neutrophils of Alder anomaly.
The background condition in Alder anomaly is mucopolysaccharidosis, collectively, a group of inherited disorders where a deficiency of lysosomal enzymes are lacking that are needed to degrade mucopolysaccharides. The inclusions observed in the leukocytes represent partially degraded mucopolysaccharides within lysosomes. Accompanying conditions are hepatosplenomegaly, corneal opacities, and mental retardation.