A study of apolipoproteins E and A-I in cutaneous amyloids

Abstract

Background Apolipoprotein E (apoE) is present in a variety of biochemically different amyloid deposits, including Alzheimer's disease, systemic amyloidosis and primary cutaneous amyloidosis (PCA). Among the three closely related alleleic forms of apoE, the ε4 allele is linked to Alzheimer's disease. Apolipoprotein A‐I (apoA‐I), another apolipoprotein, is also found in senile plaques of Alzheimer's disease and in amyloid of aortic atherosclerotic plaques. Furthermore, apoA‐I has recently been found to be associated with hereditary cutaneous and cardiac amyloidosis. Objectives To determine whether the apoE ε4 allele is associated with increased risk of PCA and whether apoE and apoA‐I are present in PCA and common secondary cutaneous amyloidosis (SCA) (i.e. basal cell carcinoma, Bowen's disease and seborrhoeic keratosis). Methods We examined the apoE genotype in 57 Chinese patients with PCA and 58 normal healthy control subjects of similar age. In addition, immunohistochemical staining was performed to determine the localization of apoE and apoA‐I in skin tissues from 15 patients with SCA and 15 with PCA. Results The frequency of the ε4 allele in the PCA group was not significantly higher than that in the control group (8·8% vs. 6·9%, P > 0·05). ApoE was present in amyloid deposits in both PCA and SCA, but apoA‐I was not detected in these cutaneous amyloid deposits. Conclusions ApoE is also a component of amyloid deposits in SCA. Although the genetic susceptibility of certain apoE isoforms may not be a crucial factor in the development of PCA and, although apoA‐I is not associated with amyloid deposits of PCA and SCA, the role of apolipoproteins in amyloidogenesis deserves further scrutiny.