Morphological studies on CLN2

Abstract

Electron microscopic, fluorescence microscopic, and immunohistochemical studies earlier performed on archival cerebral tissue from Max Bielchowsky's original three patients revealed curvilinear bodies rich in subunit C of mitochondrial ATP synthase (SCMAS). Recent progress in the elucidation of CLN2, i.e. identification of the defective lysosomal enzyme tripeptidyl-peptidase I (TPP-I) and mutations in the CLN2 gene have further corroborated earlier data. Immunohistochemically the absence of the TPP-I protein could be confirmed in the archival tissues using pathological controls. Unlike biochemistry, immunohistochemistry enables examination of these archival tissues elucidating the causative defect. Complementary molecular studies identified mutations in the CLN2 gene in the archival tissues and thereby convincingly demonstrated that these three children truly had classic late infantile neuronal ceroid lipofuscinosis (LINCL), now called CLN2. This archival study documents the possibilities to revalidate disease-specific original nosologic reports. Chloroquine is toxic to lysosomal enzymes and results in lysosomal storage. The material is autofluorescent and gives the ultrastructural pattern of curvilinear profiles, thus resembling classic late infantile NCL, representing a good experimental model. In humans chloroquine therapy may cause a myopathy (and retinopathy) and, as recently suggested, an encephalopathy marked by lysosomal accretion in several cell types including neurons. Immunohistochemically, SCMAS also accumulates, further strengthening morphologic similarity between LINCL and human chloroquine intoxication.