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Primary local orbital amyloidosis: biochemical identification of the immunoglobulin light chain III subtype in a small formalin fixed, paraffin wax embedded tissue sample

¹ Heller Institute of Medical Research, Sheba Medical Centre, Tel-Hashomer, 52621, Israel and Tel-Aviv University, Sackler School of Medicine, Israel
² Laboratory of Neurotoxicology, National Institute of Mental Health, Bethesda, 20892-1262 MD, USA
³ Department of Pathology, Western Galilee Hospital, Nahariya Medical Centre, 22100 Israel
⁴ Haematology Unit, Western Galilee Hospital
⁵ Department of Ophthalmology, Western Galilee Hospital

Correspondence to:
Dr B Kaplan
Heller Institute of Medical Research, Sheba Medical Centre, Tel Hashomer 52621, Israel; kaplanb{at}sheba.health.gov.il Background: Amyloidosis refers to a heterogeneous group of disorders associated with the deposition of chemically distinct amyloid fibril proteins. Precise determination of chemical amyloid type has diagnostic, therapeutic, and prognostic relevance. Although immunohistochemical techniques are used routinely to determine the amyloid type, the results can be negative or inconclusive, so that biochemical characterisation is often required. The development and application of new biochemical microtechniques suitable for examination of extremely small tissue samples is essential for precise identification of the deposited amyloid proteins.

Aims: To investigate biochemically the amyloid proteins present in a formalin fixed paraffin wax embedded orbital tissue from a patient with localised orbital amyloidosis in whom immunohistochemistry was not helpful in the determination of amyloid type.

Methods: Extraction of amyloid proteins from fixed tissue and their identification was carried out by a recently developed microtechnique. An extremely small tissue sample was dewaxed and extracted with formic acid. The extracted material was analysed using electrophoresis, western blotting, and amino acid sequencing.

Results: Biochemical examination of the extracted proteins showed the presence of immunoglobulin (Ig) derived amyloid proteins, which were composed of the N-terminal fragments of the Ig light chain III subtype (AL-III) (16, 8, and 3 kDa).

Conclusions: This is the first chemically proved AL case reported in association with primary localised orbital amyloidosis. The biochemical microtechnique used was useful in achieving a precise diagnosis of amyloid disease, in a case where the results of routine immunohistochemical examination of amyloid were inconclusive.

Abbreviations: AL, immunoglobulin light chain derived protein; Ig, immunoglobulin

Keywords: immunoglobulin light chains; microtechnique; orbital amyloidosis