Mass spectrometric-based proteomic analysis of amyloid neuropathy type in nerve tissue

Objective: To determine the specific type of amyloid from nerve biopsies using laser microdissection (LMD) and mass spectrometric (MS)-based proteomic analysis. Design, Setting, and Patients: Twenty-one nerve biopsy specimens (17 sural, 3 sciatic, and 1 root amyloidoma) infiltrated by amyloid were studied. Immunohistochemical subtyping was unable to determine the specific amyloid type for these 21 cases, but the clinical diagnosis was made based on additional testing. Clinical diagnosis was made through evaluation of serum monoclonal proteins, biopsy of bone marrow for acquired monoclonal immunoglobulin light chain amyloidosis, and kindred evaluations with DNA sequencing of transthyretin (TTR) and gelsolin (GSN) genes. Our study included 8 cases of acquired monoclonal immunoglobulin light chain amyloidosis, 11 cases of transthyretin amyloidosis (3 with the Val30Met mutation, 2 with the Val32Ala mutation, 2 with the Thr60Ala mutation, 1 with the Ala109Ser mutation, 1 with the Phe64Leu mutation, 1 with the Ala97Ser mutation, and 1 not sequenced), and 2 cases of gelsolin amyloidosis (1 with the Asp187Asn mutation and 1 not sequenced). One patient with transthyretin amyloidosis and 1 patient with gelsolin amyloidosis with no specific mutation identified were diagnosed based on genetic confirmation in their first-degree relative. Congophilic proteins in the tissues of these 21 cases underwent LMD, were digested into tryptic peptides, and were analyzed using liquid chromatography electrospray tandem MS. Identified proteins were reviewed using bioinformatics tools with interpreters blinded to clinical information. Main Outcome Measure: Specific amyloid type was ascertained by LMD tandem MS and compared with clinical diagnosis. Results: Specific types of amyloid were accurately detected by LMD/MS in all cases (8 cases of acquired monoclonal immunoglobulin light chain amyloidosis, 2 cases of gelsolin amyloidosis, and 11 cases of transthyretin amyloidosis). Incidental serum monoclonal proteins did not interfere with detection of transthyretin amyloidosis in 2 patients. Additionally, specificTTRmutations were identified in 10 cases by LMD/MS. Serum amyloid P-component and apolipoprotein E proteins were commonly found among all cases. Conclusions: Proteomic analysis of nerve tissue using LMD/MS distinguishes specific types of amyloid independent of clinical information. This new proteomic approach will enhance both diagnostic and research efforts in amyloidosis and other neurologic diseases.