Spectrum of Mutations in the Batten Disease Gene, CLN3

Abstract

Batten disease (juvenile-onset neuronal ceroid lipofuscinosis [JNCL]) is an autosomal recessive condition characterized by accumulation of lipopigments (lipofuscin and ceroid) in neurons and other cell types. The Batten disease gene, CLN3, was recently isolated, and four disease-causing mutations were identified, including a 1.02-kb deletion that is present in the majority of patients (The International Batten Disease Consortium 1995). One hundred eighty-eight unrelated patients with JNCL were screened in this study to determine how many disease chromosomes carried the 1.02-kb deletion and how many carried other mutations in CLN3. One hundred thirty-nine patients (74%) were found to have the 1.02-kb deletion on both chromosomes, whereas 49 patients (41 heterozygous for the 1.02-kb deletion) had mutations other than the 1.02-kb deletion. SSCP analysis and direct sequencing were used to screen for new mutations in these individuals. Nineteen novel mutations were found: six missense mutations, five nonsense mutations, three small deletions, three small insertions, one intronic mutation, and one splice-site mutation. This report brings the total number of disease-associated mutations in CLN3 to 23. All patients homozygous for mutations predicted to give rise to truncated proteins were found to have classical JNCL. However, a proportion of the patients (n = 4) who were compound heterozygotes for a missense mutation and the 1.02-kb deletion were found to display an atypical phenotype that was dominated by visual failure rather than by severe neurodegeneration. All missense mutations were found to affect residues conserved between the human protein and homologues in diverse species.

btn1, theSchizosaccharomyces pombehomologue of the human Batten disease geneCLN3, regulates vacuole homeostasis

“…There are ten missense mutations in CLN3 (see, http://www.ucl.ac.uk/ncl) that change conserved amino acid residues, most of which cause classic JNCL disease. However, some result in an altered disease course (Munroe et al, 1997) suggesting that the mutant protein retains some residual function. We first examined the location of three GFP-Btn1 proteins carrying different missense mutations 3 hours after repression of their expression in btn1⌬ cells.…”

Analysis of Potential Biomarkers and Modifier Genes Affecting the Clinical Course of CLN3 Disease

“…To date, >40 different mutations in CLN3 have been described (summarized in a mutation database: http://www.ucl.ac.uk/ ncl/cln3.shtml). CLN3 disease is recessive, and 85% of CLN3 patients carry a 1-kb deletion that causes the loss of exons 7 and 8 (5). Although the CLN3 protein is well conserved from yeast to humans, its function is a matter of debate.…”

Homogeneous Polymerase Chain Reaction Nucleobase Quenching Assay to Detect the 1-kbp Deletion in CLN3 That Causes Batten Disease

“…4,6 In a large study, Munroe et al 6 found that 74% of 188 unrelated affected individuals from 18 different countries were homozygous for this mutation, and a further 22% were compound heterozygotes for the deletion and another mutation. Thus, a test for only the CLN3 1-kbp deletion in a patient with some suspicion of BD would give either a diagnosis (homozygous result) or raise the level of suspicion (heterozygous result) in over 90% of patients who actually do have this disease.…”

“…With no other known high frequency CLN3 mutations, further molecular diagnosis of BD requires a variety of methods including mutation scanning and sequencing for micromutations and Southern blots for large deletions. 6,11,12 The absence of the CLN3 1-kbp deletion in a patient with some suspicion of BD might also prompt further consideration of other diagnoses. is the opposite of that seen when using a dual probe fluorescence resonance energy transfer system to generate the fluorescent signal.…”

“…4 This mutation accounts for about 80 to 85% of the mutation load for BD. 4,6 The goal of this work was to develop and validate a low-cost rapid assay that could be used to detect the common BD mutation. under a protocol approved by the University of Rochester IRB.…”