Novel deletion mutations of OPTN in amyotrophic lateral sclerosis in Japanese

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motor neuron death in the brain and spinal cord. Many disease genes for ALS have been identified; however, each disease gene is responsible for very small fractions of ALS. Recently, mutations of the gene encoding optineurin (OPTN) are reported in familial and sporadic ALS. OPTN is also responsible for a small number of ALS, 3.8% of familial and 0.29% of sporadic ALS in Japanese. The low prevalence may be an underestimation due to incomplete screening of the mutation. To examine OPTN mutations more extensively, we screened the OPTN deletions using a quantitative PCR system. We examined 710 Japanese ALS subjects who had previously been found to have no OPTN mutations by a screening using a PCR-direct sequence strategy. We identified 3 kinds of deletions in 5 patients; one was homozygous, and the remaining were heterozygous. All deletions occurred due to the Alu-mediated recombination and are expected to result in null alleles. Our results suggest that the OPTN deletion mutation in ALS is not infrequent and the prevalence of the OPTN mutation in Japanese sporadic ALS is considerably high.