Marinesco-Sjögren syndrome (MSS) is an autosomal recessive multisystem disorder characterized by cerebellar ataxia, cataracts, progressive muscular weakness, and developmental and mental retardation. Recently, mutations in the SIL1 gene on chromosome 5q31 have been shown to be a cause of MSS. We sequenced the entire SIL1-coding region in 3 unrelated Japanese patients with classical MSS and identified a novel homozygous frameshift insertion mutation, 936_937insG, in exon 9 in all 3 patients.