Large deletion involving the 5'-UTR in the spastin gene caused mild phenotype of autosomal dominant hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) due to mutations in the spastin gene (SPG4) located to 2p22-p21 is the most common form of autosomal dominant (AD) HSP. We performed PCR-based direct sequencing of SPG4, followed by a linkage analysis and subsequent Southern blot analysis in large Japanese kindred where 20 of 33 members were evaluated neurologically, and consequently 6 were affected with HSP. Clinical evaluation showed that the mean age at disease onset of the patients was older and the disability was less severe than those of previously reported typical patients with SPG4 mutations. Direct sequencing of genomic DNA and RT-PCR product did not show a SPG4 mutation despite of a strong linkage to the SPG4 locus at 2p. Southern blot analysis suggested a deletion involving the 5′-UTR of SPG4. Further sequence analysis confirmed a heterozygous 2307-bp deletion spanning from the 5′-UTR to intron 1 of SPG4. The results suggested that transcription of the mutated allele starts from an authentic initiation site, but lacks an authentic translational start site of exon 1 because of a deficient splice donor site and coding region. The abnormal transcripts may result in rapid RNA decay. The novel refractory mutation we identified widens the spectrum of SPG4 mutations. These findings suggest that structural genomic abnormalities of SPG4 are more frequent than expected, and this explains previously reported cases more feasibly in which SPG4 mutations were failed to be identified but the disease was linked to 2p. © 2005 Wiley-Liss, Inc.