Recent studies identified rare missense mutations in amyotrophic lateral sclerosis (ALS) patients in the TARDBP gene encoding TAR DNA binding protein (TDP)‐43, the major protein of the ubiquitinated inclusions (UBIs) found in affected motor neurons (MNs). The aim of this study was to further define the spectrum of TARDBP mutations in a large cohort of 666 Italian ALS patients (125 familial and 541 sporadic cases). The entire coding region was sequenced in 281 patients, while in the remaining 385 cases only exon 6 was sequenced. In 18 patients, of which six are familial, we identified 12 different heterozygous missense mutations (nine novel) all locating to exon 6, which were absent in 771 matched controls. The c.1144G>A (p.A382T) variation was observed in seven patients, thus representing the most frequent TARDBP mutation in ALS. Analysis of microsatellites surrounding the TARDBP gene indicated that p.A382T was inherited from a common ancestor in 5 of the 7 patients. Altogether, the frequency of TARDBP gene mutations appears to be particularly high in Italian ALS patients compared to individuals of mainly Northern European origin (2.7% vs. 1%). Western blot analysis of lymphocyte extracts from two patients carrying the p.A382T and p.S393L TARDBP mutations showed the presence of lower molecular weight TDP‐43 bands, which were more abundant than observed in healthy controls and patients negative for TARDBP mutations. In conclusion, this report contributes to the demonstration of the causative role of the TARDBP gene in ALS pathogenesis and indicates that mutations may affect the stability of the protein even in nonneuronal tissues. Hum Mutat 0, 1–7, 2009.

Hereditary spastic paraplegias are a heterogeneous group of neurodegenerative disorders, clinically classified in pure and complex forms. Genetically, more than 70 different forms of spastic paraplegias have been characterized. A subgroup of complicate recessive forms has been distinguished for the presence of thin corpus callosum and white matter lesions at brain imaging. This group includes several genetic entities, but most of the cases are caused by mutations in the KIAA1840 (SPG11) and ZFYVE26 genes (SPG15). We studied a cohort of 61 consecutive patients with complicated spastic paraplegias, presenting at least one of the following features: mental retardation, thin corpus callosum and/or white matter lesions. DNA samples were screened for mutations in the SPG11 /KIAA1840, SPG15/ ZFYVE26, SPG21 /ACP33 , SPG35 /FA2H , SPG48 /AP5Z1 and SPG54 /DDHD2 genes by direct sequencing. Sequence variants were found in 30 of 61 cases: 16 patients carried SPG11/ KIAA1840 gene variants (26.2%), nine patients carried SPG15 /ZFYVE26 variants (14.8%), three patients SPG35 /FA2H (5%), and two patients carried SPG48/ AP5Z1 gene variants (3%). Mean age at onset was similar in patients with SPG11 and with SPG15 (range 11–36), and the phenotype was mostly indistinguishable. Extrapyramidal signs were observed only in patients with SPG15, and epilepsy in three subjects with SPG11. Motor axonal neuropathy was found in 60% of cases with SPG11 and 70% of cases with SPG15. Subjects with SPG35 had intellectual impairment, spastic paraplegia, thin corpus callosum, white matter hyperintensities, and cerebellar atrophy. Two families had a late-onset presentation, and none had signs of brain iron accumulation. The patients with SPG48 were a 5-year-old child, homozygous for a missense SPG48/ AP5Z1 variant, and a 51-year-old female, carrying two different nonsense variants. Both patients had intellectual deficits, thin corpus callosum and white matter lesions. None of the cases in our cohort carried mutations in the SPG21 /ACP33 and SPG54/ DDH2H genes. Our study confirms that the phenotype of patients with SPG11 and with SPG15 is homogeneous, whereas cases with SPG35 and with SPG48 cases present overlapping features, and a broader clinical spectrum. The large group of non-diagnosed subjects (51%) suggests further genetic heterogeneity. The observation of common clinical features in association with defects in different causative genes, suggest a general vulnerability of the corticospinal tract axons to a wide spectrum of cellular alterations. * Abbreviations : ALS : amyotrophic lateral sclerosis SNP : single nucleotide polymorphism SPG : spastic paraplegia