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Hereditary spastic paraplegias (HSPs) are neurodegenerative motor neuron diseases characterized by progressive age-dependent loss of corticospinal motor tract function. Although the genetic basis is partly understood, only a fraction of cases can receive a genetic diagnosis, and a global view of HSP is lacking. By using whole-exome sequencing in combination with network analysis, we identified 18 previously unknown putative HSP genes and validated nearly all of these genes functionally or genetically. The pathways highlighted by these mutations link HSP to cellular transport, nucleotide metabolism, and synapse and axon development. Network analysis revealed a host of further candidate genes, of which three were mutated in our cohort. Our analysis links HSP to other neurodegenerative disorders and can facilitate gene discovery and mechanistic understanding of disease.

Objective: Hereditary spastic paraplegias (HSPs) are very heterogeneous inherited neurodegenerative disorders. Our group recently identified ZFYVE26 as the gene responsible for one of the clinical and genetic entities, SPG15. Our aim was to describe its clinical and mutational spectra., Methods: We analyzed all exons of SPG15/ZFYVE26 gene by direct sequencing in a series of 60 non-SPG11 HSP subjects with associated mental or MRI abnormalities, including 30 isolated cases. The clinical data were collected through the SPATAX network., Results: We identified 13 novel truncating mutations in ZFYVE26, 12 of which segregated at the homozygous or compound heterozygous states in 8 new SPG15 families while 1 was found at the heterozygous state in a single family. Two of 3 splice site mutations were validated on mRNA of 2 patients. The SPG15 phenotype in 11 affected individuals was characterized by early onset HSP, severe progression of the disease, and mental impairment dominated by cognitive decline. Thin corpus callosum and white matter hyperintensities were MRI hallmarks of the disease in this series., Conclusions: The mutations are truncating, private, and distributed along the entire coding sequence of ZFYVE26, which complicates the analysis of this gene in clinical practice. In our series of patients with hereditary spastic paraplegia-thin corpus callosum, the largest analyzed so far, SPG15 was the second most frequent form (11.5%) after SPG11. Both forms share similar clinical and imaging presentations with very few distinctions, which are, however, insufficient to infer the molecular diagnosis when faced with a single patient.

Hereditary spastic paraplegias (HSPs) are genetically and phenotypically heterogeneous disorders. Both "uncomplicated" and "complicated" forms have been described with various modes of inheritance. Sixteen loci for autosomal-recessive "complicated" HSP have been mapped. The SPG15 locus was first reported to account for a rare form of spastic paraplegia variably associated with mental impairment, pigmented maculopathy, dysarthria, cerebellar signs, and distal amyotrophy, sometimes designated as Kjellin syndrome. Here, we report the refinement of SPG15 to a 2.64 Mb genetic interval on chromosome 14q23.3-q24.2 and the identification of ZFYVE26, which encodes a zinc-finger protein with a FYVE domain that we named spastizin, as the cause of SPG15. Six different truncating mutations were found to segregate with the disease in eight families with a phenotype that included variable clinical features of Kjellin syndrome. ZFYVE26 mRNA was widely distributed in human tissues, as well as in rat embryos, suggesting a possible role of this gene during embryonic development. In the adult rodent brain, its expression profile closely resembled that of SPG11, another gene responsible for complicated HSP. In cultured cells, spastizin colocalized partially with markers of endoplasmic reticulum and endosomes, suggesting a role in intracellular trafficking.

Hereditary spastic paraplegia (HSP) type 15 is an autosomal recessive (AR) form of complicated HSP mainly characterized by slowly progressive spastic paraplegia, mental retardation, intellectual deterioration, maculopathy, distal amyotrophy, and mild cerebellar signs that has been associated with the Kjellin syndrome. The locus for this form of HSP, designated SPG15, was mapped to an interval of 19 cM on chromosome 14q22-q24 in two Irish families. We performed a clinical-genetic study of this form of HSP on 147 individuals (64 of whom were affected) from 20 families with AR-HSP. A genome-wide scan was performed in three large consanguineous families of Arab origin after exclusion of linkage to several known loci for AR-HSP (SPG5, SPG7, SPG21, SPG24, SPG28, and SPG30). The 17 other AR-HSP families were tested for linkage to the SPG15 locus. Only the three large consanguineous families showed evidence of linkage to the SPG15 locus (2.4 > Z (max) > 4.3). Recombinations in these families reduced the candidate region from approximately 16 to approximately 5 Mbases. Among the approximately 50 genes assigned to this locus, two were good candidates by their functions (GPHN and SLC8A3), but their coding exons and untranslated regions (UTRs) were excluded by direct sequencing. Patients had spastic paraplegia associated with cognitive impairment, mild cerebellar signs, and axonal neuropathy, as well as a thin corpus callosum in one family. The ages at onset ranged from 10 to 19 years. Our study highlights the phenotypic heterogeneity of SPG15 in which mental retardation or cognitive deterioration, but not all other signs of Kjellin syndrome, are associated with HSP and significantly reduces the SPG15 locus.

Hereditary spastic paraplegias (HSPs) are genetically and phenotypically heterogeneous. Both "uncomplicated" and "complicated" forms have been described, with autosomal dominant, autosomal recessive, and X-linked inheritance. Hitherto, ten autosomal dominant "uncomplicated" HSP (ADHSP) loci have been mapped. Here, we report linkage of ADHSP with markers of the 8p21.1-q13.3 chromosomal region in a large French family, including 29 examined at-risk individuals. The age at onset varied from 8 to 60 years with a mean of 31.6 +/- 16.4 years. Multipoint and two-point LOD-score calculations as well as haplotype reconstruction in this region gave support to the location of this novel ADHSP locus (SPG37) in a 43.5 cM genetic interval flanked by loci D8S1839 and D8S1795. The region was shared by all definitely (n = 13), probably (n = 3) and possibly (n = 2) affected patients with a maximum LOD score of 4.20 at the D8S601 locus. Two candidate genes, encoding the kinesin family member 13B and neuregulin 1 (isoforms SMDF and GFF2), were screened for mutations, but no disease-causing alterations were identified. Interestingly, another region, on chromosome 10q22.3-23.31, was found to segregate in all affected patients (but not in probably or possibly affected subjects) and in a high proportion of healthy at risk individuals, suggesting that this locus might act as a modifier of the phenotype.

Thirty-three different loci for hereditary spastic paraplegias (HSP) have been mapped, and 15 responsible genes have been identified. Autosomal recessive spastic paraplegias (ARHSPs) usually have clinically complex phenotypes but the SPG5, SPG24, and SPG28 loci are considered to be associated with pure forms of the disease. We performed a genome-wide scan in a large French family. Fine mapping of the refined SPG5 region on chromosome 8q12 was performed in another 17 ARHSP families with additional microsatellite markers. After exclusion of known ARHSP loci, the genome-wide screen provided evidence of linkage with a maximal multipoint lod score of 2.6 in the D8S1113-D8S1699 interval. This interval partially overlapped SPG5 and reduced it to a 5.9 megabase (Mb)-region between D8S1113 and D8S544. In a family of Algerian origin from a series of 17 other ARHSP kindreds, linkage to the SPG5 locus was supported by a multipoint lod score of 2.3. The direct sequencing of the coding exons of seven candidate genes did not detect mutations/polymorphisms in the index cases of both linked families. The phenotype of the two SPG5-linked families consisted of spastic paraparesis associated with deep sensory loss. In several patients with long disease durations, there were also mild cerebellar signs. The frequency of SPG5 was approximately 10% (2/18) in our series of ARHSP families with pure or complex forms. We have refined the SPG5 locus to a 3.8 cM interval and extended the phenotype of this form of ARHSP to include slight cerebellar signs., ((c) 2007 Wiley-Liss, Inc.)

Autosomal recessive spastic ataxias are a heterogeneous group of neurodegenerative diseases usually characterized by the early onset of cerebellar and pyramidal signs. With the collaboration of the clinical European and Mediterranean SPATAX network, we identified 15 families with 34 affected members presenting with ataxia and pyramidal signs or spasticity that were not linked to the ARSACS locus on chromosome 13. In an informative consanguineous Moroccan family, we mapped a novel locus, SAX2, to chromosome 17p13. The minimal linked interval lies in a region of 6.1 cM flanked by markers D17S1845/1583 and D17S1854 (Z(max) = 3.21). Three of the remaining 14 families were also possibly linked to SAX2. The overall clinical picture in nine patients was cerebellar ataxia with pyramidal signs and/or spasticity. Onset occurred before the age of 15 years in two families and in adulthood in the other two. Interestingly, in the largest SAX2 family, the presenting clinical sign was dysarthria, which is not common in other forms of inherited ataxias or spastic ataxias, whereas gait difficulties appeared later. Most cases also showed fasciculations suggesting that both lower and upper motor neurons are involved in the disease process. No mutations were found in the coding exons of KIF1C, ARRB2 and ANKFY1, three genes in the candidate region.