Alteration of ganglioside biosynthesis responsible for complex hereditary spastic paraplegia.

Hereditary spastic paraplegias (HSPs) form a heterogeneous group of neurological disorders. A whole-genome linkage mapping effort was made with three HSP-affected families from Spain, Portugal, and Tunisia and it allowed us to reduce the SPG26 locus interval from 34 to 9 Mb. Subsequently, a targeted capture was made to sequence the entire exome of affected individuals from these three families, as well as from two additional autosomal-recessive HSP-affected families of German and Brazilian origins. Five homozygous truncating (n = 3) and missense (n = 2) mutations were identified in B4GALNT1. After this finding, we analyzed the entire coding region of this gene in 65 additional cases, and three mutations were identified in two subjects. All mutated cases presented an early-onset spastic paraplegia, with frequent intellectual disability, cerebellar ataxia, and peripheral neuropathy as well as cortical atrophy and white matter hyperintensities on brain imaging. B4GALNT1 encodes ß-1,4-N-acetyl-galactosaminyl transferase 1 (B4GALNT1), involved in ganglioside biosynthesis. These findings confirm the increasing interest of lipid metabolism in HSPs. Interestingly, although the catabolism of gangliosides is implicated in a variety of neurological diseases, SPG26 is only the second human disease involving defects of their biosynthesis.

Deletion analysis of SMN and NAIP genes in Tunisian patients with spinal muscular atrophy.

BACKGROUND: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder involving degeneration of anterior horn cells of spinal cord, resulting in progressive muscle weakness and atrophy. AIMS: The purpose of our study was to determine the frequency of SMN and NAIP deletions in Tunisian SMA patients. MATERIALS AND METHODS: Polymerase chain reaction (PCR) combined with restriction fragment length polymorphism (RFLP) was used to detect the deletion of exon 7 and exon 8 of SMN1 gene, as well as multiplex PCR for exon 5 and 13 of NAIP gene. RESULTS: Fifteen (45.4%) out of 33 SMA patients were homozygously deleted for exons 7 and/or 8 of SMN1. Homozygous deletion of NAIP gene was observed in 20% (3 / 15) of patients. CONCLUSIONS: The molecular diagnosis system based on PCR-RFLP analysis can conveniently be applied in the clinical testing, genetic counseling, prenatal diagnosis, and pre-implantation genetic diagnosis of SMA.

Loss of function of glucocerebrosidase GBA2 is responsible for motor neuron defects in hereditary spastic paraplegia.

Spastic paraplegia 46 refers to a locus mapped to chromosome 9 that accounts for a complicated autosomal-recessive form of hereditary spastic paraplegia (HSP). With next-generation sequencing in three independent families, we identified four different mutations in GBA2 (three truncating variants and one missense variant), which were found to cosegregate with the disease and were absent in controls. GBA2 encodes a microsomal nonlysosomal glucosylceramidase that catalyzes the conversion of glucosylceramide to free glucose and ceramide and the hydrolysis of bile acid 3-O-glucosides. The missense variant was also found at the homozygous state in a simplex subject in whom no residual glucocerebrosidase activity of GBA2 could be evidenced in blood cells, opening the way to a possible measurement of this enzyme activity in clinical practice. The overall phenotype was a complex HSP with mental impairment, cataract, and hypogonadism in males associated with various degrees of corpus callosum and cerebellar atrophy on brain imaging. Antisense morpholino oligonucleotides targeting the zebrafish GBA2 orthologous gene led to abnormal motor behavior and axonal shortening/branching of motoneurons that were rescued by the human wild-type mRNA but not by applying the same mRNA containing the missense mutation. This study highlights the role of ceramide metabolism in HSP pathology.

REEP1 mutations in SPG31: frequency, mutational spectrum, and potential association with mitochondrial morpho-functional dysfunction.

Hereditary spastic paraplegias (HSP) constitute a heterogeneous group of neurodegenerative disorders characterized at least by slowly progressive spasticity of the lower limbs. Mutations in REEP1 were recently associated with a pure dominant HSP, SPG31. We sequenced all exons of REEP1 and searched for rearrangements by multiplex ligation-dependent probe amplification (MLPA) in a large panel of 175 unrelated HSP index patients from kindreds with dominant inheritance (AD-HSP), with either pure (n = 102) or complicated (n = 73) forms of the disease, after exclusion of other known HSP genes. We identified 12 different heterozygous mutations, including two exon deletions, associated with either a pure or a complex phenotype. The overall mutation rate in our clinically heterogeneous sample was 4.5% in French families with AD-HSP. The phenotype was restricted to pyramidal signs in the lower limbs in most patients but nine had a complex phenotype associating axonal peripheral neuropathy (= 5/11 patients) including a Silver-like syndrome in one patient, and less frequently cerebellar ataxia, tremor, dementia. Interestingly, we evidenced abnormal mitochondrial network organization in fibroblasts of one patient in addition to defective mitochondrial energy production in both fibroblasts and muscle, but whether these anomalies are directly or indirectly related to the mutations remains uncertain.

A new locus (SPG46) maps to 9p21.2-q21.12 in a Tunisian family with a complicated autosomal recessive hereditary spastic paraplegia with mental impairment and thin corpus callosum.

Hereditary spastic paraplegia (HSP) with thin corpus callosum (TCC) and mental impairment is a frequent subtype of complicated HSP, often inherited as an autosomal recessive (AR) trait. It is clear from molecular genetic analyses that there are several underlying causes of this syndrome, with at least six genetic loci identified to date. However, SPG11 and SPG15 are the two major genes for this entity. To map the responsible gene in a large AR-HSP-TCC family of Tunisian origin, we investigated a consanguineous family with a diagnosis of AR-HSP-TCC excluded for linkage to the SPG7, SPG11, SPG15, SPG18, SPG21, and SPG32 loci. A genome-wide scan was undertaken using 6,090 SNP markers covering all chromosomes. The phenotypic presentation in five patients was suggestive of a complex HSP that associated an early-onset spastic paraplegia with mild handicap, mental deterioration, congenital cataract, cerebellar signs, and TCC. The genome-wide search identified a single candidate region on chromosome 9, exceeding the LOD score threshold of +3. Fine mapping using additional markers narrowed the candidate region to a 45.1-Mb interval (15.4 cM). Mutations in three candidate genes were excluded. The mapping of a novel AR-HSP-TCC locus further demonstrates the extensive genetic heterogeneity of this condition. We propose that testing for this locus should be performed, after exclusion of mutations in SPG11 and SPG15 genes, in AR-HSP-TCC families, especially when cerebellar ataxia and cataract are present.

CYP7B1 mutations in pure and complex forms of hereditary spastic paraplegia type 5.

Thirty-four different loci for hereditary spastic paraplegias have been mapped, and 16 responsible genes have been identified. Autosomal recessive forms of spastic paraplegias usually have clinically complex phenotypes but the SPG5, SPG24 and SPG28 loci are considered to be associated with 'pure' forms of the disease. Very recently, five mutations in the CYP7B1 gene, encoding a cytochrome P450 oxysterol 7-alpha hydroxylase and expressed in brain and liver, have been found in SPG5 families. We analysed the coding region and exon-intron boundaries of the CYP7B1 gene by direct sequencing in a series of 82 unrelated autosomal recessive hereditary spastic paraplegia index patients, manifesting either a pure (n = 52) or a complex form (n = 30) of the disease, and in 90 unrelated index patients with sporadic pure hereditary spastic paraplegia. We identified eight, including six novel, mutations in CYP7B1 segregating in nine families. Three of these mutations were nonsense (p.R63X, p.R112X, p.Y275X) and five were missense mutations (p.T297A, p.R417H, p.R417C, p.F470I, p.R486C), the last four clustering in exon 6 at the C-terminal end of the protein. Residue R417 appeared as a mutational hot-spot. The mean age at onset in 16 patients was 16.4 +/- 12.1 years (range 4-47 years). After a mean disease duration of 28.3 +/- 13.4 years (10-58), spasticity and functional handicap were moderate to severe in all cases. Interestingly, hereditary spastic paraplegia was pure in seven SPG5 families but complex in two. In addition, white matter hyperintensities were observed on brain magnetic resonance imaging in three patients issued from two of the seven pure families. Lastly, the index case of one family had a chronic autoimmune hepatitis while his eldest brother died from cirrhosis and liver failure. Whether this association is fortuitous remains unsolved, however. The frequency of CYP7B1 mutations were 7.3% (n = 6/82) in our series of autosomal recessive hereditary spastic paraplegia families and 3.3% (n = 3/90) in our series of sporadic pure spastic paraplegia. The recent identification of CYP7B1 as the gene responsible for SPG5 highlights a novel molecular mechanism involved in hereditary spastic paraplegia determinism.

Screening of ARHSP-TCC patients expands the spectrum of SPG11 mutations and includes a large scale gene deletion.

Autosomal recessive spastic paraplegia with thinning of corpus callosum (ARHSP-TCC) is a complex form of HSP initially described in Japan but subsequently reported to have a worldwide distribution with a particular high frequency in multiple families from the Mediterranean basin. We recently showed that ARHSP-TCC is commonly associated with mutations in SPG11/KIAA1840 on chromosome 15q. We have now screened a collection of new patients mainly originating from Italy and Brazil, in order to further ascertain the spectrum of mutations in SPG11, enlarge the ethnic origin of SPG11 patients, determine the relative frequency at the level of single Countries (i.e., Italy), and establish whether there is one or more common mutation. In 25 index cases we identified 32 mutations; 22 are novel, including 9 nonsense, 3 small deletions, 4 insertions, 1 in/del, 1 small duplication, 1 missense, 2 splice-site, and for the first time a large genomic rearrangement. This brings the total number of SPG11 mutated patients in the SPATAX collection to 111 cases in 44 families and in 17 isolated cases, from 16 Countries, all assessed using homogeneous clinical criteria. While expanding the spectrum of mutations in SPG11, this larger series also corroborated the notion that even within apparently homogeneous population a molecular diagnosis cannot be achieved without full gene sequencing.

Complicated forms of autosomal dominant hereditary spastic paraplegia are frequent in SPG10.

Hereditary spastic paraplegias (HSP) constitute a heterogeneous group of neurodegenerative disorders characterized by slowly progressive spasticity of the lower extremities. Only a few different mutations in the SPG10 gene, KIF5A, have been described in pure dominant forms of the disease. We sequenced the motor domain of KIF5A in a large panel of 205 European HSP patients with either pure or complicated forms of the disease. We identified eight different heterozygous missense mutations, seven novels, in eight different families of French origin. Residue R280 was a mutational hot spot. Interestingly, the patients in 7/8 families had a complex phenotype, with peripheral neuropathy, severe upper limb amyotrophy (Silver syndrome-like), mental impairment, parkinsonism, deafness and/or retinitis pigmentosa as variably associated features. We report the largest series of SPG10 families described so far, which extends both the mutational spectrum of the disease and its phenotype, which now includes complicated forms of HSP. SPG10 mutations were found in 10% of our complicated forms of HSP, suggesting that mutations in KIF5A represent the major cause of complicated AD-HSP in France.

Identification of the SPG15 gene, encoding spastizin, as a frequent cause of complicated autosomal-recessive spastic paraplegia, including Kjellin syndrome.

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 with mental impairment and thin corpus callosum in Tunisia: SPG11, SPG15, and further genetic heterogeneity.

OBJECTIVE: To perform a clinical and genetic study of Tunisian families with autosomal recessive (AR) hereditary spastic paraplegia with thin corpus callosum (HSP-TCC). DESIGN: Linkage studies and mutation screening. SETTING: Reference Center for Neurogenetics in South and Center Tunisia. PARTICIPANTS: Seventy-three subjects from 33 "apparently" unrelated Tunisian families with AR HSP. MAIN OUTCOME MEASURES: Families with AR HSP-TCC were subsequently tested for linkage to the corresponding loci using microsatellite markers from the candidate intervals, followed by direct sequencing of the KIAA1840 gene in families linked to SPG11. RESULTS: We identified 8 Tunisian families (8 of 33 [24%]), including 19 affected patients, fulfilling the clinical criteria for HSP-TCC. In 7 families, linkage to either SPG11 (62.5%) or SPG15 (25%) was suggested by haplotype reconstruction and positive logarithm of odds score values for microsatellite markers. The identification of 2 recurrent mutations (R2034X and M245VfsX) in the SPG11 gene in 5 families validated the linkage results. The neurological and radiological findings in SPG11 and SPG15 patients were relatively similar. The remaining family, characterized by an earlier age at onset and the presence of cataracts, was excluded for linkage to the 6 known loci, suggesting further genetic heterogeneity. CONCLUSIONS: Autosomal recessive HSP-TCC is a frequent subtype of complicated HSP in Tunisia and is clinically and genetically heterogeneous. SPG11 and SPG15 are the major loci for this entity, but at least another genetic form with unique clinical features exists.

Spastic paraplegia 15: linkage and clinical description of three Tunisian families.

Hereditary spastic paraplegias (HSP) are a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by slowly progressive spasticity of the lower limbs. The locus designated spastic paraplegia 15 (SPG15), located in a 16-Mb interval on chromosome 14q, is associated with a rare autosomal recessive complicated form of HSP known as Kjellin's syndrome. In this study, we describe three additional families, of Tunisian origin, linked to the SPG15 locus, one of which had a significant multipoint LOD score of 3.46. In accordance with previous reports, the phenotype of our patients consisted of early onset spastic paraparesis associated with mental impairment and severe progression. Retinal degeneration was not observed, however, but we extended the phenotype of this form to include peripheral neuropathy and white matter abnormalities on MRI. Interestingly, like retinal degeneration, thin corpus callosum is not a constant feature in this entity.

Mutations in SPG11 are frequent in autosomal recessive spastic paraplegia with thin corpus callosum, cognitive decline and lower motor neuron degeneration.

Hereditary spastic paraplegias (HSP) are neurodegenerative diseases mainly characterized by lower limb spasticity associated, in complicated forms, with additional neurological signs. We have analysed a large series of index patients (n = 76) with this condition, either from families with an autosomal recessive inheritance (n = 43) or isolated patients (n = 33), for mutations in the recently identified SPG11 gene. We found 22 truncating mutations, including the first four splice-site mutations, segregating in seven isolated cases and 13 families. Nineteen mutations were novel. Two recurrent mutations were found in Portuguese and North-African patients indicating founder effects in these populations. The mutation frequency varied according to the phenotype, from 41%, in HSP patients presenting with a thin corpus callosum (TCC) visualized by MRI, to 4.5%, in patients with mental impairment without a TCC. Disease onset occurred during the first to the third decade mainly by problems with gait and/or mental retardation. After a mean disease duration of 14.9 +/- 6.6 years, the phenotype of 38 SPG11 patients was severe with 53% of patients wheelchair bound or bedridden. In addition to mental retardation, 80% of the patients showed cognitive decline with executive dysfunction. Interestingly, the phenotype also frequently included lower motor neuron degeneration (81%) with wasting (53%). Slight ocular cerebellar signs were also noted in patients with long disease durations. In addition to a TCC (95%), brain MRI revealed white matter alterations (69%) and cortical atrophy (81%), which worsened with disease duration. In conclusion, our study reveals the high frequency of SPG11 mutations in patients with HSP, a TCC and cognitive impairment, including in isolated patients, and extends the associated phenotype.