Novel WFS1 Variants in Two Moroccan Families with Wolfram Syndrome.

Background: Wolfram syndrome (WFS) is an autosomal recessive disorder that often leads to diabetes, optic atrophy, and sensorineural hearing loss. The aim of this study was to determine the clinical characteristics and the genetic cause of the first two Moroccan families presenting with WFS. Methods: The clinical features of five members of two WFS families were evaluated. Whole-exome sequencing was conducted to explore the underlying genetic cause in the affected patients. Results: Two homozygous variants in the WFS1 gene were identified, each in one of the two families studied: a missense c.1329C>G variant (p.Ser443Arg) and a nonsense mutation c.1113G>A (p.Trp371Ter). These variants affected conserved amino acid residues, segregated well in the two families, and are absent from genetic databases and in controls of Moroccan origin. Bioinformatics analysis classified the two variants as pathogenic by in silico tools and molecular modeling. Conclusion: Our study identified for the first time two variants in Moroccan patients with WFS that extends the mutational spectrum associated with the disease.

Gene Panel Sequencing Analysis Revealed a Strong Contribution of Rare Coding Variants to the Risk of Parkinson's Disease in Sporadic Moroccan Patients.

Parkinson's disease (PD) is a neurodegenerative movement disorder which can be either familial or sporadic. While it is well known that monogenic mutations are not a very common cause of PD, GWAS studies have shown that an additional fraction of the PD heritability could be explained by rare or common variants. To identify the rare variants that could influence the risk of PD in the Moroccan population, a cohort of 94 sporadic PD patients negative for the LRRK2 G2019S mutation was subjected to NGS gene panel sequencing, and gene dosage using the MLPA method. Mean age of onset at enrollment was 51.7 ± 11.51 years, and 60% of patients were men. We identified 70 rare variants under 0.5% of frequency in 16 of the 20 genes analyzed, of which 7 were novel. Biallelic disease-causing variants in genes with recessive inheritance were found in 5 PD cases (5.31%), whereas 13 patients (13.8%) carried likely pathogenic variants in genes with dominant inheritance. Moreover, 8 patients (8.5%) carried a single variant in MAPT or POLG, whereas co-occurrence of rare variants involving more than one gene was observed in 28 patients (30%). PD patients with variants in recessive genes had a younger mean age at onset than patients with dominant ones (33.40 (12.77) vs. 53.15 (6.63), p < 0.001), while their clinical features were similar. However, patients with rare variants in the risk factor genes or in more than one gene tended to have less resting tremor (p < 0.04), but more dystonia (p < 0.006) and dementia (p < 0.002) than those without any rare variants in known PD-associated genes. Our results showed a significant enrichment of rare variants particularly in LRRK2, VPS13C, POLG, and MAPT and underline their impact on the risk of sporadic form of the disease.

Gene Panel Sequencing Identifies Novel Pathogenic Mutations in Moroccan Patients with Familial Parkinson Disease.

In the past two decades, genetic studies of familial forms of Parkinson's disease (PD) have shown evidence that PD has a significant genetic component. Indeed, 12 genes are strongly involved in PD causality, three of them having dominant inheritance and 9 causing early-onset autosomal recessive forms, including 3 with a typical PD and 6 with an atypical parkinsonism. The aim of this study was to determine the genetic basis of familial PD in Moroccan patients. We selected 18 Moroccan index case with familial forms of PD. Patients were first screened for exon-rearrangements by MLPA kit. They were then analyzed by gene panel next-generation sequencing (NGS). Functional variants with minor allele frequencies < 0.5% in public databases were considered potential candidate variants to PD. In the 18 PD patients with a positive family history that were analyzed, MLPA assays identified PRKN deletions in two patients: a homozygous exon 3-5 deletion and a heterozygous exon 4 deletion. Sixteen rare SNV were identified by NGS, four of them were novel. Seven mutations were categorized as pathogenic, five as likely pathogenic, two to be of uncertain significance, and 3 were predicted to be likely benign but may give a weaker pathogenic effect and could contribute to PD since they were found in late-onset PD patients. Rare or novel mutations that could be related to the disease were identified in 72% of these patients (13/18), including nine with bi-allelic pathogenic/likely pathogenic variants in genes causing recessive PD, particularly PRKN and PINK1. Mutations in genes with dominant inheritance were found in 4/18 patients (22%).

A Specific Diplotype H1j/H2 of the MAPT Gene Could Be Responsible for Parkinson's Disease with Dementia.

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease. Five to ten percent of patients have monogenic form of the disease, while most of sporadic PD cases are caused by the combination of genetic and environmental factors. Microtubule-associated protein tau (MAPT) has been appointed as one of the most important risk factors for several neurodegenerative diseases including PD. MAPT is characterized by an inversion in chromosome 17 resulting in two distinct haplotypes H1 and H2. Studies described a significant association of MAPT H1j subhaplotype with PD risk, while H2 haplotype was associated with Parkinsonism, particularly to its bradykinetic component. We report here an isolated case displaying an akinetic-rigid form of PD, with age of onset of 41 years and a good response to levodopa, who developed dementia gradually during the seven years of disease progression. The patient does not carry the LRRK2 G2019S mutation, copy number variations, nor pathogenic and rare variants in known genes associated with PD. MAPT subhaplotype genotyping revealed that the patient has the H1j/H2 diplotype, his mother H1j/H1j, his two healthy brothers H1j/H1v and his deceased father was by deduction H1v/H2. The H1j/H2 diplotype was shown in a total of 3 PD patients among 80, who also did not have known PD-causing mutation and in 1 out of 92 healthy individual controls. The three patients with this diplotype all have a similar clinical phenotype. Our results suggest that haplotypes H1j and H2 are strong risk factor alleles, and their combination could be responsible for early onset of PD with dementia.

Novel pathogenic VPS13A mutation in Moroccan family with Choreoacanthocytosis: a case report.

BACKGROUND: Choreoacanthocytosis (ChAc), is a rare neurodegenerative disease, characterized by movement disorders and acanthocytosis in the peripheral blood smears, and various neurological, neuropsychiatric and neuromuscular signs. It is caused by mutations in VPS13A gene with autosomal recessive pattern of inheritance. CASE PRESENTATION: Here we report two patients belonging to a consanguineous Moroccan family who present with movement disorder pathology. They were suspected to have choreoacanthocytosis according to biological, clinical and radiological finding. Thus, whole-exome sequencing was performed for precise diagnosis and identified a homozygous novel nonsense mutation c.337C > T (p.Gln113*) in exon 5 of VPS13A in the two affected siblings. CONCLUSION: Here, we report a novel nonsense p.Gln113* mutation in VPS13A identified by whole-exome sequencing, which caused ChAc in a Moroccan family. This is the first description of ChAc in Morocco with genetic confirmation, that expands the mutation diversity of VPS13A and provide clinical, neuroimaging and deep brain stimulation findings.

Genetic Analysis of Undiagnosed Juvenile GM1-Gangliosidosis by Microarray and Exome Sequencing.

GM1 gangliosidosis is an autosomal recessive lysosomal storage disorder due to mutations in the lysosomal acid 3-galactosidase gene, GLB1. It is usually classified into three forms, infantile, juvenile, or adult, based on age at onset and severity of central nervous system involvement. Because of their broad clinical spectrum and their similarity to many other aetiologies, including inherited neurodegenerative and metabolic diseases, it is often difficult to diagnose such diseases. Recently, whole exome sequencing (WES) has become increasingly used when a strong hypothesis cannot be formulated based on the clinical phenotype. Here, we present three patients belonging to a consanguineous Moroccan family with a GM1-gangliosidosis with unusual clinical onset and atypical radiological presentation that had eluded diagnosis for over a decade. To identify the disease-causing mutation, we performed a whole exome sequencing and a chromosomal microarray genotyping in order to reduce the number of genetic variants to be interpreted, by focusing the data analysis only on the linked loci. The already known pathogenic missense mutation c.601G>A in GLB1 (p.R201C) was found at homozygous state in the proband V.1 and at heterozygous state in his father IV.1. The mutation was validated by Sanger sequencing and segregated in all the family members according to a recessive mode of inheritance. Outside of the linked loci, we found the EXOSC8 p.Ser272Thr mutation at heterozygous state in all the patients and their mother IV.2. This mutation was reported to cause pontocerebellar hypoplasia type 1C and could act as a modifying factor that exacerbates the brain atrophy of patients. Our study identified the first GLB1 mutation in North Africa in patients with unexpected brain-MRI outcomes extending the clinical spectrum of the GM1-gangliosidosis.

Mutation Analysis of Consanguineous Moroccan Patients with Parkinson's Disease Combining Microarray and Gene Panel.

During the last two decades, 15 different genes have been reported to be responsible for the monogenic form of Parkinson's disease (PD), representing a worldwide frequency of 5-10%. Among them, 10 genes have been associated with autosomal recessive PD, with PRKN and PINK1 being the most frequent. In a cohort of 145 unrelated Moroccan PD patients enrolled since 2013, 19 patients were born from a consanguineous marriage, of which 15 were isolated cases and 4 familial. One patient was homozygous for the common LRRK2 G2019S mutation and the 18 others who did not carry this mutation were screened for exon rearrangements in the PRKN gene using Affymetrix Cytoscan HD microarray. Two patients were determined homozygous for PRKN exon-deletions, while another patient presented with compound heterozygous inheritance (3/18, 17%). Two other patients showed a region of homozygosity covering the 1p36.12 locus and were sequenced for the candidate PINK1 gene, which revealed two homozygous point mutations: the known Q456X mutation in exon 7 and a novel L539F variation in exon 8. The 13 remaining patients were subjected to next-generation sequencing (NGS) that targeted a panel of 22 PD-causing genes and overlapping phenotypes. NGS data showed that two unrelated consanguineous patients with juvenile-onset PD (12 and 13 years) carried the same homozygous stop mutation W258X in the ATP13A2 gene, possibly resulting from a founder effect; and one patient with late onset (76 years) carried a novel heterozygous frameshift mutation in SYNJ1. Clinical analysis showed that patients with the ATP13A2 mutation developed juvenile-onset PD with a severe phenotype, whereas patients having either PRKN or PINK1 mutations displayed early-onset PD with a relatively mild phenotype. By identifying pathogenic mutations in 45% (8/18) of our consanguineous Moroccan PD series, we demonstrate that the combination of chromosomal microarray analysis and NGS is a powerful approach to pinpoint the genetic bases of autosomal recessive PD, particularly in countries with a high rate of consanguinity.

Evidence for prehistoric origins of the G2019S mutation in the North African Berber population.

The most common cause of the monogenic form of Parkinson's disease known so far is the G2019S mutation of the leucine-rich repeat kinase 2 (LRRK2) gene. Its frequency varies greatly among ethnic groups and geographic regions ranging from less than 0.1% in Asia to 40% in North Africa. This mutation has three distinct haplotypes; haplotype 1 being the oldest and most common. Recent studies have dated haplotype 1 of the G2019S mutation to about 4000 years ago, but it remains controversial whether the mutation has a Near-Eastern or Moroccan-Berber ancestral origin. To decipher this evolutionary history, we genotyped 10 microsatellite markers spanning a region of 11.27 Mb in a total of 57 unrelated Moroccan PD patients carrying the G2019S mutation for which the Berber or Arab origin was established over 3 generations based on spoken language. We estimated the age of the most recent common ancestor for the 36 Arab-speaking and the 15 Berber-speaking G2019S carriers using the likelihood-based method with a mutation rate of 10-4. Data analysis suggests that the shortest haplotype originated in a patient of Berber ethnicity. The common founder was estimated to have lived 159 generations ago (95% CI 116-224) for Arab patients, and 200 generations ago (95% CI 123-348) for Berber patients. Then, 29 native North African males carrying the mutation were assessed for specific uniparental markers by sequencing the Y-chromosome (E-M81, E-M78, and M-267) and mitochondrial DNA (mtDNA) hypervariable regions (HV1 and HV2) to examine paternal and maternal contributions, respectively. Results showed that the autochthonous genetic component reached 76% for mtDNA (Eurasian and north African haplogroups) and 59% for the Y-chromosome (E-M81 and E-M78), suggesting that the G2019S mutation may have arisen in an autochthonous DNA pool. Therefore, we conclude that LRRK2 G2019S mutation most likely originated in a Berber founder who lived at least 5000 years ago (95% CI 3075-8700).

LRRK2 G2019S Mutation: Prevalence and Clinical Features in Moroccans with Parkinson's Disease.

Background. The LRRK2 G2019S mutation is the most common genetic determinant of Parkinson's disease (PD) identified to date. This mutation, reported in both familial and sporadic PD, occurs at elevated frequencies in Maghreb population. In the present study, we examined the prevalence of the G2019S mutation in the Moroccan population and we compared the motor and nonmotor phenotype of G2019S carriers to patients with idiopathic Parkinson's disease. Methods. 100 PD patients were assessed for motor and nonmotor symptoms, current medication, and motor complication including motor fluctuations and dyskinesia. The LRRK2 G2019S mutation was investigated by direct sequencing in patients and ethnically matched controls, all of Moroccan origin. Results. Among the 100 PD Moroccan patients, 41 (41%) were carriers of the G2019S mutation. The mutation frequency was higher among probands with autosomal dominant inheritance (76%) than among sporadic ones (28%). Interestingly, G2019S mutation was also found in 5% of control individuals. Clinically, patients carrying the G2019S mutation have more dystonia (OR = 4.6, p = 0.042) and more sleep disorders (OR = 2.4, p = 0.045) than noncarriers. Conclusions. The LRRK2 G2019S prevalence in Morocco is the highest in the world reported to date. Some clinical features in G2019S carriers such as dystonia and sleep disturbances are worth noting.

A Novel Homozygous p.L539F Mutation Identified in PINK1 Gene in a Moroccan Patient with Parkinsonism.

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Ten of fifteen causative genes linked to familial forms of PD have been reported to cause autosomal recessive forms. Among them, mutations in the PTEN-induced kinase 1 (PINK1) gene were shown to be responsible for a phenotype characterized by early onset, good response to levodopa, and a benign course. Using chromosomal microarray analysis and Sanger sequencing, we identified a homozygous G/C substitution in a 58-year-old Moroccan man diagnosed with recessive inherited Parkinson's disease. This G-to-C transition occurred at position 1617 leading to an amino acid change L/F at position 539 located in highly conserved motif in the C terminal sequence of PINK1. Interestingly, the c.1617G>C substitution is absent in 192 ethnically matched control chromosomes. Our findings have shown that the p.L539F is a novel mutation located in the C terminal sequence of the PINK1 protein that could be pathogenic and responsible for a clinical phenotype resembling idiopathic Parkinson's disease with rapid progression and early cognitive impairment.

Mutations in CAPN1 Cause Autosomal-Recessive Hereditary Spastic Paraplegia.

Hereditary spastic paraplegia (HSP) is a genetically and clinically heterogeneous disease characterized by spasticity and weakness of the lower limbs with or without additional neurological symptoms. Although more than 70 genes and genetic loci have been implicated in HSP, many families remain genetically undiagnosed, suggesting that other genetic causes of HSP are still to be identified. HSP can be inherited in an autosomal-dominant, autosomal-recessive, or X-linked manner. In the current study, we performed whole-exome sequencing to analyze a total of nine affected individuals in three families with autosomal-recessive HSP. Rare homozygous and compound-heterozygous nonsense, missense, frameshift, and splice-site mutations in CAPN1 were identified in all affected individuals, and sequencing in additional family members confirmed the segregation of these mutations with the disease (spastic paraplegia 76 [SPG76]). CAPN1 encodes calpain 1, a protease that is widely present in the CNS. Calpain 1 is involved in synaptic plasticity, synaptic restructuring, and axon maturation and maintenance. Three models of calpain 1 deficiency were further studied. In Caenorhabditis elegans, loss of calpain 1 function resulted in neuronal and axonal dysfunction and degeneration. Similarly, loss-of-function of the Drosophila melanogaster ortholog calpain B caused locomotor defects and axonal anomalies. Knockdown of calpain 1a, a CAPN1 ortholog in Danio rerio, resulted in abnormal branchiomotor neuron migration and disorganized acetylated-tubulin axonal networks in the brain. The identification of mutations in CAPN1 in HSP expands our understanding of the disease causes and potential mechanisms.

Clinical and genetic data of Huntington disease in Moroccan patients.

BACKGROUND: Huntington's disease (HD) occurs worldwide with prevalence varying from 0.1 to 10/100,000 depending of the ethnic origin. Since no data is available in the Maghreb population, the aim of this study is to describe clinical and genetic characteristics of Huntington patients of Moroccan origin. METHODS: Clinical and genetics data of 21 consecutive patients recruited from 2009 to 2014 from the outpatient clinic of six medical centers were analyzed. Statistical analysis was performed using descriptive statistics. RESULTS: Twenty one patients from 17 families were diagnosed positive for the IT15 gene CAG expansion. Clinical symptoms were predominantly motor (19/21). Twelve patients had psychiatric and behavioral disorders, and 11 patients had cognitive disorders essentially of memory impairment. Analysis of genetic results showed that 5 patients had reduced penetrant (RP) alleles and 16 had fully penetrant (FP) alleles. The mean CAG repeat length in patients with RP alleles was 38.4 ± 0.54, and 45.37 ± 8.30 in FP alleles. The age of onset and the size of the CAG repeat length showed significant inverse correlation (p <0.001, r = -0.754). CONCLUSION: Clinical and genetic data of Moroccan patients are similar to those of Caucasian populations previously reported in the literature.

Exome sequencing links corticospinal motor neuron disease to common neurodegenerative disorders.

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.

KIF1C mutations in two families with hereditary spastic paraparesis and cerebellar dysfunction.

BACKGROUND: Hereditary spastic paraparesis (HSP) (syn. Hereditary spastic paraplegia, SPG) are a group of genetic disorders characterised by spasticity of the lower limbs due to pyramidal tract dysfunction. Nearly 60 disease loci have been identified, which include mutations in two genes (KIF5A and KIF1A) that encode motor proteins of the kinesin superfamily. Here we report a novel genetic defect in KIF1C of patients with spastic paraparesis and cerebellar dysfunction in two consanguineous families of Palestinian and Moroccan ancestry. METHODS AND RESULTS: We performed autozygosity mapping in a Palestinian and classic linkage analysis in a Moroccan family and found a locus on chromosome 17 that had previously been associated with spastic ataxia type 2 (SPAX2, OMIM %611302). Whole-exome sequencing revealed two homozygous mutations in KIF1C that were absent among controls: a nonsense mutation (c.2191C>T, p.Arg731*) that segregated with the disease phenotype in the Palestinian kindred resulted in the entire absence of KIF1C protein from the patient's fibroblasts, and a missense variant (c.505C>T, p.Arg169Trp) affecting a conserved amino acid of the motor domain that was found in the Moroccan kindred. CONCLUSIONS: Kinesin genes encode a family of cargo/motor proteins and are known to cause HSP if mutated. Here we identified nonsense and missense mutations in a further member of this protein family. The KIF1C mutation is associated with a HSP subtype (SPAX2/SAX2) that combines spastic paraplegia and weakness with cerebellar dysfunction.

CLN6 p.I154del mutation causing late infantile neuronal ceroid lipofuscinosis in a large consanguineous Moroccan family.

The neuronal ceroid-lipofuscinosis (NCL) are a heterogeneous group of neurodegenerative diseases characterized by the lysosomal accumulation of ceroid and lipofuscin with mitochondrial ATP synthase subunit C in various tissues. Clinical features include progressive mental and motor deterioration, myoclonus, seizure, visual failure and premature death. Ten CLN genes have been identified, among them CLN6 genes for which 55 disease-causing mutations have already been reported. The authors describe here a large consanguineous Moroccan family with three affected patients due to the p.I154del mutation that has been exclusively reported in Portuguese patients. This is the first published report of a genetic study in a Moroccan family with NCL. A relatively inexpensive CLN6 mutation screening should be considered first in Morocco as an initial diagnosis step when the disease course is consistent with late infantile neuronal ceroid-lipofuscinosis.

Alteration of fatty-acid-metabolizing enzymes affects mitochondrial form and function in hereditary spastic paraplegia.

Hereditary spastic paraplegia (HSP) is considered one of the most heterogeneous groups of neurological disorders, both clinically and genetically. The disease comprises pure and complex forms that clinically include slowly progressive lower-limb spasticity resulting from degeneration of the corticospinal tract. At least 48 loci accounting for these diseases have been mapped to date, and mutations have been identified in 22 genes, most of which play a role in intracellular trafficking. Here, we identified mutations in two functionally related genes (DDHD1 and CYP2U1) in individuals with autosomal-recessive forms of HSP by using either the classical positional cloning or a combination of whole-genome linkage mapping and next-generation sequencing. Interestingly, three subjects with CYP2U1 mutations presented with a thin corpus callosum, white-matter abnormalities, and/or calcification of the basal ganglia. These genes code for two enzymes involved in fatty-acid metabolism, and we have demonstrated in human cells that the HSP pathophysiology includes alteration of mitochondrial architecture and bioenergetics with increased oxidative stress. Our combined results focus attention on lipid metabolism as a critical HSP pathway with a deleterious impact on mitochondrial bioenergetic function.

An autosomal recessive leucoencephalopathy with ischemic stroke, dysmorphic syndrome and retinitis pigmentosa maps to chromosome 17q24.2-25.3.

BACKGROUND: Single-gene disorders related to ischemic stroke seem to be an important cause of stroke in young patients without known risk factors. To identify new genes responsible of such diseases, we studied a consanguineous Moroccan family with three affected individuals displaying hereditary leucoencephalopathy with ischemic stroke, dysmorphic syndrome and retinitis pigmentosa that appears to segregate in autosomal recessive pattern. METHODS: All family members underwent neurological and radiological examinations. A genome wide search was conducted in this family using the ABI PRISM linkage mapping set version 2.5 from Applied Biosystems. Six candidate genes within the region linked to the disease were screened for mutations by direct sequencing. RESULTS: Evidence of linkage was obtained on chromosome 17q24.2-25.3. Analysis of recombination events and LOD score calculation suggests linkage of the responsible gene in a genetic interval of 11 Mb located between D17S789 and D17S1806 with a maximal multipoint LOD score of 2.90. Sequencing of seven candidate genes in this locus, ATP5H, FDXR, SLC25A19, MCT8, CYGB, KCNJ16 and GRIN2C, identified three missense mutations in the FDXR gene which were also found in a homozygous state in three healthy controls, suggesting that these variants are not disease-causing mutations in the family. CONCLUSION: A novel locus for leucoencephalopathy with ischemic stroke, dysmorphic syndrome and retinitis pigmentosa has been mapped to chromosome 17q24.2-25.3 in a consanguineous Moroccan family.

Refinement of the SPG15 candidate interval and phenotypic heterogeneity in three large Arab families.

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.

Spastic paraplegia 5: Locus refinement, candidate gene analysis and clinical description.

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.