Chokri Mhiri

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.

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 β-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.

SPG15 is the second most common cause of hereditary spastic paraplegia with thin corpus callosum

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.

Tunisian hereditary spastic paraplegias: clinical variability supported by genetic heterogeneity

Hereditary spastic paraplegias (HSP) constitute a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by slowly progressive spasticity of the lower extremities. We performed the first clinical, epidemiological and genetic study of HSP in Southern Tunisia. We investigated 88 patients belonging to 38 unrelated Tunisian HSP families. We could establish the minimal prevalence of HSP in the district of Sfax at 5.75/100,000. Thirty‐one percent of the families had a pure HSP, whereas 69% had a complicated form. The mode of inheritance was almost exclusively compatible with an autosomal recessive trait (97%, 37/38). Taking into account previously published results and new data generated in this work, genetic studies revealed significant or putative linkage to known HSP loci in 13 families (34.2%) to either SPG11 (7/38, 18.4%), SPG15 (4/38, 10.5%) or to SPG4 and SPG5 in one family each. The linkage results could be validated through the identification of two recurrent truncating mutations (R2034X and M245VfsX246) in the SPG11 gene, three different mutations (Q493X, F683LfsX685 and the novel S2004T/r.?) in the SPG15 gene, the recurrent R499C mutation in the SPG4 gene as well as the new R112X mutation in the SPG5 gene. SPG11 and SPG15 are the major responsible HSP genes in Tunisia.

Epidemic West Nile Virus Encephalitis in Tunisia

West Nile fever (WNF) is a mosquito-borne flavivirus infection. It is epidemic in Africa and Asia. In autumn 1997, a WNF epidemic occurred in the Sfax area (southeastern Tunisia). Fifty-seven patients were hospitalized with aseptic meningitis and/or encephalitis. Search for specific anti-West Nile virus (WNV) antibodies in serum and cerebrospinal fluid (CSF) was performed using an ELISA test. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the WNV genome in CSF and brain specimens. Recent central nervous system (CNS) infection by WNV was confirmed in 30 patients, probable infection in 17 and it was excluded in 10. In the confirmed subgroup, patients with encephalitis were older than those with meningitis. CSF showed pleocytosis, high protein (47%) and normal glucose levels. Brain computed tomography-scan (CT-scan) and magnetic resonance imaging (MRI) were normal. RT-PCR disclosed WNV genome in the CSF in two cases and in a brain specimen in one. Three patients died rapidly, the remaining cases had favorable prognosis. Autopsy was performed in two cases and showed nonspecific lesions of encephalitis. No viral inclusions were seen with light microscopy. Seropositivity rate in patients’ proxies for WNV was 23.4%. Prognosis of CNS involvement during WNF seemed to be poor in older patients. This is the first WNV encephalitis epidemic report in the Sfax area of Tunisia.

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 Kjellins 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.

Clinical features and disability progression in multiple sclerosis in Tunisia: Do we really have a more aggressive disease course?

BACKGROUND Few epidemiological data are available on multiple sclerosis (MS) patients in North Africa (NA). Studies of immigrants from NA showed a more aggressive course compared to European patients. OBJECTIVE The aim of this study is to describe clinical and long term course characteristics of MS in Tunisia and to compare it to European cohorts. METHOD A total of 437 MS patients from three hospital based cohorts in Tunisia and having prospective follow up between 2010 and 2012 were analyzed. We considered as endpoints the time to reach EDSS scores of 3, 4 and 6 in the different clinical forms of MS and the beginning of a secondary progressive (SP) phase. RESULTS Sex ratio was 2.34. Mean age of onset was 30.3 years. The course was relapsing-remitting (RR) in 91% of patients and primary progressive (PP) in 9%. The most frequent isolated onset symptoms were respectively motor (28%), optic neuritis (20%) and sensory (16%) dysfunction. Median time to SP onset was 19.1 years. Median times from onset of multiple sclerosis to assignment of a score of 3, 4 and 6 were 8, 10.7 and 15 years respectively. Benign form of MS represented 31.5%. Median interval from the onset of the disease to EDSS score of 3, 4 and 6 was shorter in PP-MS than in RR-MS. However, there was no difference between these two groups for the median time from the assignment of EDSS 4 to the assignment EDSS 6. CONCLUSIONS Our study shows that Tunisian MS patients have a quite similar clinical feature to European patients. Still, larger MS multicenter cohort studies in NA with longer follow-up duration could clearly respond to the issue.

Using KASP technique to screen LRRK2 G2019S mutation in a large Tunisian cohort

BackgroundIn North African populations, G2019S mutation in LRRK2 gene, encoding for the leucine-rich repeat kinase 2, is the most prevalent mutation linked to familial and sporadic Parkinson’s disease (PD). Early detection of G2019S by fast genetic testing is very important to guide PD’s diagnosis and support patients and their family caregivers for better management of their life according to disease’s evolution.MethodsIn our study, a genetic PD’s diagnosis tool was developed for large scale genotyping using Kompetitive Allele Specific PCR (KASP) technology. We investigated G2019S’s frequency in 250 Tunisian PD patients and 218 controls.ResultsWe found that 33.6% of patients and 1.3% of controls were carriers. Demographic characteristics of patients with G2019S had no differences compared with non-carrier patients. Thereby, we could emphasize the implication of G2019S in PD without any distinctive demographic factors in the studied cohort. Sixty patients out of 250 were genotyped using Taqman assay and Sanger sequencing. The genotyping results were found to be concordant with KASP assay.ConclusionsThe G2019S mutation frequency in our cohort was similar to that reported in previous studies. Comparing to Taqman assay and Sanger sequencing, KASP was shown to be a reliable, time and cost effective genotyping assay for routine G2019S screening in genetic testing laboratories.

Acute aortic dissection presenting as painless paraplegia: a case report.

BackgroundAcute aortic dissection is an extreme emergency that is generally manifested by violent chest pain irradiating to a patient’s back and abdomen. Paraplegia due to spinal cord ischemia and infarction as a presenting manifestation of aortic dissection has been found in 2 to 5 % of patients. However, painless paraplegia is exceedingly rare and limited to a few case reports in the literature. We describe a new case with this unusual presentation of aortic dissection and here we emphasize that this condition must be considered in all patients with painless paraplegia.Case presentationA 70-year-old Arab man with no previous known medical or surgical conditions was hospitalized for brutal heaviness of his lower limbs associated to urinary retention. A neurological examination revealed flaccid paraplegia without sensory disorder. His blood pressure and his pulse were in normal ranges. He was afebrile. His peripheral pulses were not checked. Laboratory investigations eliminated multiple organ failure. Spinal magnetic resonance imaging realized in emergency was normal. He had a cardiopulmonary arrest 1 day after his hospitalization. His autopsy report concluded a type A aortic dissection with an intimal tear at his aortic isthmus with intrapericardial rupture and extension to his intercostal and lumbar arteries.ConclusionsAcute aortic dissection is an extreme emergency that can lead to death unless there is an early diagnosis. It must be considered in any patient with paraplegia even painless. Clinical examination has a major role to play in diagnosing this condition. Apart from the neurological examination, palpation of peripheral pulses and blood pressure measurements in all four limbs is of paramount importance. Then further investigations must be carried out consisting of aortic angiography by computed tomography or by magnetic resonance imaging.

Nouvelle mutation du gène ATP7B responsable d’une maladie de Wilson avec atteinte neurologique sévère

Fig. 1 – Arbre généalogique. Le symbole d’individu noir correspond au sujet atteint (flèche : cas index ; carré hachuré : frère probablement atteint ; * : sujets prélevés). Family pedigree (black symbol: affected member; arrow: index case; hatched square: probable affected brother; *: individuals for whom DNA was available). Nouvelle mutation du gène ATP7B responsable d’une maladie de Wilson avec atteinte neurologique sévère