Hereditary spastic paraplegia associated with thin corpus callosum

Unexpected complexity in the molecular diagnosis of spastic paraplegia 11

BACKGROUND

Spastic paraplegia 11 (SPG11) is the most prevalent form of autosomal recessive hereditary spastic paraplegia, resulting from biallelic pathogenic variants in the SPG11 gene (MIM *610844).

METHODS

The proband is a 36-year-old female referred for genetic evaluation due to cognitive dysfunction, gait impairment, and corpus callosum atrophy (brain MRI was normal at 25-years-old). Diagnostic approaches included CGH array, next-generation sequencing, and whole transcriptome sequencing.

RESULTS

CGH array revealed a 180 kb deletion located upstream of SPG11. Sequencing of SPG11 uncovered two rare single nucleotide variants: the novel variant c.3143C>T in exon 17 (in cis with the deletion), and the previously reported pathogenic variant c.6409C>T in exon 34 (in trans). Whole transcriptome sequencing revealed that the variant c.3143C>T caused exon 17 skipping.

CONCLUSION

We report a novel sequence variant in the SPG11 gene resulting in exon 17 skipping, which, along with a nonsense variant, causes Spastic Paraplegia 11 in our proband. In addition, a deletion upstream of SPG11 was identified in the patient, whose implication in the phenotype remains uncertain. Nonetheless, the deletion apparently affects cis-regulatory elements of the gene, suggesting a potential new pathogenic mechanism underlying the disease in a subset of undiagnosed patients. Our findings further support the hypothesis that the origin of thin corpus callosum in patients with SPG11 is of progressive nature.

Janus-faced spatacsin (SPG11): involvement in neurodevelopment and multisystem neurodegeneration

Hereditary spastic paraplegia (HSP) is a heterogeneous group of rare motor neuron disorders characterized by progressive weakness and spasticity of the lower limbs. HSP type 11 (SPG11-HSP) is linked to pathogenic variants in the SPG11 gene and it represents the most frequent form of complex autosomal recessive HSP. The majority of SPG11-HSP patients exhibit additional neurological symptoms such as cognitive decline, thin corpus callosum, and peripheral neuropathy. Yet, the mechanisms of SPG11-linked spectrum diseases are largely unknown. Recent findings indicate that spatacsin, the 280 kDa protein encoded by SPG11, may impact the autophagy-lysosomal machinery. In this update, we summarize the current knowledge of SPG11-HSP. In addition to clinical symptoms and differential diagnosis, our work aims to link the different clinical manifestations with the respective structural abnormalities and cellular in vitro phenotypes. Moreover, we describe the impact of localization and function of spatacsin in different neuronal systems. Ultimately, we propose a model in which spatacsin bridges between neurodevelopmental and neurodegenerative phenotypes of SPG11-linked disorders.

A new locus (SPG47) maps to 1p13.2-1p12 in an Arabic family with complicated autosomal recessive hereditary spastic paraplegia and thin corpus callosum

The hereditary spastic paraplegias (HSP) are a heterogeneous group of genetic neurodegenerative disorders in which the main feature is progressive spasticity of the lower limbs due to pyramidal tract dysfunction. Clinically HSP are divided into two forms: a pure form that presents with progressive lower limb spasticity and weakness, sensory signs and bladder dysfunction, and a complicated form, associated with more extensive neurological and extra neurological signs as well as pathological findings on brain imaging. The clinical variability observed in HSP is supported by the large underlying genetic heterogeneity. Hereditary spastic paraplegia with thin corpus callosum (HSP-TCC) is a frequent subtype of complicated HSP clinically characterized by a slowly progressive spastic paraparesis with cognitive impairment and thin corpus callosum (TCC). SPG11, the most frequent gene associated with HSP-TCC, encodes spatacsin, a protein of unknown function. We describe two siblings from an Arabic consanguineous family with slowly progressive spastic paraparesis, mental retardation, seizures, thin corpus callosum and periventricular white matter abnormalities. Homozygosity mapping identified a novel single candidate region of 7.3 Mb on chromosome 1p13.2-1p12. The finding of a new locus for AR-HSP-TCC further demonstrates the extensive genetic heterogeneity of this condition.

MR imaging findings in autosomal recessive hereditary spastic paraplegia

BACKGROUND AND PURPOSE

Hereditary spastic paraplegia (HSP) is a disorder characterized by degeneration of the corticospinal tracts and posterior column of the spinal cord. Previously described radiologic findings included nonspecific brain abnormalities such as brain atrophy and white matter lesions, as well as atrophy of the spinal cord. In our study, we aimed to better characterize brain and spine MR imaging findings in a series of patients with HSP.

MATERIALS AND METHODS

Nine patients from 4 different Lebanese families with the autosomal recessive form of HSP were included in the study. All patients underwent brain and whole-spine MR imaging. We assessed the presence of white matter abnormalities mainly along the corticospinal tracts, brain atrophy, thinning of the corpus callosum, and the presence of spinal cord atrophy or abnormal signal intensity.

RESULTS

Imaging revealed mild brain atrophy (44%), atrophy of the corpus callosum (55%), white matter lesions (67%), abnormal T2 high signal intensity in the posterior limb of the internal capsule (55%), and mild spinal cord atrophy (33%).

CONCLUSIONS

The MR imaging findings of HSP are nonspecific and variable; however, the most prominent features include atrophy of the corpus callosum, T2 signal intensity in the posterior limb of the internal capsule, and spinal cord atrophy.

Hereditary spastic paraplegia with hypoplastic corpus callosum in a Turkish family

Hereditary spastic paraplegia is composed of a heterogeneous group of neurodegenerative disorders and is classified as pure or complicated due to its clinical variability. Autosomal recessive hereditary spastic paraplegia with hypoplastic corpus callosum is a rare form of complicated hereditary spastic paraplegia. In complicated hereditary spastic paraplegia, autosomal dominant, autosomal recessive, and X-linked modes of inheritance have been noted. The diagnostic criteria of autosomal recessive hereditary spastic paraplegia with hypoplastic corpus callosum are inheritance consistent with autosomal recessive trait, slowly progressive spastic paraparesis and mental detoriation, hypoplasia of corpus callosum revealed by brain computerized tomography or magnetic resonance imaging, and exclusion of other disorders by magnetic resonance imaging of the spine and brain as well as other laboratory tests. In this report, the authors present the case of 3 affected siblings in a family from Turkey, whereas 1 child and the con-sanguineous parents were healthy. To the authors' knowledge, it is the first reported case of autosomal recessive hereditary spastic paraplegia with hypoplastic corpus callosum from Turkey.

Thin corpus callosum and amyotrophy in spastic paraplegia—Case report and review of literature

We report the clinical, structural, functional and genetic characterization of a 37-year-old Caucasian female, presenting as a sporadic case of complicated spastic paraplegia with thin corpus callosum (CC), cognitive impairment, amyotrophy of the hand muscles and a sensorimotor neuropathy and review the literature for spastic paraplegia with thin CC. Magnetic resonance imaging (MRI) examination revealed a thin CC with fronto-parietal cortical atrophy. 18Fluordesoxyglucose positron emission tomography (FDG-PET) showed reduced cortical and thalamic metabolism. By transcranial magnetic stimulation, we delineated a severe impairment of transcallosal inhibition. Sequence analysis did not reveal disease causing mutations in the genes SLC12A6 (Andermann), Spastin (SPG 4), BSCL2 (SPG 17) and Spartin (SPG 20). We reviewed the literature for HSP with thin CC and found 113 HSP patients with thin CC previously described (35 with linkage to chromosome 15q13-15). Thin CC and peripheral neuropathy often appear together in spastic paraplegia and might be indicative for combined degeneration mechanism of central and peripheral axons.

Spastic paraplegia with thin corpus callosum: description of 20 new families, refinement of the SPG11 locus, candidate gene analysis and evidence of genetic heterogeneity

We studied 20 Mediterranean families (40 patients) with autosomal recessive hereditary spastic paraplegia and thin corpus callosum (ARHSP-TCC, MIM 604360) to characterize their clinical and genetic features. In six families (17 patients) of Algerian Italian, Moroccan, and Portuguese ancestry, we found data consistent with linkage to the SPG11 locus on chromosome 15q13-15, whereas, in four families (nine patients of Italian, French, and Portuguese ancestry) linkage to the SPG11 locus could firmly be excluded, reinforcing the notion that ARHSP-TCC is genetically heterogeneous. Patients from linked and unlinked families could not be distinguished on the basis of clinical features alone. In SPG11-linked kindred, haplotype reconstruction allowed significant refinement to 6 cM, of the minimal chromosomal interval, but analysis of two genes (MAP1A and SEMA6D) in this region did not identify causative mutations. Our findings suggest that ARHSP-TCC is the most frequent form of ARHSP in Mediterranean countries and that it is particularly frequent in Italy.