A novel form of autosomal recessive hereditary spastic paraplegia caused by a new SPG7 mutation.
ABSTRACT Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous neurodegenerative disorder characterized by progressive spastic paraparesis of the lower limbs.
To identify the genotype and characterize the phenotype in a family with a novel form of complicated autosomal recessive hereditary spastic paraparesis (ARHSP).
Six subjects of a Turkish family were examined by clinical evaluation, detailed neuropsychological testing, neurophysiologic studies, MRI, diffusion tensor imaging (DTI), and mutation analysis of SPG7 gene.
Three individuals were affected by a juvenile-onset form of complicated ARHSP due to the missense mutation c.2075G>C in exon 15 of the SPG7 gene in the homozygous state, substituting serine with threonine at codon 692. As additional clinical features, cerebellar syndrome, supranuclear palsy, and cognitive impairment, particularly disturbance of attention and executive functions, were found. MRI showed cerebellar atrophy and mild frontal cerebral atrophy. DTI revealed bilateral disturbance of white matter integrity in corticospinal tracts, frontal lobes, and the midbrain.
The new SPG7 gene mutation leads to a novel complicated autosomal recessive hereditary spastic paraparesis phenotype that widens the spectrum of different brain systems that are optionally affected in hereditary spastic paraplegia (HSP). In this novel phenotype, spastic paraparesis is related to cerebral damage of corticospinal tracts. Impairment of attention and executive functions is due to white matter loss in frontal lobes. Furthermore, supranuclear palsy is caused by white matter damage in the midbrain. This multisystem affection, which was detected by the use of diffusion tensor imaging, may reflect a mitochondrial dysfunction that contributes to the underlying pathogenesis of SPG7-HSP.
- Journal of neurology. 07/2014;
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ABSTRACT: Spastic paraplegia 7 is an autosomal recessive disorder caused by mutations in the gene encoding paraplegin, a protein located at the inner mitochondrial membrane and involved in the processing of other mitochondrial proteins. The mechanism whereby paraplegin mutations cause disease is unknown. We studied two female and two male adult patients from two Norwegian families with a combination of progressive external ophthalmoplegia and spastic paraplegia. Sequencing of SPG7 revealed a novel missense mutation, c.2102A>C, p.H 701P, which was homozygous in one family and compound heterozygous in trans with a known pathogenic mutation c.1454_1462del in the other. Muscle was examined from an additional, unrelated adult female patient with a similar phenotype caused by a homozygous c.1047insC mutation in SPG7. Immunohistochemical studies in skeletal muscle showed mosaic deficiency predominantly affecting respiratory complex I, but also complexes III and IV. Molecular studies in single, microdissected fibres showed multiple mitochondrial DNA deletions segregating at high levels (38-97%) in respiratory deficient fibres. Our findings demonstrate for the first time that paraplegin mutations cause accumulation of mitochondrial DNA damage and multiple respiratory chain deficiencies. While paraplegin is not known to be directly associated with the mitochondrial nucleoid, it is known to process other mitochondrial proteins and it is possible therefore that paraplegin mutations lead to mitochondrial DNA deletions by impairing proteins involved in the homeostasis of the mitochondrial genome. These studies increase our understanding of the molecular pathogenesis of SPG7 mutations and suggest that SPG7 testing should be included in the diagnostic workup of autosomal recessive, progressive external ophthalmoplegia, especially if spasticity is present.PLoS ONE 01/2014; 9(1):e86340. · 3.53 Impact Factor
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ABSTRACT: Mutations in the spastic paraplegia 7 (SPG7) gene encoding paraplegin are responsible for autosomal recessive hereditary spasticity. We screened 135 unrelated index cases, selected in five different settings: SPG7-positive patients detected during SPG31 analysis using SPG31/SPG7 multiplex ligation-dependent probe amplification (n = 7); previously reported ambiguous SPG7 cases (n = 5); patients carefully selected on the basis of their phenotype (spasticity of the lower limbs with cerebellar signs and/or cerebellar atrophy on magnetic resonance imaging/computer tomography scan and/or optic neuropathy and without other signs) (n = 24); patients with hereditary spastic paraparesis referred consecutively from attending neurologists and the national reference centre in a diagnostic setting (n = 98); and the index case of a four-generation family with autosomal dominant optic neuropathy but no spasticity linked to the SPG7 locus. We identified two SPG7 mutations in 23/134 spastic patients, 21% of the patients selected according to phenotype but only 8% of those referred directly. Our results confirm the pathogenicity of Ala510Val, which was the most frequent mutation in our series (65%) and segregated at the homozygous state with spastic paraparesis in a large family with autosomal recessive inheritance. All SPG7-positive patients tested had optic neuropathy or abnormalities revealed by optical coherence tomography, indicating that abnormalities in optical coherence tomography could be a clinical biomarker for SPG7 testing. In addition, the presence of late-onset very slowly progressive spastic gait (median age 39 years, range 18-52 years) associated with cerebellar ataxia (39%) or cerebellar atrophy (47%) constitute, with abnormal optical coherence tomography, key features pointing towards SPG7-testing. Interestingly, three relatives of patients with heterozygote SPG7 mutations had cerebellar signs and atrophy, or peripheral neuropathy, but no spasticity of the lower limbs, suggesting that SPG7 mutations at the heterozygous state might predispose to late-onset neurodegenerative disorders, mimicking autosomal dominant inheritance. Finally, a novel missense SPG7 mutation at the heterozygous state (Asp411Ala) was identified as the cause of autosomal dominant optic neuropathy in a large family, indicating that some SPG7 mutations can occasionally be dominantly inherited and be an uncommon cause of isolated optic neuropathy. Altogether, these results emphasize the clinical variability associated with SPG7 mutations, ranging from optic neuropathy to spastic paraplegia, and support the view that SPG7 screening should be carried out in both conditions.Brain 10/2012; 135(Pt 10):2980-93. · 10.23 Impact Factor