Paula Byrne

SPG15, a new locus for autosomal recessive complicated HSP on chromosome 14q

The authors studied two families with autosomal recessive hereditary spastic paraplegia (HSP) complicated by the presence of additional symptoms of pigmented maculopathy, distal amyotrophy, dysarthria, mental retardation, and further intellectual deterioration. Evidence was obtained for linkage to a locus on chromosome 14q that is distinct from the SPG3 locus for autosomal dominant HSP (D14S77: lod score of 4.20 at zero recombination). Haplotype construction of nearby markers confirms the existence of this novel HSP locus (SPG15) and narrows it to a 19-cM interval flanked by D14S1038 and D14S61.

Age-related cognitive decline in hereditary spastic paraparesis linked to chromosome 2p

Objectives: To investigate whether cognitive decline is part of the phenotype of SPG4-linked hereditary spastic paraparesis (HSP) and to determine whether cognitive changes are present in haplotype carriers before the onset of paraparesis. Background: The major locus for “pure” autosomal dominant HSP is the SPG4 locus on chromosome 2p. Cognitive impairment linked to this locus has been described in two families. Methods: The authors identified 19 families with “pure” autosomal dominant HSP. Five had linkage to the SPG4 locus (maximum lod score for D2S2374: 5.99 at zero recombination in four smaller families and 3.86 at zero recombination in the largest family). Haplotype construction identified a disease haplotype for all families; 41 individuals carried this haplotype (30 affected by HSP, 11 unaffected). All haplotype carriers and 41 matched controls underwent Cambridge Cognitive (CAMCOG) examination. Nonparametric significance tests were used comparing total and subset scores. Results: Haplotype carriers affected by HSP had lower total CAMCOG scores than control subjects (85.86/107 versus 96.2/107; p < 0.0005). The subsets of orientation, memory, language expression, and comprehension were also significantly lower. Ten individuals had scores ≤80/107, indicating mild dementia. Unaffected haplotype carriers had mean total CAMCOG scores lower than control subjects (91.82/107 versus 98.09/107; p = 0.016). In both groups cognitive decline was age-dependent and scores diverged from control subjects from age 40. All SPG4-linked families showed the effect. Conclusion: Mild, age-related cognitive impairment is a feature common to these families. It illustrates variable phenotypic expression at this locus and may be the first manifestation of the disease gene in individuals as yet unaffected by paraparesis.

Phenotype of AD-HSP due to mutations in the SPAST gene Comparison with AD-HSP without mutations

Background: “Pure” autosomal dominant hereditary spastic paraparesis (AD-HSP) is clinically and genetically heterogeneous. There are at least seven genetic loci with varying ages at onset and disability. The SPAST gene at the SPG4 locus on chromosome 2p is the major disease gene for AD-HSP. Objectives: To investigate whether there are distinct clinical features among families with AD-HSP due to SPAST mutations compared with families excluded from SPG4. Methods: Nineteen families with “pure” AD-HSP were identified, and the clinical features of family members were compared using a standard protocol. With use of genetic studies, the families were divided into two groups for comparison: those with mutations in SPAST, the “mutation-positive” group, and those excluded from SPG4 on the basis of linkage studies, the “SPG4-excluded” group. Results: Twenty-nine individuals from four families had mutations in SPAST, whereas 22 individuals from three families comprised the SPG4-excluded group; in 11 families, the pattern of linkage was unknown. In the one remaining family, no mutations were found despite strong linkage to SPG4. Different mutations were identified in the four SPAST pedigrees, but the clinical picture was similar in each. Comparison of the mutation-positive group with the SPG4-excluded group revealed an older age at onset (p = 0.03), more disability (p = 0.001), more rapidly progressive paraparesis (p = 0.044), and more cognitive impairment (p = 0.024) among affected individuals with SPAST mutations, not confounded by disease duration. Conclusion: Despite different mutations, SPAST families have a similar phenotype that can be distinguished from other genetic groups.

The hereditary spastic paraplegia protein spartin localises to mitochondria

Hereditary spastic paraplegia describes a diverse group of disorders characterized by progressive paraparesis primarily affecting lower limbs. In Troyer syndrome, an autosomal recessive form of hereditary spastic paraplegia, patients have dysarthria, distal amyotrophy, developmental delay and short stature in addition to spastic paraparesis. It is caused by a frameshift mutation (1110delA) in SPG20 leading to premature truncation of spartin, a protein with no known function. The objective of this study was to determine the subcellular localization of spartin and investigate the effect of the 1110delA mutation. We observed cytoplasmic expression of spartin in all transfected cell lines. Using superimposed organelle markers or immunocytochemistry staining, we established that spartin localizes to mitochondria and that this localization is dependent on sequences in the C‐terminal region. Mutant spartin containing the 1110delA mutation has lost mitochondrial localization. Immunocytochemistry staining using anti‐alpha‐tubulin antibody provided evidence for partial co‐localization of spartin with microtubules. Analysis of fluorescence resonance energy transfer indicated that sequences in the amino terminal are important in mediating microtubule interaction. This study provides the first evidence of spartin subcellular localization and identifies it as the third mitochondrial protein implicated in hereditary spastic paraplegia. Our results suggest that Troyer syndrome may be due to defective microtubule‐mediated trafficking of mitochondria and/or mitochondrial dysfunction.

Further evidence of dementia in SPG4-linked autosomal dominant hereditary spastic paraplegia

Objective: To investigate the progression of cognitive impairment and its behavioral aspects in patients with SPG4-linked autosomal dominant hereditary spastic paraplegia (SPG4-ADHSP). Methods: Sixteen patients, 45 years or older, from five families with SPG4-ADHSP were prospectively assessed. Eleven of these, from three families, were followed and 10 had two cognitive examinations using the Cambridge Cognitive Assessment (CAMCOG) 2.9 years apart. The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE), the Neuropsychiatric Inventory (NPI), and the Nurses’ Observation Scale for Geriatric Patients (NOSGER) were completed by close relatives of the 11 patients at the second assessment. Eleven matched control subjects had CAMCOG examinations 3.1 years apart. Results: The mean CAMCOG score at the initial assessment was lower for the 10 HSP patients (73.5/107) than for 10 control subjects (91.7/107, p = 0.005). After 2.9 years, the HSP patients experienced a fall in the mean CAMCOG by 9.1 points to 64.4/107 (p = 0.008). The mean CAMCOG score for the control subjects (90.8/107) fell by only 0.9 points after 3.1 years (p = 0.36). The CAMCOG scores of two HSP patients moved from the mild (60 to 80) into the moderate dementia category (35 to 59) and in three other patients into the mild dementia range from borderline normal scores (81 to 85). IQCODE scores were abnormal in 9/11 HSP patients and 1/11 controls (p = 0.001). Seven of the 11 HSP patients were considered as having dementia. Conclusion: This study indicates an active progression of cognitive deterioration and dementia in older patients with SPG4-ADHSP.

Spastin, the most commonly mutated protein in hereditary spastic paraplegia interacts with Reticulon 1 an endoplasmic reticulum protein

Spastin, an ATPase belonging to the AAA family of proteins is most commonly mutated in autosomal dominant hereditary spastic paraplegias (HSP). Spastin is a multifaceted protein with versatile role in cellular events, principally involved in microtubule dynamics. To gain further insight into the molecular function of spastin, we used the yeast two-hybrid approach to identify novel interacting partners of spastin. Using spastin as bait, we identified reticulon 1 (RTN1) and reticulon 3 (RTN3) as potential spastin interacting proteins. RTN1 and RTN3 belong to the reticulon (RTN) gene family, which are primarily expressed in the endoplasmic reticulum. Moreover, RTN1 is known to play a role in vesicular transport processes. Using in vitro and in vivo immunoprecipitation experiments, we were able to demonstrate that RTN1 interacts specifically with spastin. Intracellular distribution studies using immunostaining and overexpression of epitope-tagged protein revealed an obvious colocalization of spastin and RTN1 in discrete vesicles in the cytoplasm. Spastin mediates its interaction with RTN1 through its N-terminal region containing a microtubule-interacting and trafficking domain. It is interesting to note that the aberrant intracellular distribution of a truncated spastin protein was rescued by coexpression with RTN1, which highlights the physiological significance of this interaction. Our findings strengthen the hypothesis that disruption of intracellular vesicular transport processes could cause HSP. It is interesting to note that RTN1 is localized to 14q23.1 where SPG15 locus was mapped. Therefore, we considered RTN1 as a candidate gene for the SPG15 locus, but our mutational analysis possibly excludes RTN1 as causative gene.

Linkage of AD HSP and cognitive impairment to chromosome 2p: haplotype and phenotype analysis indicates variable expression and low or delayed penetrance

We report linkage of a family affected with autosomal dominant hereditary spastic paraparesis (HSP) and/or cognitive impairment to the HSP locus on chromosome 2p. To date all families linked to this locus have been affected with ‘pure’ HSP. The specific pattern of cognitive impairment in this family is characterised primarily by deficits in visuo-spatial functions. We also present genetic studies that indicate variable expression and low or delayed penetrance. We have constructed a haplotype flanked by polymorphic markers D2S400 and D2S2331 that was present in 12 individuals affected with spastic paraparesis. The severity of spasticity varied markedly among these individuals. In addition four of these individuals (aged 62–70) also had a specific form of cognitive impairment. The disease haplotype was also present in an individual (age 57) who had an identical pattern of cognitive impairment as the only sign of the disease supporting the hypothesis that spastic paraparesis and cognitive impairment are the result of variable expression of a single gene (rather than a co-incidental occurrence). Haplotype reconstruction for all participating family members revealed the presence of this disease haplotype in six individuals who had normal neurological and neuropsychological examinations. All six are below the maximal age of onset in the family – 60 years. This is evidence for low or late penetrance of the AD HSP gene in this family. The identification of normal individuals carrying the disease haplotype demonstrates the importance of genetic studies in combination with clinical examination when counselling at risk family members.

Dementia in SPG4 hereditary spastic paraplegia: Clinical, genetic, and neuropathologic evidence

Background: Cognitive impairment and dementia has been reported in autosomal dominant hereditary spastic paraparesis (HSP) linked to the SPG4 locus. There has only been one postmortem examination described; not all accept that progressive cognitive decline is a feature of this disorder. Objective: A family with SPG4-HSP known to have a deletion of exon 17 in the spastin gene (SPG4delEx17) was cognitively assessed over a 7-year period. The index family member died and a postmortem examination was performed. Methods: Thirteen family members older than 40 years were clinically and cognitively assessed using the Cambridge Cognitive Assessment over a 7-year period. The presence of SPG4delEx17 was assessed; a neuropathologic examination of the brain of the index family member was performed. Results: Cognitive decline occurred in 6 of the 13 family members and in all 4 older than 60 years. Two genetic deletions were identified: SPG4delEx17 in 12 of the 13 family members and a deletion of SPG6 (SPG6del) in 5. Eight individuals had the SPG4delEx17 deletion only; 4 had evidence of progressive cognitive impairment. Four family members had both SPG4delEx17 and SPG6del; 2 of these had cognitive impairment. One family member with the SPG6del alone had neither HSP nor cognitive impairment. The index case with both deletions died with dementia; the brain showed widespread ubiquitin positivity within the neocortex and white matter. Conclusion: Cognitive decline and dementia is a feature of SPG4-HSP due to a deletion of exon 17 of the spastin gene.

Identification of novel spartin‐interactors shows spartin is a multifunctional protein

Hereditary spastic paraplegia describes a group of neurodegenerative diseases characterized by lower limb progressive weakness and spasticity. Troyer syndrome is an autosomal recessive form of hereditary spastic paraplegia caused by a frameshift mutation (1110delA) in the SPG20 gene encoding spartin protein, the cellular function of which remains unknown. Knowledge about spartin‐interactors is also very limited. In this study, we apply a broad spectrum of proteomics techniques to identify novel spartin‐binding proteins. We used a Tandem Affinity Purification technique followed by HPLC‐mass spectrometry to characterize potential spartin‐binding partners. Selected putative interactions were confirmed by co‐immunoprecipitation experiments. We identified 94 potential spartin‐binding proteins which were grouped into functional categories. We performed co‐immunoprecipitation experiments to confirm that spartin interacts with GRP78, GRP75 and nucleolin proteins. Additionally, our mass spectrometry results confirmed previously published information about spartin interaction with ubiquitin and the E3 ubiquitin‐protein ligases, AIP4/Itch and AIP5/WWP1. Our studies suggest that spartin is a multifunctional protein and for the first time we suggest a role for spartin in protein folding and turnover both in mitochondria and endoplasmic reticulum. We also show for the first time interaction between spartin and a nucleolar protein, nucleolin.

Health locus of control and attributions of cause and blame in adjustment to spinal cord injury.

Study design:The Symptom Checklist 90 Revised (SCL-90-R) was used to assign participants to either a good adjustment group or a poor adjustment group. Group differences were analyzed with χ 2, t-tests and correlations on factors shown in previous research to be related to coping with spinal cord injury (SCI).Objectives:This study examines health locus of control (HLC) and attributions of cause and blame in relation to SCI. The replication of study findings in multiple settings is a cornerstone of the evidence base for developing interventions. Previous studies do not show a consensus on the role of attributions of cause and blame in persons with SCI. Similarly, their relationship to adjustment after SCI is unclear. Another attribution, HLC, is similarly analyzed in relation to adjustment.Setting:Republic of Ireland.Methods:Thirty people with SCI participated. They rated scales measuring psychological adjustment, locus of control (LOC) for health and attributions of cause and blame for the injury.Results:The well-adjusted group had a less external HLC. In addition, participants who were well adjusted endorsed the notion they could have avoided their accident significantly more than the poorly adjusted group. Similarly, they rated the belief that they could have caused the accident at a somewhat greater level. They did not, however, blame themselves any more or any less.Conclusion:Results are consistent with general LOC theory, and suggest an adaptive or protective internal LOC for accepting responsibility for the injury.