P C Byrne

St Vincent's University Hospital, Dublin, Leinster, Ireland

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Publications (17)90.54 Total impact

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    ABSTRACT: Mutations in the receptor expression enhancing protein 1 (REEP1) have recently been reported to cause autosomal dominant hereditary spastic paraplegia (HSP) type SPG31. In a large collaborative effort, we screened a sample of 535 unrelated HSP patients for REEP1 mutations and copy number variations. We identified 13 novel and 2 known REEP1 mutations in 16 familial and sporadic patients by direct sequencing analysis. Twelve out of 16 mutations were small insertions, deletions or splice site mutations. These changes would result in shifts of the open-reading-frame followed by premature termination of translation and haploinsufficiency. Interestingly, we identified two disease associated variations in the 3'-UTR of REEP1 that fell into highly conserved micro RNA binding sites. Copy number variation analysis in a subset of 133 HSP index patients revealed a large duplication of REEP1 that involved exons 2-7 in an Irish family. Clinically most SPG31 patients present with a pure spastic paraplegia; rare complicating features were restricted to symptoms or signs of peripheral nerve involvement. Interestingly, the distribution of age at onset suggested a bimodal pattern with the appearance of initial symptoms of disease either before the age of 20 years or after the age of 30 years. The overall mutation rate in our clinically heterogeneous sample was 3.0%; however, in the sub-sample of pure HSP REEP1 mutations accounted for 8.2% of all patients. These results firmly establish REEP1 as a relatively frequent autosomal dominant HSP gene for which genetic testing is warranted. We also establish haploinsufficiency as the main molecular genetic mechanism in SPG31, which should initiate and guide functional studies on REEP1 with a focus on loss-of-function mechanisms. Our results should be valid as a reference for mutation frequency, spectrum of REEP1 mutations, and clinical phenotypes associated with SPG31.
    Brain 05/2008; 131(Pt 4):1078-86. · 9.92 Impact Factor
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    ABSTRACT: Hereditary spastic paraplegias (HSPs) are genetically and phenotypically heterogeneous disorders. Both "uncomplicated" and "complicated" forms have been described with various modes of inheritance. Sixteen loci for autosomal-recessive "complicated" HSP have been mapped. The SPG15 locus was first reported to account for a rare form of spastic paraplegia variably associated with mental impairment, pigmented maculopathy, dysarthria, cerebellar signs, and distal amyotrophy, sometimes designated as Kjellin syndrome. Here, we report the refinement of SPG15 to a 2.64 Mb genetic interval on chromosome 14q23.3-q24.2 and the identification of ZFYVE26, which encodes a zinc-finger protein with a FYVE domain that we named spastizin, as the cause of SPG15. Six different truncating mutations were found to segregate with the disease in eight families with a phenotype that included variable clinical features of Kjellin syndrome. ZFYVE26 mRNA was widely distributed in human tissues, as well as in rat embryos, suggesting a possible role of this gene during embryonic development. In the adult rodent brain, its expression profile closely resembled that of SPG11, another gene responsible for complicated HSP. In cultured cells, spastizin colocalized partially with markers of endoplasmic reticulum and endosomes, suggesting a role in intracellular trafficking.
    The American Journal of Human Genetics 05/2008; 82(4):992-1002. · 11.20 Impact Factor
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    Human Mutation 08/2007; 28(7):739-40. · 5.21 Impact Factor
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    ABSTRACT: To investigate the progression of cognitive impairment and its behavioral aspects in patients with SPG4-linked autosomal dominant hereditary spastic paraplegia (SPG4-ADHSP). 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. 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. This study indicates an active progression of cognitive deterioration and dementia in older patients with SPG4-ADHSP.
    Neurology 03/2004; 62(3):407-10. · 8.25 Impact Factor
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    ABSTRACT: 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.
    Neurology 06/2001; 56(9):1230-3. · 8.25 Impact Factor
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    ABSTRACT: "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. To investigate whether there are distinct clinical features among families with AD-HSP due to SPAST mutations compared with families excluded from SPG4. 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. 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. Despite different mutations, SPAST families have a similar phenotype that can be distinguished from other genetic groups.
    Neurology 01/2001; 55(12):1794-800. · 8.25 Impact Factor
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    ABSTRACT: Autosomal dominant hereditary spastic paraplegia (AD-HSP) is a group of genetically heterogeneous neurodegenerative disorders characterized by pro- gressive spasticity of the lower limbs. Five AD-HSP loci have been mapped to chromosomes 14q, 2p, 15q, 8q and 12q. The SPG4 locus at 2p21-p22 has been shown to account for approximately 40% of all AD-HSP families. SPG4 encoding spastin, a putative nuclear AAA protein, has recently been identified. Here, sequence analysis of the 17 exons of SPG4 in 87 unrelated AD-HSP patients has resulted in the detection of 34 novel mutations. These SPG4 mutations are scattered along the coding region of the gene and include all types of DNA modification including missense (28%), nonsense (15%) and splice site point (26.5%) mutations as well as deletions (23%) and insertions (7.5%). The clinical analysis of the 238 mutation carriers revealed a high proportion of both asymptomatic carriers (14/238) and patients unaware of symptoms (45/238), and permitted the redefinition of this frequent form of AD-HSP.
    Human Molecular Genetics 04/2000; · 7.69 Impact Factor
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    ABSTRACT: 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. 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. 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. 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 < or =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. 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.
    Neurology 04/2000; 54(7):1510-7. · 8.25 Impact Factor
  • Advances in Enzyme Regulation 02/2000; 40:353-403.
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    ABSTRACT: 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.
    European Journal of HumanGenetics 01/1998; 6(3):275-82. · 4.32 Impact Factor
  • Irish Journal of Medical Science 10/1997; 166(4). · 0.51 Impact Factor
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    ABSTRACT: The conversion of serine and tetrahydrofolate to glycine and 5,10 methylene tetrahydrofolate by serine hydroxymethyltransferase (SHMT, EC 2.1.2.1) is the major route for the provision of one-carbon units for biosynthetic reactions. SHMT cDNAs have been cloned from both rabbit and man, and a human mitochondrial SHMT gene sequence has recently been reported. We have isolated phage clones containing human genomic sequences homologous to cytosolic SHMT and have found these to contain a processed pseudogene (SHMT-psl) with a 90% identity to cloned SHMT cDNAs. SHMT ps1 contains 2335 nt that are homologous to SHMT but it has an additional leader sequence of 203 nt of unknown origin. The complete SHMT-ps.1 sequence of 2538 nt is bounded by two 16 nt direct repeats that are characteristic of retroelement insertion sites. Two phage clones containing SHMT-ps1 have been mapped by fluorescence in situ hybridisation to 1p32.3–33. ln addition, an SHMT cDNA clone hybridized to the same region and to 17p11.2–12. The latter is consistent with a previous localisation of the gene for cytosolic SHMT.
    Human Genetics 02/1996; 97(3):340-344. · 4.63 Impact Factor
  • K Snell, P C Byrne, P G Sanders
    Biochemical Society Transactions 12/1995; 23(4):623S. · 2.59 Impact Factor
  • P C Byrne, P G Sanders, K Snell
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    ABSTRACT: We have investigated the role of an open reading frame upstream of and overlapping that coding for rabbit cytosolic serine hydroxymethyltransferase in the post-transcriptional regulation of enzyme expression. Elimination of the AUG codon initiating translation of the upstream open reading frame by site-directed mutagenesis (to an AUC codon) was assessed by a transfection assay in COS-1 cells. The mutation relieves translational repression with a 100-fold increase in expressed serine hydroxymethyltransferase activity compared to control-transfected cells and in the absence of any increase in the level of serine hydroxymethyltransferase mRNA. The upstream open reading frame may play a regulatory role in changing levels of expression of serine hydroxymethyltransferase through a translational control mechanism.
    Biochemical and Biophysical Research Communications 10/1995; 214(2):496-502. · 2.41 Impact Factor
  • Advances in experimental medicine and biology 02/1994; 370:739. · 1.83 Impact Factor
  • P C Byrne, P G Sanders, K Snell
    Biochemical Society Transactions 03/1993; 21(1):36S. · 2.59 Impact Factor
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    P C Byrne, P G Sanders, K Snell
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    ABSTRACT: A rabbit liver cDNA library in phage lambda gt10 was screened using a portion of the coding sequences for rabbit cytosolic serine hydroxymethyltransferase (amino acids 244-420) that had been amplified by PCR, with total rabbit liver RNA as a template. A clone of 2.3 kb (pUS1203) was isolated and the nucleotide sequence showed that it contained an open reading frame of 1452 bp, which coded for serine hydroxymethyltransferase and was flanked by 155 bp at the 5' end and 653 bp at the 3' end. The full-length cDNA was cloned into an expression vector and transfected into COS-1 cells. Serine hydroxymethyltransferase activity was increased by 33% in the transfected cells and a new protein band of the appropriate size was seen by SDS/PAGE analysis of proteins extracted from transfected cells. The protein sequence for rabbit cytosolic serine hydroxymethyltransferase derived from the cDNA nucleotide sequence was compared with three other derived or known prokaryotic and eukaryotic sequences. An overall sequence similarity of 34% was noted between all four sequences, whereas the similarity between the rabbit cytosolic and mitochondrial isoforms was 62%.
    Biochemical Journal 09/1992; 286 ( Pt 1):117-23. · 4.65 Impact Factor

Publication Stats

359 Citations
90.54 Total Impact Points

Institutions

  • 2000
    • St Vincent's University Hospital
      Dublin, Leinster, Ireland
  • 1998–2000
    • University College Dublin
      Dublin, Leinster, Ireland
  • 1992–1996
    • University of Surrey
      Guilford, England, United Kingdom
  • 1994–1995
    • Institute of Cancer Research
      Londinium, England, United Kingdom