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Background: Huntington’s disease is caused by expansion of a polyglutamine tract found in the amino-terminal of the ubiquitously expressed protein huntingtin. Well studied in its mutant form, huntingtin has a wide variety of normal functions, loss of which may also contribute to disease progression. Widespread transcriptional dysfunction occurs in brains of Huntington’s disease patients and in transgenic mouse and cell models of Huntington’s disease. Methods: To identify new transcriptional pathways altered by the normal and/or abnormal function of huntingtin, we probed several nuclear receptors, normally expressed in the brain, for binding to huntingtin in its mutant and wild-type forms. Results: Wild-type huntingtin could bind to a number of nuclear receptors; LXRα, PPARγ, VDR and TRα1. Over-expression of huntingtin activated, while knockout of huntingtin decreased, LXR mediated transcription of a reporter gene. Loss of huntingtin also decreased expression of the LXR target gene, ABCA1. In vivo, huntingtin deficient zebrafish had a severe phenotype and reduced expression of LXR regulated genes. An LXR agonist was able to partially rescue the phenotype and the expression of LXR target genes in huntingtin deficient zebrafish during early development. Conclusion: Our data suggest a novel function for wild-type huntingtin as a co-factor of LXR. However, this activity is lost by mutant huntingtin that only interacts weakly with LXR.

Codon reiteration disorders are caused by abnormal expansions of either polyglutamine or polyalanine tracts within the coding region of a protein. These mutations impair normal protein folding, resulting in aggregate formation in the affected tissues. Huntington's disease is the most common of the nine disorders caused by polyglutamine expansion mutations. The most extensively studied polyalanine expansion disorder is oculopharyngeal muscular dystrophy. There may be a link between diseases caused by polyglutamine and polyalanine expansion mutations as it has been shown that the expanded CAG/polyglutamine tract within the SCA3 gene can shift to the GCA[corrected]/polyalanine frame. Here, we show that this frameshifting phenomenon is more widespread and occurs in Huntington's disease. We have shown both +1 frameshift and +2 frameshift products (which may contain polyalanine or polyserine tracts, respectively) in human postmortem Huntington's disease brains and in a transgenic mouse model of Huntington's disease. Our data suggest that +1 and +2 frameshift products are generated at low levels. This may be relevant to the pathogenesis of human Huntington's disease, as we have previously shown that both polyserine and polyalanine-containing proteins are modifiers of mutant huntingtin toxicity, with low expression levels of polyalanine-containing proteins having a protective effect.

Apolipoprotein E (APOE) polymorphisms are unequivocally associated with risk for Alzheimer's disease (AD). It is crucial to understand how this genetic factor affects dementia risk in the general population, as well as in narrowly diagnosed, selected, patient groups.We assessed the cross sectional association between APOE genotype and dementia status in a community based sample, the MRC Cognitive Function and Ageing Study (MRC CFAS). In addition, we tested the effects of APOE genotypes on the differences in MMSE scores between the first and third assessment waves (about six years apart), an index of cognitive decline.The APOE epsilon4 allele conferred increased risk for dementia (OR=1.5, 95% CI=1.1 to 2.2) compared to epsilon3 in the MRC CFAS sample. Compared with APOE epsilon3/epsilon 3 subjects, those with the epsilon3/epsilon4 genotypes were not at significantly higher risk for dementia (OR=1.1, 95% CI=0.6 to 1.9), although epsilon4/epsilon4 subjects were (OR= 3.8, 95% CI=1.0 to 14.0). Risk estimates were not different between men and women. Notably, our risk estimates for dementia were significantly lower than those reported for a diagnosis of Alzheimer's disease. MMSE scores at wave 3 and the difference in MMSE between baseline and at the third assessment wave were not different across APOE genotypes.The APOE epsilon4 allele is a weaker predictor for dementia in the general population than for AD. This may be because dementia can be caused by non-AD pathological processes and because most prevalent dementia occurs at an age when the APOE epsilon4 effect on AD risk (and therefore dementia) has started to decline.

Dementia is the most common neurodegenerative condition affecting older people. It is estimated that around 550 000 subjects aged 65 years and over in England and Wales suffer from dementia of mild or greater severity.1 Prevalence increases exponentially with age, from around 1% of 65 year olds to approximately 30% of people aged 85 years and older.2 Most cases (60-70%) of incident dementia have clinical diagnoses of Alzheimer's disease, while 15-20% are accounted for by vascular dementia (VaD).3 However, Alzheimer-type and vascular pathology frequently occur in the same person, the neuropathological features associated with AD and VaD are present in many cognitively intact people, and some demented subjects do not have the neuropathological hallmarks of AD or VaD.4 Alzheimer's disease risk is unequivocally associated with polymorphisms in the apolipoprotein E ( APOE ) gene. However, APOE accounts for around half of the genetic risk for AD. Recent data suggest that the angiotensin-I converting enzyme or ACE gene (chromosome 17q23) may also be involved in genetic susceptibility to AD.6,7 ACE (OMIM *1061805) is a dipeptidyl carboxypeptidase that plays an important role in blood pressure regulation and electrolyte balance by hydrolysing angiotensin-I into angiotensin-II, a potent vasopressor and aldosterone stimulating peptide, and inactivating bradykinin, a potent vasodilator. An insertion (I)/deletion (D) polymorphism situated in intron 16 of the gene accounts for 50% of the interperson variability of plasma ACE concentration, and its links with myocardial infarction and other ischaemic heart disease and longevity have been studied extensively.5 There are few published studies on the association between the ACE I/D polymorphism and AD risk: Kehoe et al 6 reported increased risk for AD among I allele carriers; however, this result was not uniformly replicated in subsequent studies. Results from our pooled analysis suggest a slightly increased risk …

BACKGROUND—Hereditary spastic paraparesis is a genetically heterogeneous condition. Recently, mutations in the spastin gene were reported in families linked to the common SPG4 locus on chromosome 2p21-22. OBJECTIVES—To study a population of patients with hereditary spastic paraparesis for mutations in the spastin gene (SPG4) on chromosome 2p21-22. METHODS—DNA from 32 patients (12 from families known to be linked to SPG4) was analysed for mutations in the spastin gene by single strand conformational polymorphism analysis and sequencing. All patients were also examined clinically. RESULTS—Thirteen SPG4 mutations were identified, 11 of which are novel. These mutations include missense, nonsense, frameshift, and splice site mutations, the majority of which affect the AAA cassette. We also describe a nucleotide substitution outside this conserved region which appears to behave as a recessive mutation. CONCLUSIONS—Recurrent mutations in the spastin gene are uncommon. This reduces the ease of mutation detection as a part of the diagnostic work up of patients with hereditary spastic paraparesis. Our findings have important implications for the presumed function of spastin and schemes for mutation detection in HSP patients. Keywords: spastin; hereditary spastic paraparesis; mutation; recessive

Huntington's disease (HD) is thought to show true dominance, since subjects with two mutant alleles have been reported to have similar ages at onset of disease compared to heterozygous sibs. We have investigated this phenomenon using a cell culture model. Protein aggregate formation was used as an indicator for pathology, as intraneuronal huntingtin inclusions are associated with pathology in vitro and in vivo. We showed that cytoplasmic and nuclear aggregates are formed by constructs comprising part of exon 1 of huntingtin with 41, 51, 66, or 72 CAG repeats, in a rate that correlates with repeat number. No inclusions were seen with 21 CAG repeat constructs. Mutant and wild type huntingtin fragments can be sequestered into inclusions seeded by a mutant huntingtin. Wild type huntingtin did not enhance or interfere with protein aggregation. The rate of protein aggregation was dose dependent for all mutant constructs tested. These experiments suggested a model for the dominance observed in HD; the decrease in the age at onset of a mutant homozygote may be small compared to the variance in the age at onset for that specific repeat number in heterozygotes. Our experiments also provide a model, which may explain the different repeat size ranges seen in patients and healthy controls for the different polyglutamine diseases. Keywords: Huntington's disease; huntingtin; CAG repeats; true dominance

Accurate clinical diagnosis of the spinocerebellar ataxias (SCAs) can be difficult because of overlap in phenotype with other disorders and variation in clinical manifestations. Six SCA loci have been mapped and four disease causing genes identified, in addition to the causative gene for Friedreich's ataxia (FA). All of the identified mutations are expansions of trinucleotide repeat tracts. The SCA2 and SCA6 genes were published recently. The extent of the normal CAG size ranges at these loci and the relative frequencies of the known causes of SCA in the UK are not known. This study first investigated the normal size ranges of the SCA2 and SCA6 loci by genotyping control populations of West African and South African subjects, since African populations generally show the greatest allelic diversity. We found one allele larger than the previously determined normal range for SCA2, and our results at the SCA6 locus agreed with the previously reported normal range. The second component of the study assessed the relative frequencies of the SCA1, 2, 3, and 6, DRPLA, and FA trinucleotide repeat mutations in 146 patients presenting with SCA-like symptoms referred to genetic diagnostic laboratories in the UK. We detected mutations in 14% of patients referred with a diagnosis of autosomal dominant SCA, and in 15% of patients referred with spinocerebellar ataxia where we did not have sufficient family history data available to allow categorisation as familial or sporadic cases. Friedreich's ataxia accounted for 3% of the latter category of cases in our sample, but the most common causes of SCA were SCA2 and SCA6.

The CAG repeat number in the Huntington's disease (HD) gene accounts for about 50% of the variation seen in age at onset of HD. In order to determine whether promoter sequence variation can contribute to the residual variation in age at onset, we studied the conserved 303 bp region upstream of the +1 translation start site in the HD gene in a population of 56 control East Anglians, 30 Africans, 34 Japanese, and 208 English Huntington's disease patients. A surprisingly high degree of variation was found. Seven alleles were identified, comprising four polymorphisms: two single base pair substitutions, a 6 bp VNTR present as one or two copies, and a 20 bp VNTR with one to three copies of the tandem repeat. No correlation between polymorphisms and age at onset of symptoms was found in HD patients. The 6 bp and 20 bp stretches are present only in single copies in the chimpanzees and gorilla, suggesting that these VNTRs have evolved by duplication of the core sequences in the human lineage.

Previous investigations of cognitive function in myotonic dystrophy (DM) suggested that DM subjects have impairment of general intelligence and severe defects in executive function. These studies had to neglect patients with mild clinical disease, since they were generally performed before the availability of DNA testing for DM. We have investigated a group of milder DM cases (defined both by their degree of disability and CTG expansion size) and have not found any defect in general intelligence using the National Adult Reading Test, Standard Progressive Matrices, and Mini-Mental State examination. Three executive function tests were used. The cognitive estimates test and the Wisconsin Card Sorting Test showed tendencies towards impairment, which were of borderline significance, but the verbal fluency task was performed normally. However, in the face of normal general intelligence, mild DM subjects as a group show impairment of memory function. This suggests that memory function may be more sensitive to small CTG repeat expansions than general intelligence.

OBJECTIVES—Recent data suggest that wild type huntingtin can protect against apoptosis in the testis of mice expressing full length huntingtin transgenes with expanded CAG repeats. It is not clear if this protective effect was confined to particular cell types, or if wild type huntingtin exerted its protective effect in this model by simply reducing the formation of toxic proteolytic fragments from mutant huntingtin. METHODS—We cotransfected neuronal (SK-N-SH, human neuroblastoma) and non-neuronal (COS-7, monkey kidney) cell lines with HD exon 1 (containing either 21 or 72 CAG repeats) construct DNA and either full length wild type huntingtin or pFLAG (control vector). RESULTS—Full length wild type huntingtin significantly reduced cell death resulting from the mutant HD exon 1 fragments containing 72 CAG repeats in both cell lines. Wild type huntingtin did not significantly modulate cell death caused by transfection of HD exon 1 fragments containing 21 CAG repeats in either cell line. CONCLUSIONS—Our results suggest that wild type huntingtin can significantly reduce the cellular toxicity of mutant HD exon 1 fragments in both neuronal and non-neuronal cell lines. This suggests that wild type huntingtin can be protective in different cell types and that it can act against the toxicity caused by a mutant huntingtin fragment as well as against a full length transgene. Keywords: Huntington's disease; huntingtin; apoptosis

Genetic and environmental factors play roles in the aetiology of ruptured intracranial aneurysms. Hypertension has been reported as a risk factor for intracranial aneurysm haemorrhage. We have tested if genotypes at the angiotensin converting enzyme (ACE) gene locus are associated with ruptured intracranial aneurysms. The insertion/deletion polymorphism in the ACE gene was genotyped in 258 subjects presenting in East Anglia with ruptured intracranial aneurysms (confirmed at surgery or angiographically) and 299 controls from the same region. ACE allele frequencies were significantly different in the cases and the controls (alleles χ21=4.67, p=0.03). The I allele was associated with aneurysm risk (odds ratio for I allele v D allele = 1.3 (95% CI=1.02-1-65); odds ratio for II v DD genotype = 1.67 (95% CI=1.04-2.66)). The I allele at the ACE locus is over-represented in subjects with ruptured intracranial aneurysms. These data are supported by non-significant trends in the same direction in two previous smaller studies. Thus, this allele may be associated with risk for ruptured intracranial aneurysms. Keywords: ACE I allele; ruptured intracranial aneurysms

We report on a myotonic dystrophy (DM) family exhibiting instability of normal sized (CTG)n alleles in the DM kinase gene on the non-DM chromosome. At least two mutational events involving normal DM alleles must have occurred in this family; one was characterised as a 34-35 (CTG)n repeat mutation. These findings represent a dissociation between (CTG)n repeat instability and myotonic dystrophy. Furthermore, this family highlights genetic counselling issues relating to the pathogenicity of alleles at the upper end of the normal size range and the risk of further expansion into the disease range.

The formation of intracellular amyloid-like inclusions by mutant proteins is a feature of two groups of codon reiteration diseases, for which there are currently no treatments. The first group that was described includes the nine known neurodegenerative conditions caused by polyglutamine (polyQ) repeat expansions resulting from CAG trinucleotide repeat mutations, exemplified by Huntington’s disease (HD).1 HD is caused by a tract of more than 37 uninterrupted polyglutamines in exon 1 of the HD gene product, huntingtin. Genetic and transgenic studies are consistent with a model where expanded polyglutamines cause disease by conferring a novel toxic function on the disease proteins.1–3 The second type of codon reiteration mutation results in autosomal dominant oculopharyngeal muscular dystrophy (OPMD).4 OPMD is caused by the abnormal expansion of a (GCG)n trinucleotide repeat in the coding region of the polyadenine binding protein 2 gene ( PABP2 ): a (GCG)6 repeat is expanded to (GCG)8–13 in most patients. In some rare cases, insertion mutations such as (GCG)6GCA(GCG)2, (GCG)6GCA(GCG)3 and (GCG)6(GCA)3(GCG)2 are seen.5,6 In PABP2 , (GCG)6 codes for the first six alanines in a homopolymeric stretch of 10 alanines. Thus, disease is associated with expansions of 12 or more uninterrupted alanines in this nuclear protein. OPMD is characterised by aggregates in muscle cell nuclei comprising mutant PABP2 as a major component.4,7–9 The role of inclusions in these diseases has been vigorously disputed.1 Nevertheless, strategies that target protein misfolding frequently reduce aggregate formation and cell death in parallel. In mammalian cell based models of both polyglutamine and polyalanine diseases, the mutant proteins are much more prone to aggregate formation than their wild-type counterparts and cause significantly more cell death.10,11 In such models, …

Editor—Autosomal dominant polycystic kidney disease (ADPKD) is a multisystem disease with intrafamilial phenotypic heterogeneity. Cerebral aneurysms develop in 10-20% of patients with ADPKD.1 2 Aneurysm rupture may precede the development of hypertension or renal manifestations of the disease.2 Two ADPKD loci ( PKD1 and PKD2 ) map to chromosomes 16p and 4q, respectively. Reports of unlinked pedigrees have suggested the existence of a third unmapped locus.3-7 We report a three generation white family with an ADPKD like disease, unlinked to the PKD1 or PKD2 loci (fig 1, table 1). Other genetic causes of renal cysts, such as tuberous sclerosis and von Hippel-Lindau disease, have been excluded clinically and linkage to the known loci for these diseases is unlikely. This family supports the case for a third locus for ADPKD, but differs from the previously described unlinked pedigrees by its presentation with cerebral aneurysm rupture. Figure 1 Pedigree with autosomal dominant polycystic kidney disease. View this table: Table 1 Clinical details of family members Ethical approval for this study was granted by the local research ethics committee. The family was identified because three members had sustained a subarachnoid haemorrhage. All family members who were older than 18 were invited for examination and screening for intracranial aneurysms by magnetic resonance angiography (MRA). There was no clinical evidence of tuberous sclerosis, von Hippel-Lindau disease, or autosomal recessive polycystic …

Editor—The hereditary spastic paraplegias (HSPs) are clinically characterised by progressive lower limb spasticity. The spasticity may occur in isolation (“pure”) or may be complicated by other major clinical features. Autosomal dominant, autosomal recessive, and X linked recessive inheritance patterns have been described for pure and complicated forms of HSP.1 ,2 There are loci for ADPHSP on chromosomes 2p (SPG4, MIM 182601),3 ,4 8q (SPG8, MIM 603563),5 ,6 14q (SPG3, MIM 182600),7 15q (SPG6, MIM 600363),8and 19q (SPG12).9 In addition, we recently mapped an ADPHSP locus on chromosome 12q13 (SPG10, MIM 604187) in a large UK family, family 4.10 This locus was narrowed to a 9.2 cM region between markers D12S368 and D12S83. Clinical features and diagnostic criteria for family 4 have previously been described.10 ,11 Briefly, subjects were classified as being affected if they had lower limb hyperreflexia in addition to at least one of the following: progressive spastic gait abnormality, bilateral extensor plantar reflex, or bilateral sustained (⩾5 beats) ankle or knee clonus. Subjects were classified as being possibly affected if lower limb hyperreflexia was present without other abnormal signs and as being normal if they had an entirely normal neurological examination. Thirteen members of family 4 are affected by ADPHSP and the family has a relatively young mean age at onset of 10.8 (SD 9.6) years (range 8-40). We have now genotyped additional markers D12S803, D12S390, D12S270, D12S1618, and D12S355 for subjects from family 4, using previously described methods.10 Primer sequences for these markers are available from the Genethon …

OBJECTIVES—The only locus unequivocally associated with late onset Alzheimer's disease (AD) risk is APOE. However, this locus accounts for less than half the genetic variance. A recent study suggested that the A allele of the 3'UTR biallelic polymorphism in the LBP-1c/CP2/LSF gene was associated with reduced AD risk. Samples were diagnosed predominantly by clinical rather than pathological criteria. We have sought to replicate this finding in a series of necropsy confirmed, late onset AD cases and non-demented controls. METHODS—The 3'UTR polymorphism in the LBP-1c/CP2/LSF gene was typed in 216 necropsy confirmed AD cases and 301 non-demented controls aged >73 years. RESULTS—We found different LBP-1c/CP2/LSF allele distributions in our AD cases and controls (p=0.048); the A allele was associated with reduced AD risk. The allele and genotype frequencies observed in our cases and controls were similar to those previously reported. No significant effects emerged when the data were adjusted for age, sex, or apoE ε4 carrier status. CONCLUSIONS—Our data support LBP-1c/CP2/LSF as a candidate gene/risk factor for AD and provide justification for future studies to investigate the role of this gene in Alzheimer's disease. Keywords: Alzheimer's disease; LBP-1c/CP2/LSF; dementia; MRC/CFAS study

A recent study suggested that the insertion (I) allele in intron 16 of the angiotensin converting enzyme gene (ACE) is associated with Alzheimer's disease (AD) risk. In our series of 239 necropsy confirmed late onset AD cases and 342 elderly non-demented controls aged >73 years, we found significantly different ACE genotype distributions in the case and control groups (p=0.007). Homozygotes for both the I and D alleles were associated with a higher risk compared to DI heterozygotes. While the APOE ε4 allele was strongly associated with AD risk in our series, we found no evidence for an interaction between the APOE and ACE loci. In addition, no interactions were observed between ACE and gender or age at death of the AD cases. A meta-analysis of all published reports (12 case-control series in total) suggested that both the II and ID ACE genotypes are associated with increased AD risk (odds ratio (OR) for II v DD 1.36, 95% confidence interval (CI)=1.13-1.63, OR for DI v DD 1.33, 95% CI=1.14-1.53, p=0.0002). Keywords: Alzheimer's disease; ACE gene; I allele

Editor—The hereditary spastic paraplegias are characterised by progressive spasticity, predominantly affecting the lower limbs. They have been divided into “pure” or complicated forms.1 ,2 Four loci for autosomal dominant pure hereditary spastic paraplegia (ADPHSP) have been mapped, on chromosomes 2p ( SPG4 ), 8q ( SPG6 ), 14q ( SPG3 ), and 15q ( SPG6 ).1-3 Cognitive impairment may be present in apparently “pure” hereditary spastic paraplegia. Tedeschi et al 4 found subclinical cognitive deficits in seven patients with autosomal recessive or autosomal dominant pure hereditary spastic paraplegia, when compared to normal, unrelated controls. Webb and Hutchinson5 investigated 31 patients from 12 kindreds with ADPHSP (loci not described) and found subclinical cognitive impairment, apparently restricted to cases over 50 years old. In addition, the description of an SPG4 linked family with paraplegia complicated by subcortical dementia suggests that “pure” hereditary spastic paraplegia and hereditary spastic paraplegia complicated by frank dementia may be allelic disorders.6 As a pilot study, we investigated the presence of subclinical cognitive impairment in family members from four Welsh ADPHSP families (families 26, 27, 28, and 36) using the Mini-Mental State Examination. Diagnostic criteria and clinical details for these families have been described previously.7 None of the subjects had an existing diagnosis …

he hereditary spastic paraplegias (HSPs) are a group of single gene disorders in which the corticospinal tracts fail to develop normally, or degenerate after initially normal development. The HSPs all share the principal clinical feature of progressive lower limb spastic paralysis, and are subdivided into pure and complicated forms, depending on the presence of additional neurological or non-neurological features. 12 The pure HSPs tend to be associated with neurodegeneration, rather than abnormal development, and histopathological studies in pure HSP show a length-dependent ‘‘dying back’’ of the terminal ends of the corticospinal tract axons, with the longest axons being involved first. 1 The SPG4 gene, spastin, is the most important pure HSP gene, being responsible for approximately 40% of definite autosomal dominant pure HSP and a smaller proportion of sporadic cases and cases with uncertain family history. 34 The 616 amino acid spastin protein is a widely expressed AAA (ATPases associated with diverse cellular activities) protein. 5

Peter Harper’s first two editions of Huntington’s disease have been widely regarded as key reference works for those working on this disease and related polyglutamine disorders. For the third edition, he has teamed up with Gillian Bates and Lesley Jones to produce a worthy successor to the previous editions. This book covers a wide range of topics relevant to this condition with sections devoted to clinical features, genetics, neurobiology, structural biology, cell biology, animal studies, care of HD patients, and therapeutic approaches. The editors have assembled an authoritative group of authors …