Two novel presenilin-1 mutations (Y256S and Q222H) are associated with early-onset Alzheimer's disease

Mutations in the gene encoding presenilin 1 (PS-1) account for 50% of early-onset familial Alzheimer's disease (EOFAD) cases. In this study, we identified two missense mutations in the coding sequence of the presenilin (PS-1) gene in two EOFAD pedigrees. AD was confirmed in one pedigree by autopsy. Mutation analysis of PCR products amplified from genomic DNA templates showed two novel PS-1 mutations resulting in Gln222His and Tyr256Ser. The two novel mutations are located within predicted transmembrane domains five (TM-5) and six (TM-6), respectively, and are associated with very early ages of onset. The Tyr256Ser is associated with one of the youngest age of AD onset, 25 years, which is consistent with a drastic change in function of the altered PS-1 protein. A morphometric analysis of the cortical degenerative changes of the Tyr256Ser case, showed severe involvement of the primary motor cortex, which correlated well with the pyramidal changes, including tetraspasticity. Immunoblot analysis showed the Tyr256Ser case had the greatest expression of Abeta(1-40) and Abeta(1-42), which was confirmed by ELISA, compared to other PS-1 mutant FAD cases and age-matched controls and, thus, contributes to the severity of the disease pathology.     

Comparative analysis of cortical gene expression in mouse models of Alzheimer's disease

Three mouse models of Alzheimer's disease (AD) were used to assess changes in gene expression potentially critical to amyloid beta-peptide (Abeta)-induced neuronal dysfunction. One mouse model harbored homozygous familial AD (FAD) knock-in mutations in both, amyloid precursor protein (APP) and presenilin 1 (PS-1) genes (APP(NLh/NLh)/PS-1(P264L/P264L)), the other two models harbored APP over-expression of FAD mutations (Tg2576) with the PS-1 knock-in mutation at either one or two alleles. These mouse models of AD had varying levels of Abeta40 and Abeta42 and different latencies and rates of Abeta deposition in brain. To assess changes in gene expression associated with Abeta accumulation, the Affymetrix murine genome array U74A was used to survey gene expression in the cortex of these three models both prior to and following Abeta deposition. Altered genes were identified by comparing the AD models with age-matched control littermates. Thirty-four gene changes were identified in common among the three models in mice with Abeta deposition. Among the up-regulated genes, three major classes were identified that encoded for proteins involved in immune responses, carbohydrate metabolism, and proteolysis. Down-regulated genes of note included pituitary adenylate cyclase-activating peptide (PACAP), brain-derived neurotrophic factor (BDNF), and insulin-like growth factor I receptor (IGF-IR). In young mice without detectable Abeta deposition, there were no regulated genes common among the three models, although 40 genes were similarly altered between the two Tg2576 models with the PS-1 FAD knock-in. Finally, changes in gene expression among the three mouse models of AD were compared with those reported in human AD samples. Sixty-nine up-regulated and 147 down-regulated genes were found in common with human AD brain. These comparisons across different genetic mouse models of AD and human AD brain provide greater support for the involvement of identified gene expression changes in the neuronal dysfunction and cognitive deficits accompanying amyloid deposition in mammalian brain.     

Presenilin-1 is associated with Alzheimer's disease amyloid.

Mutations in presenilin (PS)-1 and -2, located on chromosome 14 and 1 respectively, are the major association with early-onset familial Alzheimer's disease (FAD). FAD has also been linked to mutations in the amyloid beta precursor protein (beta PP), and the presence of the apolipoprotein E4 allele is a risk factor for late-onset AD. The role of PS in FAD and in sporadic AD is unclear. We previously reported the presence of a PS-1 carboxyl-terminal epitope in neuritic plaques (Wisniewski T, Palha JA, Ghiso J, Frangione B: S182 protein in Alzheimer's disease neuritic plaques. Lancet 1995, 346:1366). In the present study, we examined a number of biochemically different cerebral and systemic amyloidoses, finding the PS-1 carboxy epitope only in association with amyloid beta (A beta) lesions. We confirm the presence of this epitope ultrastructurally in neuritic plaques. In addition, biochemical and amino acid sequence data are presented for an association of the 18-kd carboxy fragment of PS-1 with neuritic plaques with a start at residue 300. Three of the proteins with linkage to AD have now been found as components of neuritic plaques. It remains to be determined whether all of these proteins are involved in the same or different pathological pathway(s) and which of these proteins is the most important for the common, late-onset form of AD.     

Alzheimer's presenilin 1 causes chromosome missegregation and aneuploidy

Mutations in the presenilin 1 gene cause most early onset familial Alzheimer's disease (FAD). Here, we report that a defect in the cell cycle - improper chromosome segregation - can be caused by abnormal presenilin function and therefore may contribute to AD pathogenesis. Specifically we find that either over-expression or FAD mutation in presenilin 1 (M146L and M146V) leads to chromosome missegregation and aneuploidy in vivo and in vitro: (1) Up to 20% of lymphocytes and neurons of FAD-PS-1 transgenic and knocking mice are aneuploid by metaphase chromosome analysis and in situ hybridization. (2) Transiently transfected human cells over-expressing normal or mutant PS-1 develop similar aneuploidy within 48 h, including trisomy 21. (3) Mitotic spindles in the PS-1 transfected cells contain abnormal microtubule arrays and lagging chromosomes. Several mechanisms by which chromosome missegregation induced by presenilin may contribute to Alzheimer's disease are discussed.     

Mutation analysis impact on the genetic counseling of sporadic hemophilia B families

Previous studies have shown that hemophilia B (HB) is the result of several different mutations, mostly single nucleotide substitutions, in the factor IX (FIX) gene. In order to evaluate the impact of mutation analysis on genetic counseling in sporadic and uninformative HB familial pedigrees, we re-analyzed by the conformation sensitive gel electrophoresis (CSGE) technique 14 patients, previously studied by restriction fragment length polymorphisms (RFLPs). A single mutation was present within the FIX gene of each patient: 12 mutations were single base substitutions, 1 was a base insertion, and 1 was a four nucleotide deletion; 4/12 mutations have not been described so far. By identifying the detrimental mutations in affected males, carrier status was correctly diagnosed in all the women we studied; 3/12 de novo events were found in maternal meioses with a 25% mutation rate. Identification of the genetic defect was also successfully applied to three prenatal diagnoses.     

Alzheimer's presenilin 1 is a putative membrane receptor for rab GDP dissociation inhibitor

Mutations in the presenilin 1 ( PS-1 ) gene cause Alzheimer's disease (AD). These mutations alter the processing of the amyloid precursor protein (APP) by increasing the production of the fibrillogenic amyloid fragment, Abeta1-42/43. Since the secretase activities that process APP are localized in different intracellular compartments, it is likely that membrane transport is a key factor in the pathogenesis of AD. In this report we provide evidence for a direct connection between PS-1 and membrane transport. We show that the N-terminus of PS-1 binds to rab GDP dissociation inhibitor (rabGDI), a regulatory factor in vesicle transport. In PS-1-deficient neurons we found a 2-fold decrease in the amount of rabGDI associated with membranes. Our findings are compatible with PS-1 being a membrane receptor for rabGDI. This is in line with a role of PS-1 in the regulation of protein trafficking in the ER/Golgi, which can modulate the production of Abeta.     

Presenilin mutations in Alzheimer's disease

The presenilins (PS-1 and PS-2) are 2 members of a novel family of genes encoding integral membrane proteins recently implicated in Alzheimer's disease (AD) pathology. To date, 43 mutations have been identified in PS-1 and 2 in PS-2 that lead to familial presenile AD (onset before age 65 years). The normal and pathological functions of the PS proteins (ps-1 and ps-2) are unknown, but their high degree of homology predicts similar biological activities. Homologies with ps from other species suggest that they may play a role in intracellular protein sorting and trafficking, in intercellular cell signaling, or in cell death. Since to date only missense mutations and in-frame deletions were identified, it is believed that mutated ps act through either a gain of (dys-)function or a dominant negative effect. In vivo and in vitro studies have linked PS mutations to amyloid deposition, an early pathological event in AD brains. Hum Mutat 11:183–190, 1998. © 1998 Wiley-Liss, Inc.     

Missense mutations in the chromosome 14 familial Alzheimer's disease presenilin 1 gene

Mutations in the presenilin genes (PS-1 and PS-2) cause early onset autosomal dominant Alzheimer's disease (AD). Eight early-onset, autopsy-documented familial AD kindreds were screened for mutations in PS-1, and seven different mutations were identified. Three of these were new mutations (G209V, A426P, and E120D), two were previously reported mutations in new families, and three mutations were confirmed in previously published families. Two of these new mutations are found within predicted transmembrane domains (TMDs 4, 7, and 8). The A426P mutation is the most C-terminal PS-1 mutation identified to date. Hum Mutat 11:216–221, 1998. © 1998 Wiley-Liss, Inc.     

Familial Alzheimer's disease co-segregates with a Met 146 Ile substitution in presenilin-1

The presenilin-1 ( PS-1 )/ S 182 gene at chromosome 14q24.3 is, when mutated, the most common disease gene in autosomal dominant early-onset Alzheimer's disease. Substitution of methionine 146 of the gene product for either valine or leucine co-segregates with Alzheimer's disease with the age of onset in the late thirties or early forties. Here we describe a new substitution of methionine 146 for isoleucine that co-segregates with Alzheimer's disease with age of the onset in the early forties. All identified missense mutations in methionine codon 146 replace one hydrophobic amino acid (Met) with another (Val, Leu, Ile) and correspond to any nucleotide change at the first or third position of the codon. Second position mutations invariably lead to replacement of the hydrophobic methionine with a hydrophilic amino acid that may severely affect the function of the protein. The fact that no second position mutations have been identified so far may support the hypothesis that the protein product of PS-1 plays a crucial role during development.     

ApoE genotype is a risk factor in nonpresenilin early-onset alzheimer's disease families

The apolipoprotein E (ApoE) genotype is a significant risk factor and modulator of age of onset of Alzheimer's disease (AD). We analyzed the effect of the ApoE genotype in two distinct early-onset familial AD groups: families with a mutation in the presenilin-1 gene (PS-1) on chromosome 14, and families without a mutation detectable in the PS-1, presenilin-2 (PS-2), and the amyloid precursor protein (APP) gene (non-PS early-onset familial AD). The ApoE genotype is clearly shown not to modulate age of onset in families with a mutation in the PS-1 gene and families with no lesion detectable in either the presenilin or APP gene. The effects of a double dose of ApoE4 on age of onset were not assessed in the PS-1 AD families due to the lack of any affected ApoE4 homozygotes in the sample set; this insufficiency will need to be assessed in further studies. There was no association between the ApoE4 allele and AD in the PS-1 families. Non-PS early-onset AD families were shown to have a significantly higher frequency of ApoE4 compared to controls and the PS-1 AD group. These observations are important and suggest that 1) other genetic and environmental factors modify the AD phenotype in PS-1 and non-PS early-onset families; and 2) the ApoE4 allele is a significant risk factor in the etiology of non-PS early-onset AD and will be a useful adjunct in the diagnosis of unaffected family members. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 81:117–121, 1998. © 1998 Wiley-Liss, Inc.     

Association between presenilin-1 polymorphism and maternal meiosis II errors in Down syndrome

Several lines of evidence suggest a shared genetic susceptibility to Down syndrome (DS) and Alzheimer disease (AD). Rare forms of autosomal-dominant AD are caused by mutations in the APP and presenilin genes (PS-1 and PS-2). The presenilin proteins have been localized to the nuclear membrane, kinetochores, and centrosomes, suggesting a function in chromosome segregation. A genetic association between a polymorphism in intron 8 of the PS-1 gene and AD has been described in some series, and an increased risk of AD has been reported in mothers of DS probands. We therefore studied 168 probands with free trisomy 21 of known parental and meiotic origin and their parents from a population-based material, by analyzing the intron 8 polymorphism in the PS-1 gene. An increased frequency of allele 1 in mothers with a meiosis II error (70.8%) was found compared with mothers with a meiosis I error (52.7%, P < 0.01), with an excess of the 11 genotype in the meiosis II mothers. The frequency of allele 1 in mothers carrying apolipoprotein E (APOE) epsilon4 allele (68.0%) was higher than in mothers without epsilon4 (52.2%, P < 0.01). We hypothesize that the PS-1 intronic polymorphism might be involved in chromosomal nondisjunction through an influence on the expression level of PS-1 or due to linkage disequilibrium with biologically relevant polymorphisms in or outside the PS-1 gene.     

FAD mutant PS-1 gene-targeted mice: increased A beta 42 and A beta deposition without APP overproduction

To investigate the consequences of mutant presenilin-1 (PS-1) expression under the control of the normal PS-1 gene, a gene-targeted mouse bearing the FAD mutation P264L was made. Gene-targeted models are distinct from transgenic models because the mutant gene is expressed at normal levels, in the absence of the wild-type protein. PS-1(P264L/P264L) mice had normal expression of PS-1 mRNA, but levels of the N- and C-terminal protein fragments of PS-1 were reduced while levels of the holoprotein were increased. When crossed into Tg(HuAPP695.K670N/M671L)2576 mice, the PS-1(P264L) mutation accelerated the onset of amyloid (Abeta) deposition in a gene-dosage dependent manner. Tg2576/PS-1(P264L/P264L) mice also had Abeta deposition that was widely distributed throughout the brain and spinal cord. APP(NLh/NLh)/PS-1(P264L/P264L) double gene-targeted mice had elevated levels of Abeta42, sufficient to cause Abeta deposition beginning at 6 months of age. Abeta deposition increased linearly over time in APP(NLh/NLh)/PS-1(P264L/P264L) mice, whereas the increase in Tg2576 mice was exponential. The APP(NLh/NLh)/PS-1(P264L/P264L) double gene-targeted mouse represents an animal model that exhibits Abeta deposition without overexpression of APP.     

Intronic sequence variants of the CDKN2A gene in melanoma pedigrees

Germ-line mutations of the tumor-suppressor gene CDKN2A predispose individuals to melanoma in families worldwide. However, coding mutations of CDKN2A have not been detected in a significant proportion of those affected. The identification of a disease-associated intronic mutation of CDKN2A in UK families, which has proved to be the most common CDKN2A mutation as yet identified in this population, has highlighted the possibility that additional causal mutations may lie within the intronic sequence of the gene. In this article, we describe the comprehensive screening of 109 English and 26 Australian melanoma pedigrees for intronic mutations of CDKN2A. In total, 24 sequence variants were identified across the two introns of the gene. We show evidence that two of the CDKN2A intronic variants (IVS1 + 1104 C > A and IVS1 - 1104 C > G) predispose to melanoma. IVS1 + 1104 was shown to result in the aberrant splicing of both p16(INK4a) and p14(ARF) mRNA. Overall, however, the proportion of English melanoma families with these variants is small.     

Clinical testing for the nevoid basal cell carcinoma syndrome in a DNA diagnostic laboratory.

PURPOSE: This study determines which clinical features predict positive test results among samples submitted for DNA-based diagnostic nevoid basal cell carcinoma syndrome (NBCCS) testing, and further defines the mutational spectrum of the PTCH gene. METHODS: DNA was extracted from peripheral blood leukocytes, and polymerase chain reaction products from exons 1 to 23 of the PTCH gene were directly sequenced. Pedigree phenotypic information was obtained by written questionnaire. RESULTS: Among 106 presumably unrelated pedigrees, 44 independent mutations were found in 47 families. There were 11 nonsense mutations; 1 in-frame deletion; 17 deletions, 6 insertions, and 1 deletion-insertion that generated frameshifts; 5 splice-site mutations; 1 in-frame duplication; and 2 presumptive missense mutations. Twenty-seven of 46 pedigrees (58.7%) with two or more typical radiographic or pathologic features of NBCCS tested positive for PTCH mutations. Of these, 26 had jaw cysts in combination with other characteristics or neoplasms including basal cell carcinomas, palmar pits, skeletal abnormalities, ocular abnormalities, medulloblastomas, cardiac or ovarian fibromas, calcification of the falx cerebri, polydactyly, cleft lip and/or palate, and agenesis of the corpus callosum or other central nervous system malformations. None of the 13 pedigrees solely affected by multiple or early-onset basal cell carcinomas and none of the four pedigrees with jaw cysts alone had PTCH mutations. CONCLUSIONS: Pedigrees with multiple features of NBCCS were most likely to test positive for PTCH mutations. Pedigrees with multiple or early-onset basal cell carcinomas without other features of the disease did not test positive for PTCH mutations.     

Linkage of familial alzheimer disease to chromosome 14 in two large early-onset pedigrees: Effects of marker allele frequencies on lod scores

Alzheimer disease (AD) is a devastating neurodegenerative disease leading to global dementia. In addition to sporadic forms of AD, familial forms (FAD) have been recognized. Mutations in the amyloid precursor protein (APP) gene on chromosome (CHR) 21 have been shown to cause early-onset AD in a small number of pedigrees. Recently, linkage to markers on CHR 14 has been established in several early-onset FAD pedigrees. We now report lod scores for CHR 14 markers in two large early-onset FAD pedigrees. Pairwise linkage analysis suggested that in these pedigrees the mutation is tightly linked to the loci D14S43 and D14S53. However, assumptions regarding marker allele frequencies had a major and often unpredictable effect on calculated lod scores. Therefore, caution needs to be exercised when single pedigrees are analyzed with marker allele frequencies determined from the literature or from a pool of spouses. © 1993 Wiley-Liss, Inc.     

Presence of a major WFS1 mutation in Spanish Wolfram syndrome pedigrees

Wolfram syndrome (WS) is an autosomal recessive neurodegenerative disease mainly characterized by familial diabetes mellitus and optic atrophy. WS patients frequently present with other clinical features such as diabetes insipidus, renal abnormalities, psychiatric disorders, and a variety of neurologic symptoms: deafness, ataxia, peripheral neuropathy. A gene responsible for Wolfram Syndrome (WFS1) has been recently identified on chromosome 4p16.1. Twenty-two Wolfram patients from 16 Spanish families were screened for mutations in the WFS1 coding region by SSCP analysis and direct sequencing. Since WS has been considered a mitochondrial disorder for some time, mitochondrial DNA (mtDNA) in these families was also examined. WFS1 mutations were detected in 75% of families (12 of 16). One of these mutations, an insertion of 16 base pairs in exon 4, turned out to be notably frequent in Spanish pedigrees. As many as 50% of pedigrees with WFS1 mutations harbored this insertion, either in one (33% of cases) or in two chromosomes (67%). Ten other mutations were identified: 7 missense changes, 2 deletions, and 1 nonsense mutation. Only 3 of these changes had been previously described in non-Spanish pedigrees. Large mtDNA rearrangements and LHON point mutations were detected in four and six families, respectively. No correlation could be established between WFS1 gene mutations and specific point mutations or rearrangements in mtDNA. We would suggest first screening for the 16-bp insertion in exon 4 when a new Spanish WS case is reported.     

Lewy Bodies Contain Altered α-Synuclein in Brains of Many Familial Alzheimer’s Disease Patients with Mutations in Presenilin and Amyloid Precursor Protein Genes

Missense mutations in the α-synuclein gene cause familial Parkinson’s disease (PD), and α-synuclein is a major component of Lewy bodies (LBs) in sporadic PD, dementia with LBs (DLB), and the LB variant of Alzheimer’s disease (AD). To determine whether α-synuclein is a component of LBs in familial AD (FAD) patients with known mutations in presenilin (n = 65) or amyloid precursor protein (n = 9) genes, studies were conducted with antibodies to α-, β-, and γ-synuclein. LBs were detected with α- but not β- or γ-synuclein antibodies in 22% of FAD brains, and α-synuclein-positive LBs were most numerous in amygdala where some LBs co-localized with tau-positive neurofibrillary tangles. As 12 (63%) of 19 FAD amygdala samples contained α-synuclein-positive LBs, these inclusions may be more common in FAD brains than previously reported. Furthermore, α-synuclein antibodies decorated LB filaments by immunoelectron microscopy, and Western blots revealed that the solubility of α-synuclein was reduced compared with control brains. The presence of α-synuclein-positive LBs was not associated with any specific FAD mutation. These studies suggest that insoluble α-synuclein aggregates into filaments that form LBs in many FAD patients, and we speculate that these inclusions may compromise the function and/or viability of affected neurons in the FAD brain.     

结节性硬化症家系的基因诊断及产前诊断

目的 对结节性硬化症(tuberous sclerosis complex,TSC)患者进行基因突变检测,并在基因诊断结果明确的基础上应用于产前诊断.方法 应用聚合酶链反应-变性高效液相色谱(polymerase chain reaction-denaturing high-performance liquid chromatography,PCR-DHPLC)、DNA测序技术,对19个家系的21例TSC患者进行TSC1和TSC2基因的突变检测.结果 在19个家系21例患者中发现17种不同的基因突变,其中13种突变未见报道,包括TSCj基因的c.2672delA、c.2672insA和TSC2基因的c.4918insCGCC、c.1143delG、Intron27+1 G＞A、c.1957-1958delAG、Intron5+1 G＞A、c.910insCT、c.2753C＞G、c.4078dupAGCAAGTCCAGCTCCTC、Intron 11-1 G＞A、Intron 14+1 G＞A、c.684 C＞A.对7个家系进行了产前诊断,其中6个家系的胎儿均未发现其家系先证者所具有的突变,胎儿出生后电话随访至1～4岁无TSC的症状出现.而另一家系的胎儿携带有和母亲一样的突变,经遗传咨询后,家属选择了引产.结论 本研究证实的TSC基因突变中,有76.5%(13/17)的突变均未在其他研究中被发现,说明中国人群TSC基因的突变谱可能与其他人群具有较明显的差异;本研究中TSC基因诊断率为89.5%(17/19),提示TSC的发生可能还有其它未知的遗传病因;在有家族史的病例中,TSC1与TSC2有相似的突变比例,而在散发病例中,TSC2的突变更加常见;13种新突变患者的父母均无类似突变,说明TSC致病基因具有较高的自发突变率.     

中国人家族性腺瘤性患肉病患者结肠腺瘤性患肉病基因的胚系突变

目的 探讨中国人家族性腺瘤性息肉病(familial adenomatous polyposis,FAr)患者的结肠腺瘤性息肉病(adenomatous polyposis coli,APC)基因的胚系突变类型.方法 对9个FAP家系18名成员进行多重连接依赖性探针扩增(multiplex ligation-dependent probe amplification,MLPA)检测APC基因有无大片段缺失.再应用PCR扩增APC基因的15个外显子区域,经变性高效液相色谱(denaturing high performance liquid chromatography,DHPLC)对每个扩增片段进行筛查,流出峰异常的片段,经DNA测序验证小片段的改变.结果 9个家系中有3个家系发现有APC基因的胚系突变:家系2为c.3184-3187 del CAhA,家系4为c.5432C＞T,家系9为c.3925-3929 del AAAAG.3种突变中c.5432C＞T在数据库中未见报道.结论 中国人不同的APC基因的胚系突变可引起FAP;无APC胚系突变的FAP患者的发病可能存在其他的机制.