Single Heterozygous Mutation Research Articles

Late-Onset Nephropathic Cystinosis

Cystinosis is an autosomal recessive disease characterized by the intralysosomal accumulation of cystine, as a result of a defect in cystine transport across the lysosomal membrane. Three clinical forms have been described on the basis of severity of symptoms and age of onset: infantile cystinosis, characterized by renal proximal tubulopathy and progression to end-stage renal disease before 12 yr of age; juvenile form, with a markedly slower rate of progression; and adult form, with only ocular abnormalities. Fourteen patients in nine unrelated families with noninfantile cystinosis were studied. Information about clinical outcome, biochemical data, renal histopathologic data, and genotyping was collected. Eight patients had Fanconi syndrome. Proteinuria was present in all patients. Serum creatinine at last follow-up, without specific treatment, ranged between 69 and 450 mumol/L, at an age of 12 to 56 yr. Four patients reached end-stage renal disease by 12 to 28 yr. Renal biopsies, available in four cases, disclosed focal segmental glomerulosclerosis in three and crystals in three. Genetic screening showed that patients were compound heterozygous for mutations in the CTNS gene in four families and homozygous in two families. Patients had at least one "mild" mutation. A single heterozygous mutation was identified in one family and none in two families (only 72% mutations found). Renal involvement is heterogeneous in patients with noninfantile cystinosis even within families, and renal disease should be assessed even in families of patients with seemingly isolated ocular forms.

A novel mutation in NFKBIA/IKBA results in a degradation-resistant N-truncated protein and is associated with ectodermal dysplasia with immunodeficiency

Alterations in nuclear factor kappa B (NF-kappaB) essential modulator (NEMO; HUGO-approved symbol IKBKG) underlie most cases of ectodermal dysplasia with immune deficiency (EDI), a human disorder characterized by anhidrosis with diminished immunity. EDI has also been associated with a single heterozygous mutation at position Ser32 of the NF-kappaB inhibitor IkappaBalpha, one of two phosphorylation sites that are essential for targeting IkappaBalpha for proteasomal degradation and hence for activation of NF-kappaB. We report a novel heterozygous nonsense mutation in the IKBA (HUGO-approved symbol, NFKBIA) gene of a 1-year-old male child with EDI that introduces a premature termination codon at position Glu14. An in-frame methionine downstream of the nonsense mutation allows for reinitiation of translation. The resulting N-terminally truncated protein lacks both serine phosphorylation sites and inhibits NF-kappaB signaling by functioning as a dominant negative on NF-kappaB activity in lymphocytes and monocytes. These findings support the scanning model for translation initiation in eukaryotes and confirm the critical role of the NF-kappaB in the human immune response.

Genetic investigation of four meiotic genes in women with premature ovarian failure

The goal of this study was to determine whether mutations of meiotic genes, such as disrupted meiotic cDNA (DMC1), MutS homolog (MSH4), MSH5, and S. cerevisiae homolog (SPO11), were associated with premature ovarian failure (POF). Case-control study. Blood sampling, karyotype, hormonal dosage, ultrasound, and ovarian biopsy were carried out on most patients. However, the main outcome measure was the sequencing of genomic DNA from peripheral blood samples of 41 women with POF and 36 fertile women (controls). A single heterozygous missense mutation, substitution of a cytosine residue with thymidine in exon 2 of MSH5, was found in two Caucasian women in whom POF developed at 18 and 36 years of age. This mutation resulted in replacement of a non-polar amino acid (proline) with a polar amino acid (serine) at position 29 (P29S). Neither 36 control women nor 39 other patients with POF possessed this genetic perturbation. Another POF patient of African origin showed a homozygous nucleotide change in the tenth of DMC1 gene that led to an alteration of the amino acid composition of the protein (M200V). The symptoms of infertility observed in the DMC1 homozygote mutation carrier and in both patients with a heterozygous substitution in exon 2 of the MSH5 gene provide indirect evidence of the role of genes involved in meiotic recombination in the regulation of ovarian function. MSH5 and DMC1 mutations may be one explanation for POF, albeit uncommon.

Five Novel Mutations in F13B Gene Resulting in FXIII Deficiency.

Introduction. FXIII deficiency is a rare autosomal recessive disorder affecting approximatly 1 out of 1–3 million inhabitans. The disease is characterized by bleeding, impaired wound repair and spontaneous abortions in females. Extracellular FXIII molecule has a tetramer structure composing of two catalytic A-subunits and two B-subunits that act as a carrier molecules. Based on genotype there are two types of FXIII deficiency: A-subunit deficiency (XIIIA) when mutations affect F13A gene and much rarely B-subunit deficiency (XIIIB) when mutations affect F13B gene. Both types result in absence of FXIII catalytical activity in plasma. To date, only five families with isolated B-subunit deficiency have been described in the literature. Here we report five novel mutations, affecting F13B gene and resulting in FXIII deficiency.Materials and Methods. FXIII activity was measured by photometric assay according to Fickenscher et al. (1991). Fiveteen exons of F13A gene as well as 12 exons of F13B gene and their flanking regions were amplified by PCR. Sequencing was performed on an automated sequencing system.Results and Discussion. Five german origin patients with mildly reduced FXIII deficiency have been routinely investigated in order to identify genetic defects within F13A and F13B genes. All patients have shown single heterozygous mutations in F13B gene, revealing two missense, one deletion, one insertion, and one splice site mutation. There were no genetic defects in F13A gene. Patient E.M. (female, born 1947, FXIII activity 47–53%, postoperative bleeding) had a missense mutation in exon 2 (c.73 T>C, Cys5Arg) resulting in disruption of disulfide bond between amino acids Cys5 and Cys56. Patient H.D. (male, born 1983, FXIII activity 54%, epistaxis) showed a missense mutation in exon 3 (c.406C>T, Leu116Phe). It may cause instability of disulfide bond between neighbouring Cys117 and Cys71 in the second domain. Patient E.R. (female, born 1989, FXIII activity 53%, increased bleeding during menstruation) was heterozygous for an in-frame deletion (c.471–473delATT) resulting in deletion of Leu138. Patient O.S. (female, born 1983, FXIII activity 46–57%, bleeding after tonsillectomy) had a small insertion (c.1959insT) in the exon 12 changing the distal amino acid (634–641) sequence and predisposing a synthesis of additional 21 new amino acids at the Carboxy-termini of FXIIIB-Subunit due to disruption of Stop codon at position 641. Patient P.G. (male, born 1974, FXIII activity 43%, bleeding after tooth extraction) was heterozygous for a splice site mutation in intron 3 (IVS3-1 G>C). Interestingly this patient turned out also to have a mild von Willebrand Syndrome (FVIII activity 76%, vWF:RiCo 48%, vWF:Ag 56%, vWF-Collagen-Binding activity 0.54, AB0 blood group A).In conclusion,1.our results suggest higher prevalence of FXIIIB deficiency as it was thought before,2.Patients having mild (heterozygous) FXIIIB deficiency may bleed upon provocations.

Rare heterozygous parkin variants in French early-onset Parkinson disease patients and controls

Background:Mutations in the parkin gene cause autosomal recessive early-onset parkinsonism. The effect of single heterozygous mutations in parkin is still unclear. The aim of this study was to evaluate the...

Deciphering the role of heterozygous mutations in genes associated with parkinsonism

The association of six genes with monogenic forms of parkinsonism has unambiguously established that the disease has a genetic component. Of these six genes, LRRK2 (leucine-rich repeat kinase 2, or PARK8), parkin (PARK2), and PINK1 (PTEN-induced putative kinase 1, or PARK6) are the most clinically relevant because of their mutation frequency. Insights from initial familial studies suggest that LRRK2-associated parkinsonism is dominantly inherited, whereas parkinsonism linked to parkin or PINK1 is recessive. However, screening of patient cohorts has revealed that up to 70% of people heterozygous for LRRK2 mutations are unaffected, and that more than 50% of patients with mutations in parkin or PINK1 have only a single heterozygous mutation. Deciphering the role of heterozygosity in parkinsonism is important for the development of guidelines for genetic testing, for the counselling of mutation carriers, and for the understanding of late-onset Parkinson's disease. We discuss the roles of heterozygous LRRK2 mutations and heterozygous parkin and PINK1 mutations in the development of parkinsonism, and propose an integrated aetiological model for this complex disease.

ATP13A2 missense mutations in juvenile parkinsonism and young onset Parkinson disease

To assess the prevalence, nature, and associated phenotypes of ATP13A2 gene mutations among patients with juvenile parkinsonism (onset <21 years) or young onset (between 21 and 40 years) Parkinson disease (YOPD). We studied 46 patients, mostly from Italy or Brazil, including 11 with juvenile parkinsonism and 35 with YOPD. Thirty-three cases were sporadic and 13 had positive family history compatible with autosomal recessive inheritance. Forty-two had only parkinsonian signs, while four (all juvenile-onset) had multisystemic involvement. The whole ATP13A2 coding region (29 exons) and exon-intron boundaries were sequenced from genomic DNA. A novel homozygous missense mutation (Gly504Arg) was identified in one sporadic case from Brazil with juvenile parkinsonism. This patient had symptoms onset at age 12, levodopa-responsive severe akinetic-rigid parkinsonism, levodopa-induced motor fluctuations and dyskinesias, severe visual hallucinations, and supranuclear vertical gaze paresis, but no pyramidal deficit nor dementia. Brain CT scan showed moderate diffuse atrophy. Furthermore, two Italian cases with YOPD without atypical features carried a novel missense mutation (Thr12Met, Gly533Arg) in single heterozygous state. We confirm that ATP13A2 homozygous mutations are associated with human parkinsonism, and expand the associated genotypic and clinical spectrum, by describing a homozygous missense mutation in this gene in a patient with a phenotype milder than that initially associated with ATP13A2 mutations (Kufor-Rakeb syndrome). Our data also suggest that ATP13A2 single heterozygous mutations might be etiologically relevant for patients with YOPD and further studies of this gene in Parkinson disease are warranted.

Construction and validation of a Parkinson's disease mutation genotyping array for the Parkin gene

Parkin mutations account for the majority of familial and sporadic early onset Parkinson's disease (EOPD) cases with a known genetic association. More than 100 mutations have been described in the Parkin gene that includes homozygous, compound heterozygous, and single heterozygous mutations. We have designed a Parkin mutation genotyping array (gene chip) that includes published Parkin sequence variants and allows their simultaneous detection. The chip was validated by screening 85 PD cases and 47 controls previously tested for Parkin mutations. Similar genotyping microarrays have been developed for other genetically heterogeneous diseases including age-related macular degeneration. Here, we show the utility of a genotyping array for Parkinson's disease by analysis of 60 subjects from the Genetic Epidemiology of Parkinson Disease (GEPD) study that includes 15 early-onset PD case probands and 45 relatives.

Biological effects of the PINK1 c.1366C&gt;T mutation: implications in Parkinson disease pathogenesis

PINK1 gene mutations are a cause of recessively inherited, early-onset Parkinson's disease. In some patients, a single heterozygous mutation has been identified, including the recurrent c.1366C>T transition. The interpretation of this finding remains controversial. Furthermore, the c.1366C>T mutation is associated with lower levels of PINK1 transcript, raising the question of whether mRNA levels correlate with the clinical status. We sequenced genomic DNA and copy DNA (cDNA) from 20 subjects carrying the c.1366C>T mutation in the homozygous (n = 5) or heterozygous (n = 15) state. In 17 mutation carriers, messenger RNA (mRNA) was quantified by real-time PCR using four different assays (PINK1 exon 5-6 or exon 7-8 relative to control genes SDHA or YWHAZ). Genomic sequencing confirmed the presence and zygosity of PINK1 mutations. cDNA sequencing in heterozygous mutation carriers revealed a strong wild-type and a much weaker or almost absent mutant signal, whereas in the homozygous patients, only the mutant signal was detected. Homozygous and heterozygous carriers showed PINK1 mRNA levels relative to a reference gene in the range of 0.1-0.2 and 0.5-0.6, respectively, compared with values of 0.9-1.0 in mutation-negative individuals. Treatment of lymphoblasts from a heterozygous mutation carrier with cycloheximide markedly increased the mutant transcript signal. We conclude that the recurrent PINK1 c.1366C>T mutation exerts a major effect at the mRNA level (80-90% reduction), most likely via nonsense-mediated mRNA decay. The absence of correlation between PINK1 mRNA levels and clinical status in heterozygous mutation carriers suggests that other genetic or environmental factors play a role in determining the phenotypic variability associated with the c.1366C>T mutation.

Clinical Spectrum of Homozygous and Heterozygous PINK1 Mutations in a Large German Family With Parkinson Disease

Although homozygous mutations in the PTEN-induced putative kinase 1 (PINK1) gene have been unequivocally associated with early-onset Parkinson disease (PD), the role of single heterozygous PINK1 mutations is less clear. To investigate the role of homozygous and heterozygous PINK1 mutations in a large German pedigree (family W). Mutation analysis of PINK1 and results of standardized neurological and motor examination by 3 independent movement disorder specialists, including blinded video rating. University of Lübeck. Twenty family members. The PINK1 genotype and PD status of all family members. The index patient of family W carried a homozygous nonsense mutation (c.1366C>T; p.Q456X) and presented with a phenotype closely resembling idiopathic PD but with an onset at 39 years of age. The family included a total of 4 affected homozygous members (age, 60-71 years; age at onset, 39-61 years), 6 members with slight or mild signs of PD (affected) and a heterozygous mutation (age, 31-49 years), and 5 unaffected heterozygous mutation carriers (age, 34-44 years). Although none of the heterozygous affected family members was aware of their signs (asymptomatic), the clinical findings were unequivocal and predominantly or exclusively present on their dominant right-hand side, eg, unilaterally reduced or absent arm swing and unilateral rigidity. The heterozygous members were all considerably younger than the affected homozygous mutation carriers. Heterozygous PINK1 mutations may predispose to PD, as was previously suggested by the presence of dopamine hypometabolism in asymptomatic mutation carriers. Long-term follow-up of our large family W provides an excellent opportunity to further evaluate the role of single heterozygous PINK1 mutations later in life, which will have major implications on genetic counseling.

Case-Control Study of the Parkin Gene in Early-Onset Parkinson Disease

Mutations in parkin are estimated to account for as much as 50% of familial Parkinson disease (PD) and 18% of sporadic PD. Single heterozygous mutations in parkin in both familial and sporadic cases may also increase susceptibility to PD. To our knowledge, all previous studies have been restricted to PD cases; this is the first study to systematically screen the parkin coding regions and exon deletions and duplications in controls. To determine the frequency and spectrum of parkin variants in early-onset PD cases (aged < or =50 years) and controls participating in a familial aggregation study. We sequenced the parkin gene in 101 cases and 105 controls. All cases and controls were also screened for exon deletions and duplications by semiquantitative multiplex polymerase chain reaction. Thirteen (12.9% [95% confidence interval, 7%-21%]) of the 101 cases had a previously described parkin mutation: 1 was homozygous, 11 were heterozygous, and 1 was a compound heterozygote. The mutations Arg42Pro (exon 2) and Arg275Trp (exon 7) were recurrent. The previously reported synonymous substitution Leu261Leu (c.884A>G) was identified in 4 (3.9%) of 101 cases and 2 (2%) of 105 controls (P = .44). Excluding the synonymous substitution Leu261Leu (heterozygotes), 10 (9.9% [95% confidence interval, 4.6%-17.5%]) carried mutations. The frequency of mutations among cases that were not selected based on family history of PD is similar to what has previously been reported in sporadic PD. The similar frequency of Leu261Leu in cases and controls suggests it is a normal variant rather than a disease-associated mutation. We confirmed that heterozygous parkin mutations may increase susceptibility for early-onset PD.

Analysis of Mutations in the Urate Transporter 1 (URAT1) Gene of Japanese Patients with Hypouricemia in Northern Japan and Review of the Literature

Background. Renal hypouricemia is an autosomal recessive disorder resulting from inactivating mutations in the urate transporter 1 (URAT1) encoded by SLC22A12. To date, 10 mutations have been identified and W258X in the URAT1 gene is the predominant cause in middle to southwestern Japan. However, it is still unclear whether there is a regional specific distribution of mutations in northern Japan. In this study, we analyzed mutations in the URAT1 gene of five Japanese patients with renal hypouricemia in northern Japan. Methods. Peripheral blood mononuclear cells were isolated from patients with hypouricemia and healthy control subjects. A mutation analysis of the URAT1 gene was performed completely by direct automated sequencing of polymerase chain reaction-amplified DNA products. Results. We identified two mutations. These mutations [c.269G>A (R90H) and c.774G>A (W258X)] have been reported in Japanese patients. Two of five patients were homozygotes (W258X), two carried single heterozygous mutations (W258X), and the remaining one was a compound heterozygote (R90H and W258X). Conclusions. Our study suggests that there is no regional different distribution of the URAT1 genetic mutations in Japanese with renal hypouricemia.

Homozygous and Compound Heterozygous Mutations in ZMPSTE24 Cause the Laminopathy Restrictive Dermopathy

Restrictive dermopathy (RD) is a lethal human genetic disorder characterized by very tight, thin, easily eroded skin, rocker bottom feet, and joint contractures. This disease was recently reported to be associated with a single heterozygous mutation in ZMPSTE24 and hypothesized to be a digenic disorder (Navarro et al, Lamin A and ZMPSTE24 (FACE-1) defects cause nuclear disorganization and identify restrictive dermopathy as a lethal neonatal laminopathy. Hum Mol Genet 13:2493-2503, 2004). ZMPSTE24 encodes an enzyme necessary for the correct processing and maturation of lamin A, an intermediate filament component of the nuclear envelope. Here we present four unrelated patients with homozygous mutations in ZMPSTE24 and a fifth patient with compound heterozygous mutations in ZMPSTE24. Two of the three different mutations we found are novel, and all are single base insertions that result in messenger RNA frameshifts. As a consequence of the presumed lack of ZMPSTE24 activity, prelamin A, the unprocessed toxic form of lamin A, was detected in the nuclei of both cultured cells and tissue from RD patients, but not in control nuclei. Abnormally aggregated lamin A/C was also observed. These results indicate that RD is an autosomal recessive laminopathy caused by inactivating ZMPSTE24 mutations that result in defective processing and nuclear accumulation of prelamin A.

Analysis of the PINK1 gene in a cohort of patients with sporadic early-onset parkinsonism in Taiwan

Mutations in the PINK1 gene have been shown to cause autosomal recessive Parkinson's disease (PD) and/or early onset sporadic PD in Italy, Spain, North America, Ireland, and Asia. However, there are limited data on PINK1 mutations in sporadic early onset Asian PD patients. To determine the prevalence of PINK1 mutation in Taiwanese population, we conducted genetic analysis of PINK1 mutation in 73 early onset sporadic PD and 94 normal control subjects. We only identified a novel single heterozygous mutation R 407Q mutation in exon 6 of this gene in one patient at the age onset of 54. Overall, these data indicate that PINK1 mutations are rare in our population. Based on our results, unless common mutational hotspots are identified, routine testing for this mutation at least in our population may not be cost-effective.

Total Iodide Organification Defect: Clinical and Molecular Characterization of an Italian Family

Thyroid peroxidase (TPO) deficiency is frequently involved in total iodide organification defects (TIOD). According to the recessive mode of inheritance, mutations are found in homozygous or in compound heterozygous states. However, a single heterozygous TPO mutation is reported in a high percentage (approximately 20%) of patients with typical TIOD phenotype. In the present study, the genetic and clinical evaluation of a TIOD family is reported. The propositus is an Italian girl with congenital hypothyroidism and positive perchlorate discharge test. Two TPO frameshift mutations were documented: a C deletion at 477 in exon 5, and a GGCC duplication at 1277 in exon 8. Unaffected family members, heterozygous for one of the two TPO mutations, were also studied in order to evaluate in vivo the functional activity of a single TPO allele. They have been found to have normal thyroid morphology and function with normal perchlorate test. In conclusion, the present study reports the clinical and molecular investigations in an Italian TIOD family. The results show that the TIOD phenotype in the propositus is associated to a compound heterozygous pattern, while a single TPO mutation does not significantly affect in vivo the efficiency of iodide organification. Therefore, extensive analyses of TPO gene and 2p25 locus are needed in the frequent TIOD cases in whom conventional investigations disclosed only one mutant allele.

Early-onset parkinsonism associated with PINK1 mutations

To assess the prevalence, nature, and associated phenotypes of PINK1 gene mutations in a large series of patients with early-onset (<50 years) parkinsonism. The authors studied 134 patients (116 sporadic and 18 familial; 77% Italian) and 90 Italian controls. The whole PINK1 coding region was sequenced from genomic DNA; cDNA was analyzed in selected cases. Homozygous pathogenic mutations were identified in 4 of 90 Italian sporadic cases, including the novel Gln456Stop mutation; single heterozygous truncating or missense mutations were found in another 4 Italian sporadic cases, including two novel mutations, Pro196Leu and Gln456Stop. Pathogenic mutations were not identified in the familial cases. Novel (Gln115Leu) and known polymorphisms were identified with similar frequency in cases and controls. In cases carrying single heterozygous mutation, cDNA analysis detected no additional mutations, and revealed a major pathogenic effect at mRNA level for the mutant C1366T/Gln456Stop allele. All patients with homozygous mutations had very early disease onset, slow progression, and excellent response to l-dopa, including, in some, symmetric onset, dystonia at onset, and sleep benefit, resembling parkin-related disease. Phenotype in patients with single heterozygous mutation was similar, but onset was later. PINK1 homozygous mutations are a relevant cause of disease among Italian sporadic patients with early-onset parkinsonism. The role of mutations found in single heterozygous state is difficult to interpret. Our study suggests that, at least in some patients, these mutations are disease causing, in combination with additional, still unknown factors.

Analysis of class switch recombination and somatic hypermutation in patients affected with autosomal dominant hyper-IgM syndrome type 2

Autosomal recessive form of hyper-IgM syndrome type 2 (AR-HIGM2) is secondary to mutations affecting both alleles of AICDA gene encoding activation-induced cytidine deaminase, characterized by defects of immunoglobulin class switch recombination (CSR) and somatic hypermutation (SHM) in most of the patients. We herein report the immunological phenotype of seven patients carrying a single heterozygous R190X mutation in AICDA. Variable defect in in vivo CSR inherited as an autosomal dominant (AD) trait strongly suggests that this heterozygous AICDA mutation causes HIGM (AD-HIGM2). In AD-HIGM2 B cells, CSR was consistently found impaired in vitro. However, in contrast to AR-HIGM2, the CSR-induced double-stranded DNA breaks in the switch region of IgM heavy chain gene were detected. The SHM frequency in V regions of IgM heavy chain gene in B cells was normal in all (but one patient). The characteristics of the AD-HIGM2 phenotype indicate that the AID C-terminal region may be involved in DNA repair machinery required for CSR.

Novel parkin mutations detected in patients with early‐onset Parkinson's disease

A multiethnic series of patients with early-onset Parkinson's disease (EOP) was studied to assess the frequency and nature of parkin/PARK2 gene mutations and to investigate phenotype-genotype relationships. Forty-six EOP probands with an onset age of < 45 years, and 14 affected relatives were ascertained from Italy, Brazil, Cuba, and Turkey. The genetic screening included direct sequencing and exon dosage using a new, cost-effective, real-time polymerase chain reaction method. Mutations were found in 33% of the indexes overall, and in 53% of those with family history compatible with autosomal recessive inheritance. Fifteen parkin alterations (10 exon deletions and five point mutations) were identified, including four novel mutations: Arg402Cys, Cys418Arg, IVS11-3C > G, and exon 8-9-10 deletion. Homozygous mutations, two heterozygous mutations, and a single heterozygous mutation were found in 8, 6, and 1 patient, respectively. Heterozygous exon deletions represented 28% of the mutant alleles. The patients with parkin mutations showed significantly earlier onset, longer disease duration, more frequently symmetric onset, and slower disease progression than the patients without mutations, in agreement with previous studies. This study confirms the frequent involvement of parkin and the importance of genetic testing in the diagnostic work-up of EOP.

Identification of Ten Novel Mutations Associated with Inherited Coagulation Factor V Deficiency.

Factor V is a rare bleeding disorder characterized by low levels of plasma and/or platelet factor V, with an estimated prevalence of 1/1,000,000 and results from defects in the factor V gene. Human coagulation factor V (FV), a single chain glycoprotein, is synthesized in hepatocytes and megakaryocytes with 80% circulating free in plasma and the remainder being released upon platelet activation. The factor V gene comprises 25 exons ranging in size from 72bp to 2820bp coding for a protein which is oriented as A1-A2-B-A3-C1-C2 domains. FV is activated to its active form (FVa) by thrombin or activated factor X (FXa) which removes the B domain, generating a heavy chain and a light chain that are linked together in the presence of calcium ions. FVa binds to FXa and serves as its cofactor in the prothrombinase complex to convert prothrombin to thrombin. There is a high degree of homology between the A and C domains of FV and FVIII.We have investigated 8 unrelated patients from two centres with phenotypic and clinical charisteristics of FV deficiency. Mutation screening was carried out in these patients using Denaturing high performance liquid chromatography (dHPLC) and sequencing. Probable causative mutations were identified in all patients.A total of 10 novel mutations were identified in 8 patients and were located in the A1, A2, A3 and B domains. No mutations were identified in the C domain, and entries on the FV mutation database support our findings that mutations in this domain are less common than elsewhere in this gene. 5/8 patients were diagnosed with mild-moderate FV deficiency, and single heterozygous mutations were identified in each of these patients. 3 missense , 1 donor splicesite and 1 nonsense mutation were identified in the A1, A3 and B domains. The remaining 3/8 patients had severe FV deficiency (FV levels <2u/dl). One was compound heterozygous for 2 missense mutations in the A3 domain; one had a missense mutation in the A2 domain and a frameshift mutation (insertion of a single base pair) in the A3 domain. We have as yet identified only a heterozygous missense mutation in the third patient with severe FV deficiency. Phenotypic data and family history are strongly suggestive of the presence of a second mutation. Quantitative DNA analysis has confirmed the presence of 2 FV alleles, and RNA analysis is in progress to identify the second mutation.100 normal alleles were analysed by dHPLC analysis or allele specific amplification to exclude these changes from being polymorphisms. We also have examined the homology between factor V and factor VIII, and the degree of similarity, between native and mutant amino acids to support these mutations as being causative of FV deficiency.

PINK1 mutations are associated with sporadic early-onset parkinsonism.

We have recently reported homozygous mutations in the PINK1 gene in three consanguineous families with early-onset parkinsonism (EOP) linked to the PARK6 locus. To further evaluate the pathogenic role of PINK1 in EOP and to draw genotype-phenotype correlates, we performed PINK1 mutation analysis in a cohort of Italian EOP patients, mostly sporadic, with onset younger than 50 years of age. Seven of 100 patients carried missense mutations in PINK1. Two patients had two PINK1 mutations, whereas in five patients only one mutation was identified. Age at onset was in the fourth-fifth decade (range, 37-47 years). The clinical picture was characterized by a typical parkinsonian phenotype with asymmetric onset and rare occurrence of atypical features. Slow progression and excellent response to levodopa were observed in all subject. Two of 200 healthy control individuals also carried one heterozygous missense mutation. The identification of a higher number of patients (5%) than controls (1%) carrying a single heterozygous mutation, along with previous positron emission tomography studies demonstrating a preclinical nigrostriatal dysfunction in PARK6 carriers, supports the hypothesis that haploinsufficiency of PINK1, as well as of other EOP genes, may represent a susceptibility factor toward parkinsonism. However, the pathogenetic significance of heterozygous PINK1 mutations still remains to be clarified.