Common European Mutation Research Articles

One mutation, two distinct disease variants: unravelling the impact of transthyretin amyloid fibril composition.

Although hereditary transthyretin (h-ATTR) amyloidosis is a monogenetic disease, a large variation in its phenotype has been observed. The common hypothesis of amyloid fibril formation involves dissociation of the transthyretin (TTR) tetramer into monomers that after misfolding reassemble into amyloid fibrils. This notion is partly challenged by the finding of two distinct types of amyloid fibrils. One of these, type A, consists of C-terminal ATTR fragments and full-length TTR, whereas the other, type B, consists only of full-length TTR. All organs of an individual patient contain ATTR deposits of either type A or type B fibrils, and the composition in each individual remains unchanged over time. The finding of two distinct types of ATTR fibrils suggests that there are at least two different pathways in operation for ATTR fibril formation. For the most common European mutation, TTR Val30Met, ATTR fibril composition is related to the outcome of liver transplantation, which is the first successful treatment for the disease, and the penetrance of the trait. In addition, the presence of C-terminal ATTR fragments has an impact on the affinity for various tracers used for noninvasive imaging of amyloid depositions such as 99 m-technetium-diphosphono-propanodicarboxylic acid scintigraphy and positron emission tomography utilizing Pittsburgh component B, and even for the gold standard diagnostic procedure, tissue biopsy stained by Congo red and examined under polarized light. The importance of amyloid fibril composition needs to be taken into consideration when designing clinical trials of treatment modalities, and also in the evaluation of diagnostic methods such as imaging techniques.

Gene mutations in Wilson disease in Egyptian children: Report on two novel mutations

Background and study aimsWilson disease (WD) is an autosomal recessive disorder, caused by defects in copper-transporting P-type adenosine triphosphatase (ATPase) encoded by the ATP7B gene, resulting in the deposition of copper in the liver and brain with significant disability or death if left untreated. An available regimen of treatment gives hope to those predisposed to the disease if diagnosed early. The objective of this study was to determine the frequency of the most common European mutation (p.H1069Q) in Egyptian children with WD, in addition to screening for previously reported mutations in the Egyptian patients in our selected group. Patients and methodsDirect DNA sequencing was applied to exons (13, 14, 18, and 19) of the ATP7B gene for 19 patients previously diagnosed with WD. Then DNA sequencing and pedigree analysis were performed in the families of the patients showing variations in their results for the purpose of family screening and carrier detection. Six out of 19 patients were studied with their families (three families). ResultsWe identified five variants of which two were novel among the studied patients. One of the novel variants was synonymous substitution (p.A1074A) in 16% of patients and the other was predicted to be missense disease-causing mutations (p.T1076I) in 16% of patients, and three previously published mutations p.H1069Q were detected in 5% of patients, p.P1273Q in 10% of patients, and a silent variant p.A1003A in 26% of patients. ConclusionScreening for the two exons 14 and 18 of the ATP7B gene is important in Egyptian patients especially in suspected patients without hepatic manifestations.

MUTYH-associated polyposis (MAP): evidence for the origin of the common European mutations p.Tyr179Cys and p.Gly396Asp by founder events

MUTYH-associated polyposis (MAP) is an autosomal recessive adenomatous polyposis caused by biallelic germline mutations of the base-excision-repair gene MUTYH. In MAP patients of European origin, the combined allele frequency of the mutations p.Tyr179Cys and p.Gly396Asp ranges between 50 and 82%, while these mutations have not been identified in Far Eastern Asian populations, supporting the hypothesis that a founder effect has occurred at some point in European history. To investigate the natural history of the two common European MUTYH alleles, we genotyped six gene-flanking microsatellite markers in 80 unrelated Italian and German MAP patients segregating one or both mutations and calculated their age in generations (g) by using DMLE+2.2 software. Three distinct common haplotypes, one for p.Tyr179Cys and two for p.Gly396Asp, were identified. Estimated mutation ages were 305 g (95% CS: 271-418) for p.Tyr179Cys and 350 g (95% CS: 313-435) for p.Gly396Asp. These results provide evidence for strong founder effects and suggest that the p.Tyr179Cys and p.Gly396Asp mutations derive from ancestors who lived between 5-8 thousand years and 6-9 thousand years B.C., respectively.

Eight new mutations and the expanding phenotype variability in muscular dystrophy caused by ANO5

Description of 8 new ANO5 mutations and significant expansion of the clinical phenotype spectrum associated with previously known and unknown mutations to improve diagnostic accuracy. DNA samples of 101 patients in 95 kindreds at our quaternary referral center in Finland, who had undetermined limb-girdle muscular dystrophy (LGMD), calf distal myopathy, or creatine kinase (CK) elevations of more than 2,000 IU/L, were selected for ANO5 genetic evaluation, and the clinical findings of patients with mutations were retrospectively analyzed. A total of 25 patients with muscular dystrophy caused by 11 different recessive mutations in the ANO5 gene were identified. The vast majority of mutations, 8 of 11, proved to be previously unknown new mutations. The most frequent mutation, c.2272C>T (p.R758C), was present in 20 patients. The phenotypes associated with this and the common European mutation, c.191dupA, varied from nearly asymptomatic high hyperCKemia to severe LGMD with consistently milder phenotypes in female patients. Mutations in ANO5 are a frequent cause of undetermined muscular dystrophy, with both distal and proximal presentation. Other types include high hyperCKemia, myalgia, or calf hypertrophy over decades without significant weakness, especially in female patients. Mutations are distributed all over the gene, indicating that muscular dystrophy caused by ANO5 can be expected to occur in all populations.

De novo SCN1A mutations in migrating partial seizures of infancy

To determine the genetic etiology of the severe early infantile onset syndrome of malignant migrating partial seizures of infancy (MPSI). Fifteen unrelated children with MPSI were screened for mutations in genes associated with infantile epileptic encephalopathies: SCN1A, CDKL5, STXBP1, PCDH19, and POLG. Microarray studies were performed to identify copy number variations. One patient had a de novo SCN1A missense mutation p.R862G that affects the voltage sensor segment of SCN1A. A second patient had a de novo 11.06 Mb deletion of chromosome 2q24.2q31.1 encompassing more than 40 genes that included SCN1A. Screening of CDKL5 (13/15 patients), STXBP1 (13/15), PCDH19 (9/11 females), and the 3 common European mutations of POLG (11/15) was negative. Pathogenic copy number variations were not detected in 11/12 cases. Epilepsies associated with SCN1A mutations range in severity from febrile seizures to severe epileptic encephalopathies including Dravet syndrome and severe infantile multifocal epilepsy. MPSI is now the most severe SCN1A phenotype described to date. While not a common cause of MPSI, SCN1A screening should now be considered in patients with this devastating epileptic encephalopathy.

On the origin and diffusion of BRCA1 c.5266dupC (5382insC) in European populations

The BRCA1 mutation c.5266dupC was originally described as a founder mutation in the Ashkenazi Jewish (AJ) population. However, this mutation is also present at appreciable frequency in several European countries, which raises intriguing questions about the origins of the mutation. We genotyped 245 carrier families from 14 different population groups (Russian, Latvian, Ukrainian, Czech, Slovak, Polish, Danish, Dutch, French, German, Italian, Greek, Brazilian and AJ) for seven microsatellite markers and confirmed that all mutation carriers share a common haplotype from a single founder individual. Using a maximum likelihood method that allows for both recombination and mutational events of marker loci, we estimated that the mutation arose some 1800 years ago in either Scandinavia or what is now northern Russia and subsequently spread to the various populations we genotyped during the following centuries, including the AJ population. Age estimates and the molecular evolution profile of the most common linked haplotype in the carrier populations studied further suggest that c.5266dupC likely entered the AJ gene pool in Poland approximately 400-500 years ago. Our results illustrate that (1) BRCA1 c.5266dupC originated from a single common ancestor and was a common European mutation long before becoming an AJ founder mutation and (2) the mutation is likely present in many additional European countries where genetic screening of BRCA1 may not yet be common practice.

Comprehensive analysis of the gene encoding filaggrin uncovers prevalent and rare mutations in ichthyosis vulgaris and atopic eczema

We recently reported two common filaggrin (FLG) null mutations that cause ichthyosis vulgaris and predispose to eczema and secondary allergic diseases. We show here that these common European mutations are ancestral variants carried on conserved haplotypes. To facilitate comprehensive analysis of other populations, we report a strategy for full sequencing of this large, highly repetitive gene, and we describe 15 variants, including seven that are prevalent. All the variants are either nonsense or frameshift mutations that, in representative cases, resulted in loss of filaggrin production in the epidermis. In an Irish case-control study, the five most common European mutations showed a strong association with moderate-to-severe childhood eczema (chi2 test: P = 2.12 x 10(-51); Fisher's exact test: heterozygote odds ratio (OR) = 7.44 (95% confidence interval (c.i.) = 4.9-11.3), and homozygote OR = 151 (95% c.i. = 20-1,136)). We found three additional rare null mutations in this case series, suggesting that the genetic architecture of filaggrin-related atopic dermatitis consists of both prevalent and rare risk alleles.

P0019 PP SURGICAL MANAGEMENT OF PFIC

Introduction: There are at least 3 causes of low gammaGT progressive familial intrahepatic cholestasis (PFIC). Mutations in 2 genes have so far been shown to underlie the condition:ABCB11 and ATP8B1, causing BSEP and FIC1 deficiency respectively. Both partial external biliary diversion and liver transplantation have been used to treat these patients. The outcome of both treatments has been examined in a large group of children. Methods: Over 100 patients have confirmed mutations in A BCB11 or ATP8B1. From this cohort we have selected those who have had partial external biliary diversion and / or liver transplantation. Results: Partial biliary diversion or ileal bypass (PBD) has been performed in 31 BSEP patients. 10/31 had a poor response to PBD, of these 7 have subsequently required liver transplantation. Patients with at least one copy of mutation D482G appear to have a better outcome than other patients. A good response to PBD was seen in 9/11 with this mutation. In 5/11 pruritus resolved. Only 1/11 with D482G have needed transplantation, but 6/20 without it have. The most common European mutation, E297G, also appears to confer advantage. Growth improved in 9/12, but pruritus resolved in only 3/12. A total of 29 BSEP patients have undergone OLT. 25/29 are completely well. 2 have had diarrhoea, 6 have not fully regained growth. PBD has been performed in 19 FIC1 patients. 5 of these 19 patients subsequently underwent OLT. In the other 14, outcomes have been variable. 3 have shown an overall good response. 4 have resolved pruritus. However, in 4 patients PBD was of no or minimal benefit, and in another 4 initial improvement was followed by a recurrence of symptoms. 24 FIC1 patients have had OLT including 5 of who previously had PBD. 2 patients died from OLT complications. Following OLT, 8/22 surviving patients have had pancreatic problems, 17/22 have had problems with post-OLT diarrhoea and in 18/22 allograft steatosis or steatohepatitis were noted on biopsy. 12/22 have had no or minimal catch-up growth, and puberty remains delayed in 5/8. Only 1/22 transplanted FIC1 patients have had none of these problems, this patient was a compound heterozygote for 1 mutation usually associated with PFIC and one BRIC mutation. Conclusion: In this cohort of low gammaGT PFIC patients important differences in outcome were found to be dependent on genetic basis. For BSEP deficiency PBD appears to depend on mutations found, but OLT seems to work well. An overall good response to PBD was seen in 8/11 patients with D482G, and 9/12 with E294G. In FIC1 deficiency response to PBD poor, but complications and symptoms post-transplant were very significant. Surgical treatment for FIC1 deficiency may still be necessary, but other forms of treatment must be sought. Results are presented on behalf of the International consortium.

Wilson disease: novel mutations in the ATP7B gene and clinical correlation in Brazilian patients.

Wilson disease (WD) is a rare inherited autosomal recessive disorder caused by a defect in a metal transporting P-type ATPase, resulting in copper overload in various tissues and cells. The aim was to assess both the phenotype in Brazilian WD patients and the corresponding ATP7B genotype. Sixty subjects belonging to 46 pedigrees diagnosed as WD were included in this study. Direct sequencing of all 21 exons within ATP7B and their flanking introns was performed. Demographic, clinical, laboratory and histopathological data at the time of diagnosis were obtained. We identified twenty-five mutations, twelve of them reported for the first time. The c.3402delC mutation had the highest allelic frequency (30.8%), followed by the c.2123T>C (p.L708P) (16.7%). Exons 8 and 15 were the site of 62.5% of the mutations. The common European mutation c.3207C>A (p.H1069Q) was not present at all. Phenotype varied greatly among individuals with the same ATP7B genotype. Our data confirm the heterogeneity of ATP7B genotype in Brazilian WD patients. The mutational spectrum is compatible with the Brazilian history of Mediterranean immigration; however, new mutations, and different frequencies and phenotype associated with the previously known mutations characterize this population. Exons 8 and 15 should be preferentially screened in WD cases from Brazil. Phenotype variation among subjects with the same ATP7B genotype suggests that modifying factors play an additional role in the pathogenesis of WD.

Occurrence, distribution, and phenotype of arylsulfatase A mutations in patients with metachromatic leukodystrophy

Occurrence, distribution, and phenotype of arylsulfatase A (ASA) mutations were investigated in 27 patients with metachromatic leukodystrophy (MLD) from Central Europe, mainly from Austria (n = 15) and Poland (n = 9). Genomic DNA from leukocytes, fibroblasts, or paraffin-embedded, formalin-fixed brain or nerve tissue, respectively, was tested by natural or mutated primer-modulated PCR restriction, fragment length polymorphism for the eight most common European mutations: R84Q, S96F, 459+1G > A, I179S, A212V, 1204+1G > A, P426L, and 1401del11bp. The overall identification rate of unrelated MLD alleles was the highest, in adult (90%), medium in juvenile (50%), and lowest in late infantile (36%) MLD patients. The two common alleles, 459+1G > A and P426L, together accounted for 42% of all 50 unrelated MLD alleles investigated; I179S was observed in 6 of 50 MLD alleles (12%). Thus, I179S was far more frequent than hitherto thought and appears to be a third common mutation in Europe. Moreover, a different allelic distribution between Austrian and Polish juvenile patients was disclosed, indicating genetic heterogeneity of MLD even within Central Europe. The genotype-phenotype correlation suggested by Polten et al. [N Engl J Med 324:18-22, 1991] was not followed by all of our MLD patients. Moreover, some MLD patients with identical ASA mutations presented with different phenotypes. This may be due, at least in some cases, to the presence of an additional mutation on individual mutant alleles. Therefore, prediction of the clinical course from single mutation analysis is not possible.