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This booklet summarizes our current knowledge of founder mutation populations (‘extended families’) in the Netherlands, among other aspects providing insight in where these patients can be expected (coloured maps of the prevalence in the 99 Dutch postal code regions are provided for every phenotype) and what their precise phenotype is.

Inhoudsopgave

Voorwerk

1. Introduction

Arthur Wilde, Peter van Tintelen

2. Founder mutations among the Dutch*

Samenvatting
Many genetic disorders demonstrate mutations that can be traced to a founder, sometimes a person who can be identified. These founder mutations have generated considerable interest, because they facilitate studies of prevalence and penetrance and can be used to quantify the degree of homogeneity within a population. This paper reports on founder mutations among the Dutch and relates their occurrence to the history and demography of the Netherlands. International migration, regional and religious endogamy, and rapid population growth played key roles in shaping the Dutch population. In the first millenniums BC and AD, the Netherlands were invaded by Celts, Romans, Huns, and Germans. In more recent times, large numbers of Huguenots and Germans migrated into the Netherlands. Population growth within the Netherlands was slow until the 19th century, when a period of rapid population growth started. Today, the Dutch population numbers 16 million inhabitants. Several different classes of founder mutations have been identified among the Dutch. Some mutations occur among people who represent genetic isolates within this country. These include mutations for benign familial cholestasis, diabetes mellitus, type I, infantile neuronal ceroid lipofuscinosis, L-DOPA responsive dystonia, and triphalangeal thumb. Although not related to a specific isolate, other founder mutations were identified only within the Netherlands, including those predisposing for hereditary breast-ovarian cancer, familial hypercholesterolemia, frontotemporal dementia, hereditary paragangliomas, juvenile neuronal ceroid lipofuscinosis, malignant melanoma, protein C deficiency, and San Filippo disease. Many of these show a regional distribution, suggesting dissemination from a founder. Some mutations that occur among the Dutch are shared with other European populations and others have been transmitted by Dutch émigrés to their descendents in North America and South Africa. The occurrence of short chromosomal regions that have remained identical by descent has resulted in relatively limited genetic heterogeneity for many genetic conditions among the Dutch. These observations demonstrate the opportunity for gene discovery for other diseases and traits in the Netherlands.
Maurice P A Zeegers, Frans van Poppel, Robert Vlietinck, Liesbeth Spruijt, Harry Ostrer

3. Recurrent and Founder Mutations in the Netherlands: the Long-QT Syndrome*

Samenvatting
Background and objective
The long-QT syndrome (LQTS) is associated with premature sudden cardiac deaths affecting whole families and is caused by mutations in genes encoding for cardiac proteins. When the same mutation is found in different families (recurrent mutations), this may imply either a common ancestor (founder) or multiple de novo mutations. We aimed to review recurrent mutations in patients with LQTS.
Methods
By use of our databases, we investigated the number of mutations that were found recurrently (at least three times) in LQT type 1–3 patients in the Netherlands. We studied familial links in the apparently unrelated probands, and we visualised the geographical distribution of these probands. Our results were compared with published literature of founder effects in LQTS outside the Netherlands.
Results
We counted 14 recurrent LQT mutations in the Netherlands. There are 326 identified carriers of one of these mutations. For three of these mutations, familial links were found between apparently unrelated probands.
Conclusion
Whereas true LQT founder mutations are described elsewhere in the world, we cannot yet demonstrate a real founder effect of these recurrent mutations in the Netherlands. Further studies on the prevalence of these mutations are indicated, and haplotype-sharing of the mutation carriers is pertinent to provide more evidence for founder mutation-based LQTS pathology in our country.
N. Hofman, R. Jongbloed, P. G. Postema, E. Nannenberg, M. Alders, A. A. M. Wilde

4. Founder mutations in the Netherlands: SCN5a 1795insD, the first described arrhythmia overlap syndrome and one of the largest and best characterised families worldwide*

Samenvatting
In this part of a series on founder mutations in the Netherlands, we review a Dutch family carrying the SCN5a 1795insD mutation. We describe the advances in our understanding of the premature sudden cardiac deaths that have accompanied this family in the past centuries. The mutation carriers show a unique overlap of long-QT syndrome (type 3), Brugada syndrome and progressive cardiac conduction defects attributed to a single mutation in the cardiac sodium channel gene SCN5a. It is at present one of the largest and best-described families worldwide and we have learned immensely from the mouse strains with the murine homologue of the SCN5a 1795insD mutation (SCN5a 1798insD). From the studies currently performed we are about to obtain new insights into the phenotypic variability in this monogenic arrhythmia syndrome, and this might also be relevant for other arrhythmia syndromes and the general population. (Neth Heart J 2009;17:422–8.)
P.G. Postema, M.P. Van den Berg, J.P. Van Tintelen, F. Van den Heuvel, M. Grundeken, N. Hofman, W.P. Van der Roest, E.A. Nannenberg, I.P.C. Krapels, C.R. Bezzina, A.A.M. Wilde

5. Founder mutations in the Netherlands: familial idiopathic ventricular fibrillation and DPP6*

Samenvatting
In this part of a series on founder mutations in the Netherlands, we review familial idiopathic ventricular fibrillation linked to the DPP6 gene. Familial idiopathic ventricular fibrillation determines an intriguing subset of the inheritable arrhythmia syndromes as there is no recognisable phenotype during cardiological investigation other than ventricular arrhythmias highly associated with sudden cardiac death. Until recently, it was impossible to identify presymptomatic family members at risk for fatal events. We uncovered several genealogically linked families affected by numerous sudden cardiac deaths over the past centuries, attributed to familial idiopathic ventricular fibrillation. Notably, ventricular fibrillation in these families was provoked by very short coupled monomorphic extrasystoles. We were able to associate their phenotype of lethal arrhythmic events with a haplotype harbouring the DPP6 gene. While this gene has not earlier been related to cardiac arrhythmias, we are now able, for the first time, to identify and to offer timely treatment to presymptomatic family members at risk for future fatal events solely by genetic analysis. Therefore, when there is a familial history of unexplained sudden cardiac deaths, a link to the DPP6 gene may be explored as it may enable risk evaluation of the remaining family members. In addition, when closely coupled extrasystoles initiate ventricular fibrillation in the absence of other identifiable causes, a link to the DPP6 gene should be suspected.
P. G. Postema, I. Christiaans, N. Hofman, M. Alders, T. T. Koopmann, C. R. Bezzina, P. Loh, K. Zeppenfeld, P. G. A. Volders, A. A. M. Wilde

6. Founder mutations in hypertrophic cardiomyopathy patients in the Netherlands*

Samenvatting
In this part of a series on cardiogenetic founder mutations in the Netherlands, we review the Dutch founder mutations in hypertrophic cardiomyopathy (HCM) patients.
HCM is a common autosomal dominant genetic disease affecting at least one in 500 persons in the general population. Worldwide, most mutations in HCM patients are identified in genes encoding sarcomeric proteins, mainly in the myosin-binding protein C gene (MYBPC3, OMIM #600958) and the beta myosin heavy chain gene (MYH7, OMIM #160760). In the Netherlands, the great majority of mutations occur in the MYBPC3, involving mainly three Dutch founder mutations in the MYBPC3 gene, the c.2373_2374insG, the c.2864_2865delCT and the c.2827C>T mutation. In this review, we describe the genetics of HCM, the genotype-phenotype relation of Dutch founder MYBPC3 gene mutations, the prevalence and the geographic distribution of the Dutch founder mutations, and the consequences for genetic counselling and testing. (Neth Heart J 2010;18:248-54.)
I. Christiaans, E.A. Nannenberg, D. Dooijes, R.J.E. Jongbloed, M. Michels, P.G. Postema, D. Majoor-Krakauer, A. van den Wijngaard, M.M.A.M. Mannens, J.P. van Tintelen, I.M. van Langen, A.A.M. Wilde

7. Recurrent and founder mutations in the Netherlands: cardiac Troponin I (TNNI3) gene mutations as a cause of severe forms of hypertrophic and restrictive cardiomyopathy*

Samenvatting
Background
About 2-7% of familial cardiomyopathy cases are caused by a mutation in the gene encoding cardiac troponin I (TNNI3). The related clinical phenotype is usually severe with early onset. Here we report on all currently known mutations in the Dutch population and compared these with those described in literature.
Methods
The TNNI3 gene was screened for mutations in all coding exons and flanking intronic sequences in a large cohort of cardiomyopathy patients. All Dutch index cases carrying a TNNI3 mutation that are described in this study underwent extensive cardiological evaluation and were listed by their postal codes.
Results
In 30 families, 14 different mutations were identified. Three TNNI3 mutations were found relatively frequently in both familial and non-familial cases of hypertrophic cardiomyopathy (HCM) or restrictive cardiomyopathy (RCM). Haplotype analysis showed that p.Arg145Trp and p.Ser166Phe are founder mutations in the Netherlands, while p.Glu209Ala is not. The majority of Dutch TNNI3 mutations were associated with a HCM phenotype. Mean age at diagnosis was 36.5 years. Mutations causing RCM occurred less frequently, but were identified in very young children with a poor prognosis.
Conclusion
In line with previously published data, we found TNNI3 mutations to be rare and associated with early onset and severe clinical presentation.
A. van den Wijngaard, P. Volders, J. P. Van Tintelen, J. D. H. Jongbloed, M. P. van den Berg, R. H. Lekanne Deprez, M. M. A. M. Mannens, N. Hofmann, M. Slegtenhorst, D. Dooijes, M. Michels, Y. Arens, R. Jongbloed, B. J. M. Smeets

8. Recurrent and founder mutations in the Netherlands: mutation p.K217del in troponin T2, causing dilated cardiomyopathy*

Samenvatting
Background
About 30% of dilated cardiomyopathy (DCM) cases are familial. Mutations are mostly found in the genes encoding lamin A/C, beta-myosin heavy chain and the sarcomeric protein cardiac troponin-T (TNNT2). Mutations in TNNT2 are reported in approximately 3% of DCM patients. The overall phenotype caused by TNNT2 mutations is thought to be a fully penetrant, severe disease. This also seems to be true for a recurrent deletion in the TNNT2 gene; p.K217del (also known as p.K210del).
Methods
We compared the phenotype of all Dutch patients identified as carrying the TNNT2 p.K217del mutation with those described in the literature. All index patients underwent cardiological evaluation. Family screening was done in all described families.
Results
Six DCM patients carrying the TNNT2 p.K217del mutation were identified from four Dutch families. Mean age of disease manifestation was 33 years. Heart transplantation was required in three of them at ages 12, 18 and 19 years. These outcomes are comparable with those described in the literature.
Conclusion
Carriers of the TNNT2 p.K217del mutation in our Dutch families, as well as in families described in the literature before, generally show a severe, early-onset form of DCM. (Neth Heart J 2010;18:478–85.)
E. Otten, R.H. Lekanne dit Deprez, M.M. Weiss, M. van Slegtenhorst, M. Joosten, J.J. van der Smagt, N. de Jonge, W.S. Kerstjens-Frederikse, M.T.R. Roofthooft, A.H.M.M. Balk, M.P. van den Berg, J.S. Ruiter, J.P. van Tintelen

9. Recurrent and founder mutations in the Netherlands: the cardiac phenotype of DES founder mutations p.S13F and p.N342D*

Samenvatting
Background
Desmin-related myopathy (DRM) is an autosomally inherited skeletal and cardiac myopathy, mainly caused by dominant mutations in the desmin gene (DES). We describe new families carrying the p.S13F or p.N342D DES mutations, the cardiac phenotype of all carriers, and the founder effects.
Methods
We collected the clinical details of all carriers of p.S13F or p.N342D. The founder effects were studied using genealogy and haplotype analysis.
Results
We identified three new index patients carrying the p.S13F mutation and two new families carrying the p.N342D mutation. In total, we summarised the clinical details of 39 p.S13F carriers (eight index patients) and of 21 p.N342D carriers (three index patients). The cardiac phenotype of p.S13F carriers is fully penetrant and severe, characterised by cardiac conduction disease and cardiomyopathy, often with right ventricular involvement. Although muscle weakness is a prominent and presenting symptom in p.N342D carriers, their cardiac phenotype is similar to that of p.S13F carriers. The founder effects of p.S13F and p.N342D were demonstrated by genealogy and haplotype analysis.
Conclusion
DRM may occur as an apparently isolated cardiological disorder. The cardiac phenotypes of the DES founder mutations p.S13F and p.N342D are characterised by cardiac conduction disease and cardiomyopathy, often with right ventricular involvement.
K. Y. van Spaendonck-Zwarts, A. J. van der Kooi, M. P. van den Berg, E. F. Ippel, L. G. Boven, W.-C. Yee, A. van den Wijngaard, E. Brusse, J. E. Hoogendijk, P. A. Doevendans, M. de Visser, J. D. H. Jongbloed, J. P. van Tintelen

10. Recurrent and founder mutations in the Netherlands: Plakophilin-2 p.Arg79X mutation causing arrhythmogenic right ventricular cardiomyopathy/dysplasia*

Samenvatting
Background
Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is an inherited cardiac disease with reduced penetrance and a highly variable expression. Mutations in the gene encoding the plakophilin-2 gene (PKP2) are detected in about 50% of ARVC/D patients. The p.Arg79X mutation in PKP2 has been identified in Europe and North America and has been functionally characterised. We evaluated the prevalence of the p.Arg79X mutation in PKP2 in the Dutch population.
Methods
Twelve index patients and 41 family members were evaluated in three university hospitals in the Netherlands. The diagnosis of ARVC/D was established according to the recently revised Task Force Criteria. Segregation of the p.Arg79X mutation was studied and haplotypes were reconstructed to determine whether the p.Arg79X mutation was a recurrent or a founder mutation.
Results
The p.Arg79X mutation in PKP2 was identified in 12 index patients. Haplotype analysis revealed a shared haplotype among Dutch p.Arg79X mutation carriers, indicating a common founder. Six index patients (50%) had a first- or second-degree relative who had died of sudden cardiac death below 40 years of age. At age 60, only 60% of the mutation carriers had experienced any symptoms. There was no significant difference in symptom-free survival and event-free survival between men and women.
Conclusion
We have identified the largest series of patients with the same desmosome gene mutation in ARVC/D reported to date. This p.Arg79X mutation in PKP2 is a founder mutation in the Dutch population. The phenotypes of PKP2 p.Arg79X mutation carriers illustrate the clinical variability and reduced penetrance often seen in ARVC/D. (Neth Heart J 2010;18:583–91.)
P. A. van der Zwaag, M. G. P. J. Cox, C. van der Werf, A. C. P. Wiesfeld, J. D. H. Jongbloed, D. Dooijes, H. Bikker, R. Jongbloed, A. J. H. Suurmeijer, M. P. van den Berg, R. M. W. Hofstra, R. N. W. Hauer, A. A. M. Wilde, J. P. van Tintelen

11. Recurrent and founder mutations in the Netherlands – Phospholamban p.Arg14del mutation causes arrhythmogenic cardiomyopathy*

Samenvatting
Background
Recently, we showed that the c.40_42delAGA (p.Arg14del) mutation in the phospholamban (PLN) gene can be identified in 10–15 % of Dutch patients with dilated cardiomyopathy or arrhythmogenic cardiomyopathy. The arrhythmogenic burden of the p.Arg14del mutation was illustrated by the high rate of appropriate ICD discharges and a positive family history for sudden cardiac death.
Methods
Our goal was to evaluate the geographical distribution and the origin of this specific mutation in the Netherlands and to get an estimation of the prevalence in a Dutch population cohort. Therefore, we investigated the postal codes of the places of residence of PLN p.Arg14del mutation carriers and places of birth of their ancestors. In addition, a large population-based cohort (PREVEND) was screened for the presence of this mutation.
Results
By April 2012, we had identified 101 probands carrying the PLN p.Arg14del mutation. A total of 358 family members were also found to carry this mutation, resulting in a total of 459 mutation carriers. The majority of mutation carriers live in the northern part of the Netherlands and analysing their grandparents’ places of birth indicated that the mutation likely originated in the eastern part of the province of Friesland. In the PREVEND cohort we identified six heterozygous PLN p.Arg14del mutation carriers out of 8,267 subjects (0.07 %).
Conclusion
The p.Arg14del mutation in the PLN gene is the most frequently identified mutation in Dutch cardiomyopathy patients. The mutation that arose 575–825 years ago is likely to have originated from the eastern part of the province of Friesland and is highly prevalent in the general population in the northern part of the Netherlands.
P. A. van der Zwaag, I. A. W. van Rijsingen, R. de Ruiter, E. A. Nannenberg, J. A. Groeneweg, J. G. Post, R. N. W. Hauer, I. C. van Gelder, M. P. van den Berg, P. van der Harst, A. A. M. Wilde, J. P. van Tintelen

12. Recurrent and founder mutations in the Netherlands: Extensive clinical variability in Marfan syndrome patients with a single novel recurrent fibrillin-1 missense mutation*

Background/Methods
Marfan syndrome (MFS) is a heritable connective tissue disorder usually caused by a mutation in the fibrillin 1 (FBN1) gene. Typical characteristics of MFS that have been described include dolichostenomelia, ectopia lentis and aortic root dilatation. However, there is great clinical variability in the expression of the syndrome’s manifestations, both between and within families. Here we discuss the clinical variability of MFS by describing a large four-generation Dutch family with MFS.
Results
Nineteen individuals of one family with a single missense FBN1 mutation (c.7916A>G) were identified. The same mutation was found in one unrelated person. Clinical variability was extensive and not all mutation carriers fulfilled the diagnostic criteria for MFS. Some patients only expressed mild skeletal abnormalities, whereas aortic root dilation was present in eight patients, an acute type A aortic dissection was recorded in two other patients, and a mitral valve prolapse was present in eight patients. In some patients cardiac features were not present on initial screening, but did however develop over time.
Conclusion
MFS is a clinically highly variable syndrome, which means a meticulous evaluation of suspected cases is crucial. Mutation carriers should be re-evaluated regularly as cardiovascular symptoms may develop over time. (Neth Heart J 2010;18:85–9.)
J. J. J. Aalberts, A. G. Schuurman, G. Pals, B. J. C. Hamel, G. Bosman, Y. Hilhorst-Hofstee, D. Q. C. M. Barge-Schaapveld, B. J. M. Mulder, M. P. van den Berg, J. P. van Tintelen

13. Founder mutations in the Netherlands: geographical distribution of the most prevalent mutations in the low-density lipoprotein receptor and apolipoprotein B genes*

Samenvatting
Background
In the Netherlands, a screening programme was set up in 1994 in order to identify all patients with familial hypercholesterolaemia (FH). After 15 years of screening, we evaluated the geographical distribution, possible founder effects and clinical phenotype of the 12 most prevalent FH gene mutations.
Methods
Patients who carried one of the 12 most prevalent mutations, index cases and those identified between 1994 and 2009 through the screening programme and whose postal code was known were included in the study. Low-density lipoprotein cholesterol (LDL-C) levels at the time of screening were retrieved. The prevalence of identified FH patients in each postal code area was calculated and visualised in different maps.
Results
A total of 10,889 patients were included in the study. Mean untreated LDL-C levels ranged from 4.4 to 6.4 mmol/l. For almost all mutations, a region of high prevalence could be observed. In total, 51 homozygous patients were identified in the Netherlands, of which 13 true homozygous for one of the 12 most prevalent mutations. The majority of them were living in high-prevalence areas for that specific mutation.
Conclusions
Phenotypes with regard to LDL-C levels varied between the 12 most prevalent FH mutations. For most of these mutations, a founder effect was observed. Our observations can have implications with regard to the efficiency of molecular screening and physician’s perception of FH and to the understanding of the prevalence and distribution of homozygous patients in the Netherlands.
D. M. Kusters, R. Huijgen, J. C. Defesche, M. N. Vissers, I. Kindt, B. A. Hutten, J. J. P. Kastelein
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