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The effect of loss-of-function variants in the Filaggrin gene on food allergy.

(2013) Ginkel, C.D. van

Introduction:
Food allergy is a potentially lethal disease with a high prevalence which reduces quality of life in children. Although the pathway leading to anaphylaxis is quite straight forward, the mechanism which determines the difference between asymptomatic sensitisation and clinical reactivity is as yet unknown.
The aim of this study was to determine the effect of loss of function gene variants in the filaggrin gene on clinical reactivity, as diagnosed by the Double Blind, Placebo-Controlled Food Challenge(DBPCFC) in children suspected of being food allergic. Data of their parents was included to improve the quality of the genotyping data and to replicate the analysis. The use of this genotypic data as a new screening tool for food allergy was analysed. Furthermore the effect of these variants on sensitisation and the severity of the test reaction is studied.
Materials and Methods:
All enrolled children were tested by means of the DBPCFC and cases were identified as children with at least one positive DBPCFC. Parents were defined as food allergic when this is reported in history. IgE was measured by the CAP-FEIA and outcomes >0.35 kU/l were defined as positive. Symptoms of the reaction during the food challenge were recorded and depending on the involved organ systems, a severity score was made ranging from 0 to 12. DNA from the children and their parents was collected by buccal mucosa samples. DNA was extracted, purified and four gene variants were genotyped: R501X, S3247X, 2282Del4 and R2447X. The quality control of the genotypic information was performed with Haploview. Chi-square tests and both logistic and linear regression analysis were used to study the effect of these gene variants on the defined outcomes. The trio analysis was performed by the FBAT toolkit.
Results:
A total of 173 trios enrolled the study. 18 children were excluded from further analysis due to genotyping errors, non-Caucasian ethnicity, diagnostic irregularities or mendelian errors which indicate unlikely inheritance patterns. Therefore, the results are based on 155 children and their parents. Risk alleles were identified by R501X, S3247X, 2282Del4 and R2447X. From the studied population, 33 children had at least one loss of function variant of the filaggrin gene and of these, 29 were clinically reactive to at least one food. The odds ratio for having at least one loss-of-function gene variant in the filaggrin gene and being clinically reactive was 4.866 (95% CI: 1.6-14.7, p=0.005) and the relative risk is approximately 1.5. No significant confounders were identified for this association. The association between loss-of-function gene variants in the filaggrin gene and food allergy was significantly replicated when including the parents. Based on the data, a significant model was developed with clinical reactivity as outcome and presence of loss-of-function gene variants, gender, specific IgE and eczema ever reported in history as independent variables. With a cut-of value of .90, this model had a specificity of 98.1% to predict food allergy in our high risk population. The model selected 29 patients of which 28 were clinically reactive to at least one food. No association was found between the studied variants of the filaggrin gene and specific IgE values and the severity of the reaction during the DBPCFC.
Conclusion:
Loss-of-function variants of the filaggrin gene were found to be associated with clinical reactivity to at least one food with an relative risk of 1.5 as confirmed by DBPCFC. This means that in our population, high risk children with loss-of-function gene variants in the filaggrin gene are one and a half times more likely to be clinically reactive to at least one food, compared to high risk children carrying wild type alleles. Our data suggest that the filaggrin gene does not play a role in sensitisation and the severity of food allergy. In our high risk population, we are now able to predict clinical reactivity in a proportion of our population. After validating this model in other populations, this could be the first genetic test to be useful in the diagnosis of food allergy in children. Use of this model could reduce the need for the time-demanding DBPCFC.





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ID 1786
Moeder ID 1544
Volgorde Ginkel, C.D. van
Naam GinkelCDvan
Publiceren yes
OAI-naam Student_thesis
Path root/geneeskunde/2013/GinkelCDvan/
Gemaakt op: 2013-11-19 10:02:22
Gemodificeerd op: 2013-11-19 10:02:22
Digitaal ID 528b373ac53c1
Afstudeerrichting opleiding/afstudeerrichting 1
Studierichting Studierichting 1
Titel The effect of loss-of-function variants in the Filaggrin gene on food allergy.
Ruilverkeer mogelijk no
Printen in opdracht no
Aantal pagina's 48
Publicatiejaar 2013
Taal en
Engelse samenvatting Introduction:
Food allergy is a potentially lethal disease with a high prevalence which reduces quality of life in children. Although the pathway leading to anaphylaxis is quite straight forward, the mechanism which determines the difference between asymptomatic sensitisation and clinical reactivity is as yet unknown.
The aim of this study was to determine the effect of loss of function gene variants in the filaggrin gene on clinical reactivity, as diagnosed by the Double Blind, Placebo-Controlled Food Challenge(DBPCFC) in children suspected of being food allergic. Data of their parents was included to improve the quality of the genotyping data and to replicate the analysis. The use of this genotypic data as a new screening tool for food allergy was analysed. Furthermore the effect of these variants on sensitisation and the severity of the test reaction is studied.
Materials and Methods:
All enrolled children were tested by means of the DBPCFC and cases were identified as children with at least one positive DBPCFC. Parents were defined as food allergic when this is reported in history. IgE was measured by the CAP-FEIA and outcomes >0.35 kU/l were defined as positive. Symptoms of the reaction during the food challenge were recorded and depending on the involved organ systems, a severity score was made ranging from 0 to 12. DNA from the children and their parents was collected by buccal mucosa samples. DNA was extracted, purified and four gene variants were genotyped: R501X, S3247X, 2282Del4 and R2447X. The quality control of the genotypic information was performed with Haploview. Chi-square tests and both logistic and linear regression analysis were used to study the effect of these gene variants on the defined outcomes. The trio analysis was performed by the FBAT toolkit.
Results:
A total of 173 trios enrolled the study. 18 children were excluded from further analysis due to genotyping errors, non-Caucasian ethnicity, diagnostic irregularities or mendelian errors which indicate unlikely inheritance patterns. Therefore, the results are based on 155 children and their parents. Risk alleles were identified by R501X, S3247X, 2282Del4 and R2447X. From the studied population, 33 children had at least one loss of function variant of the filaggrin gene and of these, 29 were clinically reactive to at least one food. The odds ratio for having at least one loss-of-function gene variant in the filaggrin gene and being clinically reactive was 4.866 (95% CI: 1.6-14.7, p=0.005) and the relative risk is approximately 1.5. No significant confounders were identified for this association. The association between loss-of-function gene variants in the filaggrin gene and food allergy was significantly replicated when including the parents. Based on the data, a significant model was developed with clinical reactivity as outcome and presence of loss-of-function gene variants, gender, specific IgE and eczema ever reported in history as independent variables. With a cut-of value of .90, this model had a specificity of 98.1% to predict food allergy in our high risk population. The model selected 29 patients of which 28 were clinically reactive to at least one food. No association was found between the studied variants of the filaggrin gene and specific IgE values and the severity of the reaction during the DBPCFC.
Conclusion:
Loss-of-function variants of the filaggrin gene were found to be associated with clinical reactivity to at least one food with an relative risk of 1.5 as confirmed by DBPCFC. This means that in our population, high risk children with loss-of-function gene variants in the filaggrin gene are one and a half times more likely to be clinically reactive to at least one food, compared to high risk children carrying wild type alleles. Our data suggest that the filaggrin gene does not play a role in sensitisation and the severity of food allergy. In our high risk population, we are now able to predict clinical reactivity in a proportion of our population. After validating this model in other populations, this could be the first genetic test to be useful in the diagnosis of food allergy in children. Use of this model could reduce the need for the time-demanding DBPCFC.
Nederlandse samenvatting Introductie:
Voedselallergie is een hoog prevalente en mogelijk lethale ziekte die de kwaliteit van leven bij kinderen nadelig beïnvloedt. Het mechanisme achter anafylaxie is uitgebreid beschreven in de literatuur maar het mechanistisch verschil tussen asymptomatische sensibilisatie en klinische reactiviteit is tot nu toe onbekend. Het doel van dit onderzoek was om het effect van bepaalde varianten van het filaggrine gen op klinische reactiviteit te onderzoeken, waarbij klinische reactiviteit wordt vastgesteld door middel van de Dubbel Blinde, Placebo-Gecontroleerde Voedsel Provocatie( DBPCVP). Daarnaast werd er gekeken naar de relatie tussen deze varianten en sensibilisatie en de ernst van de reactie tijdens de voedsel provocatie.
Materiaal en methode:
Alle geïncludeerde kinderen zijn getest door middel van de DBPCVP. Ze werden geclassificeerd als ‘klinisch reactief’ als ze ooit een positieve uitslag bij een DBPCVP hebben gehad, voor welk voedingsmiddel dan ook. IgE werd gemeten door middel van de CAP-FEIA test en waarden boven de 0.35kU/l werden gedefinieerd als positief. Symptomen van de reactie tijdens de voedsel provocatie werden geregistreerd en aan de hand van de betrokken orgaansystemen werd er een ernst score opgesteld die kon variëren tussen 0 en 12. DNA van de kinderen en hun ouders werd geïsoleerd uit wangslijmvlies en vier genvarianten in het filaggrine gen werden gegenotypeerd: R501XZ, S3247X, 2282Del4 en R2447X. De ouders werden betrokken bij het onderzoek om de betrouwbaarheid van de genotyperings data te vergroten en om de onderzoeksvragen te repliceren in een grotere populatie. De ouders werden als voedsel allergisch gedefinieerd als ze dit aangaven in de anamnese. Voor de kwaliteit controle werd gebruik gemaakt van Haploview. De associatie tussen genotype en fenotype werd onderzocht met behulp van de chi kwadraat test, logistische en lineaire regressie. De trio’s werden geanalyseerd met behulp van de FBAT toolkit.
Resultaten:
In totaal werden er 173 trio’s geïncludeerd in de studie. 18 kinderen werden uitgesloten van verdere analyse door te lage genotyperings waarden, niet-kaukasische etniciteit, diagnostische onregelmatigheden of onwaarschijnlijke overervingspatronen(mendelian errors). Risico allelen werden geïdentificeerd aan de hand van de R501X, S3247X, 2282Del4 en R2447X. Van de 155 kinderen hadden 33 minstens 1 risico allel in hun filaggrine gen, waarvan 29 kinderen klinisch reactief waren. De odds ratio voor deze associatie was 4.9 (95% CI: 1.6-14.7, p=0.005) en het relatief risico is ongeveer 1.5. Er werden geen significante confounders geïdentificeerd voor deze associatie en deze associatie werd significant gerepliceerd in de trio’s. Op basis van deze data is een model ontwikkeld om klinische reactiviteit te voorspellen in onze hoog risico populatie. Naast de aanwezigheid van risico allelen, wordt hierin ook het geslacht, specifiek IgE waarden en eczeem in de anamnese meegenomen als onafhankelijke variabelen. Bij een afkapwaarde van .90 heeft dit model een specificiteit van 98.1%. Het selecteert in onze populatie 29 kinderen waarvan 28 daadwerkelijk klinisch reactief zijn. Er werd geen associatie gevonden tussen de bestudeerde genvarianten en sensibilisatie, dan wel de ernst van de reactie tijdens de DBPCVP.
Conclusie:
Het hebben van risico allelen in het filaggrine gen is geassocieerd met klinische reactiviteit tegen ten minste één voedingsmiddel. Het relatief risico van deze associatie is 1.5, wat betekent dat kinderen met een risico allel in het filaggrine gen een bijna anderhalf maal grotere kans hebben om klinisch reactief te zijn, wanneer vergeleken met kinderen zonder deze risico allelen die ook sterk verdacht worden van voedselallergie. We zijn met het ontwikkelde model in staat om in een proportie van deze hoog risico populatie te voorspellen welke kinderen klinisch reactief zijn en welke niet. Na validatie in andere populaties zou dit model mogelijk de eerste genetische test kunnen zijn om voedselallergie bij kinderen te diagnosticeren zonder de tijdrovende DBPCVP.
Onderwijsinstelling Medical Sciences
Type embargo abstract openbaar, scriptie op aanvraag
Auteur(s) Ginkel, C.D. van
UMCG begeleider(s) Dubois, Prof. Dr. A.E.J.; Koppelman, Prof. Dr. G.H,; Flokstra- de Blok, Dr. B.M.J.
Auteur(s) Ginkel, C.D. van
UMCG begeleider(s) Dubois, Prof. Dr. A.E.J.; Koppelman, Prof. Dr. G.H,; Flokstra- de Blok, Dr. B.M.J.


 
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