The Importance of Sweat Testing for Older Siblings of Patients with CysticFibrosis Identified by Newborn Screening

Anne Munck, MD, Elise Houssin, and Michel Roussey, MD

We report cystic fibrosis (CF) care center instructions for sweat testing in older siblings after implementation of theFrench nationwide newborn screening program, and we evaluate the incidence of unrecognized CF. Nearly 9% offamilies with an infant screened for CF were unaware of an affected older sibling. We strongly recommend sweattesting for all first-degree older children. (J Pediatr 2009;155:928-30)

Implementation of newborn screening programs is in-creasing worldwide to ensure the healthiest possible startfor these newly diagnosed patients.1,2 France (and the

Reunion Island) began a nationwide newborn screeningprogram in 2002 that combined an immunoreactive tryp-sinogen (IRT) assay and DNA mutation analysis on driedblood samples at day 3.3 Data from regional screening lab-oratories and cystic fibrosis (CF) care centers were central-ized at the French Association for the Screening andPrevention of Infant Handicap, with close collaboration be-tween these organizations.3 A Cystic Fibrosis FoundationWorkshop Report4 recommended performing a sweat testfor ‘‘all first-degree siblings and for any half-siblings whohave signs or symptoms of CF or who have 2 parentsknown to be carriers.’’ The opportunity of diagnosing anolder sibling with CF has not yet been evaluated in the lit-erature, and clear guidance on management of older sib-lings is warranted. We report French CF care centerinstructions for sweat testing (ST) in older siblings, andwe assess characteristics of the older sibling diagnosed afterCF screening of an infant sibling.

Methods

Centers involved in regional CF newborn screening before2002 were excluded from the study to evaluate only the im-pact of a recent nationwide newborn screening program. Inthis retrospective survey sent to all selected pediatric CFcare centers, physicians were asked for their protocol forolder siblings (with 1 consensual answer per center) and re-ports of all families with older siblings issued from the par-ents of infants with CF newborn screening detected at eachcenter between 2002 and 2006. Additional data on this oldersibling cohort with CF included date of birth, sex, age, andsymptoms at initial consultation, sweat test value, andDNA mutation analysis.

CF Cystic fibrosis

IRT Immunoreactive trypsinogen

ENT Ear nose and throat

CFTR Cystic fibrosis transmembrane regulator

ST Sweat testing

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Results

Twenty-seven of 28 pediatric CF care centers (96%) com-pleted both questionnaires. Forty-four percent stated thatST was systematically performed on first-degree siblings,36% of centers performed it when the older siblings hadnot been previously screened, and 20% did so only when clin-ically relevant. No questionnaire mentioned discrepancies inresponses among physicians on a team.

Between 2002 and 2006, 596 newborn screened babies werediagnosed with CF. Data on kindred were available for 91%of these patients, and 300 older siblings were identifiedfrom 214 families. Data on their sweat test values were avail-able for 212 children (71%) from 178 families. Among these212 children, a CF diagnosis was reported in 36; 19 had anestablished CF diagnosis before the birth of the baby screenedfor CF, and 17 were identified after the birth of the infantscreened for CF. Findings at initial consultation in these oldersiblings with CF are summarized in the Table.

Median (range) age at diagnosis for the latter cohortwas 60 months (21-135); 59% had symptoms at initialconsultation, mainly with respiratory (90%) and digestive(60%) symptoms, failure to thrive (30%), or ear, nose, andthroat problems (30%). Sweat testing values at initial con-sultation showed, for conductivity (n = 6), unequivocalpositive values ranging from 92 to 115 mmol/L and, forchloride electrolytes (n = 11), values from 48 to 133mmol/L. Three patients with chloride values in the inter-mediate range were symptom free and presentedF508del/R117H-7 T-9 T (n = 2 siblings) or F508del/R347H (n = 1) genotypes. Four additional symptom-freesiblings had positive chloride ST values with F508del/G745X, F508del/R117H-7 T, and F508del/F508del geno-types. Among these newly diagnosed older siblings, 2were false-negative cases from the CF newborn screening

From the French Association for the Screening and Prevention of Infant HandicapAFDPHE (A.M., E.H., M.R.), Pediatric CF Center, University Hospital AP-HP RobertDebre (A.M.), Paris, and the Pediatric CF Center, University Hospital, Rennes (M.R.),France

The authors declare no conflicts of interest.

0022-3476/$ - see front matter. Copyright ª 2009 Mosby Inc.

All rights reserved. 10.1016/j.jpeds.2009.06.018

Vol. 155, No. 6 � December 2009

Table. Findings at initial consultation in CF older siblings diagnosed after birth of a baby with CF detected at newbornscreening

Symptoms Sweat testing CFTR analysis

Patients* Respiratory Digestive Failure to thrive ENT None Method Ch/Co Value (mmol/L) Mut 1 Mut 2

F, 67 X X Co 94 F508del 3272-26A > GM, 31 X X X X Co 100 R553X I507delM, 135 X X X Ch 133 F508del F508delF, 21† X Co 115 G542X G542XM, 71 X X X Ch 110 F508del N1303 KF, 29 X Co 110 621 + 1 G > T R347PF, 29 X Co 92 F508del F508delM, 60 X X Ch 101 F508del —F, 31 X X Ch 78 Y122X G622DM, 40 X X X Ch 108 F508del F508delF, 117 X Ch 50 F508del R347HF, 26† X Ch 103 F508del G745XF, 81 X Co 94 F508del F508delF, 82z X Ch 52 F508del R117H 7 T-9 TF, 61z X Ch 48 F508del R117H 7 T-9 TM, 80 X Ch 94 F508del R117H 7 T-9 TM, 30 X Ch 102 F508del R117H 7 T-9 T

Co, Conductivity; Ch, chloride.*Sex, age at presentation (m).†False-negative cases.zSiblings in the same family.

program, because they were born after 2002, but their IRTvalues at day 3 were below the cut-off level (28, 61 mmol/L); they were diagnosed at 21 and 26 months (Table).CFTR gene analysis identified 33 of 34 mutations (Table);gene analysis is still under way for 1 patient.

Discussion

We evaluated the impact of a nationwide newborn screen-ing program on the opportunity to diagnose CF amongolder siblings. Our first aim was to evaluate instructionsgiven at centers by French physicians for ST in older sib-lings. We were able to pinpoint substantial discrepancies,because only 44% of the centers systematically requireda sweat test. It is noteworthy that 2 CF diagnoses in oldersiblings (12.5%) were false-negative cases according to thenewborn screening program and would have been missedif the sweat test had not been systematically performed.Furthermore, 20% of the French CF centers asked fora sweat test only if the older children had symptoms. Giventhese different policies, there may be an underestimated in-cidence of 9% of families unaware of an affected older sib-ling. Thus, if we consider our 7 symptom-free siblings, 2had mutations associated with classical CF disease, 1 withvariable phenotype expression (an intermediate chlorideST: 50 mmol/L, F508del/R347H) and 4 children (from 3families) combined a severe mutation with R117H againsta background polythymidine sequence of intron 8 7 T-9T, with 2 ST that were positive. Although the R117H mu-tation combined with a severe mutation is associated withphenotypic variability, these children require clinical mon-itoring in a CF care center.4 Many of these individuals may

never express the disease,5 but, on rare occasions, patientsmay show classical CF manifestations6-8; therefore correla-tions between phenotype and the poly (T) variant in cishave limitations. The benefit of detecting infants after new-born screening with mild CF diagnosis has not beenproven, and the choice of the most appropriate CFTR mu-tations2,9 remains a matter of debate. To meet newbornscreening program goals for level of disease, a Europeanconsensus on screening algorithms in equivocal situations10

has recently been drafted. Longitudinal epidemiologic dataon individuals with class IV and V mutations are still verylimited.11

Our study emphasized that CF newborn screening can beoptimized by effective communication of diagnostic re-sults,12,13 including well-developed counseling and the rec-ommendation that ST be arranged for all first-degreesiblings, with gene analysis prescribed only in case of a posi-tive sweat test result.

Acknowledgments available at www.jpeds.com. n

Submitted for publication Feb 2, 2009; last revision received May 5, 2009;

accepted Jun 10, 2009.

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Munck, Houssin, and Roussey

December 2009 CLINICAL AND LABORATORY OBSERVATIONS

Acknowledgments

We thank all referring physicians from the CF care centers whoprovided clinical data: Prof M. Abely (Reims), Dr S. Bui (Bor-deaux), Dr R. Chiron and Dr F. Counil (Montpellier), Prof C.Delacourt (Creteil), Dr J. Derelle (Nancy), Dr M. L. Dalphin(Besancon), Dr A. L. Fanton (Dijon), Dr E. Fleurence (SaintDenis de la Reunion), Dr C. Gambert-Abdel Rahman (Poitiers),Dr M. Gerardin (Paris), Dr M. C. Heraud (Clermont Ferrand),

The Importance of Sweat Testing for Older Siblings of Patients

Dr J. Languepin (Limoges), Dr M. Le Bourgeois (Paris), Pr G.Lenoir (Paris), Dr C. Llerena (Grenoble), Dr G. A. Loeuille(Dunkerque), Dr C. Mazzochi (Lyon), Dr L. Mely (Giens), DrL. Moreau (Nice), Dr J. C. Pautard (Amiens), Dr M. Renouil(Saint Pierre de la Reunion,) Dr A. Sardet (Lens), Dr I. Sermet(Paris), Prof J. Sarles (Marseille), Dr E. Tassin (Versailles) andDr L. Weiss (Strasbourg), Dr N. Wizla (Lille).We also gratefully acknowledge Dr P. M. Farrell (Madison, Wis-consin) for critical reading of the manuscript.

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