Test Name
Cystic Fibrosis Pathogenic Variant Analysis (CFMDX)
CPT Code
81220
Methodology
Polymerase Chain Reaction (PCR)
Single Nucleotide Extension (SNE)
Matrix-Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry
Turnaround Time
10 days
Specimen Requirements
Type:
Whole blood
Volume:
4 mL
Tube/Container:
Lavender BD Hemogard™ K2EDTA Tubes
Transport Temperature:
Ambient (within 48 hours)

Stability
Ambient:
48 hours
Refrigerated:
7 days (stored at 2-8 °C)
Frozen:
Unacceptable
Additional Information
Background
Cystic fibrosis (CF) (OMIM#219700) is a multisystem genetic disease of sodium chloride transport that commonly involves the lungs, pancreas, intestines, liver, sweat glands, and male reproductive system. Respiratory failure is the leading cause of death among individuals with CF, with a median life expectancy of 41 years (CF Foundation).[1]
CF is one of the most common inherited conditions among Caucasians and is diagnosed in approximately 1 in 3,000 individuals.[2-3] The condition is less common but does occur among all other racial groups. CF has an autosomal recessive inheritance pattern and heterozygous mutation carriers (1 in 25-30 Caucasians) are unaffected. If both partners in a couple are mutation carriers, there is a 25% chance for each child to have CF and a 50% chance for each child to be a carrier.
The cystic fibrosis transmembrane conductance regulator (CFTR) gene was isolated in 1989.[4] The most common pathogenic variant, deltaF508, was identified in the same year and represents 70% of CF mutations among Caucasians.[5] To date, more than 1,800 gene variants have been found, though most are quite rare.[6] Mutations in CFTR have also been identified in individuals with atypical presentations, such as acute or chronic recurrent pancreatitis and isolated congenital absence of vas deferens (CAVD), as well as in individuals with late-onset or mild CF symptoms.[7]
Carrier Screening
To identify couples at risk of having a child with CF, both the American College of Medical Genetics and Genomics and the American College of Obstetricians and Gynecologists recommend that CF carrier screening be offered routinely to women of reproductive age.[8] Mutation screening should include the pan-ethnic panel of the 23 most common CTFR pathogenic variants.
Diagnostic Confirmation
In both pediatric and adult patients in whom CFTR-related disorders are suspected, genetic testing is routinely performed as an initial diagnostic test or as confirmation of clinical findings, or sweat chloride testing, which remains the standard diagnostic test.[9]
Newborn screening (NBS) for cystic fibrosis is now offered universally in the United States through each state’s mandatory NBS program.[10] Initial screening measures a digestive enzyme, immunoreactive trypsinogen (IRT). Because elevations in IRT may have other causes, a CFTR mutation analysis is often performed as a secondary screen, though this varies by state.
Since the advent of routine carrier screening and NBS, many individuals with CF are recognized at, or even before, birth.
Methodology
DNA samples are amplified in a multiplex reaction for regions of interest in CFTR. Initial amplification is followed by single base extension (SBE) reactions to detect known CFTR variants. The extension products are analyzed using matrix-assisted laser desorption/ionization–time of flight (MALDI-TOF) mass spectrometry. Multiple variants may be detected because each CFTR variant assay contains a primer of unique length and mass, allowing specific genotypes to be assigned.
Mutations Detected
The variants included on the Cystic Fibrosis Pathogenic Variant Analysis assay represent clinically-validated variants classified as CF-causing in the CFTR2 database at Johns Hopkins University, a product of the Clinical and Functional Translation of CFTR (CFTR2) initiative. The assay tests for 140 CF-causing variants; one variant (F508C) associated with Congenital Absence of the Vas Deferens (CAVD); one ACMG-recommended panel variant (R117H) classified as a Mutation of Varying Clinical Consequence by CFTR2; one conditionally reported modifying variant (Poly T); and two conditionally-reported benign variants (I506V and I507V). This panel includes the 23 pathogenic variants recommended for universal carrier screening by the American College of Medical Genetics. The panel also encompasses all variants that are detected by the Ohio Newborn Screening Panel.
Interpretation
Results should be used and interpreted in the context of clinical evaluation. This test does not detect all variants in the CFTR gene and it is possible that this individual could have a CFTR variant not included in this test. Therefore, the failure to identify a variant does not guarantee that other CFTR variants are not present in the sample being analyzed.
Variants identified by this assay vary in frequency among different populations.[9, 11] Residual CF carrier risk following a negative Cystic Fibrosis Pathogenic Variant Analysis result is based on ethnicity and personal/family history.
Residual Cystic Fibrosis Carrier Risk after Negative Carrier Screen
Ethnicity
Carrier Rate
Detection Rate
Residual Carrier Risk
(with negative family history)
African American
1 in 61
74%
1 in 231
Ashkenazi Jewish
1 in 24
97%
1 in 768
Asian
1 in 94
49%
1 in 183
Caucasian
1 in 25
91%
1 in 267
Hispanic
1 in 58
77%
1 in 248
As with any hybridization-based assay, underlying gene variants in oligonucleotide-binding regions can affect the alleles being probed and, consequently, the calls made. The orientation of the Poly T variant, whether in cis/trans to the R117H variant, cannot be ascertained via this assay.
Due to the complex issues surrounding cystic fibrosis, informed consent and genetic counseling are recommended for all individuals undergoing testing.
Reported Variants
Cystic Fibrosis (CFTR RefSeq# NM_000492.3)
Legacy names of 142 pathogenic variants with three *conditionally-reported variants are listed below:
1078delT
1154insTC
1213delT
1248+1G>A
1259insA
1341+1G>A
1461ins4
1525-1G>A
1548delG
1677delTA
1717-1G>A
1717-8G>A
1811+1.6kbA>G
1812-1G>A
1898+1G>A
1898+3A>G
1898+5G>A
1898+5G>T
2055del9>A
2143delT
2183AAtoG
2184delA
2184insA
2307insA
2347delG
2585delT
2622+1G>A
2711delT
2789+5G>A
394delTT
3007delG
3120+1G>A
3120G>A
3121-1G>A
3199del6
3272-26A>G
3659delC
3791delC
3849+10KbC>T
3876delA
3905insT
405+1G>A
406-1G>A
4005+1G>A
4016insT
4209TGTT>AA
4382delA
457TAT>G
574delA
621+1G>T
663delT
711+1G>T
711+3A>G
711+5G>A
712-1G>T
852del22
935delA
A455E
A559T
CFTRdele2,3
CFTRdele22,23
D110H
D1152H
deltaF508
deltaI507
E1104X
E585X
E60X
E822X
E831X
E92K
E92X
F508C
G1244E
G1349D
G178R
G330X
G542X
G551D
G85E
G970R
H199Y
I336K
K710X
L1065P
L1077P
L206W
L467P
L732X
L927P
M1101K
M1V
N1303K
P205S
P67L
Q1313X
Q220X
Q39X
Q493X
Q525X
Q552X
Q890X
Q98X
R1066C
R1066H
R1158X
R1162X
R117C
R117H
R334W
R347H
R347P
R352Q
R553X
R560K
R560T
R709X
R75X
R764X
R851X
S1196X
S1251N
S1255X
S341P
S466X
S489X
S492F
S549N
S549R-CGT
S549R-AGG
S945L
T338I
V520F
W1089X
W1204X (3611)
W1204X (3612)
W1282X
W401X
W846X
Y1092X
Y1092X
Y122X
*Poly T
*I506V
*I507V
References
1. Cystic Fibrosis Foundation Patient Registry: Annual Data Report 2017. Available at http://www.cff.org/
2. Comeau AM, Parad RB, Dorkin HL, Dovey M, Gerstle R, Haver K, Lapey A, O’Sullivan BP, Waltz DA, Zwerdling RG, Eaton RB. Population-based newborn screening for genetic disorders when multiple mutation DNA testing is incorporated: a cystic fibrosis newborn screening model demonstrating increased sensitivity but more carrier detections. Pediatr. 2004;113(6):1573-1581.
3. Sontag MK, Hammond KB, Zielenski J, Wagener JS, Accurso FJ. Two-tiered immunoreactive trypsinogen (IRT/IRT)-based newborn screening for cystic fibrosis in Colorado: screening efficacy and diagnostic outcomes. J Pediatr. 2005;147(Suppl):S83-8.
4. Rommens JM, Iannuzzi MC, Kerem BS, Drumm ML, Melmer G, Dean M, Rozmahel R, Cole JL, Kennedy D, Hidaka N, Zsiga M, Buchwald M, Riordan JR, Tsui LC, Collins FS. Identification of the cystic fibrosis gene: chromosome walking and jumping. Science. 1989;245:1059-1065.
5. Kerem BS, Rommens JM, Buchanan JA, Markiewicz D, Cox TK, Charavarti A, Buchwald M, Tsui LC. Identification of the cystic fibrosis gene: genetic analysis. Science. 1989;245:1073-1080.
6. The Clinical and Functional Translation of CFTR (CFTR2). Available at http://www.cftr2.org/
7. Cutting GR. Cystic fibrosis genetics: from molecular understanding to clinical application. Nat Rev Genet. 2015;16(1):45-56.
8. Carrier screening for genetic conditions. Committee Opinion No. 691. American College of Obstetricians and Gynecologists. Obstet Gynecol. 2017;129:e41–55.
9. Farrell PM, Rosenstein BJ, White TB, Accurso FJ, Castellani C, Gutting GR, Burie PR, LeGrys VA, Massie J, Parad RB, Rock MJ, Campbell, III, PW. Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation consensus report. J Pediatr. 2008;153:S4-S14.
10. National Newborn Screening and Genetics Resource Center. National newborn screening status report. Austin (TX) Available at http://genes-r-us.uthscsa.edu/sites/genes-r-us/files/nbsdisorders.pdf Updated Nov 02, 2014.
11. Sugarman EA, Rohlfs EM, Silverman LM, Allitto BA. CFTR mutation distribution among U.S. Hispanic and African American individuals: Evaluation in cystic fibrosis patient and carrier screening populations. Genet Med. 2004;6(5):392-99.
Additional Resources:
Ong T, Marshall SG, Karczeski BA, Sternen DL, Cheng E, Cutting GR. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2018. Cystic Fibrosis and Congenital Absence of the Vas Deferens. 2001 Mar 26 [Updated 2017 Feb 2]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1250/