Draft Genetic Test Review

---

Cystic Fibrosis
Clinical Utility

(347KB)

---

CLINICAL UTILITY

Question 26: What is the natural history of the disorder?
Question 27: What is the impact of a positive (or negative) test on patient care?
Question 28: If applicable, are diagnostic tests available?
Question 29: Is there an effective remedy or acceptable action, or other measurable benefit?
Question 30: Is there general access to that remedy or action?
Question 31: Is the test being offered to a socially vulnerable population?
Question 32: What quality assurance measures are in place?
Question 33: What are the results of pilot trials?
Question 34: What health risks can be identified for follow-up testing and/or intervention?
Question 35: What are the financial costs associated with testing?
Question 36: What are the economic benefits associated with actions resulting from testing?
Question 37: What facilities/personnel are available or easily put in place?
Question 38: What educational materials have been developed and validated, and which of these are available?
Question 39: Are there informed consent requirements?
Question 40: What methods exist for long term monitoring?
Question 41: What guidelines have been developed for evaluating program performance?

---

 

CLINICAL UTILITY

Question 33: What are the results of pilot trials?

Summary At least thirteen pilot trials of prenatal screening for cystic fibrosis have been published. They use all three screening models successfully (two-step, one-step, and expanded one-step) Both blood and buccal samples have been used Relatively few mutations were included in the panels; usually about 6 and none more than 16. Populations were usually non-Hispanic Caucasian and/or Ashkenazi Jewish Where screening uptake could be measured, it ranged between 57 and 99% (median 78 percent) Of 54 screen positive couples, 49 (91%) chose to have prenatal diagnosis. Of 18 couples with an affected fetus, 15 (83%) chose to terminate the pregnancy.

Pilot trials are an important step in translating research knowledge into practice. Types of data collected in pilot trials that cannot be obtained in other ways include:

• the rates at which health practices offer testing,

• the acceptance rates by the target population,

• the acceptance rates for diagnostic testing,

• the decision-making process when an affected pregnancy is identified,

• the overall satisfaction with the screening process,

• the analytic performance in a routine testing environment,

• the verification of prevalence estimates in the ‘real world',

• the costs and benefits of screening

The last three listed topics are addressed further in other sections. Pilot trials should be run in an environment where the data can be collected, analyzed and reported promptly. Often, pilot trials are short-lived and test relatively few subjects; these constraints place limitations on reliable estimates. This disadvantage can sometimes be overcome by combining information from multiple trials. In addition, some trials are translated into routine practice upon completion. In such instances, it might be possible to obtain supplementary information that accumulates after the trial itself has been analyzed and published.

Prenatal screening for cystic fibrosis is usually offered using either a two-step or one-step model. In the two-step (or sequential) model, the woman's sample is collected and tested. Carrier status is routinely reported. Only when a mutation is detected in the woman (about 1 in 30 women) is the partner asked to provide a sample. If a mutation is also detected in the partner (about 1 in 900 couples), the fetus is at a 1 in 4 risk of having cystic fibrosis, and prenatal diagnostic testing can be offered. In the one-step (or couple) testing, both partners provide samples prior to testing. The couple is considered positive only when an identifiable mutation is found in both (about 1 in 900). Carrier status is not routinely reported, unless a mutation is found in both the woman and the partner. In some studies, the one-step protocol is expanded to test samples from both partners, with all carriers notified. This will be called expanded one-step screening. The following three tables summarize published (and some unpublished) data from the population-based pilot trials of prenatal cystic fibrosis screening. The first pertains to descriptive and methodologic characteristics of the studies, the second describes the setting and population, along with screening and partner uptake rates, and the third presents the decision-making of screen positive couples.

Table 4-2 shows the location of each study, along with the date of its earliest published report. The number assigned to each pilot trial in Table 4-1 will be used in Tables 4-2 and 4-3 to identify it in relation to its specific results. The number screened is the actual number of women/couples who accepted testing. Data relating to women/couples with a family history of cystic fibrosis have been removed, so, in a few instances, this number is slightly smaller than that reported by the authors. Table 4-1 lists the time period for each of the studies and the methodology used in screening.

Table 4-2. Descriptive and Methodologic Characteristics of Prenatal Cystic Fibrosis Pilot Trials

Location (first published)	Study Number	Time Period	Model Type*	Sample Type**	Number of Mutations Tested	Wome (Couples) Screened
Edinburgh, Scotland (1992)	1	1990-5	2 then 1	Bl or M	6	17,544
Copenhagen, Denmark (1993)	2	1990-2	2	Bl	1 then 6	6,599
Manchester, England (1992)	3	1991-4	1 (E)*** or 2	M	4	529
Oxford, England (1993)	4	1990-2	1	Bu	3 then 6	543
East Berlin, Germany (1994)	5	1990-3	2	Bl	1 or 3	637
Maine, USA (1994)	6	1994-2000	1	Bu	7 then 11	5,747
Aberdeen, Scotland (1995)	7	Not reported	1 or 2	M	4	1,815
Rochester, NY USA (1996)	8	1993-4	2	Bl or Bu	6 then 16	4,879
N California, USA (1996)	9	1991-2	2	Bl	6 or 12	5,161
Leeds, England (1996)	10	1993-4	2	Bl or Bu	1	3,773
Milan, Italy (1996)	11	1992-4	1 (E)	Bl	7	1,114
Los Angeles, USA (1997)	12	1993-5?	2	Bu	6	3,192
New York City, USA (1997)	13	Not reported	1 (E)	Bl	5	3,792

*1 = one-step (or couple) model, 2 = two-step (or sequential) model, 1 (E) = expanded one-step model in which both partners are tested and both results are reported

**Bl= blood, Bu = buccal scrapings, M = mouthwash

***(E) = indicates an expanded one-step protocol, in which samples are tested from all women and all partners, with all carriers notified.

Table 4-3 provides more specific information about the screening process for each of the pilot trials. The trials are coded according to the study numbers assigned in Table 4-2. In some cases, a single report includes data from both one-step and two-step components of a given trial. Screening uptake rate is defined as the number of women/couples accepting testing, divided by the number offered testing. Partner uptake is defined differently for one-, or two-step trials. In two-step trials, it is the number of partners of screen positive women who opt for testing, divided by the number of screen positive women. In one-step trials, it is the number of couples who both provide samples, divided by the total number of couples who provide at least one sample. For trials employing both models, both rates are provided. Uptake rates are all higher than 50%, with most above 70%. Partner uptake rates are all high, but nearly all studies report less than 100% partner compliance. Most screening programs chose to focus in the first trimester of pregnancy.

Table 4-3. Prenatal Cystic Fibrosis Pilot Trials: Population Description and Screening Uptake Rates

Study Number	Study Setting	Payment Source	Gestational Age (wks)	Race/Ethnicity	Screening Uptake (%)	Partner Uptake (%)
						One-step	Two-step
1	Hospital Clinic	Routine	12	Scottish	78	ND	99
2	Hospital Clinic	Funded Study	12	Danish	89	-	94
3	Primary Care	Funded Study	7	English	85	92	100
4	Hospital Clinic	No Charge	<19	English	67	ND	-
5	Prenatal Clinic	No Charge	<16	German	99	-	100
6	Primary Care	insurance	12	NEC	NA	98	-
7	Hospital Clinic	Funded Study	~11	Scottish	90	94	98
8	Primary Care	Funded Study	NA	Mixed	~57	-	85
9	HMO	Funded Study	≤16	Mixed	78	-	861
10	Hospital Clinic	Funded Study	~13	English	62	-	98
11	Private Clinic	Self-Pay	~11	Italian	98	ND	-
12	HMO/Hospital	Funded Study	<18	Mixed	75	-	85
13	Referral Center	Funded Study	~12	Jewish	NA	NA	-

NA = not available, ND = not done, NEC = northern European Caucasian

¹ Excludes 7 spontaneous losses that occurred prior to the partner's sampling. Were these included, the rate would be 82 percent.

Table 4-4 shows the number of couples with positive screening results and their subsequent decision-making. Of the 54 screen positive couples, 49 (91%) chose to have prenatal diagnosis. In those, diagnosis was successfully completed in 46 (94%). Of the 18 couples with affected fetuses, 15 (83%) chose to terminate the pregnancy.

Table 4-4. Prenatal Cystic Fibrosis Pilot Trials: Results of Testing

Study Number	Number of Screen Positive Couples (%)	Number of Couples Choosing Prenatal Diagnosis		Number of Affected Fetuses	Number of Couples Choosing Termination of Pregnancy
		Chosen	Completed
1	161	14	14	7	7
2	3	3	3	1	1
3	1	1	1	0	-
4	0	-	-	-	-
5	1	1	1	1	1
6	7	6	6	3	1
7	2	2	2	0	-
8	5	4	4	0	-
9	7	7	52	13	0
10	3	2	1	0	-
11	2	2	2	1	1
12	1	1	1	1	1
13	6	6	6	3	3
Totals	54	49	46	18	15

¹ Subsequent pregnancies in carrier couples have been removed.

² Three pregnancies miscarried prior to prenatal diagnosis; cystic fibrosis was identified in one of these, using abortus material.

³ delF508 homozygous twins were identified

The following is a brief summary for each of the 13 prenatal cystic fibrosis screening pilot trials contained in the previous three tables. The number preceding the location is the study number referred to in the tables.

1. Edinburgh, Scotland – Prenatal screening for cystic fibrosis using the two-step model was offered at a hospital maternity clinic between 1990 and 1992 (Mennie et al., 1992). Overall, 4,978 women provided blood samples that were tested for six mutations (delF508, G551D, G542X, R553X, delI507, 621+1G-T). The ARMS™ methodology (both in-house and from Cellmark) was used. Mouthwash samples were collected from the partners when the woman tested positive. The trial was considered by the authors to be successful, but one drawback was noted - the need for a nurse to counsel the one in 26 women with positive results. In response to this, the group then employed the one-step model between 1992 and 1994 (Livingstone et al., 1994). During that portion of the study, 5,922 women were screened at two hospital maternity clinics using only mouthwash samples and the same 6 cystic fibrosis mutations. The one-step model was also considered by the authors to be satisfactory, and they reported it to be associated with less anxiety than the two-step model. In 1994, prenatal screening for cystic fibrosis using the one-step model was integrated into routine service (Brock, 1996). Between 1994 and 1995, an additional 6,664 women opted for screening. Overall, 17,544 women were screened, 22 at-risk couples were identified, and eight affected fetuses were diagnosed. All eight couples opted for termination. Several screen positive couples had subsequent pregnancies, including at least one affected pregnancy. These have been removed from the summaries.

2. Copenhagen, Denmark – Over two years, prenatal screening for cystic fibrosis using the two-step approach was offered to two groups of women; those attending clinic for a CVS and those attending clinic for routine prenatal care (Schwartz et al., 1993). A sample of whole blood from the woman was tested for the delF508 mutation. Partners of screen positive women were tested for 6 mutations (delF508, G551D, G542X, R553X, delI507, 621+1G-T). The Cellmark ARMS™ technology or an in-house assay were used. The authors considered the pilot trial to be successful in both settings. There is no indication that screening continued in Copenhagen after the study concluded.

3. Manchester, England – Over three years in six general practices, prenatal screening for cystic fibrosis was offered and accepted by 529 couples at the first prenatal booking; 267 allocated to the two-step model and 262 allocated to a modified one-step model (both samples were tested simultaneously and individual results were reported). Screening uptake rates were similar in the two arms. Mouthwash samples were collected and tested for the four most common mutations (delF508, G551D, G542X, 621+1G-T). The Cellmark ARMS™ kit was used. If the couple were of Jewish heritage, W1282X was also tested. The authors concluded that screening was efficient, uptake was high, but the process was associated with some anxiety (Harris et al., 1992; Harris et al., 1993; Hartley et al., 1997).

4. Oxford, England – Over one year, 543 couples attending the antenatal clinic prior to 19 weeks' gestation accepted screening using the one-step model (Wald et al., 1993). Buccal samples were collected and tested for delF508, G551D and R553X during the first four months and for an additional four mutations (G542X, 621+1G-T, W1282X/R1283M). The Cellmark ARMS™ technology was used after the first four months. The authors reported that screening was acceptable to both staff and patients and could be readily incorporated into antenatal care, but felt that the process would be better if done earlier in pregnancy. Screening was not offered after the conclusion of this study.

5. East Berlin, Germany – Over approximately two and one-half years, two-step screening was offered in two prenatal clinics with 638 women being tested prior to 16 weeks' gestation (Jung et al., 1994). Initially, whole blood was collected, but, later, dried blood spots were collected and tested for delF508. An in-house assay protocol was used. Partners of screen positive women were tested for two additional mutations (R553X and G551D). Uptake was very high, with only one woman declining to be screened. The authors concluded that screening is generally acceptable in Germany.

6. Maine, USA – Over a five year time period, one-step screening was accepted by 4,102 couples throughout the state, when offered by primary care providers (Doherty et al., 1994; Doherty et al., 1996; Bradley et al., 1998; Bradley, personal communication, 2001). Buccal scrapings were collected. During the pilot phase, seven mutations were tested, using the Cellmark ARMS™ technology (delF508, G551D, R553X, G542X, 621+1G-T, and W1282X/R1283M). Later, 5 mutations were added to the panel (N1303K, 1717-1G-T, 3849+10kbC-T, R1162X, and R334W). Couples of French Canadian heritage were tested for an additional three mutations (A455E, 711+1G-T and I148T). The authors concluded that it was feasible to incorporate one-step prenatal screening into the routine of primary care practices. Since the conclusion of the pilot trial, prenatal screening has been offered in Maine with reimbursement by nearly all third party payors. For this reason, the table includes some unpublished data.

7. Aberdeen, Scotland – Over an unstated time period women/couples were randomly allocated to one of two arms of the pilot study; 1487 women accepted two-step screening and 321 accepted one-step screening (Miedzybrodzka et al., 1995). Screening uptake rates were similar for the two groups. Mouthwash samples were collected in the second trimester or earlier and tested for four mutations (delF508, G551D, G542X and 621+1G-T). The authors reported that both methods of screening worked well in practice, with more laboratory time necessary to match samples in one-step screening, but more counseling time necessary for two-step screening.

8. Rochester, New York – Over an unstated time period, 4,879 women were screened using a two-step protocol (Loader et al., 1996). A relatively small number of these women were not pregnant and the published results did not distinguish between pregnancy and non-pregnancy. However, the overall reported rates were similar to those for pregnant women only (Rowley, personal communication, 1999). About 5 percent of the population was non-Caucasian (2.1 percent African, 1.6 percent Hispanic, 1.1 percent Asian, and 0.4 percent Native American). Blood samples were collected and tested for six mutations (delF508, G542X, G551D, R553X, W1282X and N1303K). A reverse dot blot technology from Roche Molecular Systems was used. Later in the study, 10 mutations were added (R117H, R334W, R347P, A455E, delI507, 1717-1G-A, S549N, R560T, 621+1G-T, 3849+10kbC-T). The authors reported that prenatal screening can be offered by prenatal care providers without incurring adverse outcomes associated with the process.

9. Northern California, USA – Over a 10 month time period, this large HMO offered two-step screening to its members; 5,161 women consented (Witt et al., 1996). Blood samples were collected at 16 weeks' gestation or earlier and sent to one of two laboratories. The first measured six mutations (delF508, G542X, G551D, R553X, W1282X and N1303K) the second measured six additional mutations (R117H, 621+1G-T, delI507, 1717G-A, R560T, and S549N). After six months, all specimens were tested for 12 mutations by the second laboratory. Males were always tested using the larger panel. Overall, 73% of the participants were Caucasian, 20% Hispanic, and 7.1% other racial/ethnic groups. The authors reported that large-scale prenatal population screening was acceptable. No significant deterrents to population screening were identified. In 2000, this program began offering screening for cystic fibrosis to its members as part of routine prenatal care.

10. Leeds, England – Over a 21 month period two-step screening was offered at two hospital obstetric units and eight general practices in greater Leeds; one-step screening was available upon request (Cuckle et al., 1996). A total of 3,773 women accepted testing for one mutation (delF508). An in-house assay was used. Additional, unspecified mutations were added, if the participants were of Jewish heritage. At one hospital, blood was initially collected, but eventually all sampling was by mouthwash. The authors reported that screening could be readily integrated into existing obstetric care, in both hospital and general practice settings.

11. Milan, Italy – Over a three year time period, women referred to a private, high risk obstetric clinic were offered two options: be tested using the expanded one-step model, or have the fetus tested (after a diagnostic procedure for other reasons) without knowledge of parents' carrier status (Brambati et al., 1996). A total of 1,114 couples provided blood samples in the first trimester. Initially, the samples were tested for a single mutation (delF508). An in-house ARMS™ assay was used. Later, a modified commercial kit (Innogenetics, Belgium) was used to identify an additional 7 mutations (N1303K, G542X, 1717-1G-A, W1282X, R553X, G551D and delI507). The results for couples choosing fetal testing were not always clearly distinguishable from the couples opting to be tested themselves. The authors concluded that offering testing to couples undergoing first trimester diagnostic testing is not a model for mass screening, although it may provide a useful service.

12. Los Angeles, California – Over an unstated time period, two-step screening was offered to couples attending prenatal clinics at an academic medical center and a large health maintenance organization (Grody et al., 1997). The population of 3,192 couples accepting testing was racially and ethnically diverse (50% non-Hispanic Caucasian, 28% Hispanic, 11% Asian, 7% African American, and 1% Native American). Buccal scrapings were collected and tested for six mutations (delF508, G542X, G551D, R553X, W1282X and N1303K). A commercial reverse dot blot system (Roche Molecular Systems) was used. The authors reported that their approach resulted in relatively high uptake in an ethnically diverse population, with satisfactory understanding of the subtleties of the genetics and test results and with no adverse psychosocial consequences detected.

13. New York City, USA – Over an unstated time period, couples of Jewish heritage were offered prenatal screening for Tay-Sachs disease, cystic fibrosis and Gaucher disease using the extended one-step model (Eng et al., 1997). A total of 3,792 individuals (1,896 couples) accepted testing for cystic fibrosis. Blood samples from both partners were tested for five mutations (delF508, W1282X, G542X, N1303K and 3849+10kbC-T) using an in-house assay. The authors reported that, for this population, combining DNA testing for several disorders at one time was feasible and that with proper education, informed choices could be made.

Pilot trials of cystic fibrosis screening in other settings have also been reported. Some trials have focused on identifying carrier couples prior to pregnancy, or identifying carrier status among the general populations. These studies are often called ‘population screening' trials and have been summarized elsewhere (Murray et al., 1999; Rowley et al., 1999). Screening for affected individuals could also occur soon after birth as part of newborn screening. This setting will be reviewed separately. Lastly, a program could target testing the relatives of recently diagnosed index cases. This ‘cascade' testing has been proposed as a method of population screening (Super et al., 1994), but its usefulness has been questioned (Holloway and Brock, 1994).

Additional information derived from the 13 prenatal cystic fibrosis pilot trials can be found in the following sections: estimated prevalence (Question 24), financial costs (Question 37), educational materials (Questions 39 and 40), and ELSI issues (Questions 43 through 46).

References

Bradley LA; Johnson DD; Doherty RA; Palomaki GE; Haddow JE. 1998. Routine prenatal cystic fibrosis screening in primary care offices. Am J Hum Genet 63:A13.

Brambati B, Anelli MC, Tului L. 1996. Prenatal cystic fibrosis screening in a low-risk population undergoing chorionic villus sampling for fetal karyotyping. Clin Genet 50:23-27.

Brock DJH. 1996. Prenatal screening for cystic fibrosis: 5 years' experience reviewed. Lancet 347:148-150.

Cuckle H, Quirke P, Sehmi I, Lewis F, Murray J, Cross D, et al. 1996. Antenatal screening for cystic fibrosis. Br J Obstet Gynaecol 103:795-799.

Doherty RA, Palomaki GE, Kloza EM, Erickson JL, Dostal DA, Haddow JE. 1994. Prenatal screening for cystic fibrosis. Lancet 343:172.

Doherty RA, Palomaki GE, Kloza EM, Erickson JL, Haddow JE. 1996. Couple-based prenatal screening for cystic fibrosis in primary care settings. Prenat Diagn 16:397-404.

Eng CM, Schechter C, Robinowitz J, Fulop G, Burgert T, Levy B, et al. 1997. Prenatal genetic carrier testing using triple disease screening. JAMA 278:1268-1272.

Grody WW, Dunkel-Schetter C, Tatsugawa ZH, Fox MA, Fang CY, Cantor RM, et al. 1997. PCR-based screening for cystic fibrosis carrier mutations in an ethnically diverse pregnant population. Am J Hum Genet 60:935-947.

Hartley NE, Scotcher D, Harris H, Williamson P, et al. 1997. The uptake and acceptability to patients of cystic fibrosis carrier testing offered in pregnancy by the GP. J Med Genet 34:459-464.

Holloway S, Brock DJH. 1994. Cascade testing for the identification of carriers of cystic fibrosis. J Med Screen 1:159-164.

Jung U, Urner U, Grade K, Coutelle C. 1994. Acceptability of carrier screening for cystic fibrosis during pregnancy in a German population. Hum Genet 94:19-24.

Livingstone J, Axton RA, Gilfillan A, Mennie M, Compton M, Liston WA, et al. 1994. Antenatal screening for cystic fibrosis: a trial of the couple model. BMJ 308:1459-1462.

Loader S, Caldwell P, Kozyra A, Levenkron JC, Boehm CD, Kazazian HH, et al. 1996. Cystic fibrosis carrier population screening in the primary care setting. Am J Hum Genet 59:234-247.

Mennie ME, Gilfillan A, Compton M, Curtis L, Liston WA, Pullen I, et al. 1992. Prenatal screening for cystic fibrosis. Lancet 340:214-216.

Miedzybrodzka ZH, Hall MH, Mollison J, Templeton A, Russell IT, Dean JCS, et al. 1995. Antenatal screening for carriers of cystic fibrosis: randomised trial of stepwise v couple screening. BMJ 310:353-357.

Murray J, Cuckle H, Taylor G, Littlewood J, Hewison J. 1999. Screening for cystic fibrosis. Health Technol Assess 3:1-104.

Rowley PT, Loader S, Levenkron JC. 1997. Cystic fibrosis carrier population screening: A review. Genet Test 1:53-59.

Schwartz M, Brandt NJ, Skovby F. 1993. Screening for carriers of cystic fibrosis among pregnant women: a pilot study. Eur J Hum Genet 1:239-244.

Super M, Schwartz MJ, Malone G, Roberts T, Haworth A, Dermody G. 1994. Active cascade screening for carriers of cystic fibrosis gene. BMJ 308:1462-1468.

Wald NJ, George LM, Wald NM, Mackenzie IZ. 1993. Couple screening for cystic fibrosis. Lancet 342:1307-1308.

Witt DR, Schaefer C, Hallam P, Wi S, Blumberg B, Fishbach A, et al. 1996. Cystic fibrosis heterozygote screening in 5,161 pregnant women. Am J Hum Genet 58:823-835.