Uptake of carrier testing in families after cystic fibrosis diagnosis through newborn screening

Abstract

Newborn screening (NBS) for cystic fibrosis (CF) provides the opportunity for cascade carrier testing of relatives. Uptake of testing by adult non-parent relatives of children diagnosed with CF through NBS has not been previously described, and this study describes uptake by both parents and adult non-parent relatives in Victoria, Australia. Pedigrees were taken from parents of children who were born in 2000-2004 and diagnosed with CF. A total of 40 families were eligible for the study and 30 (75%) were recruited. In all, 716 non-parent relatives were identified from the pedigrees as eligible for carrier testing, and 82 (adjusted uptake percentage: 11.8%; 95% confidence interval 8.0-15.7) have had carrier testing by March 2009. On average, 2.7 non-parent relatives per family had CF carrier testing after diagnosis through NBS. The odds of being tested were greater for females than males (adjusted odds ratio 1.61; 95% confidence interval 1.11-2.33; P=0.01) and greater for those more closely related to the child with CF (adjusted odds ratio 5.17; 95% confidence interval 2.38-11.24; P<0.001). Most relatives who undergo testing are tested immediately after the baby's diagnosis; however, some testing is undertaken up to 8 years later. These results indicate that in a clinical setting, the diagnosis of a baby with CF by NBS does not lead to carrier testing for the majority of the baby's non-parent relatives. We suggest re-contact with parents to offer cascade carrier testing.

Figure 1

Time taken for non-parent relatives to have carrier testing after the diagnosis of a child with CF through newborn screening. ^*This column represents relatives who have been tested in the eighth year after their family member was diagnosed with CF. The database search was conducted in March 2009, and hence only tests conducted in the first quarter of 2009 have been included and this column does not represent a full year. One relative was tested 39 months before the birth of the child in this study. This was because another child in the family was born with CF 15 years previously (first cousin once removed from the child in the present study). The relative (carrier risk of 1 in 4, based on relationship to child in this study) was tested when she was pregnant, which was before the birth of the child in this study.

Figure 2

Age of non-parent relatives when tested. One relative was tested at age 15, and one was tested at age 16; however, both were aged ≥18 years at the time of the interview and hence met the study inclusion criteria. The first peak represents relatives who are in their reproductive years. Relatives who are being tested at this age may be doing so to use the information for their own reproductive planning. The second peak represents relatives who are post-reproduction; these relatives may be having testing to clarify their carrier risk and to pass such information on to their own children who may be planning a pregnancy.