Carrier screening for cystic fibrosis

Wide scope prenatal diagnosis at Kuopio University Hospital 1997-1998: integration of gene tests and fetal karyotyping

OBJECTIVE

To investigate the applicability of carrier screening in women undergoing invasive prenatal diagnosis.

DESIGN

Prospective study.

SETTING

University-based clinic.

PARTICIPANTS

Two hundred and fifty-six pregnant women.

METHODS

Gene tests were offered for fragile X syndrome, aspartylglycosaminuria and infantile neuronal ceroid lipofuscinosis at the time of invasive prenatal testing.

RESULTS

The overall uptake of the tests was 92%. Previously unrecognised carriership was found in 10 women: aspartylglycosaminuria (7); infantile neuronal ceroid lipofuscinosis (2) and fragile X (1). Fetal genotyping was carried out in one carrier of aspartylglycosaminuria whose partner was also a carrier, and in one woman who was found to have fragile X premutation. Both fetuses were unaffected.

CONCLUSION

Carrier screening for single-gene disorders is feasible and well accepted among pregnant women undergoing invasive prenatal testing. The major benefit is that there is no need to consider extra invasive tests when carriership is detected. Incorporation of genetic testing into fetal karyotyping gives more security to future parents.

Prenatal screening for cystic fibrosis: an updated perspective

In U.S. white populations prenatal screening for cystic fibrosis can identify > or = 60% of pregnancies in which the risk for an affected fetus is high. Such pregnancies occur when both the mother and the father carry cystic fibrosis mutations; about one screened couple per 1000 falls into this category. The risk of the fetus being affected is 1 in 4. Prenatal screening for cystic fibrosis compares favorably with prenatal screening for spina bifida and Down syndrome, with a similar detection rate, a much lower false-positive rate, and greater odds of being affected, given a positive result. Intervention trials in Europe and the United States provide documentation of efficacy. Larger-scale trials should now be encouraged in the United States to gain further insight into program design and case management, as a way to determine the feasibility of cystic fibrosis screening as part of routine prenatal care.

Gaucher's disease in pregnancy

Gaucher's disease is an autosomal recessive lysosomal storage disease, resulting from a deficiency of the enzyme glucocerebrosidase, important for the physiologic recycling of cell membrane lipids. The clinical symptoms and disease presentations of Gaucher's disease are heterogeneous, including hepatosplenomegaly, bone "crisis" and fracture, anemia, thrombocytopenia and in some forms, rapid neurological decompensation. Similarly, the genetic variability of Gaucher's disease is diverse, and in some aspects affects phenotypic expression. Type 1 Gaucher's disease, however, usually present with less severe symptoms, at more advanced age, and is particularly amenable to enzyme replacement therapy with alglucerase. In type 1 patients with Gaucher's disease reproductive age is commonly reached and childbearing frequently desired with need for appropriate prenatal diagnosis, counseling and careful obstetrical surveillance. Although pregnancy concurrent with Gaucher's disease has been reported in the medical literature, only one small series of alglucerase treated Gaucher's disease during pregnancy exists. Without treatment, pregnancy concurrent with Gaucher's disease has several risks including an increased severity of anemia and thrombocytopenia that can potentiate postpartum bleeding, significant increases in organomegaly and possibly an increased spontaneous abortion rate. It is yet to be shown whether alglucerase reduces the risk of these complications during pregnancy and whether its use has any adverse effect on fetal development.

Prenatal cystic fibrosis screening in a low-risk population undergoing chorionic villus sampling for fetal karyotyping

Screening for cystic fibrosis (CF) has been offered to pregnant women seeking chorionic villus sampling (CVS) for prenatal chromosomal abnormality investigation. The mutation panel has increased over the years to include 8 mutations and can detect 65% of abnormal CF genes in the Italian population. Testing was offered to a total of 2214 consecutive pregnant women; 45 of them declined screening (take up rate: 98%). In 1055 of the 2169 pregnancies screened, the test was at first done on the fetus, while in the remaining cases both parents were investigated. Among parents 46 carriers were identified (2.1%), in 41 of whom the mutation was delta F508. In two couples both parents were heterozygous, and in one the fetus was affected and the pregnancy was terminated. Although CF testing offered to pregnant women undergoing invasive investigation such as CVS may not be the model for a mass screening, its very high effectiveness can represent an advantageous component of more comprehensive strategies.

Cost comparison of different methods of screening for cystic fibrosis

OBJECTIVE

To compare the costs of several proposed methods of screening for cystic fibrosis.

SETTING

England and Wales.

METHODS

The costs of screening carried out at hospital antenatal clinics, general practitioner (GP) antenatal consultations, GP surgeries, and at work were estimated using data from demonstration projects. Couple screening, stepwise screening, and screening of individuals were considered.

RESULTS

Couple screening at antenatal hospital clinics was the least expensive per carrier couple detected, amounting to 35,700 pounds (142,900 pounds for each potential cystic fibrosis fetus detected). The costs of the reagents (25 pounds per test) accounted for over 60% of this total.

CONCLUSIONS

Antenatal screening, in addition to being the most cost effective method of screening, is also medically the screening method of choice as it provides information at the latest time when effective preventive action can be taken and at a time when all people to be screened are likely to be accessible. If the costs of the reagents could be reduced to 5 pounds (still higher than the costs of most diagnostic reagents) the cost for each pregnant carrier couple offered screening would be reduced by 50% to about 18,000 pounds, and the cost of offering screening to 684,000 pregnant couples in England and Wales would be about 9 1/2 m instead of 19 m pounds.