Extended family, or cascade, screening

The Leeds Method of Management. April, 2008. Extended family, or cascade, screening [online]. Leeds Regional Adult and Paediatric Cystic Fibrosis Units, St James's University Hospital, Leeds, UK. Available from http://www.cysticfibrosismedicine.com

Once the patient’s cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations have been identified, any member of the extended family can be screened for carrier status by looking for these specific mutations. If carriers are identified they will have the option to have their partners screened when planning to have a child or, if they already have a family, the children can be offered carrier screening at an appropriate age (Super et al, 1994). In our Adult Unit, both the patients and their parents favour utilizing the information available from genetic screening to guide reproductive choices (Conway et al, 1994).

If no mutations are identified but the diagnosis is not in doubt, it is possible to identify, using samples from the affected individual and his/her parents, which of the parental chromosome 7’s segregate with the disease. If the parents have passed the same chromosome 7 to another offspring then they are considered to be a carrier.

The laboratory will be able to test a variety of samples e.g. saliva, dried blood spots, blood and solid tissue. The usual sample is 5-10ml of blood in EDTA. Unless there are already arrangements to use other tissue then the type of sample should be discussed with the laboratory.

 

References

Conway SP, Allenby K, Pond MN. Patient and parental attitudes toward genetic screening and its implications at an adult cystic fibrosis centre. Clin Genet 1994; 45: 308-312. [PubMed]

Super M, Schwarz MJ, Malone G, et al. Active cascade testing for carriers of cystic fibrosis gene. BMJ 1994; 308: 1462-1468. [PubMed]

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