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Information for clinicians

8 Genetic counselling

8a Mode of inheritance

Adult Refsum's disease is inherited in an autosomal recessive manner.

8b Risk to family members

8b(i) Parents of a proband

8b(ii) Sibs of a proband

8b(iii) Offspring of a proband

8b(iv) Other family members of a proband

8c Carrier detection

Carrier testing using molecular genetic techniques may be available on a clinical basis once the mutations have been identified in the proband.

Biochemical testing is not accurate for carrier testing, as the biochemical markers in obligate heterozygotes (carriers) are normal.

8d Related genetic counselling issues

8d(i) Family planning

The optimal time for determination of genetic risk, clarification of carrier status, and discussion of the availability of prenatal testing is before pregnancy.

8d(ii) DNA banking

DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, mutations, and diseases will improve in the future, consideration should be given to banking DNA of affected individuals. DNA banking is particularly relevant in situations in which the sensitivity of currently available testing is less than 100%.

8e Prenatal testing

8e(i) Molecular genetic testing

Prenatal diagnosis for pregnancies at increased risk is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis usually performed at about 15-18 weeks' gestation* or chorionic villus sampling (CVS) at about 10-12 weeks' gestation. Both disease-causing alleles of an affected family member must be identified before prenatal testing can be performed.

8e(ii) Biochemical genetic testing

In principle, prenatal diagnosis for pregnancies at 25% risk is possible by measurement of phytanic acid oxidation in fetal cells obtained by amniocentesis usually performed at about 15-18 weeks' gestation* or chorionic villus sampling (CVS) at about 10-12 weeks' gestation.

Requests for prenatal testing for conditions such as adult Refsum's disease, which is usually diagnosed when individuals are in their twenties and their parents have typically completed their families, are uncommon occurrences.

*Gestational age is expressed as menstrual weeks calculated either from the first day of the last normal menstrual period or by ultrasound measurements.

Next: Molecular genetics

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Page last updated 26 June 2006