Bruce Buehler, MD, Pediatrics, General, 05:37PM Mar 17, 2013
Microarray samples 180,000 known genetic sites. Now that microarray has been coupled with single nucleotide polymorphisms (SNPs), the new testing identifies the target genes and polymorphisms that can indicate loss of heterozygosity -- and possible consanguinity. Testing a child for a genetic syndrome with the new tests can indicate consanguinity without studying the parents. This raises a very significant concern about what to reveal to a family that denies any relationship, such as in first or second cousins. It also raises issues when one of the parents is adopted and had no reason to consider a family relation with the spouse, or in the case of children of sperm donors.
The important information about consanguinity is the known increase in autosomal recessive conditions and possible clinical implications for the child being tested. This is especially important for metabolic diseases with potential treatment.
Previously, if it was suspected that a person had inherited two copies of the gene from the same parent (uniparental disomy, UPD) such as Prader-Willi Syndrome or Angelman's Syndrome, separate tests had to be done. Now, the high-density SNP array will identify most UPDs. This can be very helpful in treatment.
The dilemma is how a family will react to knowing that they are closely related. Sometimes the family has no concerns due to cultural normality. But for other families it can be devastating. It is now the practice of our genetic team to review this potential information before testing. On two occasions, families decided against testing, without explaining their concerns.
The better our genetic testing, the greater the need for informed consent from the family, including the issue of consanguinity. No genetic testing should be done before the family understands some of the unexpected information they may receive.