Lindex #1842

Straughen JE, Johnson J, McLaren D, Proytcheva M, Ellis N, German J, Groden J,

A Rapid Method for Detecting the Predominant Ashkenazi Jewish Mutation in the Bloom's Syndrome Gene

Human Mutation

1998; 11: 175-178

Bloom's Syndrome (BS) is a rare, autosomal recessively transmitted genetic disorder that is relatively more prevalent in Ashkenazi Jews. Since all Ashkenazi Jews with the disorder have the same mutation due to a common ancestor, a screen for this mutation was developed by these authors.

The mutation in Ashkenazi Jews with BS is a 6 bp deletion coupled with a 7 bp insertion in BLM, the gene for BS. This mutation creates a premature stop codon and introduces a novel BstNI restriction enzyme site.

cDNA was prepared from cell lines created from a normal male, a woman with BS, and the parents of the BS patient. The cDNA was amplified by PCR and digested with BstNI. A BstNI site was engineered into the PCR primers to control for the activity of the enzyme and allow cutting of the normal allele.

Gel electrophoresis of the resulting fragments revealed that the normal subject had one band on the gel of 209 bp (a 22 bp fragment is too small to be seen on the gel). The homozygous patient with BS had two bands on the gel corresponding to 115 and 94 bp. The heterozygous parents had three bands: 209, 115, and 94 bp, representing one allele of each genotype.

Digestion of genomic DNA that was PCR amplified and then digested with BstNI in a similar fashion yielded similar results. Unaffected non-carriers had a 317 bp fragment; heterozygotes had 317, 231, and 86 bp fragments; homozygotes had 231 and 86 bp fragments.

These methods can identify carriers of BS as well as genotype high-risk fetuses.