Updated Report on PRA in Tibetan Spaniels - Maureen
Sharp October
2004
We
feel it is time to bring everyone up to date with
the PRA project. As you know the AHT have continued
to work on our project and have got so far but desperately
need blood from a few more PRA cases with their
close relatives to check their findings (possible
2-3 families just might be enough).
To
recap blood has been collected from over 294 Tibetan
Spaniels, of which 19 are affected with PRA. DNA
has been extracted from each blood sample and the
AHT have focused on a Homozygosity Mapping approach
to find markers linked to the PRA gene. They have
analysed 340 markers with 6 affected dogs and 10
carriers and identified markers, which are homozygous
for the same allele in at least 4 affected dogs
and heterozygous in at least two carriers. Twenty
markers meet the above criteria, these are located
on 16 different chromosomes. Four canine chromosomes
have two markers each that meet the criteria so
they have focused their efforts on those. They identified
8 additional markers from these four promising chromosomes
and have typed these markers on all the Tibetan
Spaniels samples. Unfortunately the results are
inconclusive due to the limited number of families
available, meaning that to date they are not able
to either confirm or exclude any of these four chromosomes.
Until
more blood samples are forthcoming the AHT have
been looking at the available canine whole genome
sequence to isolate genetic markers located in genes
that are known to cause retinal disease in humans.
They are examining them in the Tibetan Spaniel pedigree
for evidence of linkage, in the hope that if one
of them is the gene responsible for PRA it will
be so tightly linked to the disease within the pedigree
they will be able to detect the linkage. They are
also making efforts to contact other researchers
working on PRA in Lhasa Apsos, in an attempt to
pool the results. The conditions are very similar
between the two breeds so it is possible the same
gene is responsible for the two conditions. They
also continue to collect and store blood samples
from affected dogs and their close relatives.
Early
this year an Italian vet joined the AHT for a few
months and worked very hard finding genetic markers
next to genes that are known to cause PRA in other
breeds, or similar diseases in humans, and analsying
them in the Tibetan Spaniels samples for evidence
of linkage to PRA. She found a genetic marker near
to one particular gene that gave us the highest
lod score we have ever seen with the Tibetan Spaniels
and although this is encouraging we must wait developments
as it is possible it could be a false positive result.
This particular chromosome has quite a few PRA genes
on it, so they are in the process of looking further
into this.
We
understand that there is a new case of PRA in Sweden
and although we have been unsuccessful in getting
blood from Tibetan Spaniels there we are hopeful
that they, in view of the above will help. We send
our sympathies to the breeders and owners concerned
but hope that the urgent need for new blood from
PRA families and the fact that we may be very near
to a DNA test will encourage them.
We
started this project in May 2000 and I think that
congratulations are in order to the whole breed
for what we have achieved.
Maureen
Sharp (Co-ordinator - PRA Fund)
