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Dr. Johnson's Final
Report to AKC Canine Health Foundation
AKC CANINE HEALTH
FOUNDATION
251 West Garfield
Road Suite 160 Aurora, Ohio 44202
Ph: 330.995.0807
Fax: 330.995.0806
Email: akcchf@aol.com
Web: www.akcchf.org
April 16, 2001
Kevin Welch
Miniature Bull Terrier Club of
America
P.O. Box 9301
Reston, VA 20195
Re: Grant No. 1 867: Genetic
Markers for Lens Luxation in Miniature Bull Terriers Principal Investigator:
Gary Johnson, DVM, Ph.D.
Dear Mr. Welch:
We are pleased to forward to you
the final progress report for the above referenced grant, which your club is
cosponsoring.
This progress report has been
reviewed by our science officer, Dr. C. Richard Dorn, and has been approved.
If you have any questions regarding the progress of this research please
feel free to contact either Dr. Dorn at (614) 436-1101 or Deborah Lynch at
(330) 995-0807.
We extend our thanks and
appreciation to you and your Club members for your support of canine health.
Sincerely,
Erika Werne
Grants Administrator
Genetic Causes
for Lens Luxation in Miniature Bull Terriers:
Final report for
Canine Health Foundation Grant # 1867
(January 31, 2001)
Gary S. Johnson DVM Ph.D.
Department of Veterinary
Pathobiology
College of Veterinary Medicine
University of Missouri
209A Connaway Hall, Columbia, MO
65211
Phone: (573) 882-6723 Fax: (573)
884-5415 Email:
JohnsonGS@missouri.edu
The overall objective for this
project is to produce a DNA marker test that will identify carriers of lens
luxation and affected dogs prior to luxation. With this information,
Miniature Bull Terrier breeders can avoid producing additional affected dogs
and decrease the frequency of the gene in the population. We proposed to do
this through the following specific objectives;
1. Isolate genomic DNA from
members of Miniature Bull Terrier families in which lens luxation is
segregating.
2. Determine the normal
nucleotide sequence for a segment of the canine fibrillin 1 gene which
includes exon 59 and compare this sequence with corresponding sequences from
DNA from Miniature Bull Terriers with lens luxation.
3. Place canine fibrillin I
locus on the emerging canine genome linkage map.
4. Genotype Miniature Bull
Terrier lens luxation family members with respect to an informative canine
fibrillin gene marker and determine if the marker is genetically linked to
lens luxation disease.
Accomplishments on each of these
objectives have been as follows:
Objective 1) Isolate genomic DNA
from members of Miniature Bull Terrier families in which lens luxation is
segregating. In our preliminary work for this grant proposal we had
collected samples from 36 Miniature Bull Terriers who were members of
families where lens luxation had appeared. Three of these dogs were affected
with lens luxation. Since that time we have received additional samples, for
a current total of 78 Miniature Bull Terriers, including 8 who are affected
with lens luxation. Some of these families are shown in Figure 1.
Most of these DNA samples were
purified from EDT A blood by phenol/chloroform extraction. The DNA was
ethanol precipitated, re-dissolved in a tris/EDTA buffer, then stored
frozen. This DNA is kept as part of our collection 0! DNA samples from over
22,500 individuals, mostly dogs and cattle. The identification numbers aid
phenotype information supplied by the owners is compiled in a computer
spreadsheet. In addition to the electronic copies of this data, all
information supplied by owners is filed by breed for future reference.
Objective 2) Determine the
normal nucleotide sequence for a segment of the canine fibrillin 1 gene
which includes exon 59 and compare this sequence with corresponding
sequences from DNA from Miniature Bull Terriers with lens luxation. Because
a mutation in exon 59 of the human fibrillin gene has caused isolated lens
luxation in human patients 1, we amplified and sequenced an exon
59-containing gene segment of the canine fibrillin gene from Miniature Bull
Terriers with lens luxation and from dogs of other breeds with normal eyes.
In each case we obtained identical sequences for the exon 59 containing
segment.
Objective 3) Place canine
fibrillin 1 locus on the emerging canine genome linkage map. Other segments
of the fibrillin 1 gene from several dogs were amplified and sequenced. We
found three polymorphic sites and devised marker assays for each of them.
The assay developed for one of the polymorphic sites found on the fibrillin
1 gene was used to genotype the Cornell/Ralston Purina reference families,
and this data submitted to Dr. Elaine Ostrander at the Fred Hutchinson
Cancer Research Institute. The fibrillin 1 gene mapped to canine chromosome
30 between flanking type 2 markers, CXX.204 and FH2050
Objective 4) Genotype Miniature
Bull Terrier lens luxation family members with aspect to an informative
canine fibrillin gene marker and determine if the marker is genetically
linked to lens luxation disease. All three fibrillin markers were
uninformative in the Miniature Bull Terrier families, as all family members
had the same alleles. When the marker was mapped, there were 2 highly
polymorphic flanking type 2 microsatellite markers identified. These also
were found to be uninformative in the Miniature Bull Terrier pedigrees
tested.
We concluded that because of
intensive inbreeding and/or a narrow base of founders, many of the alleles
segregating in most breeds were lost from Miniature Bull Terriers, and,
thus, global mapping studies would be difficult. We also noted that lens
luxation occurred in many breeds of terriers originating in the British
Isles, but not in most non-Terrier breeds. This suggests that a founder
mutation, occurring before the various terrier breeds became closed
registries, might be responsible for the Ins, luxations in the terriers.
Tibetan Terriers, a breed unrelated to the terriers from the British Isles,
appear to be an inception. Some Tibetan Terrier breeders, however, believe
that their lens luxation problem stems from a true terrier of English
origin, which was allowed into the Tibetan Terriers registry because it
resembled a Tibetan Terrier. If this is true, Tibetan Terrier's may prove to
be an ideal breed for global mapping of the lens luxation locus. We have
therefore begun collecting DNA from Tibetan Terriers with lens luxation and
their close relatives. To date we have 65 Tibetan Terriers in this study,
including affected dogs. So far, however, none of the families are extensive
enough to support genome mapping. If lens luxation in the Tibetan Terriers
does, indeed, stem from the same founding mutation responsible for lens
luxation in the true terriers, discoveries made by studying Tibetan Terriers
should be directly applicable to lens luxation in the true terrier breeds.
In addition to the Miniature
Bull Terriers and Tibetan Terriers, we have individuals with lens luxation
and partial families in Sealyham Terriers, Basset Hounds, and Petit Basset
Griffon Vendeens. In some of these breeds the lens luxation may be secondary
to glaucoma. Thus, we have also begun to focus on glaucoma as a primary
inherited disease and are collecting DNA from affected dogs and their close
relatives, and have submitted a pre-proposal (Molecular-Genetic Causes for
Canine Lens Luxation and Glaucoma - full proposal pending) to continue this
investigation. In the glaucoma studies we have samples from 17 Basset Hounds
including 5 affected individuals, 28 Petit Basset Griffon Vendeens including
2 affected individuals, and 46 Welsh Terriers including 6 affected
individuals. In addition, we have DNA from one Welsh Springer Spaniel with
glaucoma. Mutations in three genes, myocilin,3 cytochrome P4501 B 14,5 and
the forkhead transcription factor gene FKHL76 have been shown to be
responsible for glaucoma in people. In addition, mouse studies indicate that
mutations in the tyrosinase related protein 1 gene can contribute to
development of glaucoma. We have developed markers for the canine myocillin
gene and the canine tyrosinase related protein 1 gene and are currently
testing these markers in the Basset Hound families. We intend to continue
this expanded investigation with the new grant, should our proposal be
approved.
References
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Kainulainen, R. Oavidson, L. Puhakka, L. Peltonen, A novel mutation of the
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2. M. B. Willis, K. C. Barnett,
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