Ataxia in

Working Kelpies

Alan Wilton, Jeremy Shearman, Bill Ballard

School of Biochemistry and Molecular Genetics

University of New South Wales

Aim

! identify the genetic defect causing

cerebellar abiotrophy, ataxia

! find the ONE base in 2,500,000,000

of the dog genome

How

! Linkage grant application

! ~$70,000 p.a.

! funding from WKC

!$8,000 p.a.

! in kind contributions

" personnel

" samples

Tools

! samples from affected

! samples from relatives

! samples from controls

! dog genome sequence

! information from model organisms

with ataxias (eg human)

Dog Gene Mapping

! Reasons for identifying dog disease genes

!dog health

"many genetic diseases

!model for human genetic diseases

!identification of gene function

!understanding of development

Dog Gene Mapping

! Human is a good model for dog diseases

! human genome advanced

! many disease genes identified

" make good candidates for dog diseases

Humans as models

Dog Gene Mapping

! Breeding structures

! dogs similar to most domestic animals

" take a champion dog

" breed from it widely

" line breeding -! breeding related animals (with selection)

" results in identity-by-descent

" homozygosity of autosomal recessive defects

" genetic disease

! been estimated we each carry ~5 gene defects

Same defective copy of geneinherited from common ancestor

Dog Gene Mapping

! each breed is an isolated population

! different, independent defects

! ~300 breeds

! many genetic diseases

! some will be rare in human

" such orphan diseases difficult to identify in man

" dogs make good models for human disease

Two approaches

! Candidate gene

! find a gene you think is likely to be “it”

! test it.

! Whole genome mapping

! look everywhere

! narrow down possible locations

! the look at candidates

Mice as models

Other dogs asmodels

Dog Gene Mapping

! Need good coverage of the genome

with informative loci

! microsatellites

"DNA fingerprinting

"Paternity testing

! used in locating the disease gene

DogMapping

needsPedigrees

Dog Chromosomes

39 pairs

Genetic RH HumanRed markers common to both maps

Dogs

Dog Breeding

! High use of champion dogs

! inbreeding

! reveal genetic defects carried as harmless

recessive alleles in ancestor

! often defective alleles identical-by-descent

!inherited from common ancestor

! pedigrees can get quite complicated

!many multiple matings

Research

! Locating markers close to disease

!need pedigrees with several affecteds

!need lots of markers to test

!examine inheritance of disease allele and markers

! Like looking for needle in haystack

!need test 300 markers to cover all possibilities

!need large pedigree with many affected to provelinkage

Microsatellites on ABI377

Parentage Test

DAM

SIRE

PUP

Research - Positional cloning

! once location is known

!start search for disease gene itself

!examine known genes in region

!identify new genes in region to test

!find new markers in region

" test new markers on pedigrees for closeness

!can discover gene based only on position

Affecteds only approach

! modern technology advancing fast

! microarrays

! can test 20,000 sites at one time

! for $500 per animal

! 10 affecteds + 10 controls

! look for regions where no variation

in affecteds