Transcript Dr. Beever`s Powerpoint Presentation on TH & PHA

Tibial Hemimelia (TH) and
Pulmonary Hypoplasia with
Anasarca (PHA)
_____________________
What are they, where are they and how
are they relevant
Jonathan Beever, PhD
University of Illinois
November 2, 2006
tibial hemimelia (th)

skeletal defects




other defects


failure of pelvic fusion – abdominal hernia
shortened or absent tibia – severe distortion of rear
leg structure
failure of proper neural tube closure – exposure of
brain or spinal tissue
cryptorchidism, failed Mullerian duct development
invariably lethal

calves may be live born – fail to thrive, euthanized
background

recognized in Galloway cattle in early 70’s
(Ojo et al. 1974)
 documented


sire test/selection program in UK
genetic inheritance
Reported in in Shorthorn cattle in 2000
(Lapointe et al. 2000)
3

of 6 calves reported of Canadian origin
ancestry common among all calves
genetics
 unaffected
parents (i.e., normal is dominant)
 equal frequency among sexes
 pedigree analysis reveals common ancestry on
both sides of pedigree
 expected ratios of offspring among matings
between carrier (heterozygous) parents


3:1 ratio of normal to affected offspring
recessive Mendelian inheritance


animals homozygous for defect (mutation) are
affected
both parents of affected calves must be carriers
potential impact

worldwide

putative common ancestor is early Irish import



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one of few direct imports – extensive use
circa ~1975 – multiple generations of dispersion
multiplied in US – exportation of germplasm
US (2004 perspective)


more than half of the top 10 sires for number of
Shorthorn registrations are putative carriers
popular club calf sire is suspected carrier


estimated 80,000 units of semen sold
In 2005, 21 of 24 black composite AI sires offered by a
single vendor are tested as carriers
how to find the defective gene

identification of appropriate
pedigree/population material


collect DNA samples
 ~60 individuals of known genotype status
 within “nuclear” families
genetic marker screening


even distribution/coverage across genome
 panel of 263 markers
prioritize chromosomes for analysis
 comparative biology/genomics
homozygosity analysis
PROBAND
3
3
5
1
2
1
4
1
4
4
3
1
1
1
comparative genomics
mutation screening

complete DNA sequencing of causative
gene
 ~140,000
base pairs
 resequencing of animals of known genotype


normal, carrier and affected
no variation in DNA sequence that was
consistent between all known animals
 inability
to resequence portion of gene in
affected calves

significant portion (30%) of gene absent
in affected calves
TH
normal
1
2
3
4
5
6
7
8
9
10
Figure 1. Photograph demonstrating the DNA-based test for tibial
hemimelia (TH). The DNA from each of ten individuals was used to
determine their TH status by PCR amplification of the normal
chromosome segment and the mutated chromosomal segment
simultaneously. Animals in lanes 1, 6 and 9 are homozygous
normal due to the presence of only the DNA segment representing
the normal chromosome.
Animals in lanes 2, 4 and 8 are
homozygous for the chromosome with the deletion mutation
causing TH, indicating that the samples were taken from affected
calves. Animals in lanes 3, 5, 7 and 10 possess both DNA segments
indicating that they are heterozygous or carriers of the mutation.
validation

blind testing of 45 animals of known
status
 100%

random testing of ~300 phenotypically
normal individuals
 none

accurate
homozygous for mutation
testing of 7 known sires confirmed by ASA
genetic defect policy
 only
6 of 7 genotype as carriers
resolution
 different/inconsistent phenotype?
 Pulmonary Hypoplasia with Anasarca (PHA)
 all
affected calves from inconsistent sire
genotype as homozygotes for identified
mutation
 all affected calves parentally verify to sire


except for DNA markers adjacent to causative gene
2nd mutation – complete deletion of gene
 complete
deletion of 4 genes (460,000 bp)
 very rare frequency as compared to first
curiosities

selection paradox
 carriers

are the “best”
is there a quantitative measure to define best?
 non-pathological
heterozygotes?

manifestation in
structural differences in hindquarters
 remember gene function
 perstistance
and selective increase in the
breeding population over time

almost impossible to “dilute”
pulmonary hypoplasia with anasarca (PHA)

pulmonary hypoplasia


anasarca
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tremendous fluid accumulation in affected calves
lack of lymphatic development
 absence of lymph duct and nodes, athymia
invariably lethal


absent or near absence of lungs
 normal cardiovascular system
all near term calves born dead
other

early embryonic lethal – increased open rate after
confirmed pregnancy
genetics
 unaffected
parents (i.e., normal is dominant)
 equal frequency among sexes
 pedigree analysis reveals common ancestry on
both sides of pedigree
 deficiency of affected calves given suspected
frequency

recessive Mendelian inheritance

affected pedigrees in both Shorthorn and
Maine Anjou breeds
potential impact

putative common ancestor is early French
or Canadian import



circa ~1975 – multiple generations of dispersion
multiplied in US
40 of 121 popular club calf sires are
carriers
 potential
carriers

for phenotypic selection in the
>80% of sons in AI service that are sired by a
popular carrier club calf sire are carriers
mutation screening

complete DNA sequencing of causative
gene
 resequencing


of animals of known genotype
normal, carrier and affected
single missense mutation common to
modern Shorthorn, Maine Anjou and
composite cattle
validation

“blind” testing of 144 animals of known
status
 100%

random testing of ~1000 phenotypically
normal individuals
 none

accurate
homozygous for mutation
4 suspect sires test normal
 insufficient
evidence of their status
risk assessment

do you care?

methods to assess risk
 pedigree

analysis
do your pedigrees contain suspect individuals?
 including “modern” sires that have been tested
 diagnostic

screening
random testing within your herd
 suspect pedigree representation
pedigree assessment

at what point in a pedigree doesn’t it
matter anymore?
 how

many generations?
n
(1/2) – probability of carrier
 n = number of generations between known
carrier and individual in question
 1 generation = 50%
 3 generations = 12.5%
 8 generations = 0.4%
 additive – consider all suspect individuals with
independent paths to individual
breeding management

education is key
 understand

the possibilities – desired outcome
do nothing vs. “kill ‘em all”
 up
to individual breeders vs. mandatory
testing and culling of all carrier animals

accurate identification of carriers
 selective
vs. comprehensive testing programs
 voluntary vs. mandatory
what to test

expense vs. outcome
 low

cost – no affected calves born
sires only – no affected calves born to TH-Free sires
 moderate

sires, herd matriarchs and annual replacement
heifers
 highest

cost – on the road to elimination
cost – complete management
all animals in the herd
 does not imply elimination, only management
acknowledgements


Charles P. Hannon, DVM
Nick Steinke

Brandy Marron
Geri Thurneau

USDA CSREES/ARS – LGSI
