Human twinning is not linked to the region of chromosome 4 syntenic with the sheep twinning gene FecB.
The tendency to dizygotic (DZ) twinning is inherited in both humans and sheep, and a fecundity gene in sheep (FecB) maps to sheep chromosome 6, syntenic with human 4q21-25. Our aim was to see whether a gene predisposing to human DZ twinning mapped to this region. DNA was collected from 169 pairs and 17 sets of 3 sisters (trios) from Australia and New Zealand who had each had spontaneous DZ twins, mostly before the age of 35, and from a replication sample of 111 families (92 affected sister pairs) from The Netherlands. Exclusion mapping was carried out after typing 26 markers on chromosome 4, of which 8 spanned the region likely to contain the human homologue of the sheep FecB gene. We used nonparametric affected sib pair methods for linkage analysis [ASPEX 2.2, Hinds and Risch, 1999]. Complete exclusion of linkage (lod < -2) of a gene conferring a relative risk for sibs as low as 1.5 (lambda(s) > 1.5) was obtained for all but the p terminus region on chromosome 4. Exclusion in the syntenic region was stronger, down to lambda(s) = 1.3. We concluded that if there is a gene influencing DZ twinning on chromosome 4, its effect must be minor.
Duffy
D L
DL
Genetic Epidemiology Unit, Queensland Institute of Medical Research and Joint Genetics Program, The University of Queensland, Brisbane, Queensland, Australia. davidD@qimr.edu.au
Montgomery
G W
GW
Hall
J
J
Mayne
C
C
Healey
S C
SC
Brown
J
J
Boomsma
D I
DI
Martin
N G
NG
D000328:Adult; D000818:Animals; D002874:Chromosome Mapping; D002894:Chromosomes, Human, Pair 4; D004247:DNA / Q000235:genetics; D005260:Female; D008040:Genetic Linkage; D005819:Genetic Markers; D016678:Genome; D006801:Humans; D012756:Sheep / Q000235:genetics*; D013045:Species Specificity; D014429:Twins, Dizygotic / Q000235:genetics*
D005819:Genetic Markers; D004247:DNA