A single IGF1 allele is a major determinant of small size in dogs.
Level 5 - mechanism / opinion, no new human data
Non-human animal genetic association study
PubMed 17412960 · doi:10.1126/science.1137045
What was done
Researchers conducted a genome-wide scan to identify quantitative trait loci (QTLs) influencing body size variation within a single dog breed. They then analyzed genetic variation across a 15-megabase interval surrounding a candidate locus on chromosome 15 across small and giant dog breeds to detect signatures of selective sweeps.
What was found
The genome-wide scan localized a major QTL for size on canine chromosome 15. Fine mapping revealed evidence of a selective sweep spanning the insulin-like growth factor 1 (IGF1) gene. A single IGF1 single-nucleotide polymorphism haplotype was common to all small dog breeds evaluated and nearly absent in giant breeds. The abstract reported no specific sample sizes, effect sizes, or numerical statistics.
Why it matters
This study identifies a shared IGF1 genetic variant as a key evolutionary driver of small body size across diverse domestic dog breeds.
Limits
The abstract does not state the number of dogs, breeds, or genetic markers evaluated. Because this is an observational genetic association in domestic canines, functional biochemical validation and direct translation to other species cannot be evaluated from the abstract alone.