Heterogeneity of genetic modifiers ensures normal cardiac development.
BACKGROUND
Mutations of the transcription factor Nkx2-5 cause pleiotropic heart defects with incomplete penetrance. This variability suggests that additional factors can affect or prevent the mutant phenotype. We assess here the role of genetic modifiers and their interactions.


RESULTS
Heterozygous Nkx2-5 knockout mice in the inbred strain background C57Bl/6 frequently have atrial and ventricular septal defects. The incidences are substantially reduced in the Nkx2-5(+/-) progeny of first-generation (F1) outcrosses to the strains FVB/N or A/J. Defects recur in the second generation (F2) of the F1 X F1 intercross or backcrosses to the parental strains. Analysis of >3000 Nkx2-5(+/-) hearts from 5 F2 crosses demonstrates the profound influence of genetic modifiers on disease presentation. On the basis of their incidences and coincidences, anatomically distinct malformations have shared and unique modifiers. All 3 strains carry susceptibility alleles at different loci for atrial and ventricular septal defects. Relative to the other 2 strains, A/J carries polymorphisms that confer greater susceptibility to atrial septal defect and atrioventricular septal defects and C57Bl/6 to muscular ventricular septal defects. Segregation analyses reveal that > or = 2 loci influence membranous ventricular septal defect susceptibility, whereas > or = loci and at least 1 epistatic interaction affect muscular ventricular and atrial septal defects.


CONCLUSIONS
Alleles of modifier genes can either buffer perturbations on cardiac development or direct the manifestation of a defect. In a genetically heterogeneous population, the predominant effect of modifier genes is health. (Circulation. 2010;121:1313-1321.)
Winston
Julia B
JB
Department of Pediatrics, Washington University School of Medicine, St. Louis, MO 63110, USA.
Erlich
Jonathan M
JM
Green
Courtney A
CA
Aluko
Ashley
A
Kaiser
Kristine A
KA
Takematsu
Mai
M
Barlow
Robert S
RS
Sureka
Ashish O
AO
LaPage
Martin J
MJ
Janss
Luc L
LL
Jay
Patrick Y
PY
D000818:Animals; D004195:Disease Models, Animal; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006321:Heart / Q000196:embryology*; D006330:Heart Defects, Congenital / Q000453:epidemiology / Q000235:genetics*; D006344:Heart Septal Defects, Atrial / Q000453:epidemiology / Q000235:genetics; D006345:Heart Septal Defects, Ventricular / Q000453:epidemiology / Q000235:genetics; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000235:genetics; D015994:Incidence; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D012307:Risk Factors; D014157:Transcription Factors / Q000235:genetics
D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; C484469:Nkx2-5 protein, mouse; D014157:Transcription Factors