LRP6 and osteoporosis: Mice carrying a heterozygous null mutation in Lrp6 have low bone mass.(50) Further support for a key role for Lrp6 in regulating bone development has been provided by the analysis of bone defects in mice homozygous for a hypomorphic allele of Lrp6 (ringelschwanz) caused by an R886W point mutation.(51) Mice homozygous for this allele survive to adulthood but show evidence of delayed ossification and osteoporosis.