Variation in bone morphogenetic protein 15 is not associated with spontaneous human dizygotic twinning
Zhen Zhen Zhao
2
Jodie N. Painter
1
James S. Palmer
2
Penelope M. Webb
0
Nicholas K. Hayward
4
David C. Whiteman
0
Dorret I. Boomsma
3
Nicholas G. Martin
1
David L. Duffy
1
Grant W. Montgomery
2
0
Cancer and Population Studies, Queensland Institute of Medical Research
,
Brisbane
,
Australia
1
Genetic Epidemiology, Queensland Institute of Medical Research
,
Brisbane
,
Australia
2
Molecular Epidemiology, Queensland Institute of Medical Research, Royal Brisbane Hospital
,
300 Herston Rd, Brisbane, QLD 4029
,
Australia
3
Biological Psychology Department, Free University
,
Amsterdam
,
The Netherlands
4
Oncogenomics, Queensland Institute of Medical Research
,
Brisbane
,
Australia
BACKGROUND: Spontaneous dizygotic (DZ) twinning in humans is under genetic control. In sheep, heterozygous loss of function mutations in bone morphogenetic protein 15 (BMP15) increase ovulation and hence twinning rates. METHODS: To investigate the role of BMP15 in human twinning, we typed 14 common variants, 4 rare novel variants initially detected by sequencing 279 mothers of DZ twins (MODZT) and 17 variants previously associated with premature ovarian failure (POF) in 933 DZ twinning families. We also typed five additional POF associated GDF9 variants. RESULTS: There was some evidence for association between DZ twinning and a common intronic BMP15 variant (rs3897937), but this was not significant after correction for multiple testing. Three of the four novel variants (p.Pro174Ser, p.Ala311Thr and p.Arg392Thr) occurred in 1 - 5 MODZT but were not detected in 1512 controls. We also detected three POF associated mutations in both BMP15 and GDF9 at low frequencies in MODZT and controls. CONCLUSIONS: We conclude that neither rare nor common BMP15 variants play a significant role in the variation in human DZ twinning.
Introduction
The transforming growth factor signalling pathway within the
ovary is critical for the regulation of ovarian function,
ovulation rate and fertility (Moore et al., 2004; Shimasaki et al.,
2004). Two genes in this pathway are growth differentiation
factor 9 (GDF9) on chromosome 5 and bone morphogenetic
protein 15 (BMP15) on the X chromosome. Loss of function
of Gdf9 in female mice blocks folliculogenesis during early
follicle development and leads to infertility (McGrath et al.,
1995). In sheep, the effects of mutations in both GDF9 and
BMP15 are sensitive to copy number. Heterozygous mutations
in both genes increase the frequency of twins and higher order
multiples, whereas homozygous loss of function mutations
results in ovarian dysgenesis and infertility (Galloway et al.,
2000; Hanrahan et al., 2004).
This pathway is also essential for human fertility (Di Pasquale
et al., 2004). Two sisters with hypergonadotrophic ovarian
failure due to ovarian dysgenesis were found to carry a
nonconservative amino acid substitution in the pro region of
BMP15 (p.Tyr235Cys) which acts in a dominant negative
fashion by altering BMP15 processing (Di Pasquale et al.,
2004). Rare variants in both BMP15 and GDF9 contribute to
premature ovarian failure (POF) (Di Pasquale et al., 2004,
2006; Dixit et al., 2005, 2006; Laissue et al., 2006).
Additionally, we found that some mothers of spontaneous dizygotic
(DZ) twins (MODZT) carry rare deletions and missense
mutations in the coding region of GDF9 that are significantly
associated with twinning (Montgomery et al., 2004; Palmer
et al., 2006).
BMP15 is expressed in oocytes in several mammalian
species (Laitinen et al., 1998; Galloway et al., 2000; Otsuka
et al., 2000). The protein has six conserved cysteine residues
characteristic of the TGFb superfamily, but lacks the additional
cysteine residue that strengthens dimerization in other
members of the bone morphogenetic protein family (Vitt
et al., 2001). BMP15 stimulates granulosa cell proliferation
(Otsuka et al., 2000), inhibits follicle-stimulating hormone
receptor (FSHR) expression (Otsuka et al., 2001) and
stimulates KIT ligand expression (Otsuka and Shimasaki, 2002).
Five different heterozygous mutations in the coding region
of BMP15 in different lines of sheep increase ovulation rate
and litter size (McNatty et al., 2004). It is unknown if variants
in BMP15 contribute to variation in human twinning. The
human BMP15 sequence has a number of variants that alter
the predicted protein sequence, including rs41308602
(c.308A.G) located in the second position of codon 103 of
the preproprotein that changes the amino acid from an
asparagine to a serine. We hypothesized that variation in BMP15 may
contribute to the variation in human twinning and genotyped
common variants identified from the literature and public
databases in families of MODZT and controls. We also searched
for rare variants by conducting a mutation screen of the
coding region of the BMP15 gene in a subset of MODZT and
typed these novel variants in additional families to determine
whether these are associated with DZ twinning. Further, we
typed rare BMP15 and GDF9 variants (...truncated)