The search for genes responsible for most complex diseases is a challenging task in human genetics since these diseases result from complex interactions between the environment and susceptibility alleles in multiple genes. Several single nucleotide polymorphism (SNPs) within candidate genes have been studied for association with increased susceptibility to osteoporosis and/or fracture risk [1,2]. These candidate genes are primarily involved in biological processes of bone physiology and include genes for various receptors [3-6], cytokines [7], growth factors [8-10] and structural proteins [11]. Genes not directly involved in bone biology have also been studied [12,13].

Type I collagen is the most abundant and ubiquitously expressed of the collagen superfamily of proteins that are the most abundant proteins in the human body. Genes that encode the a1(I) and a2(I) chains are located on chromosomes 17 and 7, respectively, and several polymorphisms and mutations have been identified and associated with diseases such as osteogenesis imperfecta and osteoporosis [14,15]. In 1996, a novel polymorphism in the Sp1 binding site of the COL1A1 gene promoter was associated with low bone mass and increased risk of vertebral fracture [11]. Similar studies in other populations produced conflicting results [16-21]. Two new polymorphisms in the regulatory region of the COL1A1 gene, to which primary osteoblast nuclear proteins bind, were recently identified, of which a G→T transversion at position –1997 was associated with decreased lumbar bone mineral density (BMD) and to a lesser degree, with femoral BMD in postmenopausal women [22].

Collagen undergoes several posttranslational modifications which include cross-linking and hydroxylation of proline and lysine residues, catalyzed by various isomerases and hydroxylases [15]. High serum homocysteine concentrations may interfere with cross-linking of collagen and thus affect bone quality [23]. Such increased concentrations have been observed in individuals with a low folate status who are homozygous for the C677T variant of the methylenetetrahydrofolate reductase (MTHFR) gene [24] in which substitution from alanine to valine produces a thermolabile enzyme [25]. This common variant has been associated with coronary artery disease [25], neural tube defects [26] and low bone BMD [12,27]. Suggestive linkage of femoral BMD has been reported to locus 1p36 [28-30], where the MTHFR and other candidate genes for osteoporosis are located [13]. We have studied the Sp1 and –1997 G→T polymorphisms within the promoter region of the COL1A1 gene and the MTHFR C677T variant for association with BMD in a group of postmenopausal women in Malta. (Author: this is a one-sentence paragraph)