384 ALOX12 polymorphisms are associated with fat mass in men W-J Xiao et al intron1/exon2 boundary of ALOX12, only 639 base pairs from the 50 promoter region. Moreover, based on the information from HapMap, the criterion for tagging was set at r2 40.5, and rs2073438 as a tagging SNP captured seven additional SNPs. Therefore, the significant association of rs2073438 with the TFM and PFM suggests that the SNP itself or the region around it may be important for transcription initiation efficiency or may be in strong LD with certain functional variants influencing the expression of the ALOX12 protein. Further study is needed to clarify how this intronic SNP affects protein function. Although significant associations were observed between rs312462 and the TFM and PFM using ANOVA, we failed to find significant results in our QTDT analyses (both within-family and 1000-permutation tests). As the QTDT analysis is free of confounding population-substructure effects compared with the traditional-association approach, the results of our study should be more valuable because of the robustness of the TDT approach.28 A possible reason for our result is that the heterozygosity of rs312462 is relatively low, and the statistical power of a family-based-association study depends directly on the degree of allelic heterozygosity.29 Interestingly, we found a significant association between rs2073438 and the TFM, but not the BMI. The BMI has been widely used as a surrogate phenotype for the assessment of obesity status. However, the BMI alone may not accurately reflect the percentage of body fat and the relative contribu- tions of muscle and fat,30 and as an index of body fatness, BMI is significantly influenced by age and sex.31 The subjects of this study were healthy young men aged 20–40 years. The TLM in our sample accounted for B70% of the body mass; we speculate that the BMI in this study may be skewed by the TLM so that the BMI values of these young Chinese men do not accurately reflect body fat mass. Our results are in accordance with the study of Liu et al.,32 in which the polymorphisms of the MTHFR gene were signi- ficantly associated with the BMI; however, the association diminished after adjusting for the LM. Therefore, the FM as measured by DXA is a more refined measure of obesity. ALOX12 belongs to the lipoxygenase superfamily, which catalyzes the insertion of molecular oxygen into polyunsa- turated fatty acids. It has become increasingly clear that polyunsaturated fatty acids have an important function in the control of adipogenesis and reduce the expression of many enzymes involved in lipid metabolism.33,34 Although the exact mechanisms by which polyunsaturated fatty acids exert their effects are not completely understood, several transcription factors and nuclear receptors have been identified as critical regulators of several important genes of lipid metabolism. PPARG, a nuclear transcription factor, is a dominant regulator of adipocyte-specific genes contributing to adipocyte differentiation, susceptibility to obesity and insulin sensitivity.35,36 The substrates of ALOX12 (arachidonic acids) and the products of the lipoxygenase reaction are both effective PPARG activators, and ligand activation of PPARg promotes the differentiation of mesenchymal stem cells into International Journal of Obesity adipocytes. Studies have shown that ALOX12 has an important function in obesity-related diseases, such as hypertension, diabetes and atherosclerosis.22–24 More recently, Mehrabian et al.37 showed that ALOX5, another member of the lipoxy- genase superfamily, has pleiotropic effects on adiposity and type 2 diabetes-related traits. Our results, taken together with the above studies, suggest the involvement of SNP rs2073438 and the AGAGG haplotype in ALOX12 in the variation of obesity, perhaps through a PPARG-dependent pathway. To date, 4200 different candidate genes have been asso- ciated with obesity-related phenotypes,38 and most of those genes regulate the energy balance through the complex central nervous system.39 The mRNA and protein of ALOX12 has been described mainly in neurons and also in some glial cells throughout the cerebrum, basal ganglia and hippocampus.40,41 Recently, Pratico et al.42 showed that the protein levels and activity of ALOX12 in affected frontal and temporal regions of Alzheimer’s disease brains were signifi- cantly increased. The levels of the metabolic products of ALOX12 were also markedly elevated in cerebrospinal fluid from mild cognitive impairment and Alzheimer’s disease brains.43 In these studies, they believed that ALOX12 metabolic pathway increased oxidative stress and inflamma- tory responses, which is likely to have a more active function in the pathogenesis of Alzheimer’s disease. Obesity was determined as a state of chronic oxidative stress and oxidative stress might be a major mechanism underlying the development of obesity-related co-morbidities.44,45 We suspected that there may exist ALOX12 overexpression in central nervous system similar to Alzheimer’s disease, to affect the energy balance. However, all of the above are just hypotheses and wait to be tested by further functional analyses. Polymorphism in ALOX12 has been associated with the BMD in several independent studies. Xiong et al.19 first performed an association analysis of 20 osteoporosis candidate genes on the BMD variation at three clinically important skeletal sites: the spine, hip and ultradistal radius. Their findings show that ALOX12 is a suggestive gene (0.01oPp0.05) for the BMD at the hip and ultradistal radius in the total-population sample. However, the signi- ficant association was mainly driven by the female subjects, suggesting the possibility of a sex-specific association of ALOX12 with the BMD. Extensive evidence suggests that the loci that regulate the BMD do so in a sex-specific manner in both human beings and experimental animals.19,46 The sex specificity of the associations between genes and the BMD may involve the regulation of sex steroids. In addition, Mullin et al.20 also found that three SNPs from ALOX12 were significantly associated with the BMD at the spine and hip in postmenopausal Caucasian women. In this study, we studied 400 Chinese nuclear families with male offspring and used TDT to simultaneously test the linkage and association of ALOX12 gene polymorphisms with the peak BMD. No significant within-family associations were found between ALOX12 SNPs or haplotypes and the peak BMD in young