Quantitative genetic analysis of longitudinal trends in height: preliminary results from the Louisville Twin Study

Factors Associated with Reaching Mid-Parental Height in Patients Diagnosed with Inflammatory Bowel Disease in Childhood and Adolescent Period

Background/Aims

The recent update on the Selecting Therapeutic Targets in Inflammatory Bowel Disease initiative has added normal growth in children as an intermediate target in Crohn's disease and ulcerative colitis. We aimed to investigate factors associated with reaching mid-parental height (MPH) in patients diagnosed with inflammatory bowel disease in childhood and the adolescent period.

Methods

This multicenter retrospective observational study included pediatric patients with inflammatory bowel disease that had reached adult height. Factors associated with reaching MPH were investigated by logistic regression analyses.

Results

A total of 166 patients were included in this study (128 Crohn's disease and 38 ulcerative colitis). Among them, 54.2% (90/166) had reached their MPH. Multivariable logistic regression analysis revealed that height Z-score at diagnosis and MPH Z-score were independently associated with reaching MPH (odds ratio [OR], 8.45; 95% confidence interval [CI], 4.44 to 17.90; p<0.001 and OR, 0.11; 95% CI, 0.04 to 0.24; p<0.001, respectively). According to the receiver operating characteristic curve analysis, the optimal cutoff level of "height Z-score at diagnosis minus MPH Z-score" that was associated with reaching MPH was -0.01 with an area under the curve of 0.889 (95% CI [0.835 to 0.944], sensitivity 88.9%, specificity 84.2%, positive predictive value 87.0%, negative predictive value 86.5%, p<0.001).

Conclusions

Height Z-score at diagnosis and MPH Z-score were the only factors associated with reaching MPH. Efforts should be made to restore growth in pediatric patients who present with a negative "height Z-score at diagnosis minus MPH Z-score."

Update on the predictability of tall stature from DNA markers in Europeans

Predicting adult height from DNA has important implications in forensic DNA phenotyping. In 2014, we introduced a prediction model consisting of 180 height-associated SNPs based on data from 10,361 Northwestern Europeans enriched with tall individuals (770 > 1.88 standard deviation), which yielded a mid-ranged accuracy (AUC = 0.75 for binary prediction of tall stature and R² = 0.12 for quantitative prediction of adult height). Here, we provide an update on DNA-based height predictability considering an enlarged list of subsequently-published height-associated SNPs using data from the same set of 10,361 Europeans. A prediction model based on the full set of 689 SNPs showed an improved accuracy relative to previous models for both tall stature (AUC = 0.79) and quantitative height (R² = 0.21). A feature selection analysis revealed a subset of 412 most informative SNPs while the corresponding prediction model retained most of the accuracy (AUC = 0.76 and R² = 0.19) achieved with the full model. Over all, our study empirically exemplifies that the accuracy for predicting human appearance phenotypes with very complex underlying genetic architectures, such as adult height, can be improved by increasing the number of phenotype-associated DNA variants. Our work also demonstrates that a careful sub-selection allows for a considerable reduction of the number of DNA predictors that achieve similar prediction accuracy as provided by the full set. This is forensically relevant due to restrictions in the number of SNPs simultaneously analyzable with forensically suitable DNA technologies in the current days of targeted massively parallel sequencing in forensic genetics.

Advances in pubertal growth and factors influencing it: Can we increase pubertal growth?

Puberty is a period of development characterized by partially concurrent changes which includes growth acceleration, alteration in body composition and appearance of secondary sex characteristics. Puberty is characterized by an acceleration and then deceleration in skeletal growth. The initiation, duration and amount of growth vary considerably during the growth spurt. Pubertal growth and biological maturation are dynamic processes regulated by a variety of genetic and environmental factors. Changes in skeletal maturation and bone mineral accretion concomitant with the stage of pubertal development constitute essential components in the evaluation of growth during this pubertal period. Genetic, endocrine and nutritional factors and ethnicity contribute variably to the amount of growth gained during this important period of rapid changes. Many studies investigated the possibility of increasing pubertal growth to gain taller final adult height in adolescents with idiopathic short stature (ISS). The pattern of pubertal growth, its relation to sex maturity rating and factors affecting them has been addressed in this review. The results of different trials to increase final adult height of adolescents using different hormones have been summarized. These data enables Endocrinologists to give in-depth explanations to patients and families about the efficacy and clinical significance as well as the safety of using these therapies in the treatment of adolescents with ISS.

An SNP of the ZBTB38 gene is associated with idiopathic short stature in the Chinese Han population

OBJECTIVE

Idiopathic short stature (ISS) refers to extreme short stature without any diagnostic explanation. Recently, three genome-wide association studies discovered associations between the ZBTB38 and adult height in different populations. Therefore, variations in the ZBTB38 might contribute to ISS. Furthermore, one study in Korean population showed that ZBTB38 gene was significantly associated with adult height, but not with ISS. We want to examine whether the variants in ZBTB38 are associated with ISS in Chinese Han.

METHODS

A case-control association study was performed in 268 ISS patients and 513 healthy controls from Chinese Han population. Fourteen tag SNPs were selected and genotyped using SNaPshot method. Furthermore, expression of mRNA was quantified by RT-qPCR, and assessment of allelic expression imbalance was conducted with SNaPshot method.

RESULTS

Seven ZBTB38 SNPs were significantly associated with ISS by allele tests (rs724016, rs1582874, rs11919556, rs6440006, rs7612543, rs62282002, rs18651435). And five loci were associated with ISS according to genotype (rs11919556, rs16851419, rs6440006, rs62282002, rs18651435). Notably, after applying the stringent Bonferroni correction for multiple testing, one SNP, rs16851435, remained significantly associated by allele and genotype (P = 5·30 × 10⁻⁴ for allele and P = 0·002 for genotype). Furthermore, the rs16851435 alleles were investigated association with ZTBT38 mRNA expression levels. The G allele showed a higher transcriptional activity than the T allele (P = 0·002).

CONCLUSIONS

Our study indicated that the nonsynonymous SNP (rs16851435:T > G,p.Ser319Ala) of ZBTB38 was contributed to susceptibility of ISS in the Chinese Han population.

Genetic and environmental influences on chest circumference during infancy: a longitudinal study of japanese twins

BACKGROUND

Chest circumference (CC) is suggested to be a good indicator of early life nutrition, but little is known on the heritability of CC. Thus we analysed the effects of genetic and environmental factors on the development of CC in Japanese infants.

METHODS

CC was measured longitudinally from birth until 1 year of age in a cohort of 211 monozygotic and 160 dizygotic complete Japanese twin pairs born in 1989-2002. The data were analysed using applications of structural linear equation modelling for twin data.

RESULTS

No sex-specific differences in the variance components were found. Environmental factors unique to each twin explained the major part of the variation of CC at birth whereas environmental factors shared by co-twins were more important at 1-3 months of age. From 3 months of age, the effect of genetic factors become steadily stronger and they explained the majority of the variation at 1 year of age. Strong genetic continuity in the development of CC was found, but also new sets of genes were activated during the first year of life. The origin of the environmental part of the variation could be tracked before 3 months of age. A substantial part of common and specific environmental factors affecting CC affected also birthweight.

CONCLUSIONS

CC is sensitive to intrauterine environmental factors, but these effects diminish during the first year of life, at least if postnatal environment is good. CC can be a useful indicator when identifying newborns who have suffered suboptimal pre-natal conditions.

Body Size in Five-Year-Old Twins: Heritability and Comparison to Singleton Standards

The aim of this study is to examine causes of individual differences in height, weight and body mass index (BMI) in 5-year-old children registered with the Netherlands Twin Register. In addition, we examine whether the results of twin studies can be expanded to the singleton population by comparing the data from twins to Dutch reference growth data and by looking at the twins' target height, which was derived from parental height. For 2996 5-year-old twin pairs, information on height and weight and on parental height was available. Univariate and bivariate genetic analyses of height and weight and univariate analyses of BMI were conducted. In order to compare the twins to the singleton population, standard deviation scores (SDS) for height, BMI and target height were calculated based on Dutch reference growth charts for the general population from 1997. Genetic influences were an important source of variation in height, weight and BMI and the main source of covariation between height and weight. Additive genetic factors accounted for 69% and 66% of the individual differences in height in boys and girls, respectively. For weight, heritability estimates were 59% in boys and 78% in girls and for BMI 34% and 74%. The influence of common environment on height was 25% and 27%, on weight 24% and 10% and on BMI 44% and 12% in boys and girls. The bivariate model showed a large overlap between the genes influencing height and weight. Genes explain 78% (in boys) and 76% (in girls) of the covariance between weight and height. At the age of 5 years, female twins were as tall as singleton children, while male twins were shorter than singletons. For both boys and girls, however, mean height SDS was 0.6 standard deviation scores below the mean target height. All twins had lower BMI than singletons. Twins grow fairly well compared to singletons, but they grow below their target height. This may be due to the above average height of twin parents.

Height Discordance in Monozygotic Females is not Attributable to Discordant Inactivation of X-linked Stature Determining Genes

We tested the hypothesis that X-linked genes determining stature which are subject to skewed or non-random X-inactivation can account for discordance in height in monozygotic female twins. Height discordant female monozygotic adult twins (20 pairs) were identified from the Australian Twin Registry, employing the selection criteria of proven monozygosity and a measured height discordance of at least 5 cm. Differential X-inactivation was examined in genomic DNA extracted from peripheral lymphocytes by estimating differential methylation of alleles at the polymorphic CAG triplet repeat of the Androgen receptor gene (XAR). There were 17/20 MZ pairs heterozygous at this locus and informative for analysis. Of these, 10/17 both had random X-inactivation, 5/17 showed identical X-inactivation patterns of non random inactivation and 2/17 (12%) showed discordant X-inactivation. There was no relationship between inactivation patterns and self-report chorionicity. We conclude that non-random X-inactivation does not appear to be a major contributor to intra-pair height discordance in female MZ twins.

Sex Differences in Genetic and Environmental Factors Contributing to Body-Height

Sex differences in the heritability of self-reported body-height in two Finnish twin cohorts were studied by using sex-limitation models. The first cohort was born in 1938–1949 (N = 4873 twin pairs) and the second in 1975–1979 (N = 2374 twin pairs). Body-height was greater in the younger cohort (difference of 3.1 cm for men and 2.9 cm for women). The heritability estimates were higher among men (h2 = 0.87 in the older cohort and h2 = 0.82 in the younger cohort) than women (h2 = 0.78 and h2 = 0.67, respectively). Sex-specific genetic factors were not statistically significant in either cohort, suggesting that the same genes contribute to variation in body height for both men and women. The stronger contribution of environmental factors to body-height among women questions the hypothesis that women are better buffered against environmental stress, at least for this phenotype.

Genetic and environmental influences on growth from late childhood to adulthood: a longitudinal study of two Finnish twin cohorts

OBJECTIVES

Human growth is a complex process that remains insufficiently understood. We aimed to analyze genetic and environmental influences on growth from late childhood to early adulthood.

METHODS

Two cohorts of monozygotic and dizygotic (same sex and opposite sex) Finnish twin pairs were studied longitudinally using self-reported height at 11-12, 14, and 17 years and adult age (FinnTwin12) and at 16, 17, and 18 years and adult age (FinnTwin16). Univariate and multivariate variance component models for twin data were used.

RESULTS

From childhood to adulthood, genetic differences explained 72-81% of the variation of height in boys and 65-86% in girls. Environmental factors common to co-twins explained 5-23% of the variation of height, with the residual variation explained by environmental factors unique to each twin individual. Common environmental factors affecting height were highly correlated between the analyzed ages (0.72-0.99 and 0.91-1.00 for boys and girls, respectively). Genetic (0.58-0.99 and 0.70-0.99, respectively) and unique environmental factors (0.32-0.78 and 0.54-0.82, respectively) affecting height at different ages were more weakly, but still substantially, correlated.

CONCLUSIONS

The genetic contribution to height is strong during adolescence. The high genetic correlations detected across the ages encourage further efforts to identify genes affecting growth. Common and unique environmental factors affecting height during adolescence are also important, and further studies are necessary to identify their nature and test whether they interact with genetic factors.

Final adult height of children with inflammatory bowel disease is predicted by parental height and patient minimum height Z-score

BACKGROUND

This study was designed to elucidate the contribution of parental height to the stature of children with inflammatory bowel disease (IBD), who often exhibit growth impairment. Accordingly, we compared patients' final adult heights and target heights based on measured parental heights and examined predictors of final adult height in pediatric IBD patients.

METHODS

We prospectively analyzed the growth of 295 patients diagnosed between ages 1 and 18 (211 Crohn's disease [CD], 84 ulcerative colitis [UC]) and their family members (283 mothers, 231 fathers, 55 siblings).

RESULTS

Twenty-two percent had growth impairment (height for age Z-score <-1.64, equivalent to <5th percentile on growth curve) in more than 1 measurement since diagnosis; most growth-impaired patients had CD (88% CD versus 12% UC). Parents of the growth-impaired group had lower mean height Z-scores compared to parents of nongrowth-impaired patients (-0.67 versus 0.02 for mothers [P < 0.001]; -0.31 versus 0.22 for fathers [P = 0.002]). For 108 patients who reached adult heights and had available parental heights, the growth-impaired group continued to demonstrate lower adult height Z-scores (-1.38 versus 0.07; P < 0.001). Adult heights were within 1 SD of target heights even for the growth-impaired group. Only 11.3% remained persistently growth-impaired in adulthood. Multivariate regression analysis demonstrated lower parental height and minimum patient height Z-score as significant predictors of lower final adult height in IBD.

CONCLUSIONS

Parental height is a powerful determinant of linear growth even in the presence of chronic inflammation, and should be an integral part of the evaluation of growth in IBD children.

Identification of 15 loci influencing height in a Korean population

Height is a complex genetic trait that involves multiple genetic loci. Recently, 44 loci associated with height were identified in Caucasian individuals by large-scale genome-wide association (GWA) studies. To identify genetic variants influencing height in the Korean population, we analyzed GWA data from 8842 Korean individuals and identified 15 genomic regions with one or more sequence variants associated with height (P<1 x 10(-5)). Of these, eight loci were newly identified in Koreans (SUPT3H, EXT1, FREM1, PALM2-AKAP2, NUP37-PMCH, IGF1, KRT20 and ANKRD60). The 15 significant loci account for approximately 1.0% of height variation, with a 3.7-cm difference between individuals with < or =8 height-increasing alleles (5.1%) and > or =19 height-increasing alleles (4.2%). We also examined the associations between height loci and idiopathic short stature (ISS). Five loci (SPAG17, KBTBD8, HHIP, HIST1H1D and ACAN) were significantly associated with ISS (uncorrected P<0.05), indicating that height-associated genes in the adult population are involved in extreme cases of short stature in children. This study validates previous reports of loci associated with human height and identified novel candidate regions involved in human growth and development.

Linkage analysis of adult height in a large pedigree from a Dutch genetically isolated population

Despite extensive research of genetic determinants of human adult height, the genes identified up until now allow to predict only a small proportion of the trait's variance. To identify new genes we analyzed 2,486 genotyped and phenotyped individuals in a large pedigree including 23,612 members in 18 generations. The pedigree was derived from a young genetically isolated Dutch population, where genetic heterogeneity is expected to be low and linkage disequilibrium has been shown to be increased. Complex segregation analysis confirmed high heritability of adult height, and suggested mixed model of height inheritance in this population. The estimates of the model parameters obtained from complex segregation analysis were used in parametric linkage analysis, which highlighted three genome-wide significant and additionally at least four suggestive loci involved in height. Significant peaks were located at the chromosomal regions 1p32 (LOD score = 3.35), 2p16 (LOD score = 3.29) and 16q24 (LOD score = 3.94). For the latter region, a strong association signal (FDR q < 0.05) was obtained for 19 SNPs, 17 of them were located in the CDH13 (cadherin 13) gene of which one (rs1035569) explained 1.5% of the total height variance.

Genome-wide association study identifies two novel loci containing FLNB and SBF2 genes underlying stature variation

Human stature, as an important physical index in clinical practice and a usual covariate in gene mapping of complex disorders, is a highly heritable complex trait. To identify specific genes underlying stature, a genome-wide association study was performed in 1000 unrelated homogeneous Caucasian subjects using Affymetrix 500K arrays. A group of seven contiguous markers in the region of SBF2 gene (Set-binding factor 2) are associated with stature, significantly so at the genome-wide level after false discovery rate (FDR) correction (FDR q = 0.034-0.042). Three SNPs in another SNP group in the Filamin B (FLNB) gene were also associated with stature, significantly so with FDR q = 0.042-0.048. In follow-up independent replication studies, rs10734652 in the SBF2 gene was significantly (P = 0.036) and suggestively (P = 0.07) associated with stature in Caucasian families and 1306 unrelated Caucasian subjects, respectively, and rs9834312 in the FLNB gene was also associated with stature in such two independent Caucasian populations (P = 0.008 in unrelated sample and P = 0.049 in family sample). Particularly, additional significant replication association signals were detected in Chinese, an ethnic population different from Caucasian, between rs9834312 and stature in 619 unrelated northern Chinese subjects (P = 0.017), as well as between rs10734652 and stature in 2953 unrelated southern Chinese subjects (P = 0.048). This study also provides additional replication evidence for some of the already published stature loci. These results, together with the known functional relevance of the SBF2 and FLNB genes to skeletal linear growth and bone formation, support that two regions containing FLNB and SBF2 genes are two novel loci underlying stature variation.

Genome-wide association scan for stature in Chinese: evidence for ethnic specific loci

In Caucasian, several studies have identified some common variants associated with human stature variation. However, no such study was performed in Chinese, which is the largest population in the world and evidently differs from Caucasian in genetic background. To identify common or ethnic specific genes for stature in Chinese, an initial GWAS and follow-up replication study were performed. Our initial GWAS study found that a group of 13 contiguous SNPs, which span a region of approximately 150 kb containing two neighboring genes, zinc finger protein (ZNP) 510 and ZNP782, achieved strong signals for association with stature, with P values ranging from 9.71 x 10(-5) to 3.11 x 10(-6). After false discovery rate correction for multiple testing, 9 of the 13 SNPs remain significant (FDR q=0.036-0.046). The follow-up replication study in an independent 2,953 unrelated southern Chinese confirmed the association of rs10816533 with stature (P=0.029). All the 13 SNPs were in consistently strong linkage disequilibrium (D'>0.99) and formed a single perfect haplotype block. The minor allele frequencies for the 13 contiguous SNPs have evidently ethnic difference, which range from 0.21 to 0.33 in Chinese but have as low as approximately 0.017 reported in dbSNP database in Caucasian. The present results suggest that the genomic region containing the ZNP510 and ZNP782 genes is an ethnic specific locus associated with stature variation in Chinese.

Comprehensive association analyses of IGF1, ESR2, and CYP17 genes with adult height in Caucasians

Human adult height is closely related to body growth that is regulated by multiple cytokines or hormones like growth hormone (GH) and estrogen. Our study focused on three potential candidate genes to human height, namely IGF1 (insulin-like growth factor 1), ESR2, and CYP17. We genotyped 43 single nucleotide polymorphisms (SNPs) and tested their associations in 1873 subjects from 405 nuclear families, using both the family-based quantitative transmission disequilibrium test (QTDT) and population-based ANOVA methods. Both analyses consistently detected that two novel SNPs of IGF1, rs5742694 and rs2033178, were significantly associated with human height, with the P-values of 0.0097 and 0.0057 in QTDT analyses, 0.0002/0.004 (sample 1/sample 2) and 8.46 x 10(-5)/1.92 x 10(-5) in ANOVA analyses. For ESR2, significant associations were only detected in women (rs1256061: QTDT P=0.002, ANOVA P=0.002/0.012; rs17766755: QTDT P=0.019, ANOVA P=0.023/0.006; rs1256044: QTDT P=0.022, ANOVA P=0.002/0.034). Haplotype analyses corroborated our single-SNP results. However, no association was detected between CYP17 and human height. In conclusion, we identified the important effects of IGF1 and ESR2 on adult height variation in Caucasians, and first suggested the potential sex-specific effect of ESR2 on height variation in Caucasian women. It will be valuable for other independent studies to replicate and confirm these findings.

Genetics of pubertal timing and its associations with relative weight in childhood and adult height: the Swedish Young Male Twins Study

OBJECTIVE

Previous studies have suggested that the timing of puberty is associated with BMI in childhood and adult stature. Because the genetic background of these associations is not thoroughly investigated, we aimed to analyze it in a longitudinal twin cohort.

METHODS

We studied a Swedish cohort of 99 monozygotic and 76 dizygotic twin pairs born between 1973 and 1979 with weight and length or height measured annually from birth to age 18 years. Age at onset of pubertal growth spurt, age at peak height velocity, and final height were estimated by a parametric JPA2 growth model. The genetic architecture and mutual associations of these traits and childhood BMI were analyzed by linear structural equation modeling.

RESULTS

The heritability estimate was 0.91 for age at onset of pubertal growth spurt, 0.93 for age at peak height velocity, and 0.97 for adult height. Age at onset of pubertal growth spurt was negatively associated with BMI from 1 to 10 years of age and stature in early adulthood. For age at peak height velocity, we found similar associations with childhood BMI and stature in early adulthood. These associations were explained by common genetic factors.

CONCLUSION

Growth during puberty is strictly genetically regulated. These genetic factors also explain why boys who matured early had higher BMI through childhood and taller stature in early adulthood.

Epistasis between loci on chromosomes 2 and 6 influences human height

CONTEXT

Human height is a typical and important complex trait, which is determined by both actions and interactions of multiple genes. Although an increasing number of genes or genomic regions have been discovered for their independent effects on height variation, no study has been performed to identify genes or loci that interact to control the trait.

OBJECTIVE

This study aimed to search for potential genomic regions that harbor interactive genes underlying human height.

METHODS

Here with a sample containing 3726 Caucasians, the largest one ever obtained from a single population of the same ethnicity among genetic linkage studies of human complex traits, we performed variance component linkage analyses of height based on a two-locus epistatic model. We examined pairwise genetic interaction among three regions, 9q22, 6p21, and 2q21, which achieved significant or suggestive linkage signals for height in our recent whole genome scan.

RESULTS

Significant genetic interaction between 6p21 and 2q21 was detected, with 2q21 achieving a maximum LOD score of 3.21 (P = 0.0035) under the epistatic model, compared with a maximum LOD score of 1.63 under a two-locus additive model. Interestingly, 6p21 contains a cluster of candidate genes for skeletal growth, suggesting a mechanism whereby 2q21 regulates height through 6p21.

CONCLUSION

By providing the first evidence for genetic interaction underlying human height variation, this study further delineated the genetic architecture of human height and contributed to the genetic dissection of human complex traits in general.

Association analyses of CYP19 gene polymorphisms with height variation in a large sample of Caucasian nuclear families

Human height is a complex trait regulated by multiple genetic and environmental factors. CYP19 (cytochrome P450 19) encodes aromatase, which catalyses the rate-limiting step in the conversion of androgens to estrogens. Deleterious mutations in CYP19 can result in estrogen deficiency that will influence adult height to certain extent. In the present study, we aimed to test the associations between the CYP19 gene polymorphisms with adult height variation, using family-based association methods, such as QTDT (quantitative transmission disequilibrium test) and FBAT (family-based association test) in 1,873 subjects from 405 Caucasian nuclear families. We found one SNP (rs730154) significantly associated with height by both QTDT (P=0.0030) and FBAT (P=0.0016) analyses. Haplotype analyses corroborated our single-marker results by showing that the haplotypes in block 4 containing rs730154 were significantly associated with height variation. We thus concluded that CYP19 could be one of the genetic factors influencing adult height in Caucasians. Further studies are required to identify the causal functional variants responsible for Caucasian height within the CYP19 gene.

Genetic linkage of human height is confirmed to 9q22 and Xq24

Human height is an important and heritable trait. Our previous two genome-wide linkage studies using 630 (WG1 study) and an extended sample of 1,816 Caucasians (WG2 study) identified 9q22 [maximum LOD score (MLS)=2.74 in the WG2 study] and preliminarily confirmed Xq24 (two-point LOD score=1.91 in the WG1 study, 2.64 in the WG2 study) linked to height. Here, with a much further extended large sample containing 3,726 Caucasians, we performed a new genome-wide linkage scan and confirmed, in high significance, the two regions' linkage to height. An MLS of 4.34 was detected on 9q22 and a two-point LOD score of 5.63 was attained for Xq24. In an independent sub-sample (i.e., the subjects not involved in the WG1 and WG2 studies), the two regions also achieved significant empirical P values (0.002 and 0.004, respectively) for "region-wise" linkage confirmation. Importantly, the two regions were replicated on a genotyping platform different from the WG1 and WG2 studies (i.e., a different set of markers and different genotyping instruments). Interestingly, 9q22 harbors the ROR2 gene, which is required for growth plate development, and Xq24 was linked to short stature. With the largest sample from a single population of the same ethnicity in the field of linkage studies for complex traits, our current study, together with two previous ones, provided overwhelming evidence substantiating 9q22 and Xq24 for height variation. In particular, our three consecutive whole genome studies are uniquely valuable as they represent the first practical (rather than simulated) example of how significant increase in sample size may improve linkage detection for human complex traits.

QTLs for height: results of a full genome scan in Dutch sibling pairs

Height is a highly heritable, complex trait. At present, the genes responsible for the variation in height have not yet been identified. This paper summarizes the results of previous linkage studies and presents results of an additional linkage analysis. Using data from the Netherlands Twin Register, a sib-pair-based linkage analysis for adult height was conducted. For 513 sib-pairs from 174 families complete genome scans and adult height were available. The strongest evidence for linkage was found for a region on chromosome 6, near markers D6S1053 and D6S1031 (LOD = 2.32). This replicated previous findings in other data sets. LOD scores ranging from 1.53 to 2.04 were found for regions on chromosomes 1, 5, 8, 10, and 18. The region on chromosome 18 (LOD = 1.83) also corresponded with the results of previous studies. Several chromosomal regions are now implied in the variance in height, but further study is needed to draw definite conclusions with regard to the significance of these regions for adult height.

Genetic dissection of human stature in a large sample of multiplex pedigrees

Recently, we reported a whole genome scan on a sample of 630 Caucasian subjects from 53 human pedigrees. Several genomic regions were suggested to be linked to height. In an attempt to confirm the identified genomic regions, as well as to identify new genomic regions linked to height, we conducted a whole genome linkage study on an extended sample of 1,816 subjects from 79 pedigrees, which includes the 53 pedigrees containing the original 630 subjects from our previous whole genome study and an additional 128 new subjects, and 26 further pedigrees containing 1,058 subjects. Several regions achieved suggestive linkage signals, such as 9q22.32 [MLS (multipoint LOD score) = 2.74], 9q34.3 [MLS = 2.66], Xq24 [two-point LOD score = 2.64 at the marker DXS8067], and 7p14.2 [MLS = 2.05]. The importance of the above regions is supported either by other whole genome studies or by candidate genes within these regions relevant to linear growth or pathogenesis of short stature. In addition, this study has tentatively confirmed the Xq24 region's linkage to height, as this region was also detected in the previous whole genome study. To date, our study has achieved the largest sample size in the field of genetic linkage studies of human height. Together with the findings of other studies, the current study has further delineated the genetic basis of human stature.

A major gene model of adult height is suggested in Chinese

Adult height (stature), as a complex quantitative trait, has been studied in different populations. However, few genetic studies on height were performed on the Chinese, the largest population in the world. In this study, familial correlation and segregation analyses were carried out for adult height in a Chinese sample composed of 385 nuclear families with a total of 1,169 informative individuals. The results suggest that a major gene with a recessive effect accounts for about 17.2% of the total adult height variation in the Chinese. Significant familial residual effects are found. The heritability (+/-SE) of height is estimated to be 0.647 (+/-0.122). This study, for the first time, provides evidence for the high degree of genetic determination of adult height in the Chinese population and furnishes a valuable reference for further mapping and identification of adult height genes in the Chinese.

Genetic approaches to stature, pubertal timing, and other complex traits

The factors that regulate the timing of puberty remain largely elusive, as do the factors that modulate childhood growth and adult height. However, it is clear that these developmental processes are highly heritable--much of the natural variation in growth and timing of puberty is due to genetic variation within the population. In this review, we discuss how recent genetic and genomic advances can be exploited to help understand the genetic regulation of these processes. In particular, we describe how genome-wide linkage scans and association studies, in conjunction with haplotype-based approaches, are potentially useful tools to increase our understanding of these two complex traits. Discovery of the genetic variants that regulate these two traits would expand our understanding of human neuroendocrinology, postnatal development, and the general architecture of complex genetic traits.

A whole-genome linkage scan suggests several genomic regions potentially containing QTLs underlying the variation of stature

Human height is a complex trait under the control of both genetic and environment factors. In order to identify genomic regions underlying the variation of stature, we performed a whole-genome linkage analysis on a sample of 53 human pedigrees containing 1,249 sib pairs, 1,098 grandparent-grandchildren pairs, 1,993 avuncular pairs, and 1,172 first-cousin pairs. Several genomic regions were suggested by our study to be linked with human height variation. These regions include 5q31 at 144 cM from pter on chromosome 5 (with a maximum LOD score of 2.14 in multipoint linkage analyses), Xp22 at the marker DXS1060, and Xq25 at DXS1001 on the X chromosome (with LOD scores of 1.95 and 1.91, respectively, in two-point linkage analyses). Noticeably, Xp22 happens to be the very region where a newly identified gene underlying idiopathic short stature, SHOX, maps. Based on our findings, further confirmation and fine-mapping studies are to be pursued on expanded samples and/or with denser markers for eventual identification of major functional genes involved in human height variation.

Genetic and environmental influences on the tracking of body size from birth to early adulthood

OBJECTIVE

This study identified genetic and environmental influences on the tracking of body size from birth to 16 to 18.5 years of age.

RESEARCH METHODS AND PROCEDURES

Longitudinal information was collected from a nationally representative sample of Finnish twin adolescents (birth cohorts 1975 to 1979) and their parents through questionnaires mailed when the twins were ages 16 and 18.5 years old. The sample included 702 monozygotic, 724 same-sex dizygotic, and 762 opposite-sex dizygotic sets of twins. The measures used were length, weight, ponderal index (kilograms per cubic meters), and gestational age at birth, and height, weight, and body mass index (kilograms per square meters) at 16 to 18.5 years of age. The changes in genetic and environmental influences on body size from birth to early adulthood were analyzed by quantitative genetic modeling.

RESULTS

The twins who had a higher weight or ponderal index at birth were taller and heavier in early adulthood, whereas those who were longer at birth were taller, but not heavier, later in life. Adult height was affected more by the birth size than body mass index. In the genetic modeling analyses, the genetic factors accounting for the variation of body size became more apparent with age, and both genetic and environmental influences on stature had a sizable carry-over effect from birth to late adolescence, whereas for relative weight, the influences were more age-specific.

DISCUSSION

The genetic and environmental architecture of body size changes from birth to adulthood. Even in monozygotic twins who share their genetic background, the initially larger twin tended to remain larger, demonstrating the long-lasting effects of fetal environment on final body size.

Major recessive gene(s) with considerable residual polygenic effect regulating adult height: confirmation of genomewide scan results for chromosomes 6, 9, and 12

Segregation and linkage analyses were performed for adult height in a population of 200 Dutch families, each of which was ascertained through a proband with asthma. The best-fit model from the segregation analysis was a major recessive gene with a significant residual polygenic background. Models without a polygenic component were rejected. A genomewide scan was performed, and it confirmed previous linkage results for chromosomes 6q25 (LOD = 3.06, D6S2436), 9p1 (LOD = 2.09, D9S301), and 12q1 (LOD = 1.86, D12S375). Our results provide evidence that a combination of segregation and linkage approaches is valuable in understanding genetic determination of common complex traits.

Genomewide linkage analysis of stature in multiple populations reveals several regions with evidence of linkage to adult height

Genomewide linkage analysis has been extremely successful at identification of the genetic variation underlying single-gene disorders. However, linkage analysis has been less successful for common human diseases and other complex traits in which multiple genetic and environmental factors interact to influence disease risk. We hypothesized that a highly heritable complex trait, in which the contribution of environmental factors was relatively limited, might be more amenable to linkage analysis. We therefore chose to study stature (adult height), for which heritability is approximately 75%-90% (Phillips and Matheny 1990; Carmichael and McGue 1995; Preece 1996; Silventoinen et al. 2000). We reanalyzed genomewide scans from four populations for which genotype and height data were available, using a variance-components method implemented in GENEHUNTER 2.0 (Pratt et al. 2000). The populations consisted of 408 individuals in 58 families from the Botnia region of Finland, 753 individuals in 183 families from other parts of Finland, 746 individuals in 179 families from Southern Sweden, and 420 individuals in 63 families from the Saguenay-Lac-St.-Jean region of Quebec. Four regions showed evidence of linkage to stature: 6q24-25, multipoint LOD score 3.85 at marker D6S1007 in Botnia (genomewide P<.06), 7q31.3-36 (LOD 3.40 at marker D7S2195 in Sweden, P<.02), 12p11.2-q14 (LOD 3.35 at markers D12S10990-D12S398 in Finland, P<.05) and 13q32-33 (LOD 3.56 at markers D13S779-D13S797 in Finland, P<.05). In a companion article (Perola et al. 2001 [in this issue]), strong supporting evidence is obtained for linkage to the region on chromosome 7. These studies suggest that highly heritable complex traits such as stature may be genetically tractable and provide insight into the genetic architecture of complex traits.

Identification of novel human GH-1 gene polymorphisms that are associated with growth hormone secretion and height

Height, which is partially determined by GH secretion, is genetically influenced. The purpose of this study was to identify polymorphisms in the GH-1 gene, which are associated with altered GH production. The subjects included prepubertal short children with GH insufficiency without gross pituitary abnormalities (n = 43), short children with normal GH secretion (n = 46), and normal adults (n = 294). A polymorphism in intron 4 (P-1, A or T at base 1663) was identified. Two additional polymorphic sites (P-2, T or G at base 218, and P-3, G or T at base 439) in the promoter region of the GH-1 gene were also identified and matched with the P-1 polymorphism (A or T, respectively) in more than 90% of the subjects. P-1, P-2, and P-3 were considered to be associated with GH production, and the results of P-2 are explained as a representative in this abstract. For example, the allele frequency of T at P-2 in prepubertal short children with GH insufficiency without gross pituitary abnormalities (58.1%) was significantly different from that in short children with normal GH secretion and normal adults (37.0% and 43.5%, respectively; P < 0.001). Furthermore, significant differences were observed in maximal GH peaks in provocative tests (11.1 vs. 18.2 ng/mL, P = 0.006), insulin-like growth factor I SD scores (SDS) (-2.4 vs. -0.8, P < 0.0001), and height (Ht) SDS (-3.7 vs. -3.0, P = 0/001) in children with the T/T or G/G genotypes at P-2, respectively. In the entire study group, significant differences in insulin-like growth factor SDS (T/T, -0.9; G/G, -0.2; P = 0.0009) and Ht SDS (T/T, -1.0; G/G, -0.4; P = 0.022) were observed between the T/T and G/G genotypes at P-2. These data indicate that GH secretion is partially determined by polymorphisms in the GH-1 gene, which explain some of the variations in GH secretion and Ht.

Genetic correlates of menarcheal age: a multivariate twin study

Multivariate genetic models were fitted to data from 44 pairs of MZ and 42 pairs of DZ twin girls on weight, height, and skeletal maturation at the age of menarche, in order to obtain information on genetic relationships of those measures with the age of menarche. The relationships of all three physical measures with this age were largely genetically controlled, but a genetic system controlling skeletal maturity was identified as the only genetic determinant of menarcheal age, independent of those systems of the two remaining physical measures. Heritabilities of all individual traits considered in the study were uniformly high. Possible links of genetic information with hormonal functions determining menarche are discussed.

Phenotypic assortative mating in segregation analysis

A model of phenotypic assortative mating was developed for application in segregation analysis. The model assumed a constant spouse correlation across the range of a quantitative trait or the liability to a discrete trait. Four traits were analyzed to evaluate: 1) the feasibility of applying likelihood analysis to pedigree data in order to distinguish between assortative mating and shared environmental effects as the source of spouse correlation; and 2) the impact on segregation analysis of the failure to account for either assortative mating or shared environmental effects, as appropriate. Height ratio (the ratio of sitting to standing height) and eye color comprised the traits for which the observed spouse correlation reflected assortative mating; serum cholesterol and peptic ulcers (with genotypes defined by the ABO blood group) comprised the traits for which the observed spouse correlation reflected shared environmental effects. For all four traits the test statistics agreed with the known cause of spouse correlation; however, significance was not attained for height ratio or serum cholesterol. The ability to distinguish between the causes of spouse correlation in pedigree data presumably depends on trait and sample characteristics which remain to be delineated. Despite significant spouse correlation, its omission from the segregation analysis model did not undermine the inference of major locus inheritance for any of the four traits. However, the lack of an impact for these traits does not preclude an impact for other traits of ignoring the appropriate spouse correlation in segregation analysis.

Multivariate genetic analysis of twin-family data on fears: Mx models

We describe the implementation of multivariate models of familial resemblance with the Mx package. The structural equation models allow for the effects of assortative mating, additive and dominant genes, common and specific environment, and both genetic and cultural transmission between generations. Two approaches are compared: a correlational one based on Fulker and a factor model described by Phillips and Fulker. Both are illustrated by application to published data on social fears and fear of leadership measured in monozygotic and dizygotic twins and their parents. In the example data, genetic dominance yields a more parsimonious explanation of the data than does cultural transmission, although neither is needed to obtain a good fit to the data. A model of reduced genetic correlation between generations also fits the data but has inherent limitations in this sample. Extensions to sex-limitation and more complex models are discussed.