Z-score Cutoff Research Articles

Biologically implausible values and childhood obesity surveillance

Objective To develop a methodology for updating the Centers for Disease Control and Prevention's (CDC) statistical determination of biologically implausible values (BIV) in childhood obesity anthropometric surveillance data. Methods Nurse-measured height and weight data were collected on public school students in five New Jersey cities in 2008–2009 (N=40,266). CDC methodology, using a fixed exclusion z-score range based on World Health Organization (WHO) definitions and National Center for Health Statistics and WHO 1977 growth charts, identified 1.3% of the children as BIVs. National Health and Nutrition Examination Survey (NHANES) data (2008) were used to obtain new z-score limits for anthropometric measures. Results The NHANES data yielded maximum values beyond the CDC z-score cutoffs. Application of limits from the NHANES data identified 0.08% of the sample as BIVs and resulted in an obesity estimate of 25.4%, up from 24.7% using the CDC cutoffs. Conclusions The identification of BIVs in anthropometric data should distinguish mismeasurement from truly extreme growth. Children today have body measurements that, while implausible in comparison to the CDC growth curves, are within range based on more recent data. Tools for tracking the prevalence of childhood obesity need to accommodate this shift in the distribution. Funding source: Robert Wood Johnson Foundation, Princeton, NJ

Distribution of Z-Scores in a University Cohort With an Emphasis on “High” Bone Mineral Density

High bone mineral density (BMD) is currently not defined by the International Society for Clinical Densitometry with a specific Z-score cutoff; however, it has been suggested that a Z-score greater than or equal to 2.5 is not normal. Institutional Review Board approval was obtained. We evaluated a University dual-energy X-ray absorptiometry database over the previous 24 mo to define Z-score distributions. A Z-score greater than or equal to 2.5 was selected as the outcome event of interest in a logistic regression for adjusted odds ratio. The covariates were height; weight; body mass index (BMI); gender; menopausal status; use of female hormones; presence of insufficiency fractures after 50 yr of age; previous fractures; previous surgeries (back surgeries, vertebroplasty, or kyphoplasty); transplant history; presence of long-term chronic conditions (asthma, lupus, rheumatoid arthritis, or cystic fibrosis); eating disorder; current use of glucocorticoids; smoking status; and current and past use of osteoporosis pharmacological therapies. The study included a total of 8216 patients; 7212 (87.8%) were females, and 1044 (12.2%) were males. In the total population, 13.6% had a Z-score greater than or equal to 2.5 at the lumbar spine, femoral neck, or total hip. Only 0.2% of the males and 0.8% of the females had a Z-score greater than or equal to 2.5 at all 3 sites. The 97.5th percentiles for Z-scores in our population for men and women, respectively, were 3.4 and 3.9 at the lumbar spine, 1.5 and 2.1 at the femoral neck, and 1.6 and 2.2 at the total hip. The 99th percentile for Z-scores for men and women, respectively, were 4.9 and 4.7 at the lumbar spine, 2.4 and 2.7 at the femoral neck, and 2.2 and 2.7 at the total hip. At the lumbar spine, female gender and weight were found to be risk factors for a high Z-score (≥2.5). The use of glucocorticoids, bone-active medications, BMI, and smoking were significantly less likely to predict a lumbar spine Z-score greater than or equal to 2.5. A high total-hip Z-score is predicted by increasing weight, whereas those patients using bone-active medications were less likely to have high BMD at the total hip. At the femoral neck, there were no significant risk factors related to a Z-score greater than or equal to 2.5; those taking bone-active medications were significantly less likely to have a high Z-score. These data suggest that a high Z-score is common at 1 or more sites. Further research about the criteria for the diagnosis of high BMD is warranted.

Fast-food and sweetened beverage consumption: association with overweight and high waist circumference in adolescents

Overweight and obesity have increased to epidemic proportions among adolescents and are associated with chronic non-communicable diseases and excess mortality in adulthood. The association of overweight/obesity with poor dietary habits has not been studied in adolescents in middle-income developing countries. The present study aimed to estimate the prevalence of overweight, obesity and high waist circumference (WC) in 15-19-year-old Jamaican adolescents and to investigate the association with fast-food and sweetened beverage consumption. The study enrolled 1317 (598 male, 719 female) adolescents aged 15-19 years using multistage, nationally representative sampling. Age-specific prevalence calculation used internal Z-score lines connecting with the WHO adult cut-off points. Logistic regression was used to examine the association of overweight or high WC with fast-food and sweetened beverage consumption, adjusting for potential confounders. The overall prevalence of overweight, obesity and high WC was approximately 15 %, 6 % and 10 %, respectively. Prevalence estimated using internal Z-scores was similar to that using the International Obesity Taskforce cut-off points. Obesity (8.0 % in females, 3.3 % in males) and high WC (16.2 % in females, 1.7 % in males) were significantly more prevalent in females when using internal Z-score cut-offs. High WC was associated with the absence of fruit consumption (P = 0.043) and overweight with high sweetened beverage consumption (P = 0.018). Overweight occurs frequently among Jamaican 15-19-year-olds and is associated with increased consumption of sweetened beverages. High WC is more prevalent among females and is related to low consumption of fruits and vegetables. Measures to reduce the consumption of sweetened beverages and increase fruit intake may reduce the prevalence of excess body fat among adolescents.

Prevalence of and Traits Associated with Low BMD among Female Adolescent Runners

Identify the prevalence of and traits that may increase the risk of low bone mineral density (BMD) among 93 female adolescent competitive endurance runners. Participants were 93 high school runners, ages 13-18 yr, from southern California. Eating attitudes and behaviors were assessed using the Eating Disorder Examination Questionnaire (EDE-Q). Menstrual and sports participation history were evaluated using an interviewer-assisted, self-report questionnaire. Bone mineral density (BMD) of the spine (L1-L4), total hip, and total body were measured by dual-energy x-ray absorptiometry. The -2 and -1 BMD age-matched, gender-specific z-score cutoffs were used to categorize girls as having low bone mass for age. Among the female runners, 11.8% and 28% met the -2 and -1 BMD z-score cutoffs, respectively, whereas 25.8% reported menstrual irregularity (MI). Total hip BMD, lumbar spine BMD, and lumbar spine BMD z-score were significantly lower in runners with MI after adjusting for body mass index (BMI) and lean tissue mass. Runners that participated in five or more compared with three seasons of endurance running exhibited a significantly lower total body and lumbar spine BMD z-score after adjusting for BMI, lean tissue mass, and number of menstrual cycles in the past year. Multiple regression analysis indicated that MI, participation in five or more seasons of endurance running, BMI, and lean tissue mass were independent predictors of low BMD. Female adolescent endurance runners may represent a population with an increased risk of low bone mass. Future studies are necessary to further understand the factors contributing to low bone mass in young runners and to identify behavioral strategies that will promote optimal bone mineral accumulation during the adolescent years.

First Structure of a Eukaryotic Phosphohistidine Phosphatase

Phosphatases are a diverse group of enzymes that regulate numerous cellular processes. Much of what is known relates to the tyrosine, threonine, and serine phosphatases, whereas the histidine phosphatases have not been studied as much. The structure of phosphohistidine phosphatase (PHPT1), the first identified eukaryotic-protein histidine phosphatase, has been determined to a resolution of 1.9A using multiple-wavelength anomalous dispersion methods. This enzyme can dephosphorylate a variety of proteins (e.g. ATP-citrate lyase and the beta-subunit of G proteins). A putative active site has been identified by its electrostatic character, ion binding, and conserved protein residues. Histidine 53 is proposed to play a major role in histidine dephosphorylation based on these observations and previous mutational studies. Models of peptide binding are discussed to suggest possible mechanisms for substrate recognition.

A supersecondary structure library and search algorithm for modeling loops in protein structures

We present a fragment-search based method for predicting loop conformations in protein models. A hierarchical and multidimensional database has been set up that currently classifies 105 950 loop fragments and loop flanking secondary structures. Besides the length of the loops and types of bracing secondary structures the database is organized along four internal coordinates, a distance and three types of angles characterizing the geometry of stem regions. Candidate fragments are selected from this library by matching the length, the types of bracing secondary structures of the query and satisfying the geometrical restraints of the stems and subsequently inserted in the query protein framework where their fit is assessed by the root mean square deviation (r.m.s.d.) of stem regions and by the number of rigid body clashes with the environment. In the final step remaining candidate loops are ranked by a Z-score that combines information on sequence similarity and fit of predicted and observed ϕ/ψ main chain dihedral angle propensities. Confidence Z-score cut-offs were determined for each loop length that identify those predicted fragments that outperform a competitive ab initio method. A web server implements the method, regularly updates the fragment library and performs prediction. Predicted segments are returned, or optionally, these can be completed with side chain reconstruction and subsequently annealed in the environment of the query protein by conjugate gradient minimization. The prediction method was tested on artificially prepared search datasets where all trivial sequence similarities on the SCOP superfamily level were removed. Under these conditions it is possible to predict loops of length 4, 8 and 12 with coverage of 98, 78 and 28% with at least of 0.22, 1.38 and 2.47 Å of r.m.s.d. accuracy, respectively. In a head-to-head comparison on loops extracted from freshly deposited new protein folds the current method outperformed in a ∼5:1 ratio an earlier developed database search method.