Denise M. Ney, PhD – Slide of the Week

Denice Ney Slide of the Week

Title: Males with PKU have lower bone mineral density (BMD) compared with females with PKU that may reflect higher intake of amino acid medical food.

Legend: Left – Comparison of BMD Z-scores of male and female participants with classical and variant PKU. Male participants had significantly lower total body BMD Z-Scores (p= 0.01; males, n = 6; females, n =9) and tended to have lower L1–4 spine (p= 0.13; males, n= 6; females, n =9) and total femur BMD Z-Scores (p = 0.08; males, n=4; females, n = 8) compared to female participants. Values are means±SE. BMD, bone mineral density; PKU, phenylketonuria. Right – Total femur BMD Z-scores and intake of PE from AA-MF were negatively correlated (r=−0.58, p= 0.048) based on 13 participants with PKU. AA-MF, amino acid medical foods; BMD, bone mineral density; PE, protein equivalent; PKU, phenylketonuria.

Citation: Stroup BM, Hansen KE, Krueger D, Binkley N, and Ney DM. (2019).  Sex differences in body composition and bone mineral density in phenylketonuria: A cross-sectional study.  Molecular Genetics and Metabolism Reports, 15:30-35.

Abstract: Background –  Low bone mineral density (BMD) and subsequent skeletal fragility have emerged as a long-term complication of phenylketonuria (PKU). Objective – To determine if there are differences in BMD and body composition between male and female participants with PKU.  Methods -From our randomized, crossover trial [1] of participants with early-treated PKU who consumed a low-phenylalanine (Phe) diet combined with amino acid medical foods (AA-MF) or glycomacropeptide medical foods (GMP-MF), a subset of 15 participants (6 males, 9 females, aged 15-50 y, 8 classical and 7 variant PKU) completed one dual energy X-ray absorptiometry (DXA) scan and 3-day food records after each dietary treatment. Participants reported lifelong compliance with AA-MF. In a crossover design, 8 participants (4 males, 4 females, aged 16-35 y) provided a 24-h urine collection after consuming AA-MF or GMP-MF for 1-3 weeks each. Results – Male participants had significantly lower mean total body BMD Z-scores (means ± SE, males = – 0.9 ± 0.4; females, 0.2 ± 0.3; p = 0.01) and tended to have lower mean L1-4 spine and total femur BMD Z-scores compared to female participants. Only 50% percent of male participants had total body BMD Z-scores above – 1.0 compared to 100% of females (p = 0.06). Total femur Z-scores were negatively correlated with intake of AA-MF (r = – 0.58; p = 0.048). Males tended to consume more grams of protein equivalents per day from AA-MF (means ± SE, males: 67 ± 6 g, females: 52 ± 4 g; p = 0.057). Males and females demonstrated similar urinary excretion of renal net acid, magnesium and sulfate; males showed a trend for higher urinary calcium excretion compared to females (means ± SE, males: 339 ± 75 mg/d, females: 228 ± 69 mg/d; p = 0.13). Females had a greater percentage of total fat mass compared to males (means ± SE, males: 24.5 ± 4.8%, females: 36.5 ± 2.5%; p = 0.047). Mean appendicular lean mass index was similar between males and females. Male participants had low-normal lean mass based on the appendicular lean mass index. Conclusions -Males with PKU have lower BMD compared with females with PKU that may be related to higher intake of AA-MF and greater calcium excretion.

About the Lab:  The Ney research group has conducted studies in individuals with PKU that establishes the acceptability and safety of foods made with the whey protein, glycomacropeptide, in the nutritional management of PKU, a genetic disorder caused by deficiency of the hepatic enzyme phenylalanine hydroxylase that converts the essential amino acid phenylalanine to tyrosine. To prevent brain damage and cognitive impairment, individuals with PKU must follow a lifelong, low-phenylalanine diet that is restricted in natural foods and requires ingestion of a bitter-tasting amino acid formula. Glycomacropeptide (GMP) is uniquely suited to the PKU diet because it is the only known dietary protein that contains only trace amounts of phenylalanine. Low-phenylalanine food products made from GMP provide a palatable and acceptable alternative to the amino acid formulas currently required in the PKU diet.

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