Phenylketonuria
Conditions
Keywords
Diet therapy, Low phenylalanine diet, Attention, Executive function
Brief summary
For individuals with Phenylketonuria (PKU), the investigators hypothesize that glycomacropeptide will provide an acceptable form of low-phenylalanine dietary protein that will improve dietary compliance, blood phenylalanine levels, cognitive function, and ultimately quality of life compared with the usual amino acid based diet. The study is funded by the Food and Drug Administration (FDA) Office of Orphan Products Development Grants Program, R01 FD003711.
Detailed description
Individuals with phenylketonuria (PKU) lack the enzyme phenylalanine hydroxylase that is needed to metabolize the essential amino acid phenylalanine (phe). When eating a normal diet they show an elevated level of phe in blood that is toxic to the brain. In order to prevent brain damage and cognitive impairment, individuals with PKU must follow a lifelong, low-phe diet that is restricted in natural foods and requires ingestion of a phe-free amino acid (AA) formula. Most adolescents and adults with PKU find the AA formula unpalatable and go off the diet resulting in elevated blood phe levels and neuropsychological deterioration. Glycomacropeptide (GMP), an intact protein produced during cheese making, is uniquely suited to a low-phe diet because it is the only known dietary protein that contains minimal phe. Foods and beverages made with GMP are a palatable alternative to AA formula. The long term goal is to assess the safety, efficacy and acceptability of GMP for the nutritional management of PKU. The specific aim is to conduct a randomized, two-stage, 11-wk, crossover trial comparing the GMP diet with the AA diet in 30 subjects with PKU ≥12 years of age treated since birth with a low-phe AA diet. The sites are: University of Wisconsin-Madison, Waisman Center (primary) and Harvard University, Children's Hospital Boston. Subjects will be recruited and randomized to begin the first 3-wk of the study with either a low-phe diet in which the majority of dietary protein is provided by GMP or AA medical foods and then, after a 3-wk washout with intake of their usual diet, begin the second diet for 3-wk. Dietary education will be provided in a 1-wk base period preceding initiation of each diet.
Interventions
OTHERGMP Diet/GMP Medical Foods
The intervention consists of a low-phenylalanine (Phe) diet in combination with medical foods made with the peptide GMP supplemented with limiting indispensable amino acids, as provided by Cambrooke Therapeutics, LLC. The diet is formulated to replace the protein equivalents provided by AA medical foods with GMP medical foods, keeping other dietary components constant. The GMP dietary treatment period consists of all subjects following the GMP diet for 3-wks at home. The GMP diet intervention is administered in differing orders, GMP Diet/AA Diet or AA diet/GMP Diet.
OTHERAA Diet/AA Medical Foods
The intervention consists of a low-Phe diet in combination with commercial AA medical foods as consumed in each subject's usual diet. A total of 15 different commercial AA medical foods were consumed by subjects in the study. The diet is formulated to provide each subject with their typical daily intake of protein equivalents from AA medical foods. The AA dietary treatment period consists of all subjects following the AA diet for 3-wks at home. The AA Diet comparator intervention is administered in differing orders, GMP Diet/AA Diet or AA diet/GMP Diet.
Sponsors
Boston Children's Hospital
University of Wisconsin, Madison
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
TREATMENT
Masking
NONE
Intervention model description
The study is a randomized, two-arm, crossover trial comparing the GMP diet and the AA diet in 30 subjects with PKU \> 12 years of age. Subjects were randomized to start with either the GMP diet or the AA diet which they followed for 3-wk at home, followed by a 3-wk washout period when they resumed their usual AA diet, and then 3-wk of either the GMP diet or the AA diet whichever they did not consume first. Each subject served as their own control; there was no control group. We studied medical foods - either AA or GMP medical foods which are not drugs. The FDA did not require that we have an IND.
Eligibility
Sex/Gender
ALL
Age
12 Years to 45 Years
Healthy volunteers
No
Inclusion criteria
* Identified PKU by newborn screening; started diet treatment before 1 mo age * Diagnosis of classical or variant PKU with documented phenylalanine level of greater than 600 umol/L at 7-10d of age * Follows or willing to follow PKU diet and consume amino acid medical formula providing more than 50% of protein needs * Acceptance of glycomacropeptide foods determined prior to enrollment
Exclusion criteria
* Females who are pregnant or planning pregnancy * Individuals with mental deficits due to untreated or poorly controlled PKU * Individuals with any health condition deemed to interfere with participation
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Change in the Plasma Phenylalanine Concentration of PKU Subjects Fed the Glycomacropeptide Diet Compared With the Change When Fed the Amino Acid Diet | baseline to day 22 on each diet | Plasma will be collected at each base week and after 3 weeks on each of the dietary treatments, glycomacropeptide and amino acid, following an overnight fast. Plasma phenylalanine concentration (along with the complete profile of free amino acids) will be determined with an amino acid analyzer in the Wisconsin State Lab of Hygiene. Statistical analysis to determine the significance of the change in plasma phe concentration when comparing the 2 diets will consist of ANCOVA with covariates for baseline Phe and dietary Phe intake. The change in plasma Phe concentration from day 22 (final) to day 1 (baseline) was determined after adjusting for baseline Phe level and dietary Phe intake. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Dietary Compliance | 3 week dietary treatment | Compliance with the glycomacropeptide and amino acid dietary treatments will be assessed by comparison of the intake of medical food in grams of protein from medical food per day based on subject completion of 3-day food records prior to the final study visit on day 22. Statistical analysis for a dietary treatment effect will consist of ANOVA. |
| Executive Function Assessed by BRIEF | day 22 of each dietary treatment | Completion of a standardized test, the Behavior Rating Inventory of Executive Function (BRIEF), by each subject for the GMP diet and the AA diet. Values are T-scores which have a mean of 50 points and a SD of 10 points. A T score of \<50 is considered within the normative range. Data are analyzed with a paired t-test. |
| Vitamin D (25-OH) Plasma Concentration at Day 22 | day 22 of each dietary treatment | Vitamin D was measured as a measure of the capacity for calcium absorption. Higher levels of plasma vitamin D are consistent with higher calcium absorption. |
| Bone-specific Alkaline Phosphatase (BSAP) Plasma Concentration at Day 22 | day 22 of each dietary treatment | Plasma concentration of BSAP was determined as a measure of bone turnover. |
| N-terminal Telopeptide (NTX) Plasma Concentration at Day 22 | day 22 of each dietary treatment | Plasma concentration of NTX was determined as a measure of bone resorption; higher levels indicate greater bone breakdown |
| Comparison of Phe Concentrations in Plasma With Concentrations in Dried Blood Spots | 4 times total, 2 per treatment | Concentrations of Phe in plasma and in dried blood spots collected simultaneously by subjects will be compared using 2 methodologies, regardless of intervention. At each of the 4 study visits (baseline and final for each dietary treatment): 1) venipuncture was used to collect blood and plasma was isolated and analyzed for Phe with ion exchange chromatography and 2) subjects were asked right after the venipuncture to spot their blood on filter paper for analysis of Phe with tandem mass spectroscopy (MS/MS). The discrepancy in Phe concentrations with these 2 methods was compared for each sample pair using Bland-Altman statistical analysis. Each subject should have had 4 sample pairs, 29 x 4 = 116, but we ended up with only 110 sample pairs, as explained below. |
Other
| Measure | Time frame | Description |
|---|---|---|
| Bone Mineral Density Determined by Dual-energy X-ray Absorptiometry (DXA) Scan | once during first 3 week dietary treatment | Subjects will have a single DXA test to assess bone mineral density of the lumbar spine and total body during the first dietary treatment that they are randomly assigned to start with. |
Countries
United States
Participant flow
Participants by arm
| Arm | Count |
|---|---|
| GMP Diet-AA Diet In this randomized crossover study, half of subjects will be assigned to an arm that consists of the the GMP diet followed by the AA diet referred to as the Glycomacropeptide (GMP) diet given first intervention.
Glycomacropeptide (GMP) diet given first: The intervention compares a new low-phenylalanine (phe) dietary therapy for PKU, a diet containing foods and beverages made from GMP using Glytactin provided by Cambrooke Foods LLC, with the usual amino acid (AA) low-phe dietary therapy. PKU subjects in the GMP Diet-AA Diet Arm will follow the GMP diet that will replace all of the dietary protein equivalents provided by AA formula with foods and beverages made from GMP for 3 weeks followed by a 3 wk wash out period. They will then follow the usual AA diet for 3 weeks. Each dietary treatment period will maintain constant intake of total protein and phe and last for 3 weeks in subjects living at home. | 17 |
| AA Diet - GMP Diet In this randomized crossover study, half of subjects will be assigned to an arm that consists of the AA diet followed by the GMP diet referred to as the Amino Acid (AA) Diet given first intervention.
Amino Acid (AA) Diet Given First: The intervention compares the usual amino acid (AA) low-phenylalanine (phe) dietary therapy with a new dietary therapy for PKU, a low-phe diet containing foods and beverages made from glycomacropeptide (GMP). PKU subjects in the AA Diet-GMP Diet Arm will follow their usual AA diet for 3 weeks followed by a 3 wk wash out period. They will then replace all of the protein equivalents provided in their diet by AA formula with foods and beverages made from GMP using Glytactin as provided by Cambrooke Foods, LLC. Each dietary treatment period will maintain constant intake of total protein and phe and last for 3 weeks in subjects living at home. | 15 |
| Total | 32 |
Withdrawals & dropouts
| Period | Reason | FG000 | FG001 |
|---|---|---|---|
| Intervention 1 | Withdrawal by Subject | 2 | 0 |
Baseline characteristics
| Characteristic | AA Diet - GMP Diet | GMP Diet-AA Diet | Total |
|---|---|---|---|
| Age, Categorical <=18 years | 2 Participants | 3 Participants | 5 Participants |
| Age, Categorical >=65 years | 0 Participants | 0 Participants | 0 Participants |
| Age, Categorical Between 18 and 65 years | 13 Participants | 14 Participants | 27 Participants |
| Age, Continuous | 28 years | 28 years | 28 years |
| Region of Enrollment United States | 15 Participants | 17 Participants | 32 Participants |
| Sex: Female, Male Female | 5 Participants | 14 Participants | 19 Participants |
| Sex: Female, Male Male | 10 Participants | 3 Participants | 13 Participants |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | — / — | — / — |
| other Total, other adverse events | 0 / 32 | 0 / 30 |
| serious Total, serious adverse events | 0 / 32 | 0 / 30 |
Outcome results
Primary
Change in the Plasma Phenylalanine Concentration of PKU Subjects Fed the Glycomacropeptide Diet Compared With the Change When Fed the Amino Acid Diet
Plasma will be collected at each base week and after 3 weeks on each of the dietary treatments, glycomacropeptide and amino acid, following an overnight fast. Plasma phenylalanine concentration (along with the complete profile of free amino acids) will be determined with an amino acid analyzer in the Wisconsin State Lab of Hygiene. Statistical analysis to determine the significance of the change in plasma phe concentration when comparing the 2 diets will consist of ANCOVA with covariates for baseline Phe and dietary Phe intake. The change in plasma Phe concentration from day 22 (final) to day 1 (baseline) was determined after adjusting for baseline Phe level and dietary Phe intake.
Time frame: baseline to day 22 on each diet
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | Change in the Plasma Phenylalanine Concentration of PKU Subjects Fed the Glycomacropeptide Diet Compared With the Change When Fed the Amino Acid Diet | 62 micro moles per liter plasma | Standard Error 40 |
| AA Diet/AA Medical Foods | Change in the Plasma Phenylalanine Concentration of PKU Subjects Fed the Glycomacropeptide Diet Compared With the Change When Fed the Amino Acid Diet | -85 micro moles per liter plasma | Standard Error 40 |
p-value: 0.0008ANCOVA
p-value: 0.136ANCOVA
p-value: 0.044ANCOVA
Secondary
Bone-specific Alkaline Phosphatase (BSAP) Plasma Concentration at Day 22
Plasma concentration of BSAP was determined as a measure of bone turnover.
Time frame: day 22 of each dietary treatment
Population: Samples were not obtained from 4 subjects due to a collection error by research staff. Thus the sample size is reduced from 30 to 26.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | Bone-specific Alkaline Phosphatase (BSAP) Plasma Concentration at Day 22 | 17.0 micro gram per liter | Standard Error 2.1 |
| AA Diet/AA Medical Foods | Bone-specific Alkaline Phosphatase (BSAP) Plasma Concentration at Day 22 | 17.0 micro gram per liter | Standard Error 2.2 |
Secondary
Comparison of Phe Concentrations in Plasma With Concentrations in Dried Blood Spots
Concentrations of Phe in plasma and in dried blood spots collected simultaneously by subjects will be compared using 2 methodologies, regardless of intervention. At each of the 4 study visits (baseline and final for each dietary treatment): 1) venipuncture was used to collect blood and plasma was isolated and analyzed for Phe with ion exchange chromatography and 2) subjects were asked right after the venipuncture to spot their blood on filter paper for analysis of Phe with tandem mass spectroscopy (MS/MS). The discrepancy in Phe concentrations with these 2 methods was compared for each sample pair using Bland-Altman statistical analysis. Each subject should have had 4 sample pairs, 29 x 4 = 116, but we ended up with only 110 sample pairs, as explained below.
Time frame: 4 times total, 2 per treatment
Population: Analysis of sample pairs is required to determine the discrepancy in Phe levels with the 2 methods. Each subject should have had 4 sample pairs, 29 x 4 = 116, but we ended up with only 110 sample pairs. The explanation for the difference is that several subjects did not provide dried blood spots because research staff forgot to obtain them.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | Comparison of Phe Concentrations in Plasma With Concentrations in Dried Blood Spots | 731 micro moles per liter | Standard Error 32 |
| AA Diet/AA Medical Foods | Comparison of Phe Concentrations in Plasma With Concentrations in Dried Blood Spots | 514 micro moles per liter | Standard Error 23 |
p-value: 0.0001ANOVA
Secondary
Dietary Compliance
Compliance with the glycomacropeptide and amino acid dietary treatments will be assessed by comparison of the intake of medical food in grams of protein from medical food per day based on subject completion of 3-day food records prior to the final study visit on day 22. Statistical analysis for a dietary treatment effect will consist of ANOVA.
Time frame: 3 week dietary treatment
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | Dietary Compliance | 0.74 g protein from MF/kg/day | Standard Error 0.04 |
| AA Diet/AA Medical Foods | Dietary Compliance | 0.76 g protein from MF/kg/day | Standard Error 0.05 |
p-value: 0.576ANOVA
Secondary
Executive Function Assessed by BRIEF
Completion of a standardized test, the Behavior Rating Inventory of Executive Function (BRIEF), by each subject for the GMP diet and the AA diet. Values are T-scores which have a mean of 50 points and a SD of 10 points. A T score of \<50 is considered within the normative range. Data are analyzed with a paired t-test.
Time frame: day 22 of each dietary treatment
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | Executive Function Assessed by BRIEF | 49.0 T score | Standard Error 1.8 |
| AA Diet/AA Medical Foods | Executive Function Assessed by BRIEF | 48.8 T score | Standard Error 2.1 |
p-value: 0.902t-test, 2 sided
Secondary
N-terminal Telopeptide (NTX) Plasma Concentration at Day 22
Plasma concentration of NTX was determined as a measure of bone resorption; higher levels indicate greater bone breakdown
Time frame: day 22 of each dietary treatment
Population: Samples were not obtained from 3 subjects due to a collection error by research staff. Thus the sample size is reduced from 30 to 27.
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | N-terminal Telopeptide (NTX) Plasma Concentration at Day 22 | 17.5 nmol per liter bone collagen equivalents | Standard Error 0.66 |
| AA Diet/AA Medical Foods | N-terminal Telopeptide (NTX) Plasma Concentration at Day 22 | 17.1 nmol per liter bone collagen equivalents | Standard Error 0.65 |
Secondary
Vitamin D (25-OH) Plasma Concentration at Day 22
Vitamin D was measured as a measure of the capacity for calcium absorption. Higher levels of plasma vitamin D are consistent with higher calcium absorption.
Time frame: day 22 of each dietary treatment
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| GMP Diet/GMP Medical Foods | Vitamin D (25-OH) Plasma Concentration at Day 22 | 33.8 ng per ml | Standard Error 1.7 |
| AA Diet/AA Medical Foods | Vitamin D (25-OH) Plasma Concentration at Day 22 | 33.6 ng per ml | Standard Error 1.52 |
p-value: 0.797t-test, 2 sided
Other Pre-specified
Bone Mineral Density Determined by Dual-energy X-ray Absorptiometry (DXA) Scan
Subjects will have a single DXA test to assess bone mineral density of the lumbar spine and total body during the first dietary treatment that they are randomly assigned to start with.
Time frame: once during first 3 week dietary treatment