The Effectiveness of Kuvan in Amish PKU Patients
Condition: Phenylketonuria
MeSH terms: Phenylketonurias
Study type: Interventional
Phase: Phase 4

Summary: 
      The purpose of this study is to determine if Amish patients with PKU show responsiveness
      after a high dose, prolonged Saproterin trial. The population of interest has a high
      frequency of a specific splice site mutation, the 1066-11G>A mutation. This splice site
      mutation activates a cryptic splice site resulting in an in frame insertion of 9 nucleotides
      preceding exon 11. This leads to protein conformational changes and abrogation of function.
      Previous studies of this genotype have indicated <1% residual activity of the PAH enzyme and
      an insignificant responsiveness to Saproterin. However, in this specific study Phe levels
      were evaluated only over 24 hours after a single-dose BH4 challenge at the standard dose of
      20mg/kg.

      Based on new clinical information, the investigators hypothesize that if given a prolonged
      trial of Saproterin at a higher dose, Amish patients with PKU, specifically those homozygous
      for the c.1066-11G>A mutation, will have a significant reduction in Phe levels or an increase
      in Phe tolerance and/or improvement in executive functioning and quality of life.
    

Detailed description: 
      Phenylketonuria (PKU) is caused by a deficiency of the enzyme phenylalanine hydroxylase
      (PAH). PAH is responsible for the rate limiting step in phenylalanine catabolism. This
      reaction is dependent on tetrahydrobiopterin (BH4). BH4 is a catalytic cofactor for the
      enzyme PAH. Supplementation with synthetic BH4 (saproterin dihydrochloride or KuvanTm) has
      been shown to activate residual PAH activity and lower Phe levels in certain patients. It may
      also have a chaperone effect by binding abnormal PAH protein and decreasing its degradation.
      Saproterin is an approved oral drug developed to reduce blood Phenylalanine (Phe) levels and
      increase Phe tolerance in BH4 responsive patients with hyperphenylalaninemia.

      Certain genotypes have been found to be good predictors of Saproterin responsiveness;
      however, these correlations are imperfect. Therefore the standard of care is to perform a
      trial of Saproterin therapy to assess responsiveness in every PAH patient regardless of
      genotype. Currently this recommendation does not include patients with two null mutations.

      The purpose of this study is to determine if Amish patients with PKU show responsiveness
      after a high dose, prolonged Saproterin trial. The population of interest has a high
      frequency of a specific splice site mutation, the 1066-11G>A mutation. This splice site
      mutation leads to protein conformational changes and abrogation of function. Previous studies
      of this genotype have indicated <1% residual activity of the PAH enzyme and an insignificant
      responsiveness to Saproterin. However, in this specific study Phe levels were evaluated only
      over 24 hours after a single-dose BH4 challenge at the standard dose of 20mg/kg.

      Recently, observation in several Amish patients suggests some promise that these patients may
      be responsive to Saproterin after a longer trial of the medication (Personal comment - Samuel
      Yang, MD). In addition, studies evaluating PAH enzyme activity in these patients, have found
      evidence that this genotype may need higher cofactor concentrations for optimal enzyme
      activity and therefore may require a higher dose of Saproterin then the currently recommended
      20mg/kg (9). To date, no formal clinical trial has been done.

      To answer the question of whether this genotype is responsive to Saproterin at higher doses,
      over a prolonged period, the investigators propose a randomized clinical trial comparing
      blood Phe levels in patients treated with standard-dose Saproterin to those treated with
      high-dose Saproterin. The results of this study could reveal a new population of Saproterin
      responsive PKU patients. This could call into question other null mutations of the PAH gene
      and their responsiveness to Saproterin. This may lead to the investigation of genotypes
      previously thought to be unresponsive to Saproterin. Further, diet treatment alone has proven
      to be difficult for the Amish population for cultural and economic reasons.

      This study will include patients from three local centers with the potential of a fourth, out
      of state, center participating. All patients will be enrolled through University Hospitals
      Case Medical Center. Consent will be obtained over the phone or in person.

        -  Amish patients from University Hospitals Case Western Reserve/Rainbow Babies and
           Children's Hospital/Center for Human Genetics

        -  Amish patients from Akron Children's hospital in Akron, Ohio

        -  Amish patients from The Center for Children with Special Needs (DDC clinic),
           Middlefield, Ohio

        -  Patients from Shodair Children's Hospital in Helena, Montana. These patients may be
           recruited if more patients are required to meet our enrollment goal.

      Study patients will present to their preferred clinic for 5 office visits. Initial
      testing/Part 1: length 4 weeks

      Recruited patients will present to clinic for part 1 of the study. After informed consent is
      obtained, molecular genetic testing will be performed. Testing will include sequence analysis
      of the PAH gene. This testing is necessary to identify the specific genotypes present in each
      patient. The investigators expect the majority of this population to be homozygous or
      heterozygous for the above described splice site mutation. Any patients found to have one (or
      no) identifiable mutations after sequencing will not be included in the study. Genotypes will
      be grouped and analyzed separately at the conclusion of the study. Patients who do not wish
      to undergo genetic testing will not be included in the study.

      Each patient will also have an initial blood Phe level drawn in the form of a dried blood
      spot on filter paper card that will be supplied by the testing company. All Phe testing will
      be performed in a Clinical Laboratory Improvement Amendment (CLIA) certified laboratory at
      The Clinic for Special Children in Strasburg, PA.

      Baseline assessment tools (BRIEF, PKU-QOL) will also be performed at this initial visit.
      Patients will be given a unique study number by our investigational drug pharmacy and will
      begin part 1 of the study as described below.

      In part 1 of the study, patients will not receive any medication. Each patient will be
      treated with diet alone. Patients will maintain a stable, Phe restricted diet (including
      formula) that is consistent with their diet at the time of enrollment. This will be monitored
      by food diaries kept for 3 days of each week. Specifically, patients will be expected to keep
      diaries for the 3 consecutive days leading up to blood draw. Based on these diaries, average
      weekly Phe intake and Phe tolerance will be calculated and recorded. Patients will also
      complete a food frequency tool, which will be reviewed at part 1, 2 and 3's initial visit. We
      will use all of the tools above, plus allow patients regular access to our dietician in order
      to encourage the maintenance of a stable diet.

      Blood Phe concentration will be measured weekly (each Monday) by blood spot cards. Patients
      will not require weekly clinic visits to have Phe levels drawn. Blood spot cards will be
      performed at their home and then mailed to the reference laboratory. In order to teach and
      enable patients to become comfortable performing their own blood spots at home, nursing staff
      (from the DDC clinic) will travel to each patient's house weekly for part 1 of the study
      (total of 3 home blood spots). For parts 2 and 3 of the study, those patients and families
      who are able, will perform their own blood spots at home. Those families who remain
      uncomfortable performing their own blood spots will continue to have their blood spots
      collected by home nursing.

      Initial visit:

        -  Venous blood draw for PAH gene sequencing

        -  Baseline Phe level by dried blood spot card in office

        -  Executive functioning and quality of life assessment tools (BRIEF, PKU-QOL) given

        -  Baseline diet information collected and recorded. Average weekly Phe calculated, Phe
           tolerance calculated.

        -  Food frequency tool completed and reviewed.

      Blood Phe values and Phe tolerance from part 1 of the study (on diet treatment alone) will be
      compared to blood Phe values and Phe tolerance from parts 2 and 3, on low-dose and high-dose
      treatment.

      Part 2: length - 4 weeks

      Study numbers will be randomized into "standard-dose Saproterin" or "high-dose Saproterin"
      groups (treatment group A or treatment group B). The investigational drug pharmacy will
      provide study patients with their medication in kits, at the beginning of each treatment
      period. Goal high-dose Saproterin dosing will be 40mg/kg (rounded up to the nearest 500mg),
      provided in the form of pre-packaged 500mg packets of powder. Labeled dosing on these packets
      will be covered by the investigational drug pharmacy and unidentifiable to patients.
      Standard-dose Saproterin will be 20mg/kg (rounded to the nearest 100mg) provided in the form
      of 100mg tablets. Dosing of the tablets will be unidentifiable to patients. Medication will
      be given orally once daily.

      Initial part 2 visit: after 4 week diet only period

        -  Food diaries collected for the previous 4 weeks (3 per week). Average weekly Phe
           calculated, Phe tolerance calculated.

        -  Food frequency tool completed and reviewed.

        -  Baseline Phe level drawn by dried blood spot card in office

        -  Executive functioning and quality of life assessment tools (BRIEF, PKU-QOL) given

        -  Provided with medication kits (high or standard-dose, 4 week supply)

      Final part 2 visit: after 4 weeks of treatment

        -  Food diaries collected for the previous 4 weeks (3 per week). Average weekly Phe
           calculated, Phe tolerance calculated.

        -  Executive functioning and quality of life assessment tools (BRIEF, PKU-QOL) given

        -  Empty medication bottles/packet kits collected from each patient to assess compliance

        -  Review of any potential adverse events

      This is the end of part 2. There will then be a 2 week "wash out period" where patients
      receive no treatment. The length of this washout period was determined based on the mean
      elimination half-life of saproterin and previous clinical trials. The mean elimination
      half-life of saproterin ranges from 3.9 to 17 hours. In previous trials, washout periods have
      consisted of 7 and 30 days. No efficacy assessments have been performed to differentiate or
      support one washout period over the other (BioMarin Pharmaceuticals, Inc. Data on file).
      Based on the elimination range above, we determined that a two week washout period is
      sufficient. Patients should maintain their steady diet during this time.

      Part 3: length - 4 weeks The cross-over will occur between treatment groups: A to B and B to
      A.

      Initial part 3 visit: after 2 week washout period

        -  Food diaries collected for the previous 2 weeks (3 per week). Average weekly Phe
           calculated, Phe tolerance calculated.

        -  Food frequency tool completed and reviewed.

        -  Baseline Phe level performed by dried blood spot card in office

        -  Executive functioning and quality of life assessment tools (BRIEF, PKU-QOL) given

        -  Provided with medication kits (high or standard-dose, 4 week supply)

        -  Review of any potential adverse events

      Final part 3 visit: after 4 weeks of treatment

        -  Food diaries collected for the previous 4 weeks (3 per week)

        -  Executive functioning and quality of life assessment tools (BRIEF, PKU-QOL) given

        -  Empty medication bottles/ kits collected from each patient to assess compliance

        -  Review of any potential adverse events

      During all parts, patients will maintain a stable, Phe restricted diet including formula
      (same diet as in part 1 of the study). All Phe levels will be blinded and researchers will
      not have access to them until the conclusion of the study. At the conclusion of the study,
      after all data have been analyzed, a complete list of blood Phe levels obtained during the
      study (both on high and low-dose treatment) will be sent to each patient's primary metabolic
      physician. Physicians can then discuss long term Saproterin treatment with their patients
      based on their Phe levels.

      The study will conclude after all parts are complete and groups A and B have both received a
      trial of high and standard-dose Saproterin. All medication will be discontinued at this time.
    

Intervention name(s): saproterin dihydrochloride; Diet treatment
Intervention type(s): Drug; Other
Intervention description(s): The drug will be given as described in the arm/group descriptions.; Patients will maintain a stable, Phe restricted diet (including formula) that is consistent with their diet at the time of enrollment. This will be monitored by food diaries kept for 3 days of each week.
Other intervention name(s): Kuvan treatment
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Saproterin dihydrochloride; Kuvan; Amish