Fluorodeoxyglucose Positron Emission Tomography (FDG PET) Findings in Patients With Phenylketonuria Before and After KUVAN Therapy

Plasma phenylalanine level (mg/dl) served as the primary means of evaluating brain glucose metabolism before and after sapropterin (KUVAN) therapy. Blood tests for phenylalanine levels (Phe) were collected before and 4 months after sapropterin (KUVAN) therapy. All subjects received KUVAN at a dose of 20/mg/kg/day for four months. The goal was to estimate the change in blood glucose metabolism after treatment with Sapropterin (if any), with the hypothesis that treatment would decrease plasma Phe levels.

The Hopkins Verbal Learning Test-Revised (HVLT) is a neuropsychological test designed to assess verbal memory. The test consists of 12 nouns (targets) with four words drawn from each of three semantic categories. Raw scores are derived for Total Recall (across three learning trials), Delayed Recall (after 20-25 minute delay), Retention (% retained), and a Recognition Discrimination Index (true positives minus false positives). The maximum total for each recall trial (Learning Trials 1 to 3, Delayed Recall Trial 4) is 12. Raw scores are converted to "T-scores" by means of age-based tables provided in test manual (T-scores can go from 0 - 100, with higher scores correlating with higher verbal memory function). Median HVLT Total Recall and HVLT Delayed Recall T-scores at baseline and 4 months after Sapropterin therapy were compared.

The Hopkins Verbal Learning Test-Revised (HVLT) is a neuropsychological test designed to assess verbal memory. The test consists of 12 nouns (targets) with four words drawn from each of three semantic categories. Raw scores are derived for Total Recall (across three learning trials), Delayed Recall (after 20-25 minute delay), Retention (% retained), and a Recognition Discrimination Index (true positives minus false positives). The maximum total for each recall trial (Learning Trials 1 to 3, Delayed Recall Trial 4) is 12. Raw scores are converted to "T-scores" by means of age-based tables provided in test manual (T-scores can go from 0 - 100, with higher scores correlating with higher verbal memory function). Median HVLT Total Recall and HVLT Delayed Recall T-scores at baseline and 4 months after Sapropterin therapy were compared.

The Adapted Paced Auditory Serial Addition Task (PASAT) is a measure of cognitive function that specifically assesses auditory information processing speed and flexibility, as well as calculation ability. For Rates #1 and #2, single digits are presented every 3 seconds and the patient must add each new digit to the one immediately prior to it. The score for PASAT is the total number of correct answers (out of 60, for a total possible score ranging from 0-60 with higher score preferred as it indicates higher auditory processing speed) for each trial. All scores are expressed as "z-scores" which are generated based on norms for 101 healthy adults, with separate norms for <12 years of education versus >12years of education. Using a reference population as a basis of comparison, the "z-score" is the number of standard deviations the score is above (positive) or below (negative) the mean of the reference population (zero). Possible z-scores lie on a continuous scale.

The symbol-digit modalities test (SDMT) was developed to identify individuals with neurological impairment. The SDMT requires individuals to identify nine different symbols corresponding to the numbers 1 through 9, and to practice writing the correct number under the corresponding symbol. Then they manually fill the blank space under each symbol with the corresponding number. A second oral administration is then completed. The participant is given a blank copy of the test and asked to state the correct number for each corresponding symbol. The participant is given 90 s to complete each of these administrations. A written and oral score is calculated by totaling the number of correct answers for each section. The score is the number of correctly coded items from 0-110 in 90 seconds, with a higher score representing less neurological impairment with respect to attention, scanning abilities and motor skills. The total raw score was used for purposes of this study.

The Wechsler Adult Intelligence Scale (WAIS) is a test designed to measure intelligence in adults and older adolescents. It is composed of 10 core subtests and five supplemental subtests, with the 10 core subtests comprising the Full Scale intelligence quotient (IQ). Contained within the WAIS is an assessment of digit-coding which consists of nine digit-symbol pairs followed by a list of digits. Under each digit the subject should write down the corresponding symbol as fast as possible. The number of correct symbols within the allowed time (e.g. 90 or 120 sec) is measured, with a higher score representative of a higher performance component of IQ/intelligence.

The Delis-Kaplan Executive Function System (D-KEFS) is a neuropsychological test is used to measure a variety of verbal and nonverbal executive functions for both children and adults. Among the 9 subtests is the Verbal Fluency Test which measures letter fluency, category fluency, and category switching. Verbal Fluency Test. This subtest requires an individual to randomly generate words based upon given parameters (ex., as words beginning with the letter F) and the believed areas of executive function assessed are cognitive flexibility, response inhibition, and verbal fluency. Raw scores are calculated based on the number of correct answers, which are then converted to scaled scores with a mean of 10 and standard deviation of 3. Higher scaled score represents a higher level of executive verbal and nonverbal function.