Response to Phenylketonuria to Tetrahydrobiopterin (BH4)

Phenylketonuria(PKU) is an autosomal recessive disorder caused by a defect in the enzyme
phenylalanine hydroxylase(PAH). this incidence of PKU in the US is about 1:15,000 births.
The disease is pan ethnic with more prevalence among individuals of European ancestry.
Recently, a number of patients with PKU showed a marked decrease in their blood Phe levels
when the cofactor for PAH, tetrahydrobiopterin (BH4) was given orally. All these patients
had mutations in PAH while the metabolism of BH4 was normal. These observations were
confirmed by several centers including a pilot study conducted in our institutions. In the
study in our centers, we have identified 21 of 36 patients tested who responded favorably to
BH4.

Recognizing the difficulties with phenylalanine restricted diet, an NIH Consensus Conference
on PKU held in 1999, encouraged exploring different modalities for treating PKU, and BH4 is
among these modalities. This proposal is a three year, double blind placebo control,
multi-center study. An oral load of 10 mg/kg BH4 wil be given to patients with PKU to
identify those that respond with lowering of blood Phe greater or equal to 30%. Blood Phe,
tyrosine and dietary intake will be determined at zero time and 24 hours post load. From
this group of BH4 responsive individuals, thirty-six will be enrolled in the double blind
study. subjects will be randomized to the treatment of placebo group. Those who enter the
trial will have zero time assessments including blood Phe and tyrosine, dietary intake,
physical exam, kidney function, liver function and CBC. Phe and tyrosine and diet intakes,
two prior to the study and the zero time, will be averaged and used as the baseline
measures.

The subjects will be assigned randomly to take either 10mg/kg of BH4 orally or a placebo
without BH4. Blood Phe, tyrosine and dietary intake will be obtained every other week
throughout the 12 week study period. Liver function and kidney function and CBC's will be
obtained monthly. Side effects will be evaluated and noted. Subjects will be instructed to
record two day diet diaries prior to blood Phe sampling throughout the study. The NIH
Consensus Report suggests maintaining blood Phe< 36 umol/l when less than 12 years of age or
up to 900 umol/l after 12 years of age. These levels will be used to determine the efficacy
end points of the study. At the end of three months, blood Phe and tyrosine, dietary intake,
physical exam, kidney function, liver function and CBC will be performed. At this time
efficacy of BH4 will be determined and all subjects will continue in an open label 12 weeks
BH4 treatment, (10mg/kg/day), with assessments collected as in the first phase of the study.
After the subject has had both phases they will be followed for an additional 3 months. The
additional 3 month trial on BH4 will provide long term safety data from 18 subjects who took
BH4 in both the first and second phase in a continuous fashion.

Inclusion Criteria:

- Subject and/or parent or guardian must be capable of understanding and providing
written informed consent

- Subjects must have Phenylketonuria (PKU)or hyperphenylalaninemia (HPA), defined as
baseline blood Phe levels of >600 umol/L

- Subjects must be at least 10 years of age, and may be of either gender and any ethnic
group

- Female subjects of childbearing potential must agree to use adequate birth control or
refrain from sexual activity throughout study participation

Exclusion Criteria:

- Female subjects who are pregnant or breastfeeding

- Subjects who have concurrent diseases or conditions that require medication or
treatment

- Subjects who require concomitant treatment with any drug known to inhibit folate
synthesis

- Subjects who have been treated with any investigational drug within 30 days