The pheNIX Clinical Study

Are you or a loved one diagnosed with PKU?
Learn more about participating in the pheNIX clinical study.


The pheNIX study is testing the safety and effectiveness of an investigational gene therapy for adults with classical PKU due to PAH deficiency.


You may be eligible to participate if you are between 18-55 years old, have been diagnosed with classical PKU due to PAH deficiency and you meet inclusion and exclusion study criteria.


Take a questionnaire to determine if you may qualify for the pheNIX study.

What is Phenylketonuria (PKU)?

PKU is an inherited condition caused by a defect in the PAH gene. The PAH gene helps create phenylalanine hydroxylase, the enzyme responsible for breaking down phenylalanine (Phe). Phe is an amino acid (a building block of proteins) that is obtained through the diet. If PKU is not treated, Phe can build up to harmful levels in the body. This condition is known as “PAH Deficiency”. Individuals with PAH deficiency must eat foods with minimal intact protein, or Phe, in order to achieve normal blood Phe levels. Restrictive, carefully monitored nutrition therapy remains the primary treatment for PAH deficiency as well as supplements containing tyrosine, an amino acid which is important for maintaining certain functions of the brain. Currently, a carefully maintained Phe-restricted diet can help lower blood Phe concentrations, however it does not address the underlying cause of the disease.

Understanding PAH Deficiency

PAH deficiency is caused by genetic mutations in the PAH gene. The PAH gene provides instructions for making an enzyme called phenylalanine hydroxylase. This enzyme converts the amino acid phenylalanine to other important compounds in the body. If gene mutations reduce the activity of phenylalanine hydroxylase, phenylalanine from the diet is not processed effectively. As a result, this amino acid can build up to toxic levels in the blood and other tissues. Because nerve cells in the brain are particularly sensitive to phenylalanine levels, excessive amounts can cause serious health problems.

An Investigational Gene Therapy

About The Study

Gene therapy refers to a technique that uses genes to treat, prevent or potentially cure certain diseases. The focus of gene therapy today is typically in diseases that are caused by mutations in a single gene. In these conditions, a person’s own gene has a mutation that affects the normal biological function of the protein made from this gene. Gene therapy contains a functioning gene that can be added to the patient’s cells to override the effects of a disease-causing mutation.

PKU is caused by mutations in the gene responsible for breaking down phenylalanine (Phe) as it enters the body through diet. As a result of the body’s inability to properly breakdown Phe, Phe accumulates to toxic levels in the blood causing the symptoms experienced by PKU patients. The goal of this investigational gene therapy is to replace the defective gene in the liver with a normal gene enabling the body to properly breakdown Phe in the blood. As this is an investigational gene therapy, this research may present risks that are not well-known or understood. Therefore, there may be unforeseeable risks associated with participating in this research.​


A patient would receive a single intravenous (I.V.) administration of the PAH gene therapy. This would include investigational AAV vectors containing a copy of the PAH gene.

Vectors are modified viruses designed to seek out cells in your body and deliver a working version of a malfunctioning or absent gene.

The goal of the investigational gene therapy is to enter the liver cell where it would deliver the functional gene and promoter which will help ''activate'' the gene.

The investigational gene therapy contains the PAH gene necessary to create functional phenylalanine hydroxylase protein.


Screening Period


The study will include a screening to make sure participants are healthy and are able to enroll in the study and receive a single administration of HMI-102, an investigational gene therapy for the treatment of adults with PKU.

Study Period


Following a single administration of HMI-102, participants will be observed periodically for 52 weeks to see if the gene therapy is helping the participant make their own PAH enzyme.

Follow Up Period


Finally, participants will be seen less frequently for another four years to make sure that the new gene therapy is restoring active PAH enzyme activity to cells.


By participating in the pheNIX study, you:

  • Receive study medication (HMI-102)
  • Contribute to medical research, which may help you or future patients



As this is an investigational gene therapy, some procedures or treatments used in this research may present risks that are not well-known or understood. Therefore, there may be unforseeable risks associated with participating in this research.


Travel assistance and reimbursements will also be provided to those participating in the study.

​​Getting to and from your study visits should not prevent you from participating in the pheNIX study. If you qualify for this trial, you may speak with a study representative for more information.

For You or A Loved One

Am I Eligible?

You or a loved one may qualify if you or they:

  • Are diagnosed with PKU
  • Have classical PKU due to phenylalanine hydroxylase (PAH) deficiency where the PAH gene is not working properly
  • Are 18-55 years old
  • Are willing and able to maintain your existing diet
  • Are able to take oral steroids for a period of time
  • Are willing to commit to all required study visits and tests for the entire duration of the trial

You will not be a qualified candidate for this study if any of the following apply:

  • PKU diagnosis that is not due to PAH deficiency
  • History of or a positive test result for human immunodeficiency virus (HIV)
  • History of or a positive test result for hepatitis C or hepatitis B
  • History of drug abuse or alcoholism
  • History of significant underlying liver disease
  • Pregnancy, breastfeeding, or intending to become pregnant during the study period
  • Any upcoming major surgeries
  • Unable to partake in a trial period lasting up to 5 years

There are additional study requirements to participate.  A study representative will discuss them with you.



Please fill out the form below, so that we can begin evaluating whether you or a loved one might qualify for this investigational study. The information provided will be used to contact you regarding the study.

All fields are required.

Frequently Asked Questions

What is a clinical study?

A clinical research study tests an investigational medicine or treatment in a population of volunteers. All new drug products go through the clinical study process, so participants like you play a very important role in advancing medicine for present and future generations.

What is an investigational medication?

An investigational medication has been tested in the laboratory and the U.S. Food and Drug Administration (FDA) is allowing it to be tested in people. A clinical study tests how well an investigational medication works and whether it is safe to use for a specific disease or disorder. An investigational medicine is not yet approved as safe or effective by the FDA and thus is not yet approved for sale by the FDA or other government agencies.

How does a clinical study evaluate an investigational medication?

A clinical study has a structured set of clinic visits, medical and behavioral assessments, and a drug dosing schedule you must follow. Information about how you feel and how you are reacting to the study treatment is collected.

How are my rights and safety protected as a participant during a clinical study?

Protecting the rights, well-being and safety of people who take part in clinical studies is the highest priority for clinical researchers throughout the entire study process. All clinical studies follow strict federal guidelines on how volunteers must be treated and must be reviewed and approved by an independent ethics review committee called an Institutional Review Board.  All aspects of the study will be explained to you, and you will have the opportunity to ask questions.

Can I leave the clinical study before it ends?

Although it is very important to remain in a clinical trial once enrolled, you have the right to leave a clinical study at any time, for any reason. If you decide to leave a study, talk to your study doctor first. You will want to know how leaving the study might affect your health and what other treatment options may be available.

How can I learn more about the investigational medication and this study?

More information on this clinical study can be found on or on this website.


Help spread awareness of the pheNIX study by sharing with others. To share this study information via email, click here.

Call us at 781-819-0967 for more information and to speak with a study representative.

Homology Medicines, Inc.
1 Patriots Park
Bedford, MA 01730

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About The Sponsor
Homology Medicines Inc. is a genetic company dedicated to transforming the lives of patients suffering from rare genetic diseases with significant unmet needs.