Genetic drugs developer Homology Medicines has started patient enrolment in a Phase I/II clinical trial of its investigational gene therapy HMI-102 to treat phenylketonuria (PKU) in adults.

PKU is a metabolic disorder caused by a mutation in the phenylalanine hydroxylase (PAH) gene that leads to a potentially toxic build-up of the essential amino acid, phenylalanine (Phe).

HMI-102 uses the company’s human hematopoietic stem cell-derived adeno-associated virus vectors (AAVHSCs) to deliver a functional copy of the PAH gene to the liver cells.

Dubbed pheNIX, the randomised, concurrently-controlled, dose-escalation trial is intended to assess the safety and efficacy of a single dose of the gene therapy candidate in up to 21 patients aged 18-55 years.

The study will also monitor the reduction in serum Phe levels.

The trial has been designed to facilitate the expansion of the number of participants in any dose cohort, if the Data Monitoring Committee and the Homology Review Team determine the selected dose to be safe and effective.

An expansion of a dose cohort would trigger the inclusion of a concurrent, randomised control arm that will involve classic PKU patients whose Phe levels will be tracked prior to crossover into the therapy arm.

The company expects initial results from the trial to be available by the end of this year.

Homology Medicines chief scientific officer Albert Seymour said: “Now that enrolment in the Phase I/II pheNIX study is underway, HMI-102 becomes the first gene therapy candidate for PKU to enter the clinic, which is a major advancement for patients living with this disease.”

HMI-102 holds fast track designation to treat PKU in the US, and orphan drug designation in the EU to use human hematopoietic stem cell-derived adeno-associated virus AAVHSC15 for PAH deficiency, the main cause of PKU.