According to a news release from mid-January 2023, the FDA granted Rare Pediatric Disease designation to SYNB1934 for phenylketonuria. This designation is granted to drugs or biologics being developed for rare pediatric conditions, or those affecting fewer than 200,000 people between infancy and age 18. If the drug is later approved for that condition, the drug’s sponsor (in this case, Synlogic) receives Priority Review voucher eligibility. 

Synlogic describes SYNB1934 as:

an orally administered, non-systemically absorbed drug candidate being studied as a potential biotherapeutic for phenylketonuria (PKU), an inherited metabolic disease marked by an inability to break down the amino acid phenylalanine (Phe), which can be neurotoxic. Synlogic designed its drug candidates to reduce levels of Phe in people with PKU by consuming Phe in the gastrointestinal tract, using genetic engineering of the well-characterized probiotic E. coli Nissle.

Many people with PKU currently lack effective treatment options or fail to respond to treatment. Thus, SYNB1934 could significantly change the treatment landscape if later found to be effective. 

Phenylketonuria (PKU): An Exploration

As described above, phenylketonuria is a rare genetic metabolic disease caused by PAH gene mutations. Normally, this helps the body to produce an enzyme called phenylalanine hydroxylase; this enzyme then breaks down Phe. In people with phenylketonuria, phenylalanine builds up in the body, which can cause damage. People with PKU must follow a diet that limits phenylalanine. This is normally found in protein and some artificial sweeteners. Symptoms, which typically manifest within the first few months of life, can include:

• Eczema or other skin rashes
• Low birth weight and slowed growth
• Skin and/or hair discoloration
• Intellectual and developmental delays
• Microcephaly (abnormally small head size)
• Decreased bone strength
• Hyperactivity
• Musty smelling skin, breath, and/or urine
• Cardiac defects
• Seizures

The main treatment for PKU is dietary adjustments. These treatments may include avoiding high protein foods, taking adult formula supplements, using Kuvan to reduce phenylalanine, and having a specialized baby formula.