Community Discussion Forum Parent support phe/tyr ratio

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  • #9542
    Avatar of Bill


    I was wondering if anyone had any insight into the role the phe-to-tyrosine ratio plays in cognitive development? The reason I ask is because my (almost) 2 yr old has been recently diagnosed with a cognitive development delay. He was assessed when he was 12 months old, and everything was on-track. He was re-assessed earlier this week, and now we’re being told he’s still at a 12-month old level. He has not started talking, but will babble frequently, and is slow to follow instructions when engrossed in a task. At this point, the therapist who assessed him does not believe he has autism, and we’re going to start developing a treatment plan next week.

    His PHE levels have been stable (2.5 – 3.5mg/dL) since being on-diet a week after birth and his PHE tolerance is currently 480mg. His PKU specialist had said that as long as the PHE levels are 2-6mg/dL and his tyrosine level was at least 0.5mg/dL, there should be no development issues. When I reviewed his tyrosine levels since birth, I noticed that it averaged 0.97mg/dL up to shortly before his first birthday, but since then it’s been an average of around 0.65mg/dL. 

    I’ve seen some papers that say that monitoring PHE levels alone may not be enough  and that the phe-to-tyr ratio needs to be considered since the two compete with each other to get to the brain. The theory, as I understand it, is that the higher the ratio, more phe and less tyr gets to the brain, and development is delayed. When I track my son’s phe-to-tyr ratio it does bounce around, but it is generally getting higher. And since his tyr levels dropped around 1yr, I’m not sure if this explains why he did well on his developmental assessment at 12 months, but not so well this time.

    I’m interested in understanding how other PKU specialists and dieticians use tyrosine levels in PKU treatment. Do they consider the phe-to-tyr ratio, or do they just look for a cutoff (for example, at least 0.5mg/dL)? Any suggestions on tyrosine supplements and when/if they may be needed?

    Thanks in advance for any and all help!!!

    Avatar of Tanya

    I reply with caution.

    Jacob is also slightly behind in his development. He is 15 months old. He was born a micro premie. He was 3 months early. They correct his age when it comes to development. He is therefore tested at 9 months. And the assessment showed he was 3 months behind that. 

    I chaulk it up to, hes a boy. And these charts are guidelines, and averages. We talked to his dietian to ask if PKU would be a factor in this, and she advised us no.

    As of this month Jacob was tested for 12 months. He meets all and exceeds some 12 month milestones (With the exception of going from sit to stand in the middle of a room with no aids) He can't stand long and is just learning to this doesnt surprise me.

    His speech as well is delayed. He has approx 14 words. I am not so sure they are words as she declare them, but some are mimic of speech in my opinon. Yes he has mumumum dadada uhoh, and the like. When he is in the tub if I ask for his fishy, he makes a she sound, but wouldnt say it on his own. They have signed him up for speech therapy. The wait is 9-12 months long, so hopefully he is talking away by that point, and it wont be necessary.

    So, to answer your question, Yes, we have noticed delays, but he also catches up. Also, its unclear if the delays are based on PHE or his early arrival.

    Hope this helps.


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