Diurnal variation of phenylalanine concentrations in tyrosinaemia type 1: should we be concerned?
How to cite this article Daly A., Gokmen‐Ozel H., MacDonald A., Preece M.A., Davies P., Chakrapani A. & McKiernan P. (2012) Diurnal variation of phenylalanine concentrations in tyrosinaemia type 1: should we be concerned? J Hum Nutr Diet. 25, 111–116
Background: Tyrosinaemia type 1 (HT1) is treated with a tyrosine and phenylalanine‐restricted diet, amino acids free of phenylalanine and tyrosine, and nitisinone (NTBC). Treatment guidelines recommend plasma tyrosine between 200–400 μ
Methods: Median tyrosine and phenylalanine plasma concentrations were reviewed retrospectively over 3 years in 11 subjects (median age 4 years) with HT1. Subjects routinely collected morning fasting blood samples but afternoon nonfasted samples were taken in the clinic (<10% of samples). Growth Z‐scores were calculated.
Results: The percentage of all plasma phenylalanine concentrations <30 μ
Conclusions: Blood phenylalanine concentrations were consistently lower in the afternoon. Taking blood samples at variable time points in the day may lead to variation in interpreting dietary control. A detailed study is necessary to examine the 24‐h diurnal variation of plasma phenylalanine and tyrosine in HT1. It is possible that phenylalanine concentrations may be very low for a substantive time over 24 h and the potential impact that this may have on cognitive development and growth in children is unknown.
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