A low-phenylalanine (Phe) diet affects the metabolism and diversity of gut microbial communities in children with phenylketonuria (PKU). Our study examined gut microbiota characteristics and metabolic pathways, and their correlations with clinical phenotypes in a high-incidence population.

Our findings revealed that genus Bacteroide was not only in extremely low abundance in the PKU group, but was also negatively correlated with blood Phe level. The remarkable capability of genus Bacteroides to use complex recalcitrant glycans may be the main reason for the decreased ability of glycan degradation in the PKU group.

We assessed clinical phenotypes and gut microbiota by 16S ribosomal RNA (rRNA) sequencing, and performed a correlation analysis between phenotype and gut microbiota in a PKU group (n=11) and a healthy group (n=11).

The PKU group had significantly lower microbiota diversity than the healthy group (Pshannon=0.014). Phylum-level composition differed significantly between the PKU and healthy groups (Firmicutes: 44.3% vs. 43.1%; Actinobacteria: 25.9% vs. 3.3%; Bacteroidetes: 16.6% vs. 53.2%; and Proteobacteria: 10.9% vs. 0.12%, respectively). Further, a significantly decreased level of genus Bacteroidetes (P<0.0001) in the PKU group was negatively correlated with blood Phe level (P=0.014). The microbial function prediction of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways exhibited a decreased ability of glycan degradation and glutamate metabolism in the PKU group. Conclusions: Our findings revealed that genus Bacteroide was not only in extremely low abundance in the PKU group, but was also negatively correlated with blood Phe level. The remarkable capability of genus Bacteroides to use complex recalcitrant glycans may be the main reason for the decreased ability of glycan degradation in the PKU group.