What is Phenylketonuria?
 

Phenylketonuria (PKU) is a common monogenic inherited disorder, classified as an autosomal recessive genetic condition. It is caused by mutations in the phenylalanine hydroxylase (PAH) gene, leading to congenital metabolic dysfunction that prevents normal metabolism of phenylalanine (Phe), resulting in its accumulation in the blood and organs. PKU patients typically exhibit severe developmental delay, neurological deficits, behavioral abnormalities, and epileptic seizures. In China, the overall incidence of PKU is approximately 1 in 11,000, with higher prevalence in northern populations compared to southern regions.

 

Pathogenesis
 

The fundamental cause of phenylketonuria (PKU) is pathogenic mutations in the phenylalanine hydroxylase (PAH) gene located on chromosome 12q23.2. PAH is the key enzyme catalyzing the hydroxylation of phenylalanine (Phe) to tyrosine. When this enzyme's activity is partially or completely lost, the main metabolic pathway of phenylalanine is blocked, leading to its abnormal accumulation in the blood. Elevated blood phenylalanine levels trigger alternative metabolic pathways, producing neurotoxic metabolites such as phenylpyruvate. Additionally, high concentrations of phenylalanine competitively inhibit the function of L-type amino acid transporters (LAT-1), hindering the entry of essential amino acids like tryptophan and tyrosine into the brain. This severely affects the synthesis of neurotransmitters (such as serotonin and dopamine), disrupts myelination, and induces oxidative stress, ultimately causing progressive and irreversible neurological damage.
 

In the Chinese population, PAH gene mutations are predominantly missense mutations (134 types) and splicing mutations (25 types), with high-frequency mutation sites mainly concentrated in exon 6, exon 7, and exon 12. Among these, the missense mutation p.R243Q (c.728G>A) in exon 7 is the absolute primary mutation hotspot, with a frequency as high as 17.53%. Other common mutations (frequency >3%) in order include: p.EX6-96A>G (c.611A>G), p.V399V (c.1197A>T), p.R241C (c.721C>T), p.R111 (c.331C>T), p.Y356 (c.1068C>A), p.R413P (c.1238G>C), and IVS4-1G>A (c.442-1G>A). In Caucasian populations, common PKU mutation sites are located in exon 12 and intron 12, with major mutations being R408W and IVS12+1G>A.

(Image placeholder: Research Progress in Phenylketonuria)

Gene Therapy
 

Adeno-Associated Virus (AAV) Vector Therapy: AAV vectors can deliver the normal PAH gene into hepatocytes, where it exists as an episome in the nucleus and continuously expresses PAH protein.

PTC Therapeutics' PTC-AAT project has entered clinical stages, with preliminary results showing significant reduction in blood phenylalanine levels in adult PKU patients, with effects lasting several years

.Gene Editing Therapy: Gene editing technology cuts DNA at the erroneous site, then uses the cell's own repair mechanisms and provided correct template to "rewrite" the mutated sequence to normal. Additionally, the entire normal PAH gene can be "inserted" into a safe location in the genome (such as a "safe harbor" site), enabling stable expression.

 

Mouse Models
 

PAHenu2 Mice: These mice carry a point mutation in the PAH gene (c.835T>C, p.F263S) and exhibit neurobiological features similar to human PKU patients, including cognitive dysfunction, hyperactivity, anxiety-like behavior, and reduced levels of brain monoamine neurotransmitters (such as serotonin).

PAH Conditional Knockout Mice: Liver-specific knockout of the PAH gene, suitable for studying whether liver-specific restoration of PAH expression is sufficient to treat PKU.

PAH-KO Mice: Mouse model with loss-of-function mutation in the phenylalanine hydroxylase gene, simulating the pathological characteristics of human phenylketonuria, characterized by significantly elevated blood phenylalanine levels.

 

MingCeler Biotech Facilitates Gene Therapy
 

Gene therapy offers hope for rare diseases, but its development and validation are inseparable from animal model support. Leveraging its self-developed TurboMice™ technology, MingCeler Biotech has developed multiple rare disease mouse models. The TurboMice™ technology overcomes the challenges of long modeling cycles and low success rates for complex models, enabling editing at virtually any target gene locus. Complete homozygous gene-edited mouse models can be prepared directly from embryonic stem cells in as little as 2 months.

MingCeler Biotech can customize various PKU mouse models according to client needs, such as PAHenu2 mice, PAH conditional knockout mice, and PAH-KO mice. We welcome inquiries!
 

References:

[1] Wang Jie, Zhang Shaowei, Xie Xinru, Ren Zhaorui, Wang Jiazheng, Chang Jiaxiu, Cao Guangxiang, Fu Jiafang. Research Progress on Phenylketonuria. Biomedicine, 2023, 13(3): 326-333. DOI: 10.12677/hjbm.2023.133038

[2] Li Jin, Li Jing, Li Nana, et al. Analysis of Phenylalanine Hydroxylase Gene Mutations in 80 Pediatric Patients with Phenylketonuria from Jilin and Liaoning Provinces. Journal of Chinese PLA Medical College, 2021, 42(8): 843-848, 889.

[3] Li N, Jia H, Liu Z, Tao J, Chen S, Li X, Deng Y, Jin X, Song J, Zhang L, Liang Y, Wang W, Zhu J. Molecular characterisation of phenylketonuria in a Chinese mainland population using next-generation sequencing. Sci Rep. 2015 Oct 27;5:15769. doi: 10.1038/srep15769. PMID: 26503515; PMCID: PMC4621502.

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