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Background: Hereditary tyrosinemia type III (HT III) is an extremely rare form of tyrosinemia, characterized by autosomal recessive inheritance and biallelic mutations in the HPD gene. The clinical presentation of HT III is variable and poorly understood, with symptoms ranging from developmental delay and intellectual impairment to seizures and intermittent ataxia. This study aimed to provide further insights into the clinical and genetic characteristics of HT III. Methods: A 3‐year‐old girl, identified through newborn screening, was diagnosed with HT III using targeted next‐generation sequencing. A comprehensive literature review was conducted, and the clinical, biochemical, and genetic findings of previously reported HT III patients were summarized and analyzed. Results: The genetic analysis of the proband revealed compound heterozygous mutations in the HPD gene such as c.731C>T (p.A244V) and c.656C>T (p.T219M). Notably, the HPD p.A244V mutation had not been previously documented in public databases or the scientific literature. Bioinformatics analysis classified both variants as pathogenic variants. The patient exhibited persistent tyrosinemia, elevated levels of related metabolite derivatives, confirming the diagnosis of HT III. The review of previously published cases contributed to a better understanding of the clinical and genetic characteristics associated with HT III. Conclusion: Early diagnosis and prompt treatment in infancy are crucial for managing HT III effectively. Dietary therapy, particularly during childhood, plays a significant role in disease management. The findings from this study enhance our understanding of the genotype–phenotype associations in HT III and emphasize the importance of early intervention for improved patient outcomes. [ABSTRACT FROM AUTHOR]

• HPPD gene codes a dioxygenase enzyme involved in catalysis of different molecules such as tyrosine and phenylalanine by oxidizing them to produce energy. • To identify the functional missense SNPs of HPPD gene by using multiple computational tools. • Narrowing down missense SNPs which are still not confirmed experimentally and demands the confirmation by GWAS data. • Thus, these missense SNPs could directly or indirectly destabilize the amino acid interactions causing functional deviations of protein. HPPD gene codes a dioxygenase enzyme involved in catalysis of different molecules such as tyrosine and phenylalanine by oxidizing them to produce energy. A single change in protein can trigger serious genetic disorders like Tyrosinemia type III and Hawkinsinuria. This study aims to identify the functional missense SNPs of the HPPD gene by using multiple computational tools. All deleterious missense SNPs retrieved from Ensembl and OMIM database were evaluated through six different software. Ultimately, out of 148 missense SNPs, only 27 were confirmed as diseasecausing SNPs by developing a consensus approach. These damaging SNPs were further examined to evaluate their impact on protein stability and energy including their evolutionary conservation. Native and mutated proteins structures were also designed and superimposed by I-TASSER and PyMol respectively. This work results in narrowing down missense SNPs which are still not confirmed experimentally and demands the confirmation by GWAS data. Thus, these missense SNPs could directly or indirectly destabilize the amino acid interactions causing functional deviations of protein. [ABSTRACT FROM AUTHOR]

Tyrosinemia type 3 (HT3) is a rare inborn error of tyrosine metabolism caused by mutations in the HPD gene encoding 4-hydroxyphenyl-pyruvate dioxygenase, which is transmitted in an autosomal recessive trait. The disorder is characterized by tyrosine accumulation in body fluids and massive excretion of tyrosine derivatives into urine (www.orpha.net). Since it is the least frequent form of tyrosinemia, only few cases with the variable but rather mild clinical features have been described so far. We report an 11 year old girl presenting with no clinical symptoms and with normal mental development who has been diagnosed with HT3 through metabolic screening on the basis of elevated serum level of tyrosine ranging from 425 to 535 μmol/L (normal values: 29–86 μmol/L), and elevated urinary excretion of p-hydroxyphenyl derivatives confirmed genetically with the homozygous c.479A>G (p.Tyr160Cys) missense change in the HPD gene. The girl has been only presenting with recurrent proteinuria of unknown etiology. A phenylalanine- and tyrosine-restricted diet has never been administered. Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3.

Tyrosinemia type III is an autosomal recessive disorder caused by the deficiency of 4- hydroxyphenylpyruvate dioxygenase (4-HPPD). It is characterized by elevated levels of blood tyrosine and massive excretion of its derivatives into the urine. Clinical findings of tyrosinemia type III include neurological symptoms and mental retardation. Only a few patients presenting with this disease have been described, and the clinical phenotype remains variable and unclear. We present a case, who was admitted to the hospital at the age of 4 months for recurrent seizures. Two months later, she was admitted again with status epilepticus. Laboratory data showed increased level of tyrosine in the blood. She was treated with a diet low in tyrosine and phenylalanine and anamix formula that leading to catch-up growth and improvement of her symptoms. Plasma tyrosine level dropped to normal values. In any child who presents with the neurologic symptom, some rare diagnosis like tyrosinemia type III should be considered.

It was previously reported by D’Eufemia et al. [9] that neutrophil preparations from a patient with tyrosinemia type III, i.e. with inherited deficiency of 4-hydroxyphenylpyruvate dioxygenase (HPPD), exhibited a far higher NO release than controls, when NO was estimated in terms of nitrite content in the suspending media. It was hypothesized that HPPD might participate to NO sequestration in neutrophils and that excessive NO release might reflect the lack of the scavenging action in defective cells. In recent control experiments, we found that HPPD activity in neutrophils preparations from healthy subjects is below the detection limit of the enzymatic assay (less than 3 nmol product/h per mg protein). This indicates that HPPD concentration in neutrophils is very low, if any, confirming what was already suggested in literature, and rules out the possibility of a prominent role of HPPD as NO scavenger in these cells. Moreover, we found that 500 μM l -tyrosine increases nitrite release and accumulation in suspending media of U-937 cells, a human monoblast-like lymphoma cell line which displays many characteristics of macrophages, including the expression of inducible and endothelial nitric oxide synthases. We hypothesize that the increase of nitrite release by patient's neutrophils might be related to the presence of high l -tyrosine concentrations in the blood samples (426 μmol/L instead of 52.1 ± 10.9 μmol/L as healthy subjects), rather than to HPPD deficiency of in these cells. [ABSTRACT FROM AUTHOR]

Abstract: Tyrosinemia Type III is caused by the deficiency of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD), an enzyme involved in the catabolic pathway of tyrosine. To our knowledge, only a few patients presenting with this disease have been described in the literature, and the clinical phenotype remains variable and unclear. We report the case of a boy with tyrosinemia Type III detected using neonatal screening, who is homozygous for the splice donor mutation IVS11+1G>A in intron 11 of the HPD gene. At the age of 30months, the boy''s outcome under mild protein restriction was characterized by normal growth and psychomotor development. [Copyright &y& Elsevier]

Abstract: Tyrosinemia type III (OMIM 276710) is an autosomal recessive disorder caused by the deficiency of 4-hydroxyphenylpyruvate dioxygenase (4-HPD). Few cases have been described with mental retardation or neurological symptoms. Recently it has been demonstrated that 4-HPD participates to nitric oxide (NO) intracellular sequestration in Pseudomonas aeruginosa. 4-HPD is an ubiquitous enzyme with a prominent expression in neutrophils and neurons. In the nervous system NO has been perceived to be a potential neuromodulator although prolonged excessive generation is detrimental. We analyzed NO release by neutrophils of a patient with tyrosinemia type III in order to evaluate a possible influence of 4-HPD deficiency on this process. Our patient, previously described, is a 30-year-old women with persistent tyrosinemia (450–680μmol/l) and deficient activity of 4-HPD. At 17 months of age she experienced an acute ataxia and drowsiness lasting for 10 days, but further clinical course showed persistent tyrosinemia with normal growth and psychomotor development. Neutrophils isolated from our patient exhibited a NO release greatly higher in respect to the controls (mean±SEM 23.2±1.8micromol/106 cells vs 3.5±0.5micromol/106 cells). Clinical findings of tyrosinemia type III include neurological symptoms and mental retardation but no consistent phenotype has emerged. Therefore the pathogenesis of neurological involvement is yet not well understood. Our results suggest that an excessive neutrophils of NO release could reflect the lack of scavenging action of 4-HPD. Considering the prominent expression of this enzyme in neurons, we hypothesize that excessive NO release could participate in neuronal damage explaining the neurological involvement described in patients with tyrosinemia type III. [Copyright &y& Elsevier]

The published literature on tyrosinemia type III consists of only a few case reports. In this report, we present a patient with tyrosinemia type III, autism, and mental retardation. This patient's speech improved and his autistic symptoms lessened on a tyrosine-restricted diet, although his mental retardation remained unchanged. This is the first published report of a patient with tyrosinemia type III and autism. This observation is significant due to the paucity of published information about tyrosinemia type III. [ABSTRACT FROM AUTHOR]