A novel mutation in gene of PRPS1 in a young Chinese woman with X-linked gout: a case report and review of the literature.

Pyrophosphate synthetase-1(PRS-1) is a crucial enzyme that catalyzes the synthesis of phosphoribosylpyrophosphate (PRPP) with substrate: adenosine triphosphate (ATP) and ribose-5-phophate(R5P) in the de novo pathways of purine and pyrimidine nucleotide synthesis. Mutation in PRPS1 can result in a series of diseases of purine metabolism, which includes PRS-1 superactivity. The common clinical phenotypes are hyperuricemia and hyperuricosuria. We identified a novel missense mutation in X-chromosomal gene PRPS1 in a young Chinese woman while her mother has heterogeneous genotype and phenotype. A 24-year-old Chinese female patient suffered hyperuricemia, gout, and recurrent hyperpyrexia for more than 6 years, and then was diagnosed with hyperandrogenism, insulin resistance (IR), and polycystic ovary syndrome (PCOS). A novel missense mutation, c.521(exon)G>T, p.(Gly174Val) was detected by next-generation sequencing (NGS) and confirmed by Sanger sequencing in the patient and her parents. Interestingly, her mother has the same heterozygous missense mutation but without uric acid overproduction which can be explained by the phenomenon of the skewed X-chromosome inactivation. The substituted amino acid Val for Gly174 is positioned in the pyrophosphate (PPi) binding loop, and this mutation impacts the binding rate of Mg2+-ATP complex to PRS-1, thus the assembling of homodimer is affected by changed Val174 leading to the instability of the allosteric site. Our report highlights the X-linked inheritance of gout in females caused by mutation in PRPS1 accompanied with severe metabolic disorders and recurrent hyperpyrexia.

Diabetic ketoacidosis, hyperuricemia and encephalopathy intractable to regular-dose insulin.

BACKGROUND: Diabetic ketoacidosis (DKA) in children less than 1 year of age is a rare occurrence. Typical presentation includes a prodrome of weight loss and polyuria with subsequent presentation to medical care when acidosis becomes symptomatic. CASE PRESENTATION: We describe an unusual case of a previously healthy infant with a 3 days' history of constipation, presenting acutely with abdominal pain, lethargy, and dehydration. On initial evaluation, our patient had profound encephalopathy, with marked tachypnea and work of breathing. Arterial blood gas revealed a pH of 6.9, pCO2 of 20 and a bicarbonate level of <5. There was profound leukocytosis (WBC 77 K/µL), hyperuricemia (uric acid 15.9 mg/dL), and evidence of pre-renal azotemia [blood urea nitrogen (BUN) 54, Cr 0.82]. Blood glucose was >700 mg/dL. Despite fluid resuscitation and insulin infusion of 0.1 unit/kg/h, which are the mainstays of therapy for DKA, her severe metabolic acidosis and altered mental status did not improve. Differential diagnosis for her metabolic derangements included inborn errors of metabolism, insulin receptor defects, toxic ingestions, and septic shock secondary to an underlying oncologic or intra-abdominal process. The patient was treated with broad spectrum antibiotics and rasburicase. She continued to have significant shock for the first 30 h of her hospital stay, requiring moderate vasoactive support. Due to her refractory acidosis and persistent hyperglycemia, insulin infusion was increased to 0.15 units/kg/h. A hemoglobin A1C obtained on the second hospital day revealed a level of 7.4 and helped to solidify the diagnosis. CONCLUSIONS: Metabolic acidosis in an infant requires a broad differential. Rasburicase should be considered in hyperuricemia and DKA.

Novel PRPS1 gain-of-function mutation in a patient with congenital hyperuricemia and facial anomalies.

Phosphoribosylpyrophosphate synthetase (PRPPS) superactivity (OMIM 300661) is a rare inborn error of purine metabolism that is caused by gain-of-function mutations in the X-chromosomal gene PRPS1 (Xq22.3). Clinical characteristics include congenital hyperuricemia and hyperuricosuria, gouty arthritis, urolithiasis, developmental delay, hypotonia, recurrent infections, short stature, and hearing loss. Only eight families with PRPPS superactivity and PRPS1 gain-of-function mutations have been reported to date. We report on a 7-year-old boy with congenital hyperuricemia, urolithiasis, developmental delay, short stature, hypospadias, and facial dysmorphisms. His mother also suffered from hyperuricemia that was diagnosed at age 13 years. A novel PRPS1 missense mutation (c.573G>C, p.[Leu191Phe]) was detected in the proband and his mother. Enzyme activity analysis confirmed superactivity of PRPP synthetase. Analysis of the crystal structure of human PRPPS suggests that the Leu191Phe mutation affects the architecture of both allosteric sites, thereby preventing the allosteric inhibition of the enzyme. The family reported here broadens the clinical spectrum of PRPPS superactivity and indicates that this rare metabolic disorder might be associated with a recognizable facial gestalt.

Inherited hyperuricemic disorders.

Inherited hyperuricemic disorders fall into two major classes, metabolic overproduction of purines and renal tubular undersecretion. The aim was to explore both. Methodology was a combination of personal experience and review of relevant literature. The overproduction of hyperuricemias result from deficiency of hypoxanthine-guanine phosphoribosyl transferase, overactivity of phosphoribosylpyrophosphate synthetase and deficiency of glucose-6-phosphatase. The undersecretion disorders are autosomal dominantly inherited and are heterogeneous. A major number of these patients result from mutations in the gene that codes for uromodulin. Treatment is with allopurinol.