Fructose-1,6-diphosphatase deficiency: glycerol excretion during fasting test

Fructose-1,6-bisphosphatase deficiency causes fatty liver disease and requires long-term hepatic follow-up

Liver disease, occurring during pediatric or adult age, is often of undetermined cause. Some cases are probably related to undiagnosed inherited metabolic disorders. Hepatic disorders associated with fructose-1,6-bisphosphatase deficiency, a gluconeogenesis defect, are not reported in the literature. These symptoms are mainly described during acute crises, and many reports do not mention them because hypoglycemia and hyperlactatemia are more frequently in the forefront. Herein, the liver manifestations of 18 patients affected with fructose-1,6-bisphosphatase deficiency are described and the corresponding literature is reviewed. Interestingly, all 18 patients had liver abnormalities either during follow-up (hepatomegaly [n = 8/18], elevation of transaminases [n = 6/15], bright liver [n = 7/11]) or during acute crises (hepatomegaly [n = 10/17], elevation of transaminases [n = 13/16], acute liver failure [n = 6/14], bright liver [n = 4/14]). Initial reports described cases of liver steatosis, when liver biopsy was necessary to confirm the diagnosis by an enzymatic study. There is no clear pathophysiological basis for this fatty liver disease but we postulate that endoplasmic reticulum stress and de novo lipogenesis activation could be key factors, as observed in FBP1 knockout mice. Liver steatosis may expose patients to severe long-term liver complications. As hypoglycemia becomes less frequent with age, most adult patients are no longer monitored by hepatologist. Signs of fructose-1,6-bisphosphatase deficiency may be subtle and can be missed in childhood. We suggest that fructose-1,6-bisphosphatase deficiency should be considered as an etiology of hepatic steatosis, and a liver monitoring protocol should be set up for these patients, during lifelong follow-up.

Fructose-1,6-bisphosphatase deficiency as a cause of recurrent hypoglycemia and metabolic acidosis: Clinical and molecular findings in Malaysian patients

BACKGROUND

Fructose-1,6-bisphosphatase (FBPase) deficiency is a rare autosomal recessive inborn error of gluconeogenesis. We reported the clinical findings and molecular genetic data in seven Malaysian patients with FBPase deficiency.

METHODS

All patients diagnosed with FBPase deficiency from 2010 to 2015 were included in this study. Their clinical and laboratory data were collected retrospectively.

RESULTS

All the patients presented with recurrent episodes of hypoglycemia, metabolic acidosis, hyperlactacidemia and hepatomegaly. All of them had the first metabolic decompensation prior to 2 years old. The common triggering factors were vomiting and infection. Biallelic mutations in FBP1 gene (MIM*611570) were identified in all seven patients confirming the diagnosis of FBPase deficiency. In four patients, genetic study was prompted by detection of glycerol or glycerol-3-phosphate in urine organic acids analysis. One patient also had pseudo-hypertriglyceridemia. Seven different mutations were identified in FBP1, among them four mutations were new: three point deletions (c.392delT, c.603delG and c.704delC) and one splice site mutation (c.568-2A > C). All four new mutations were predicted to be damaging by in silico analysis. One patient presented in the neonatal period and succumbed due to sepsis and multi-organ failure. Among six survivors (current age ranged from 4 to 27 years), four have normal growth and cognitive development. One patient had short stature and another had neurological deficit following status epilepticus due to profound hypoglycemia.

CONCLUSION

FBPase deficiency needs to be considered in any children with recurrent hypoglycemia and metabolic acidosis. Our study expands the spectrum of FBP1 gene mutations.

Diagnosis of inborn errors of metabolism using filter paper urine, urease treatment, isotope dilution and gas chromatography-mass spectrometry

This review will be concerned primarily with a practical yet comprehensive diagnostic procedure for the diagnosis or even mass screening of a variety of metabolic disorders. This rapid, highly sensitive procedure offers possibilities for clinical chemistry laboratories to extend their diagnostic capacity to new areas of metabolic disorders. The diagnostic procedure consists of the use of urine or filter paper urine, preincubation of urine with urease, stable isotope dilution, and gas chromatography-mass spectrometry. Sample preparation from urine or filter paper urine, creatinine determination, stable isotope-labeled compounds used, and GC-MS measurement conditions are described. Not only organic acids or polar ones but also amino acids, sugars, polyols, purines, pyrimidines and other compounds are simultaneously analyzed and quantified. In this review, a pilot study for screening of 22 target diseases in newborns we are conducting in Japan is described. A neonate with presymptomatic propionic acidemia was detected among 10,000 neonates in the pilot study. The metabolic profiles of patients with ornithine carbamoyl transferase deficiency, fructose-1,6-bisphosphatase deficiency or succinic semialdehyde dehydrogenase deficiency obtained by this method are presented as examples. They were compared to those obtained by the conventional solvent extraction methods or by the tandem mass spectrometric method currently done with dried filter blood spots. The highly sensitive, specific and comprehensive features of our procedure are also demonstrated by its use in establishing the chemical diagnosis of pyrimidine degradation defects in order to prevent side effects of pyrimidine analogs such as 5-flurouracil, and the differential diagnosis of three types of homocystinuria, orotic aciduria, uraciluria and other urea cycle disorders. Evaluation of the effects of liver transplantation or nutritional conditions such as folate deficiency in patients with inborn errors of metabolism is also described.

Rapid, simplified and sensitive method for screening fructose-1,6-diphosphatase deficiency by analyzing urinary metabolites in urease/direct preparations and gas chromatography-mass spectrometry in the selected-ion monitoring mode

Children with fructose-1,6-diphosphatase (FDPase) deficiency often experience life threatening episodes such as ketotic hypoglycemia. We report here a rapid, simplified and sensitive method to analyze glycerol-3-phosphate (G3P) and glycerol in urine, that can be used to detect FDPase deficiency. We used the urease/direct preparation and gas chromatography-mass spectrometry in the selected-ion monitoring mode, enabling detection of G3P and glycerol level in normal controls. Using this approach, FDPase deficiency can be more easily diagnosed and differentiated from glycerol kinase deficiency or glycerol infusion patients. To date, diagnosis has been essentially based on the assay of enzymes in the liver. The proposed non-invasive method provides a clinically significant diagnostic tool that may help prevent episodic attacks.

Comparative frequency and severity of hypoglycemia in selected organic acidemias, branched chain amino acidemia, and disorders of fructose metabolism

The Institution's experience with hypoglycemia in different types of organic acidemias, branched chain amino acidemia (MSUD), and disorders of fructose metabolism was reviewed retrospectively. The charts of 144 patients who were followed for 1-5 years were studied for the severity and frequency of hypoglycemia. The patients were mainly Saudi; however, 10-25% were from neighboring countries. Therefore, the observations pertain to the genetic groups in the Arabian peninsula. Organic acidemias which primarily manifest with neurologic signs, such as 4-hydroxybutyric aciduria, infantile onset 3-methylglutaconic aciduria, and glutaric aciduria type 1 never showed hypoglycemia. Patients with beta-ketothiolase deficiency, biotinidase deficiency, or intermittent or intermediate MSUD, also did not have hypoglycemia during metabolic crisis. Hypoglycemia was rare and mild among neonates with classic MSUD, ethylmalonic aciduria, and isovaleric acidemia. Less than 50% of the patients with MSUD older than 8 months, pyruvate carboxylase deficiency, methylmalonic acidemia, or propionic acidemia had hypoglycemia during metabolic crisis. On the other hand, patients with 3-hydroxy-3-methyl glutaryl-CoA lyase deficiency, holocarboxylase synthetase deficiency, medium or long-chain acyl-CoA dehydrogenase deficiency, neonatal onset 3-methylglutaconic aciduria, glutaric aciduria type 2, and disorders of fructose metabolism invariably had moderate-to-severe hypoglycemia associated with metabolic crisis. The purpose of this report is to provide the pediatrician, particularly in the Middle East, with a diagnostic guideline to the identification and management of different types of organic acidemias, based on co-existing hypoglycemia.

Hypoglycaemia: principles of diagnosis and treatment in children

The diagnostic approach to children with suspected hypoglycaemia is facilitated by the fact that two clinically distinct groups exist with little overlap: 1. Hypoglycaemias characterized by a fuel deficit only. 2. Hypoglycaemias in which the fuel deficit is overshadowed by symptoms of intoxication. This differentiation is used when taking the medical history, performing the physical examination, and planning the laboratory investigations. The latter may encompass tolerance tests, a fasting test or the use of a non-radioactive glucose isotope. Protocols for such tests are given.

Urinary sugar phosphates and related organic acids in fructose-1,6-diphosphatase deficiency

Two sisters with fructose-1,6-diphosphatase deficiency are reported. They presented with ketonuria, elevated plasma transaminase activity and severe metabolic acidosis during hypoglycaemic crises, which resembled Reye syndrome. Intravenous fructose tolerance tests provoked severe hypoglycaemia and metabolic acidosis. Fructose-1,6-diphosphatase activities in both peripheral leukocytes and cultured lymphocytes were below the limit of detection. Urinary organic acid analysis during crises revealed markedly increased excretion of lactate, ketone bodies, glycerol and glycerol-3-phosphate. We newly identified other glycolytic intermediates, glyceraldehyde, 3-phosphoglycerate and fructose-1,6-diphosphate, in the urine during hypoglycaemic attacks or after fructose tolerance tests. Identification of such compounds may be useful in the early diagnosis of this disease.

Hypoglycemia: a pathophysiologic approach

An exploration of the factors that sustain glucose levels in the normal fasting subject reveals that the single major component is conservation of glucose rather than gluconeogenesis. Conservation is achieved by recycling of glucose carbon as lactate, pyruvate and alanine, and a profound decrease in the oxidation of glucose by the brain brought about by the provision and use of ketones. What glucose continues to be oxidized is for the most part formed from glycerol. Gluconeogenesis from protein plays little part in the process. Fasting hypoglycemia results from disorders affecting either one of the two critical sustaining factors--the recycling process or the availability and use of ketones. Individual hypoglycemic entities are examined against this background.