Clinical and Molecular Characterization of Patients with Fructose 1,6-Bisphosphatase Deficiency

Fructose-1,6-bisphosphatase deficiency: estimation of prevalence in the Chinese population and analysis of genotype-phenotype association

Objective

Fructose-1,6-bisphosphatase deficiency (FBP1D) is a rare inborn error due to mutations in the FBP1 gene. The genetic spectrum of FBP1D in China is unknown, also nonspecific manifestations confuse disease diagnosis. We systematically estimated the FBP1D prevalence in Chinese and explored genotype-phenotype association.

Methods

We collected 101 FBP1 variants from our cohort and public resources, and manually curated pathogenicity of these variants. Ninety-seven pathogenic or likely pathogenic variants were used in our cohort to estimate Chinese FBP1D prevalence by three methods: 1) carrier frequency, 2) permutation and combination, 3) Bayesian framework. Allele frequencies (AFs) of these variants in our cohort, China Metabolic Analytics Project (ChinaMAP) and gnomAD were compared to reveal the different hotspots in Chinese and other populations. Clinical and genetic information of 122 FBP1D patients from our cohort and published literature were collected to analyze the genotype-phenotypes association. Phenotypes of 68 hereditary fructose intolerance (HFI) patients from our previous study were used to compare the phenotypic differences between these two fructose metabolism diseases.

Results

The estimated Chinese FBP1D prevalence was 1/1,310,034. In the Chinese population, c.490G>A and c.355G>A had significantly higher AFs than in the non-Finland European population, and c.841G>A had significantly lower AF value than in the South Asian population (all p values < 0.05). The genotype-phenotype association analyses showed that patients carrying homozygous c.841G>A were more likely to present increased urinary glycerol, carrying two CNVs (especially homozygous exon1 deletion) were often with hepatic steatosis, carrying compound heterozygous variants were usually with lethargy, and carrying homozygous variants were usually with ketosis and hepatic steatosis (all p values < 0.05). By comparing to phenotypes of HFI patients, FBP1D patients were more likely to present hypoglycemia, metabolic acidosis, and seizures (all p-value < 0.05).

Conclusion

The prevalence of FBP1D in the Chinese population is extremely low. Genetic sequencing could effectively help to diagnose FBP1D.

An extremely rare case of hypoglycemia with a novel mutation and review of the literature: fructose-1,6 bisphosphatase deficiency in an adult man

Hypoglycemia is an uncommon clinical problem among non-diabetic patients. It requires systematic evaluation to determine the etiology. It may be related to critical illness, hepatic insufficiency, renal insufficiency, cardiac insufficiency, drugs, alcohol, cortisol insufficiency, growth hormone insufficiency, insulinoma, gastric bypass surgery, and paraneoplastic (insulin-like growth factor-2-related) immune-mediated or inherited metabolic disorders. We aimed to summarize the literature and present a case who suffered from hypoglycemia throughout his life and was diagnosed with fructose-1, 6 bisphosphatase deficiency in adulthood to attract attention to the rare causes of hypoglycemia in adulthood.

Genetic variants of ABCC8 and clinical manifestations in eight Chinese children with hyperinsulinemic hypoglycemia

BACKGROUND

ABCC8 variants can cause hyperinsulinemia by activating or deactivating gene expression. This study used targeted exon sequencing to investigate genetic variants of ABCC8 and the associated phenotypic features in Chinese patients with hyperinsulinemic hypoglycemia (HH).

METHODS

We enrolled eight Chinese children with HH and analyzed their clinical characteristics, laboratory results, and genetic variations.

RESULTS

The age at presentation among the patients ranged from neonates to 0.6 years old, and the age at diagnosis ranged from 1 month to 5 years, with an average of 1.3 ± 0.7 years. Among these patients, three presented with seizures, and five with hypoglycemia. One patient (Patient 7) also had microcephaly. All eight patients exhibited ABCC8 abnormalities, including six missense mutations (c. 2521 C > G, c. 3784G > A, c. 4478G > A, c. 4532T > C, c. 2669T > C, and c. 331G > A), two deletion-insertion mutations (c. 3126_3129delinsTC and c. 3124_3126delins13), and one splicing mutation (c. 1332 + 2T > C). Two of these mutations (c. 3126_3129delinsTC and c. 4532T > C) are novel. Six variations were paternal, two were maternal, and one was de novo. Three patients responded to diazoxide and one patient responded to octreotide treatment. All there patients had diazoxide withdrawal with age. Two patients (patients 3 and 7) were unresponsive to both diazoxide and octreotide and had mental retardation.

CONCLUSIONS

Gene analysis can aid in the classification, treatment, and prognosis of children with HH. In this study, the identification of seven known and two novel variants in the ABCC8 gene further enriched the variation spectrum of the gene.

Novel compound heterozygous mutations of the FBP1 gene in a patient with hypoglycemia and lactic acidosis: A case report

BACKGROUND

Fructose-1,6-bisphosphatase (FBPase) deficiency, caused by an FBP1 mutation, is an autosomal recessively inherited metabolic disorder characterized by impaired gluconeogenesis. Due to the rarity of FBPase deficiency, the mechanism by which the mutations cause enzyme activity loss still remains unclear.

METHODS

We report a pediatric patient with typical FBPase deficiency who presented with hypoglycemia, hyperlactatemia, metabolic acidosis, and hyperuricemia. Whole-exome sequencing was used to search for pathogenic genes, Sanger sequencing was used for verification, and molecular dynamic simulation was used to evaluate how the novel mutation affects FBPase activity and structural stability.

RESULTS

Direct and allele-specific sequence analysis of the FBP1 gene (NM_000507) revealed that the proband had a compound heterozygote for the c. 490 (exon 4) G>A (p. G164S) and c. 861 (exon 7) C>A (p. Y287X, 52), which he inherited from his carrier parents. His father and mother had heterozygous G164S and Y287X mutations, respectively, without any symptoms of hypoglycemia.

CONCLUSION

Our results broaden the known mutational spectrum and possible clinical phenotype of FBP1.

Identification of genotype-biochemical phenotype correlations associated with fructose 1,6-bisphosphatase deficiency

Fructose-1,6-bisphosphatase (FBPase) deficiency, caused by an FBP1 mutation, is an autosomal recessive disorder characterized by hypoglycemic lactic acidosis. Due to the rarity of FBPase deficiency, the mechanism by which the mutations cause enzyme activity loss still remains unclear. Here we identify compound heterozygous missense mutations of FBP1, c.491G>A (p.G164D) and c.581T>C (p.F194S), in an adult patient with hypoglycemic lactic acidosis. The G164D and F194S FBP1 mutants exhibit decreased FBP1 protein expression and a loss of FBPase enzyme activity. The biochemical phenotypes of all previously reported FBP1 missense mutations in addition to G164D and F194S are classified into three functional categories. Type 1 mutations are located at pivotal residues in enzyme activity motifs and have no effects on protein expression. Type 2 mutations structurally cluster around the substrate binding pocket and are associated with decreased protein expression due to protein misfolding. Type 3 mutations are likely nonpathogenic. These findings demonstrate a key role of protein misfolding in mediating the pathogenesis of FBPase deficiency, particularly for Type 2 mutations. This study provides important insights that certain patients with Type 2 mutations may respond to chaperone molecules.

A novel variant in the FBP1 gene causes fructose-1,6-bisphosphatase deficiency through increased ubiquitination

Fructose-1,6-bisphosphatase (FBPase) deficiency is an autosomal recessive disorder characterized by impaired gluconeogenesis caused by mutations in the fructose-1,6-bisphosphatase 1 (FBP1) gene. The molecular mechanisms underlying FBPase deficiency caused by FBP1 mutations require investigation. Herein, we report the case of a Chinese boy with FBPase deficiency who presented with hypoglycemia, ketonuria, metabolic acidosis, and repeated episodes of generalized seizures that progressed to epileptic encephalopathy. Whole-exome sequencing revealed compound heterozygous variants, c.761A  >  G (H254R) and c.962C  >  T (S321F), in FBP1. The variants, especially the novel H254R, reduced protein stability and enzymatic activity in patient-derived leukocytes and transfected HepG2 and U251 cells. Mutant FBP1 undergoes enhanced ubiquitination and proteasomal degradation. NEDD4-2 was identified as an E3 ligase for FBP1 ubiquitination in transfected cells and the liver and brain of Nedd4-2 knockout mice. The H254R mutant FBP1 interacted with NEDD4-2 at significantly higher levels than the wild-type control. Our study identified a novel H254R variant of FBP1 underlying FBPase deficiency and elucidated the molecular mechanism underlying the enhanced NEDD4-2-mediated ubiquitination and proteasomal degradation of mutant FBP1.

Deciphering the disturbance mechanism of BaP on the symbiosis of Montipora digitata via 4D-Proteomics approach

The coral holobiont is mainly composed of coral polyps, zooxanthellae, and coral symbiotic microorganisms, which form the basis of coral reef ecosystems. In recent years, the severe degradation of coral reefs caused by climate warming and environmental pollution has aroused widespread concern. Benzo(a)pyrene (BaP) is a widely distributed pollutant in the environment. However, the underlying mechanisms of coral symbiosis destruction due to the stress of BaP are not well understood. In this study, diaPASEF proteomics and 16S rRNA amplicon pyrosequencing technology were used to reveal the effects of 50 μg/L BaP on Montipora digitate. Data analysis was performed from the perspective of the main symbionts of M. digitata (coral polyps, zooxanthellae, and coral symbiotic microorganisms). The results showed that BaP impaired cellular antioxidant capacity by disrupting the GSH/GSSG cycle, and sustained stress causes severe impairment of energy metabolism and protein degradation in coral polyps. In zooxanthellae, BaP downregulated the protein expression of SOD2 and mtHSP70, which then resulted in oxidative free radical accumulation and apoptosis. For coral symbiotic microorganisms, BaP altered the community structure of microorganisms and decreased immunity. Coral symbiotic microorganisms adapted to the stress of BaP by adjusting energy metabolism and enhancing extracellular electron transfer. BaP adversely affected the three main symbionts of M. digitata via different mechanisms. Decreased antioxidant capacity is a common cause of damages to coral polyps and zooxanthellae, whereas coral symbiotic microorganisms are able to appropriately adapt to oxidative stress. This study assessed the effects of BaP on corals from a symbiotic perspective, which is more comprehensive and reliable. At the same time, data from the study supports new directions for coral research and coral reef protection.

Evaluating the variety of GNAS inactivation disorders and their clinical manifestations in 11 Chinese children

BACKGROUND

The GNAS gene on chromosome 20q13.3, encodes the alpha-subunit of the stimulatory G protein, which is expressed in most tissues and regulated through reciprocal genomic imprinting. Disorders of GNAS inactivation produce several different clinical phenotypes including pseudohypoparathyroidism (PHP), pseudopseudohypoparathyroidism (PPHP), progressive osseous heteroplasia (POH), and osteoma cutis (OC). The clinical and biochemical characteristics overlap of PHP subtypes and other related disorders presents challenges for differential diagnosis.

METHODS

We enrolled a total of 11 Chinese children with PHP in our study and analyzed their clinical characteristics, laboratory results, and genetic mutations.

RESULTS

Among these 11 patients, nine of them (9/11) presented with resistance to parathyroid hormone (PTH); and nine (9/11) presented with an Albright's hereditary osteodystrophy (AHO) phenotype. GNAS abnormalities were detected in all 11 patients, including nine cases with GNAS gene variations and two cases with GNAS methylation defects. These GNAS variations included an intronic mutation (c.212 + 3_212 + 6delAAGT), three missense mutations (c.314C > T, c.308 T > C, c.1123G > T), two deletion mutations (c.565_568delGACT*2, c.74delA), and two splicing mutations (c.721 + 1G > A, c.432 + 1G > A). Three of these mutations, namely, c.314C > T, c.1123G > T, and c.721 + 1G > A, were found to be novel. This data was then used to assign a GNAS subtype to each of these patients with six cases diagnosed as PHP1a, two cases as PHP1b, one as PPHP, and two as POH.

CONCLUSIONS

Evaluating patients with PTH resistance and AHO phenotype improved the genetic diagnosis of GNAS mutations significantly. In addition, our results suggest that when GNAS gene sequencing is negative, GNAS methylation study should be performed. Early genetic detection is required for the differential diagnosis of GNAS disorders and is critical to the clinician's ability to distinguish between heterotopic ossification in the POH and AHO phenotype.

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.

Hypoglycaemia Metabolic Gene Panel Testing

A large number of inborn errors of metabolism present with hypoglycemia. Impairment of glucose homeostasis may arise from different biochemical pathways involving insulin secretion, fatty acid oxidation, ketone bodies formation and degradation, glycogen metabolism, fructose and galactose metabolism, branched chain aminoacids and tyrosine metabolism, mitochondrial function and glycosylation proteins mechanisms. Historically, genetic analysis consisted of highly detailed molecular testing of nominated single genes. However, more recently, the genetic heterogeneity of these conditions imposed to perform extensive molecular testing within a useful timeframe via new generation sequencing technology. Indeed, the establishment of a rapid diagnosis drives specific nutritional and medical therapies. The biochemical and clinical phenotypes are critical to guide the molecular analysis toward those clusters of genes involved in specific pathways, and address data interpretation regarding the finding of possible disease-causing variants at first reported as variants of uncertain significance in known genes or the discovery of new disease genes. Also, the trio's analysis allows genetic counseling for recurrence risk in further pregnancies. Besides, this approach is allowing to expand the phenotypic characterization of a disease when pathogenic variants give raise to unexpected clinical pictures. Multidisciplinary input and collaboration are increasingly key for addressing the analysis and interpreting the significance of the genetic results, allowing rapidly their translation from bench to bedside.

Antley-Bixler syndrome arising from compound heterozygotes in the P450 oxidoreductase gene: a case report

Antley-Bixler syndrome (ABS) arising from P450 oxidoreductase deficiency (PORD) is a rare, distinct craniosynostosis syndrome, accompanied by ambiguous genitalia and impaired steroidogenesis. It is reported that this disorder is caused by mutations in the P450 oxidoreductase (POR; OMIM #124015) gene via autosomal recessive inheritance. In this study, we performed a molecular analysis to verify the genetic etiology of ABS in an infant. Initially, medical exome sequencing was applied using the parents' peripheral blood genome DNA. Next, bidirectional Sanger sequencing and quantitative real-time PCR (qRT-PCR) were conducted to confirm the sequencing results. The infant was diagnosed as ABS at birth, with typical midface hypoplasia, craniosynostosis, femoral bowing, radio-ulnar synostosis, and genital anomalies. She died two months later due to severe pneumonia and congenital heart disease. The medical exome sequencing and Sanger sequencing revealed the missense mutation c.1370G>A (p.R457H) in exon 12 of POR was inherited from the father. In addition, the qRT-PCR analysis verified an exon 5 microdeletion in the POR gene of the infant and her mother. While p.R457H is a well-known pathogenic mutation, the POR exon 5 deletion is absent from the public databases. However, it is classified as pathogenic according to the American College of Medical Genetics and Genomics (ACMG) guidelines based on the evidence of PVS1, PM2, and PM3. In conclusion, this infant with ABS carried compound heterozygotic mutations in the POR gene; one was a paternal missense mutation, and the other was a maternal novel microdeletion. The mutations were inherited from the paternal grandfather and maternal grandfather, respectively. This detailed case report enriches our knowledge of the POR mutation spectrum and ABS pathogenesis.

Novel compound heterozygous variant of TOE1 results in a mild type of pontocerebellar hypoplasia type 7: an expansion of the clinical phenotype

The target of EGR1 protein 1 (TOE1) is a 3-exonuclease belonging to the Asp-Glu-Asp-Asp deadenylase family that plays a vital role in the maturation of a variety of small nuclear RNAs (snRNAs). Bi-allelic variants in TOE1 have been reported to cause a rare and severe neurodegenerative syndrome, pontocerebellar hypoplasia type 7 (PCH7) (OMIM # 614,969), which is characterized by progressive neurodegeneration, developmental delay, and ambiguous genitalia. Here, we describe the case of a 5-year-6-month-old female Chinese patient who presented with cerebral dysplasia, moderate intellectual disability, developmental delay, and dystonia. Trio whole-exome sequencing revealed two previously unreported heterozygous variants of TOE1 in the patient, including a maternal inherited splicing variant c.237-2A > G and a de novo missense variant c.551G > T, p.Arg184Leu. TA clone sequencing showed trans status of the two variants, indicating the missense variant occurred on the paternal strand in the patient. Clinical features of the patient were mostly concordant with previous reports but brain deformities (enlarged lateral ventricle and deepened cerebellum sulcus without microcephaly and reduced cerebellar volume) were less severe than in typical PCH7 patients. Moreover, the patient had no gonadal malformation, which is common and variable in patients with PCH7. In summary, we report the case of a Chinese patient with atypical PCH7 caused by a novel TOE1 compound variant. Our work suggests that variations in the TOE1 gene can lead to highly variable clinical phenotypes.

Fructose and Mannose in Inborn Errors of Metabolism and Cancer

History suggests that tasteful properties of sugar have been domesticated as far back as 8000 BCE. With origins in New Guinea, the cultivation of sugar quickly spread over centuries of conquest and trade. The product, which quickly integrated into common foods and onto kitchen tables, is sucrose, which is made up of glucose and fructose dimers. While sugar is commonly associated with flavor, there is a myriad of biochemical properties that explain how sugars as biological molecules function in physiological contexts. Substantial research and reviews have been done on the role of glucose in disease. This review aims to describe the role of its isomers, fructose and mannose, in the context of inborn errors of metabolism and other metabolic diseases, such as cancer. While structurally similar, fructose and mannose give rise to very differing biochemical properties and understanding these differences will guide the development of more effective therapies for metabolic disease. We will discuss pathophysiology linked to perturbations in fructose and mannose metabolism, diagnostic tools, and treatment options of the diseases.

Fructose-1,6-bisphosphatase deficiency with confirmed molecular diagnosis. An important cause of hypoglycemia in children

OBJECTIVES

To draw attention towards fructose-1,6-bisphosphatase (FBPase) deficiency as an important cause of hypoglycemia and lactic acidosis and to implement preventive strategies. Methods: This observational, cross-sectional study was conducted on 7 Saudi patients with genetically confirmed FBPase deficiency from 2008 to 2018 at Prince Sultan Military Medical City, Riyadh, Saudi Arabia. Results: Participants ranged in age from 1-10 years, and all presented with recurrent hypoglycemia. All but one had associated severe metabolic acidosis, and 3 patients (42.9%) presented with hypoglycemia and severe acidosis since birth. The mean duration from presentation to diagnosis was 39.4 months, as other diagnoses, like glycogen storage diseases and mitochondrial diseases needed to be ruled out. Development was normal apart from speech delay in one patient with a novel variant of the FBP1 gene. All patients have homozygous variants in the FBP1 gene.  Conclusion: Fructose-1,6-bisphosphatase is an important cause of hypoglycemia and acidosis; therefore, it is important to offer early molecular diagnostics in any child presenting with these symptoms. Molecular diagnostics should always be undertaken to confirm the diagnosis and for further preventive strategies.

Genetic Analysis of Tyrosinemia Type 1 and Fructose-1, 6 Bisphosphatase Deficiency Affected in Pakistani Cohorts

Background: Inborn errors of metabolism are inherited disorders that present in early childhood and are usually caused by monogenic recessive mutations in specific enzymes that metabolize dietary components. Distinct mutations are present in specific populations.Objective: To determine which genomic variants are present in Pakistani cohorts with hepatorenal tyrosinemia type 1 (HT1) and fructose 1,6-bisphosphatase deficiency (FBPD).Materials and Methods: We sequenced the fumaryl acetoacetate hydrolase encoding gene (FAH) including flanking regions in four unrelated HT1 cohorts and the fructose 1,6-bisphosphatase gene (FBP1) in eight FBPD cohorts.Results: We mapped two recessive mutations in FAH gene for HT1; c.1062 + 5G > A(IVS12 + 5G > A) in three families and c.974C > T(pT325M) in one. We identified three mutations in FBP1 gene; c.841G > A(p.E281K) in five FBPD families, c.472C > T(p.R158W) in two families and c.778G > A(p.G260R) in one.Conclusion: Knowledge of common variants for HTI and FBDP in our study population can be used in the future to build a diagnostic algorithm.

Biallelic ERBB3 loss-of-function variants are associated with a novel multisystem syndrome without congenital contracture

Background

Gain-of-function pathogenic variants of the Erb-B2 receptor tyrosine kinase 3 (ERBB3) gene contribute to the occurrence and development of a variety of human carcinomas through activation of phosphatidylinositol 3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (ERK) signaling. ERBB3 gene homozygous germline variants, whose loss of function may cause autosomal recessive congenital contractural syndrome, were recently identified. This study aims to identify the disease-causing gene in a Chinese pedigree with variable phenotypes involving multiple systems, including developmental delay, postnatal growth retardation, transient lower limb asymmetry, facial malformations, atrioventricular canal malformation, bilateral nystagmus and amblyopia, feeding difficulties, immunodeficiency, anemia, and liver damage, but without congenital contracture.

Methods

Trio-whole exome sequencing (WES) was performed to identify the disease-causing gene in a 24-month-old Chinese female patient. The pathogenicity of the identified variants was evaluated using in silico tools and in vitro functional studies.

Results

Trio-WES revealed compound heterozygous variants of c.1253 T > C (p.I418T) and c.3182dupA (p.N1061Kfs*16) in the ERBB3 gene. Functional studies showed that p.I418T resulted in normal expression of ERBB3, which was capable of interacting with ERBB2. However, the variant impaired ERBB3 phosphorylation, consequently blocking ERBB2 phosphorylation and AKT and ERK activation. The truncated protein resulting from the c.3182dupA variant also lacked the capacity to activate downstream signaling pathways.

Conclusions

We report the first patient with a novel multisystem syndrome disorder without congenital contracture resulting from biallelic loss-of-function variants of ERBB3.

Exon 2 deletion represents a common mutation in Turkish patients with fructose-1,6-bisphosphatase deficiency

Fructose-1,6-bisphosphatase (FBPase) deficiency is an autosomal recessive inborn error of gluconeogenesis. We aimed to investigate clinical and biochemical findings and molecular genetic data in ten Turkish patients with fructose-1,6-bisphosphatase deficiency. Ten Turkish patients who were diagnosed with fructose-1,6-biphosphatase deficiency in a single center from 2013 to 2019 were included in this study. Their clinical and laboratory data were collected retrospectively. All patients were hospitalised in intensive care unit mostly after catabolic stress conditions such as infections, starvation and rarely fructose consumption. Prognosis was good after correct diagnosis and treatment. Molecular analyses of FBP1 gene revealed a homozygous exon 2 deletion in eight patients, a novel homozygous c.910_911dupTT mutation in one patient and a homozygous IVS5 + 1G > A splicing mutation in one patient. Exon 2 deletion (previously termed exon 1) was found to be the most common mutation in Turkish fructose-1,6-biphosphatase deficiency patients.

Status epilepticus due to fructose-1,6-bisphosphatase deficiency caused by FBP1 gene mutation

INTRODUCTION

Fructose-1,6-bisphosphatase (FBPase) deficiency is a rare inherited disorder in gluconeogenesis, characterized by hypoglycemia, ketonuria, metabolic acidosis and convulsions.

CASE PRESENTATION

We describe two brothers with FBPase deficiency. The proband developed s evere hypoglycemia and progressed to status epilepticus, and the brother showed slightly hypoglycemia with a good prognosis. Whole exome sequencing (WES) identified compound heterozygous variants [c.333+1_333+2delinsTC and c.490G>A (p.Gly164Ser)] in fructose-1,6-bisphosphatase 1 gene in the two brothers, which were inherited from the father and the mother, respectively.

CONCLUSION

Genetic analysis provided a solid basis for a definite diagnosis and the determination of precision therapies for the patient.

Diagnosis of Spinal Muscular Atrophy: A Simple Method for Quantifying the Relative Amount of Survival Motor Neuron Gene 1/2 Using Sanger DNA Sequencing

Background:

Spinal muscular atrophy (SMA) is caused by homozygous deletion or compound heterozygous mutation of survival motor neuron gene 1 (SMN1), which is the key to diagnose SMA. The study was to establish and evaluate a new diagnostic method for SMA.

Methods:

A total of 1494 children suspected with SMA were enrolled in this study. Traditional strategy, including multiplexed ligation-dependent probe amplification (MLPA) and TA cloning, was used in 1364 suspected SMA children from 2003 to 2014, and the 130 suspected SMA children were tested by a new strategy from 2015 to 2016, who were also verified by MLPA combined with TA cloning. The SMN1 and SMN2 were simultaneously amplified by polymerase chain reaction using the same primers. Mutation Surveyor software was used to detect and quantify the SMN1 variants by calculating allelic proportions in Sanger sequencing. Finally, turnaround time and cost of these two strategies were compared.

Results:

Among 1364 suspected SMA children, 576 children had SMN1 homozygous deletion and 27 children had SMN1 compound heterozygous mutation. Among the 130 cases, 59 had SMN1 homozygous deletion and 8 had heterozygous deletion: the SMN1-specific peak proportion on exon 7 was 34.6 ± 1.0% and 25.5 ± 0.5%, representing SMN1:SMN2 to be 1:2 and 1:3, respectively. Moreover, five variations, including p.Ser8Lysfs *23 (in two cases), p.Leu228*, p.Pro218Hisfs *26, p.Ser143Phefs*5, and p.Tyr276His, were detected in 6/8 cases with heterozygous deletion, the mutant allele proportion was 31.9%, 23.9%, 37.6%, 32.8%, 24.5%, and 23.6%, which was similar to that of the SMN1-specific site on exon 7, suggesting that those subtle mutations were located in SMN1. All these results were consistent with MLPA and TA cloning. The turnaround times of two strategies were 7.5 h and 266.5 h, respectively. Cost of a new strategy was only 28.5% of the traditional strategy.

Conclusion:

Sanger sequencing combined with Mutation Surveyor analysis has potential application in SMA diagnosis.

Clinical and molecular genetic characterization of two patients with mutations in the phosphoglucomutase 1 (PGM1) gene

Background The phosphoglucomutase 1 (PGM1) enzyme plays a central role in glucose homeostasis by catalyzing the inter-conversion of glucose 1-phosphate and glucose 6-phosphate. Recently, PGM1 deficiency has been recognized as a cause of the congenital disorders of glycosylation (CDGs). Methods Two Chinese Han pediatric patients with recurrent hypoglycemia, hepatopathy and growth retardation are described in this study. Targeted gene sequencing (TGS) was performed to screen for causal genetic variants in the genome of the patients and their parents to determine the genetic basis of the phenotype. Results DNA sequencing identified three variations of the PGM1 gene (NM_002633.2). Patient 1 had a novel homozygous mutation (c.119delT, p.Ile40Thrfs*28). In patient 2, we found a compound heterozygous mutation of c.1172G>T(p.Gly391Val) (novel) and c.1507C>T(p.Arg503*) (known pathogenic). Conclusions This report deepens our understanding of the clinical features of PGM1 mutation. The early molecular genetic analysis and multisystem assessment were here found to be essential to the diagnosis of PGM1-CDG and the provision of timely and proper treatment.

Prenatal Diagnosis and Genetic Analysis of a Fetus with Joubert Syndrome

Objective

To diagnose and explore the genetic cause of Joubert syndrome (JS) in a fetus.

Methods

Prenatal ultrasound and magnetic resonance imaging (MRI) examinations were performed, and genetic analysis was conducted using targeted next-generation sequencing (NGS) and Sanger sequencing.

Results

Prenatal ultrasound and MRI examinations showed cerebellar vermis hypoplasia and molar tooth sign (MTS); hence the fetus was diagnosed with JS. Further genetic analysis revealed a known missense variant (c.3599C>T, p.A1200V) and a novel missense variant (c.3857G>A, p.R1286H) in the C5orf42 gene of the fetus.

Conclusion

Our study provides insights into prenatal and early diagnosis of JS and expands the variation spectrum of C5orf42 gene.

Clinical and molecular characterization of Indian patients with fructose-1, 6-bisphosphatase deficiency: Identification of a frequent variant (E281K)

Fructose-1, 6-bisphosphatase deficiency is an autosomal recessive disorder of gluconeogenesis caused by genetic defect in the FBP1 gene. It is characterized by episodic, often life-threatening metabolic acidosis, liver dysfunction, and hyperlactatemia. Without a high index of suspicion, it may remain undiagnosed with devastating consequences. Accurate diagnosis can be achieved either by enzyme assay or gene studies. Enzyme assay requires a liver biopsy and is tedious, invasive, expensive, and not easily available. Therefore, genetic testing is the most appropriate method to confirm the diagnosis. Molecular studies were performed on 18 suspected cases presenting with episodic symptoms. Seven different pathogenic variants were identified. Two common variants were noted in two subpopulations from the Indian subcontinent; p.Glu281Lys (E281K) occurred most frequently (in 10 patients) followed by p.Arg158Trp (R158W, in 4 patients). Molecular analysis confirmed the diagnosis and helped in managing these patients by providing appropriate genetic counseling. In conclusion, genetic studies identified two common variants in the Indian subcontinent, thus simplifying the diagnostic algorithm in this treatable disorder.

Targeting FBPase is an emerging novel approach for cancer therapy

Cancer is a leading cause of death in both developed and developing countries. Metabolic reprogramming is an emerging hallmark of cancer. Glucose homeostasis is reciprocally controlled by the catabolic glycolysis and anabolic gluconeogenesis pathways. Previous studies have mainly focused on catabolic glycolysis, but recently, FBPase, a rate-limiting enzyme in gluconeogenesis, was found to play critical roles in tumour initiation and progression in several cancer types. Here, we review recent ideas and discoveries that illustrate the clinical significance of FBPase expression in various cancers, the mechanism through which FBPase influences cancer, and the mechanism of FBPase silencing. Furthermore, we summarize some of the drugs targeting FBPase and discuss their potential use in clinical applications and the problems that remain unsolved.

Approach to hypoglycemia in infants and children

Hypoglycemia is a heterogeneous disorder with many different possible etiologies, including hyperinsulinism, glycogen storage disorders, fatty acid disorders, hormonal deficiencies, and metabolic defects, among others. This condition affects newborns to adolescents, with various approaches to diagnosis and management. This paper will review current literature on the history of hypoglycemia, current discussion on the definition of hypoglycemia, as well as etiologies, diagnosis, and management.