Genetic analysis of fructose-1,6-bisphosphatase (FBPase) deficiency in nine consanguineous Pakistani families

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.

Consanguinity in the Chaouia population (Morocco): prevalence, trends, determinants, fertility, and spontaneous abortions

Background

One of the aspects that helps to understand the genetic structure of a population throughout its biological history is the description of its matrimonial practices. Thus, the objective of this study is to explore consanguinity, one of these practices, to its full extent by identifying the prevalence, determinants, and trends of a consanguineous marriage, as well as its impact on fertility and spontaneous abortions in the Chaouia population, a region located in the western center of Morocco. Therefore, a survey-based cross-sectional study was conducted between January 2019 and January 2020. The sample was collected by province using a stratified random sampling approach, yielding a sample of 788 people. The association between consanguinity and socioeconomic and demographic characteristics, as well as reproductive health and pregnancy outcomes, was described using chi-square and ANOVA analysis. Multivariate logistic regression analysis was used to determine the predictors of a consanguineous marriage.

Results

Our findings revealed a consanguinity rate of 25.38%. The mean inbreeding coefficient was 0.012214. The most common type of union was between first cousins. This practice was strongly associated with an early age at marriage for both genders and with endogamy and immobility of couples, according to their place of birth. Consanguinity was significantly associated with fertility (p < 0.001) and spontaneous abortions (p = 0.029). The average number of pregnancies and spontaneous abortions was higher in consanguineous unions (5.18 ± 0.20/0.47 ± 0.08) compared to non-consanguineous unions (4.33 ± 0.10/0.31 ± 0.03).

Conclusions

Consanguinity is a deeply rooted social and cultural tradition in this population, providing individuals with a sense of social-economic stability while assuring their attachment to the group. Despite being highly associated with fertility, this practice has a significant influence on pregnancy outcomes, namely spontaneous abortions. Therefore, further studies are needed to examine the impact of consanguinity on various aspects of reproductive health and its association with numerous genetic abnormalities and diseases.

Fructose 1,6 bisphosphatase deficiency: outcomes of patients in a single center in Turkey and identification of novel splice site and indel mutations in FBP1

OBJECTIVES

Fructose 1,6 bisphosphatase (FBPase) deficiency is a rare autosomal recessively inherited metabolic disease. It is encoded by FBP1, and the enzyme catalyzes the hydrolysis of fructose-1,6-bisphosphate to fructose 6-phosphate. Patients with recurrent episodes of metabolic acidosis, hypoglycemia, hypertriglyceridemia, and hyperketonemia are present.

METHODS

In this study, we describe the clinical, biochemical, and molecular genetic features of six unrelated Turkish patients from six different families who were genetically diagnosed with FBPase deficiency in our clinic between 2008 and 2020. Their clinical and laboratory data were collected retrospectively. Next-generation sequencing (NGS) was performed for the molecular genetic analysis.

RESULTS

All patients were hospitalized with recurrent hypoglycemia and metabolic acidosis episodes. Three out of six patients were presented in the neonatal period. The mean age at diagnosis was 26 months. NGS revealed a known homozygous gross deletion including exon 2 in three patients (50%), a known homozygous c.910_911dupTT pathogenic variant in one patient (16%), a novel homozygous c.651_653delCAGinsTAA likely pathogenic variant, and another novel homozygous c.705+5G>A splice site variant. Leukocyte FBPase analysis detected no enzyme activity in the patient with homozygous c.705+5G>A splice site variant.

CONCLUSIONS

We identified two novel mutations in this study. One of them is a splice site mutation which is five bases downstream of the exon, and the other one is an indel mutation. Both of the splice site and indel mutations are exceedingly rare in FBP1, and to the best of our knowledge, there are second splice site and indel variants reported in the literature. Exon 2 deletion is the most common mutation consistent with the previous reports in Turkish patients. FBPase is a frequent cause of hypoglycemia and metabolic acidosis, and the widespread use of molecular genetic analysis would contribute to the enlightenment of advanced genetic factors and possible genotype/phenotype correlation.

Consanguineous Marriages and Dental Anomalies: A Cross-Sectional Analytical Study

Objective

To determine the correlation between consanguineous marriages and dental anomalies. Study Design. A cross-sectional analytical study.

Materials and Methods

This cross-sectional analytical multicentered study was carried out at Foundation University College of Dentistry after approval of the Ethical Research Committee (ERC) from September 2021 to November 2021 in Pakistan. All pediatric patients (4–10 years old) with dental malformations undergoing dental procedures or examinations and born with spontaneous vaginal delivery and uncomplicated cesarean section participated in the study. First, second, and third-degree relatives' marriages of parents were used to define consanguinity. The Basic Pay Scale was the reference of estimation of socioeconomic status. Participants with a history of orofacial trauma, pertinent parental history (infertility, hormonal treatment, or infectious diseases during pregnancy, conception with assisted reproductive techniques, prolonged complicated labor, premature deliveries, and twin births), and prolonged hospital admission immediately after birth were excluded from the study.

Results

The mean maternal and paternal age was recorded to be 23.86 ± 5.4 and 27.07 ± 9.6, respectively, whereas the mean age of participants was 6.60 ± 1.67. There were 297 children with congenital abnormalities, with 203 (68.4%) males and 94 (31.6%) females. The prevalence of consanguineous marriage was found to be in 210 (70.7%) participants. Congenital dental anomalies correlation was found to be significant with consanguineous marriages (p value <0.001). Consanguineous marriages were more frequent in the lower socioeconomic group when compared with the middle and upper socioeconomic groups, respectively (74.7% vs. 8.1% vs. 17.2%, p value 0.007).

Conclusion

Congenital dental anomalies were significantly prevalent in consanguineous marriages with greater incidence in lower socioeconomic groups. Consanguineous marriages have the propensity to transmute population conformation, but due to religious and social beliefs, literature is hesitant to ascribe congenital dental anomalies persuasive relevance with consanguinity.

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.

Monogenic diabetes in Pakistani infants and children: challenges in a resource poor country

OBJECTIVES

To review the data of infants and children with suspected monogenic diabetes who underwent genetic testing.

METHODS

Monogenic diabetes is a rare form of diabetes resulting from mutations in a single gene. It can be caused by dominant as well as recessive modes of inheritance. In a country like Pakistan where interfamily marriages are common the incidence of genetic disorders is increased. As Pakistan a resource-poor country, the diagnosis of insulin-dependent diabetes is often delayed and a genetic diagnosis of monogenic diabetes is extremely difficult. Children with clinical diagnosis of monogenic and syndromic diabates were recruited and blood samples were sent for genetic analysis.

RESULTS

One thousand sixty four new cases diagnosed with type 1 diabetes were registered at the National Institute of Child Health, Karachi, in the last 10 years. Of these 39 patients were selected for genetic testing who were diagnosed with diabetes/had a sibling diagnosed with diabetes before the age of nine months (n = 27) or had extra pancreatic features ( n= 12). We identified mutations in 18/27 cases diagnosed with diabetes before nine months of age. The most common genetic subtype was WolcottRallison syndrome caused by EIF2AK3 mutations (seven cases). KCNJ11 mutations were identified in two cases, ABCC8mutations were identified in four cases from three families, GCK and INS mutations were each identified in two cases, and one SLC2A2 mutation was identified in one case. A genetic diagnosis was made in 12/12 children from six families with diabetes diagnosed after the age of nine months who had extrapancreatic features. Six patients had genetically confirmed Wolfram syndrome (WFS1), three had thiamine-responsive megaloblastic anemia (SLC19A2) and three were diagnosed with histocytosis lymphadenopathy plus syndrome (SLC29A3).

CONCLUSIONS

Genetic testing is essential to confirm a diagnosis of monogenic diabetes which guides clinical management and future counselling. Our study highlights the importance of diagnosing monogenic diabetes in the largely consanguineously-married population of Pakistan.

The fructose-1,6-bisphosphatase deficiency and the p.(Lys204ArgfsTer72) variant

Fructose-1,6-bisphosphatase (FBPase) deficiency is a rare inborn error of fructose metabolism caused by pathogenic variants in the FBP1 gene. As gluconeogenesis is affected, catabolic episodes can induce ketotic hypoglycemia in patients. FBP1 analysis is the most commonly used approach for the diagnosis of this disorder. Herein, a Brazilian patient is reported. The proband, a girl born to a consanguineous couple, presented with severe hypoglycemia crisis in the neonatal period. At the age 17 months, presented a new crisis accompanied by metabolic acidosis associated with a feverish episode. Genetic analysis was performed by next-generation sequencing (NGS), identifying the NM_000507.3:c.611_614del variant in homozygosis in the FBP1 gene. In silico analysis and 3D modeling were performed, suggesting that this variant is associated with a loss of sites for substrate and Mg2+ binding and for posttranslational modifications of FBPase. The c.611_614del variant is located in a repetitive region of the FBP1 gene that appears to be a hotspot for mutational events. This frameshift creates a premature termination codon in the last coding exon which escapes the nonsense-mediated decay mechanism, according to in silico analysis. This variant results in an intrinsically disordered protein with loss of substrate recognition and post-translational modification sites.

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.

Mutational spectrum of SMPD1 gene in Pakistani Niemann-Pick disease patients

Objective:

Genetic variation analysis of rare autosomal recessive Niemann-Pick disease (NPD) Pakistani patients.

Methods:

We sequenced the SMPD1 gene including its all coding and flanking regions in seven unrelated sporadic patients suffering from Niemann-Pick disease through targeted exome sequencing. Genetic variants mapping and their protein predictions were evaluated using different bioinformatics tools and clinical phenotypes were correlated. The study was conducted from January 2018 to March 2019 at The Children’s Hospital Lahore.

Results:

We have mapped five different mutations in SMPD1 gene of enrolled patients with a novel homozygous missense variant (c.1718G>C) (p.Trp573Ser) in one patient. A missense mutation (c.1267C>T) (p.His423Tyr) has been identified in three unrelated patients. A nonsense mutation (c.1327C>T) (p.Arg443Term) and one missense mutation (c.1493G>A) (p.Arg498His) mapped in one patient each. A compound heterozygous mutation has been mapped in one patient (c.740G>A) (p.Gly247Asp); (c.1493G>A) (p.Arg498His). Pathogenic effect of novel variant has been predicted through in-silico analysis and has not been reported in general overall population in the globe.

Conclusion:

This is the first report of genetic demographic assessment of Niemann-Pick disease in Pakistan. The mapped mutations would be helpful to build a disease variants algorithm of Pakistani population. This will be used for determining disease clinical magnitude along with provision of genetic screening services in affected families.

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.

Consanguinity: A blessing or menace at population level?

Consanguinity has highly complex and multifaceted aspects with sociocultural as well as biological debates on its pros and cons. The biological upshot of consanguinity includes the increased homozygosity, which results in manifold increased risk of genetic disorders at family and population levels. On the other hand, in addition to social, cultural, political, and economic benefits, consanguineous marriages have biological advantages at the population level. The consequence of consanguineous marriages is an upsurge in the number of homozygous diseased individuals with fewer chances of mating and reduced chances of survival, therefore evolutionarily confining the transmission of disease alleles to future generations and encouraging its elimination from a population. Protective effects of consanguinity have also been observed in a few diseases in different populations. Although attractive for many reasons, nonconsanguineous marriages will cause risk alleles to spread throughout the population, making most individuals carriers, and ultimately will resume the production of recessive diseases in subsequent generations. Although consanguinity, from an evolutionary point of view, is beneficial at the population level, it increases the risk of diseases in the very next generation. Presently, there is no treatment for most of the genetic disorders; we cannot opt for consanguinity for long-term benefits. Nonconsanguineous marriages are a better strategy by which we may delay disease manifestation for some generations until science offers a viable solution.

Genetic analysis of patients with fructose-1,6-bisphosphatase deficiency

INTRODUCTION

Fructose-1,6-bisphosphatase deficiency (FBPase deficiency) is a rare inborn error of metabolism that affects gluconeogenesis. Ketotic hypoglycemia is the main symptom and can occur at any age, usually after long periods of fasting or during illness. The diagnosis may be achieved by measurement of the enzyme activity in a liver sample, but FBP1 analysis has become the most common approach.

AIM

To characterize the genotype of Southern Brazilian FBPase-deficient patients.

METHODOLOGY

The FBP1 gene of six unrelated patients (one had consanguineous parents) with previous diagnoses of FBPase deficiency (enzymatic, pts A, B, D, E; genetic through Next-Generation Sequencing-NGS, pt F; enzymatic and Sanger sequencing, pt C) was first analyzed through NGS. Pathogenic variants found in NGS were confirmed by Sanger sequencing. The pathogenicity of novel missense variants was evaluated through in silico analysis.

RESULTS

Five patients (pt A, B, D, E, F) had their genotype identified by NGS, all of them being homozygous. In Pt C, NGS detected only one pathogenic variant. Among the 11 alleles analyzed, only three variants were found, two being novel: c.958G > A and c.986T > C. In silico analysis indicated the pathogenicity of both variants. Interestingly, the three variants seem to be linked to specific haplotypes, indicating that an endogamy effect may be acting on these alleles in the population of Southern Brazil.

CONCLUSIONS

Our data suggest that NGS is a good tool for the diagnosis of FBPase deficiency. Variants c.958G > A and c.986T > C are the most prevalent variants in the country.

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.