Molecular and biochemical characterization of a novel intronic single point mutation in a Tunisian family with glycogen storage disease type III.

Genetic deficiency of the glycogen debranching enzyme causes glycogen storage disease type III, an autosomal recessive inherited disorder. The gene encoding this enzyme is designated as AGL gene. The disease is characterized by fasting hypoglycemia, hepatomegaly, growth retardation, progressive myopathy and cardiomyopathy. In the present study, we present clinical features and molecular characterization of two consanguineous Tunisian siblings suffering from Glycogen storage disease type III. The full coding exons of the AGL gene and their corresponding exon-intron boundaries were amplified for the patients and their parents. Gene sequencing identified a novel single point mutation at the conserved polypyrimidine tract of intron 21 in a homozygous state (IVS21-8A>G). This variant cosegregated with the disease and was absent in 102 control chromosomes. In silico analysis using online resources showed a decreased score of the acceptor splice site of intron 21. RT-PCR analysis of the AGL splicing pattern revealed a 7 bp sequence insertion between exon 21 and exon 22 due to the creation of a new 3' splice site. The predicted mutant enzyme was truncated by the loss of 637 carboxyl-terminal amino acids as a result of premature termination. This novel mutation is the first mutation identified in the region of Bizerte and the tenth AGL mutation identified in Tunisia. Screening for this mutation can improve the genetic counseling and prenatal diagnosis of GSD III.

Acute but transient neurological deterioration revealing adult polyglucosan body disease.

Adult polyglucosan body disease (APBD) is a metabolic disorder usually caused by glycogen branching enzyme (GBE) deficiency. APBD associates progressive walking difficulties, bladder dysfunction and, in about 50% of the cases, cognitive decline. APBD is characterized by a recognizable leukodystrophy on brain MRI. We report here a novel presentation of this disease in a 35-year old woman who presented with an acute deterioration followed by an unexpected recovery. Enzymatic analysis displayed decreased GBE activity in leukocytes. Molecular analyses revealed that only one mutated allele was expressed, bearing a p.Arg515His mutation. This is the first observation reporting acute and reversible neurological symptoms in APBD. These findings emphasize the importance of searching GBE deficiency in patients presenting with a leukodystrophy and acute neurological symptoms mimicking a stroke, in the absence of cardiovascular risk factors.

Successful treatment of severe cardiomyopathy in glycogen storage disease type III With D,L-3-hydroxybutyrate, ketogenic and high-protein diet.

Glycogen storage disease type III (GSD III) due to debranching enzyme deficiency presenting usually with hepatomegaly and hypoglycemia may be responsible for severe cardiomyopathy which is often fatal. Current treatment of GSD III is based on frequent high-carbohydrate meals that have no effect on the cardiomyopathy. We describe a 2-mo-old infant presenting with a familial form of GSD III complicated with cardiomyopathy. As conventional treatment was unable to improve his sister's cardiomyopathy who was deceased at age 11 mo, we proposed an experimental treatment combining the use of synthetic ketone bodies (D,L-3-OH butyrate) as an alternative energy source, 2:1 ketogenic diet to reduce glucose intake and high-protein diet to enhance gluconeogenesis. Twenty-four months after the onset of this treatment, echocardiography showed an improvement of cardiomyopathy. Growth and liver size remained normal, and no side effects were observed. Blood glucose levels remained within the normal range and insulin levels decreased. These findings show that synthetic ketone bodies as well as low-carbohydrate, high-lipid, and high-protein diet may be a more beneficial therapeutic choice therapeutic choice for GSD III patients with cardiomyopathy. These encouraging data need to be confirmed in more GSD III patients presenting with cardiac or muscular symptoms.

Liver glycogen storage diseases due to phosphorylase system deficiencies: diagnosis thanks to non invasive blood enzymatic and molecular studies.

Glycogen storage disease (GSD) due to a deficient hepatic phosphorylase system defines a genetically heterogeneous group of disorders that mainly manifests in children. We investigated 45 unrelated children in whom a liver GSD VI or IX was suspected on the basis of clinical symptoms including hepatomegaly, increased serum transaminases, postprandial lactatemia and/or mild fasting hypoglycemia. Liver phosphorylase and phosphorylase b kinase activities studied in peripheral blood cells allowed to suspect diagnosis in 37 cases but was uninformative in 5. Sequencing of liver phosphorylase genes was useful to establish an accurate diagnosis. Causative mutations were found either in the PYGL (11 patients), PHKA2 (26 patients), PHKG2 (three patients) or in the PHKB (three patients) genes. Eleven novel disease causative mutations, five missense (p.N188K, p.D228Y, p.P382L, p.R491H, p.L500R) and six truncating mutations (c.501_502ins361pb, c.528+2T>C, c.856-29_c.1518+614del, c.1620+1G>C, p.E703del and c.2313-1G>T) were identified in the PYGL gene. Seventeen novel disease causative mutations, ten missense (p.A42P, p.Q95R, p.G131D, p.G131V, p.Q134R, p.G187R, p.G300V, p.G300A, p.C326Y, p.W820G) and seven truncating (c.537+5G>A, p.G396DfsX28, p.Q404X, p.N653X, p.L855PfsX87, and two large deletions) were identified in the PHKA2 gene. Four novel truncating mutations (p.R168X, p.Q287X, p.I268PfsX12 and c.272-1G>C) were identified in the PHKG2 gene and three (c.573_577del, p.R364X, c.2427+3A>G) in the PHKB gene. Patients with PHKG2 mutations evolved towards cirrhosis. Molecular analysis of GSD VI or IX genes allows to confirm diagnosis suspected on the basis of enzymatic analysis and to establish diagnosis and avoid liver biopsy when enzymatic studies are not informative in blood cells.

The spectrum of liver diseases related to ABCB4 gene mutations: pathophysiology and clinical aspects.

Class III multidrug resistance P-glycoproteins, Mdr2 in mice and MDR3 in human, are canalicular phospholipid translocators involved in biliary phospholipid (phosphatidylcholine) excretion. The role of an ABCB4 gene defect in liver disease has been initially proven in a subtype of progressive familial intrahepatic cholestasis called PFIC3, a severe pediatric liver disease that may require liver transplantation. Several ABCB4 mutations have been identified in children with PFIC3 and are associated with low level of phospholipids in bile leading to a high biliary cholesterol saturation index. ABCB4 mutations are associated with loss of canalicular MDR3 protein and /or loss of protein function. There is evidence that a biallelic or monoallelic ABCB4 defect causes or predisposes to several human liver diseases (PFIC3, low phospholipid associated cholelithiasis syndrome, intrahepatic cholestasis of pregnancy, drug-induced liver injury, transient neonatal cholestasis, adult biliary fibrosis, or cirrhosis). Most patients with MDR3 deficiency have a favorable outcome with ursodeoxycholic acid (UDCA) therapy, but some PFIC3 patients who do not respond to UDCA treatment still require liver transplantation. The latter should be good candidates for a targeted pharmacologic approach and/or to cell therapy in the future.

ATP8B1 and ABCB11 analysis in 62 children with normal gamma-glutamyl transferase progressive familial intrahepatic cholestasis (PFIC): phenotypic differences between PFIC1 and PFIC2 and natural history.

UNLABELLED: Progressive familial intrahepatic cholestasis (PFIC) types 1 and 2 are characterized by normal serum gamma-glutamyl transferase (GGT) activity and are due to mutations in ATP8B1 (encoding FIC1) and ABCB11 (encoding bile salt export pump [BSEP]), respectively. Our goal was to evaluate the features that may distinguish PFIC1 from PFIC2 and ease their diagnosis. We retrospectively reviewed charts of 62 children with normal-GGT PFIC in whom a search for ATP8B1 and/or ABCB11 mutation, liver BSEP immunostaining, and/or bile analysis were performed. Based on genetic testing, 13 patients were PFIC1 and 39 PFIC2. The PFIC origin remained unknown in 10 cases. PFIC2 patients had a higher tendency to develop neonatal cholestasis. High serum alanine aminotransferase and alphafetoprotein levels, severe lobular lesions with giant hepatocytes, early liver failure, cholelithiasis, hepatocellular carcinoma, very low biliary bile acid concentration, and negative BSEP canalicular staining suggest PFIC2, whereas an absence of these signs and/or presence of extrahepatic manifestations suggest PFIC1. The PFIC1 and PFIC2 phenotypes were not clearly correlated with mutation types, but we found tendencies for a better prognosis and response to ursodeoxycholic acid (UDCA) or biliary diversion (BD) in a few children with missense mutations. Combination of UDCA, BD, and liver transplantation allowed 87% of normal-GGT PFIC patients to be alive at a median age of 10.5 years (1-36), half of them without liver transplantation. CONCLUSION: PFIC1 and PFIC2 differ clinically, biochemically, and histologically at presentation and/or during the disease course. A small proportion of normal-GGT PFIC is likely not due to ATP8B1 or ABCB11 mutations.

Liver diseases related to MDR3 (ABCB4) gene deficiency.

Class III multidrug resistance P-glycoproteins, mdr2 in mice and MDR3 in human, are canalicular phospholipid translocators involved in biliary phospholipid (phosphatidylcholine) excretion.The role of a MDR3 (ABCB4) gene defect in liver disease has been initially proven in a subtype of progressive familial intrahepatic cholestasis called PFIC3, a severe pediatric liver disease that may require liver transplantation.Several MDR3 mutations have been identified in children with PFIC3 and are associated to low level of phospholipids in bile leading to high biliary cholesterol saturation index.MDR3 mutations are associated to loss of canalicular MDR3 protein and /or to loss of protein function.There is evidence that biallelic or monoallelic MDR3 defect causes or predisposes to 6 human liver diseases (PFIC3, adult biliary cirrhosis, low phospholipid associated cholelithiasis syndrome, transient neonatal cholestasis, intrahepatic cholestasis of pregnancy, drug induced cholestasis).Some patients with MDR3 deficiency may benefit from ursodeoxycholic acid therapy and could be good candidates to a targeted pharmacological approach and/or to cell therapy in the future.

Progressive familial intrahepatic cholestasis.

Progressive familial intrahepatic cholestasis (PFIC) refers to heterogeneous group of autosomal recessive disorders of childhood that disrupt bile formation and present with cholestasis of hepatocellular origin. The exact prevalence remains unknown, but the estimated incidence varies between 1/50,000 and 1/100,000 births. Three types of PFIC have been identified and related to mutations in hepatocellular transport system genes involved in bile formation. PFIC1 and PFIC2 usually appear in the first months of life, whereas onset of PFIC3 may also occur later in infancy, in childhood or even during young adulthood. Main clinical manifestations include cholestasis, pruritus and jaundice. PFIC patients usually develop fibrosis and end-stage liver disease before adulthood. Serum gamma-glutamyltransferase (GGT) activity is normal in PFIC1 and PFIC2 patients, but is elevated in PFIC3 patients. Both PFIC1 and PFIC2 are caused by impaired bile salt secretion due respectively to defects in ATP8B1 encoding the FIC1 protein, and in ABCB11 encoding the bile salt export pump protein (BSEP). Defects in ABCB4, encoding the multi-drug resistant 3 protein (MDR3), impair biliary phospholipid secretion resulting in PFIC3. Diagnosis is based on clinical manifestations, liver ultrasonography, cholangiography and liver histology, as well as on specific tests for excluding other causes of childhood cholestasis. MDR3 and BSEP liver immunostaining, and analysis of biliary lipid composition should help to select PFIC candidates in whom genotyping could be proposed to confirm the diagnosis. Antenatal diagnosis can be proposed for affected families in which a mutation has been identified. Ursodeoxycholic acid (UDCA) therapy should be initiated in all patients to prevent liver damage. In some PFIC1 or PFIC2 patients, biliary diversion can also relieve pruritus and slow disease progression. However, most PFIC patients are ultimately candidates for liver transplantation. Monitoring of hepatocellular carcinoma, especially in PFIC2 patients, should be offered from the first year of life. Hepatocyte transplantation, gene therapy or specific targeted pharmacotherapy may represent alternative treatments in the future.

Hereditary fructose intolerance: frequency and spectrum mutations of the aldolase B gene in a large patients cohort from France--identification of eight new mutations.

We investigated the molecular basis of hereditary fructose intolerance (HFI) in 160 patients from 92 families by means of a PCR-based mutation screening strategy, consisting of restriction enzyme digestion and direct sequencing. Sixteen different mutations of the aldolase B (ALDOB) gene were identified in HFI patients. As in previous studies, p.A150P (64%), p.A175D (16%) and p.N335K (5%) were the most common mutated alleles, followed by p.R60X, p.A338V, c.360_363delCAAA (p.N120KfsX30), c.324G>A (p.K108K) and c.625-1G>A. Eight novel mutations were also identified in 10 families with HFI: a one-base deletion (c.146delT (p.V49GfsX27)), a small deletion (c.953del42bp), a small insertion (c.689ins TGCTAA (p.K230MfsX136)), one splice site mutation (c.112+1G>A), one nonsense mutation (c.444G>A (p.W148X)), and three missense mutations (c.170G>C (p.R57P), c.839C>A (p.A280P) and c.932T>C (p.L311P)). Our strategy allows to diagnose 75% of HFI patients using restriction enzymatic analysis and to enlarge the diagnosis to 97% of HFI patients when associated with direct sequencing.

CFC1 gene involvement in biliary atresia with polysplenia syndrome.

The present report describes CFC1 gene analysis in 10 patients with polysplenia syndrome. The heterozygous transition c.433G>A (Ala145Thr) located in exon 5 was identified in 5 patients, with a twice-higher frequency than in control patients. These results suggest that heterozygous CFC1 mutation may represent a genetic predisposition to biliary atresia splenic malformation syndrome.

Prenatal molecular diagnosis of inherited cholestatic diseases.

OBJECTIVES: Progressive familial intrahepatic cholestasis (PFIC) and to a lesser extent, Alagille syndrome, often lead to end-stage liver disease during childhood. We report our experience of DNA-based prenatal diagnosis of PFIC1-3 and Alagille syndrome. PATIENTS AND METHODS: Four molecular antenatal diagnoses were performed in 3 PFIC families and 17 in 11 Alagille syndrome families. DNA was isolated from chorionic villus or cultured amniocyte samples from women, without pregnancy complications. RESULTS: All four foetuses with a family history of PFIC1, 2, or 3 were heterozygous for an ATP8B1, ABCB11, or ABCB4 mutation and pregnancies were continued. Three of the infants were healthy after birth, and 1 premature infant, who had an ABCB4 mutation, experienced transient neonatal cholestasis. Among the families with a history of de novo JAG1 mutation, none of the foetuses was mutated, versus 40% of those with a history of familial mutation. Of 4 pregnant women with a JAG1-mutated foetus, 3 cut short their pregnancy and 1 gave birth to a child with overt Alagille syndrome. CONCLUSIONS: Molecular antenatal diagnosis of PFIC1-3 and Alagille syndrome is reliable because clinical outcome after birth corresponded to molecular foetal data.

A new mutation in PRKAG2 gene causing hypertrophic cardiomyopathy with conduction system disease and muscular glycogenosis.

Mutations in the gene encoding the gamma2 subunit of AMP-activated protein kinase (PRKAG2) cause familial cardiac hypertrophy and electrophysiological abnormalities, with glycogen accumulation in the heart of affected patients. The authors describe a 38-year-old man with a new heterozygous PRKAG2 mutation (Ser548Pro) manifesting by hypertrophic cardiomyopathy, severe conduction system abnormalities, and skeletal muscle glycogenosis. Considering those results, PRKAG2 gene could be a potential candidate for unexplained muscle glycogenosis associated with cardiac abnormalities.