Molecular and computational characterization of ABCB11 and ABCG5 variants in Tunisian patients with neonatal/infantile low-GGT intrahepatic cholestasis: Genetic diagnosis and genotype-phenotype correlation assessment.

Many inherited conditions cause hepatocellular cholestasis in infancy, including progressive familial intrahepatic cholestasis (PFIC), a heterogeneous group of diseases with highly overlapping symptoms. In our study, six unrelated Tunisian infants with PFIC suspicion were the subject of a panel-target sequencing followed by an exhaustive bioinformatic and modeling investigations. Results revealed five disease-causative variants including known ones: (the p.Asp482Gly and p.Tyr354 * in the ABCB11 gene and the p.Arg446 * in the ABCC2 gene), a novel p.Ala98Cys variant in the ATP-binding cassette subfamily G member 5 (ABCG5) gene and a first homozygous description of the p.Gln312His in the ABCB11 gene. The p.Gln312His disrupts the interaction pattern of the bile salt export pump as well as the flexibility of the second intracellular loop domain harboring this residue. As for the p.Ala98Cys, it modulates both the interactions within the first nucleotide-binding domain of the bile transporter and its accessibility. Two additional potentially modifier variants in cholestasis-associated genes were retained based on their pathogenicity (p.Gly758Val in the ABCC2 gene) and functionality (p.Asp19His in the ABCG8 gene). Molecular findings allowed a PFIC2 diagnosis in five patients and an unexpected diagnosis of sisterolemia in one case. The absence of genotype/phenotype correlation suggests the implication of environmental and epigenetic factors as well as modifier variants involved directly or indirectly in the bile composition, which could explain the cholestasis phenotypic variability.

Expanding the genetic and phenotypic spectrum of TRAPPC9 and MID2-related neurodevelopmental disabilities: report of two novel mutations, 3D-modelling, and molecular docking studies.

Intellectual disabilities (ID) and autism spectrum disorders (ASD) have a variety of etiologies, including environmental and genetic factors. Our study reports a psychiatric clinical investigation and a molecular analysis using whole exome sequencing (WES) of two siblings with ID and ASD from a consanguineous family. Bioinformatic prediction and molecular docking analysis were also carried out. The two patients were diagnosed with profound intellectual disability, brain malformations such as cortical atrophy, acquired microcephaly, and autism level III. The neurological and neuropsychiatric examination revealed that P2 was more severely affected than P1, as he was unable to walk, presented with dysmorphic feature and exhibited self and hetero aggressive behaviors. The molecular investigations revealed a novel TRAPPC9 biallelic nonsense mutation (c.2920 C > T, p.R974X) in the two siblings. The more severely affected patient (P2) presented, along with the TRAPPC9 variant, a new missense mutation c.166 C > T (p.R56C) in the MID2 gene at hemizygous state, while his sister P1 was merely a carrier. The 3D modelling and molecular docking analysis revealed that c.166 C > T variant could affect the ability of MID2 binding to Astrin, leading to dysregulation of microtubule dynamics and causing morphological abnormalities in the brain. As our knowledge, the MID2 mutation (p.R56C) is the first one to be detected in Tunisia and causing phenotypic variability between the siblings. We extend the genetic and clinical spectrum of TRAPPC9 and MID2 mutations and highlights the possible concomitant presence of X-linked as well as autosomal recessive inheritance to causing ID, microcephaly, and autism.

Molecular and in silico investigation of a novel ECHS1 gene mutation in a consanguine family with short-chain enoyl-CoA hydratase deficiency and Mt-DNA depletion: effect on trimer assembly and catalytic activity.

Short-chain enoyl-CoA hydratase deficiency (ECHS1D) is a rare congenital metabolic disorder that follows an autosomal recessive inheritance pattern. It is caused by mutations in the ECHS1 gene, which encodes a mitochondrial enzyme involved in the second step of mitochondrial ß-oxidation of fatty acids. The main characteristics of the disease are severe developmental delay, regression, seizures, neurodegeneration, high blood lactate, and a brain MRI pattern consistent with Leigh syndrome. Here, we report three patients belonging to a consanguineous family who presented with mitochondrial encephalomyopathy. Whole-exome sequencing revealed a new homozygous mutation c.619G > A (p.Gly207Ser) at the last nucleotide position in exon 5 of the ECHS1 gene. Experimental analysis showed that normal ECHS1 pre-mRNA splicing occurred in all patients compared to controls. Furthermore, three-dimensional models of wild-type and mutant echs1 proteins revealed changes in catalytic site interactions, conformational changes, and intramolecular interactions, potentially disrupting echs1 protein trimerization and affecting its function. Additionally, the quantification of mtDNA copy number variation in blood leukocytes showed severe mtDNA depletion in all probands.

Vitamin B1 deficiency leads to high oxidative stress and mtDNA depletion caused by SLC19A3 mutation in consanguineous family with Leigh syndrome.

Leigh syndrome (LS) and Leigh-like spectrum are the most common infantile mitochondrial disorders characterized by heterogeneous neurologic and metabolic manifestations. Pathogenic variants in SLC carriers are frequently reported in LS given their important role in transporting various solutes across the blood-brain barrier. SLC19A3 (THTR2) is one of these carriers transporting vitamin-B1 (vitB1, thiamine) into the cell. Targeted NGS of nuclear genes involved in mitochondrial diseases was performed in a patient belonging to a consanguineous Tunisian family with LS and revealed a homozygous c.1264 A > G (p.T422A) variant in SLC19A3. Molecular docking revealed that the p.T422A aa change is located at a key position interacting with vitB1 and causes conformational changes compromising vitB1 import. We further disclosed decreased plasma antioxidant activities of CAT, SOD and GSH enzymes, and a 42% decrease of the mtDNA copy number in patient blood.Altogether, our results disclose that the c.1264 A > G (p.T422A) variant in SLC19A3 affects vitB1 transport, induces a mtDNA depletion and reduces the expression level of oxidative stress enzymes, altogether contributing to the LS phenotype of the patient.

A novel homozygous PIGO mutation associated with severe infantile epileptic encephalopathy, profound developmental delay and psychomotor retardation: structural and 3D modelling investigations and genotype-phenotype correlation.

The PIGO gene encodes the GPI-ethanolamine phosphate transferase 3, which is crucial for the final synthetic step of the glycosylphosphatidylinositol-anchor serving to attach various proteins to their cell surface. These proteins are intrinsic for normal neuronal and embryonic development. In the current research work, a clinical investigation was conducted on a patient from a consanguineous family suffering from epileptic encephalopathy, characterized by severe seizures, developmental delay, hypotonia, ataxia and hyperphosphatasia. Molecular analysis was performed using Whole Exome Sequencing (WES). The molecular investigation revealed a novel homozygous variant c.1132C > T in the PIGO gene, in which a highly conserved Leucine was changed to a Phenylalanine (p.L378F). To investigate the impact of the non-synonymous mutation, a 3D structural model of the PIGO protein was generated using the AlphaFold protein structure database as a resource for template-based tertiary structure modeling. A structural analysis by applying some bioinformatic tools on both variants 378L and 378F models predicted the pathogenicity of the non-synonymous mutation and its potential functional and structural effects on PIGO protein. We also discussed the phenotypic and genotypic variability associated with the PIGO deficiency. To our best knowledge, this is the first report of a patient diagnosed with infantile epileptic encephalopathy showing a high elevation of serum alkaline phosphatase level. Our findings, therefore, widen the genotype and phenotype spectrum of GPI-anchor deficiencies and broaden the cohort of patients with PIGO associated epileptic encephalopathy with an elevated serum alkaline phosphatase level.

Identification of a novel homozygous mutation in NAXE gene associated with early-onset progressive encephalopathy by whole-exome sequencing: in silico protein structure characterization, molecular docking, and dynamic simulation.

Progressive encephalopathy with brain edema and/or leukoencephalopathy, PEBEL1, is a severe neurometabolic disorder characterized by rapidly progressive neurologic deterioration associated with a febrile illness. PEBEL1 is a lethal encephalopathy caused by NAXE gene mutations. Here we report a 6-month-old boy with mitochondrial encephalomyopathy from a consanguineous family. Molecular analysis was performed using whole-exome sequencing followed by segregation analysis. In addition, in silico prediction tools and molecular dynamic approaches were used to predict the structural effect of the mutation. Furthermore, molecular docking of the substrate NADP in both wild-type and mutated NAXE protein was carried out. Molecular analysis revealed the presence of the novel homozygous mutation c.641 T > A (p. Ile214Asn) in the NAXE gene, located at the NAD (P)H hydrate epimerase domain. In addition, bioinformatics analyses and molecular dynamics revealed that p. Ile214Asn mutation could affect the structure, stability, and compactness of the NAXE protein. Moreover, the result of the molecular docking showed that the p. Ile214Asn mutation leads to conformational changes in the catalytic cavity, thus modifying interaction with the substrate and restricting its access. We also compared the phenotype of our patient with those of previously reported cases with PEBEL syndrome. All bioinformatics findings provide evidence that the NAXE variant Asn214 disrupts NAXE protein functionality leading to an insufficient NAD (P)HX repair system and the development of clinical features of PEBEL1 syndrome in our patient. To our knowledge, our case is the 21st case of PEBEL1 patient worldwide and the first case in North Africa.

Pustular psoriasis of pregnancy: Clinical and genetic characteristics in a series of eight patients and review of the literature.

Pustular psoriasis of pregnancy (PPP) can lead to life-threatening complications. The objective of this study is to report clinical and genetic spectrum, prognostic factors and management options. A retrospective study was designed including eight PPP patients. Clinical data were collected, and performed genetic and statistical analysis to identify factors associated with fetal complications, resistance to treatment and post-partum flare extension. A systematic review of the literature was also carried out. Eight Tunisian patients, with a mean age of 23 ± 3.3 years, were included. They presented 14 flares (F) during pregnancies and one flare after delivery. Additional GPP flares outside pregnancy periods were noted in 2/8 of patients. The mean duration of PPP flares was 16.66 ± 7.8 weeks. The first flare occurred at a gestational age of 26 ± 5 weeks. Only 2/8 studied patients presented a homozygous mutation c.80 T > C (p.L27P) in IL36RN gene. Used treatments were topical steroids (n = 12F), systemic steroids (n = 5F), ciclosporin (n = 1F), UVB (n = 1F) and acitretin (in post-partum n = 6F). Complications were oligoamnios (n = 2), intra-uterine growth retardation (n = 1), fetal death in utero (n = 1), prematurity (n = 3), low weight at birth (n = 2). A significant association was found between (i) occurrence of fetal complications and early gestational age at the onset (p = 0.036), (ii) resistance to topical steroids and body surface affected area (p = 0.008), (iii) presence of mutation c.80 T > C in PPP flares and low serum levels of calcium (p = 0.01). Our systematic review of the literature identified 39 patients with 41 flares of PPP. Only 7/39 patients presented a causative mutation in IL36RN and CARD14 genes. PPP is characterized by a phenotypic heterogeneity and can be associated to IL36RN mutations. Its early onset can be associated with fetal complications. Systemic steroids and cyclosporine remain the most used therapies.

Mitochondrial disease patients with novel ND4 12058A > C and ND1 m.3911A > G variations: implications for a role in the phenotype following a bioinformatic investigation.

Mitochondrial diseases include a wide group of clinically heterogeneous disorders caused by a dysfunction of the mitochondrial respiratory chain and can be related to mutations in nuclear or mitochondrial DNA genes. In the present report, we performed a whole mitochondrial genome screening in two patients with clinical features of mitochondrial diseases. Mutational analysis revealed the presence of two undescribed heteroplasmic mitochondrial variations, the m.3911A > G (E202G) variant in the MT-ND1 gene found in two patients (P1 and P2) and the m.12058A > C (E433D) pathogenic variant in the MT-ND4 gene present only in patient P2 who had a more severe phenotype. These two substitutions were predicted to be damaging by several bioinformatics tools and lead to amino acid changes in two conserved residues localized in two important functional domains of the mitochondrial subunits of complex I. Furthermore, the 3D modeling suggested that the two amino acid changes could therefore alter the structure of the two subunits and may decrease the stability and the function of complex I. The two described pathogenic variants found in patient P2 could act synergically and alter the complex I function by affecting the proton pumping processes and the energy production and then could explain the severe phenotype compared to patient P1 presenting only the E202G substitution in ND1.

Mutations in aARS genes revealed by targeted next-generation sequencing in patients with mitochondrial diseases.

Mitochondrial diseases are a clinically heterogeneous group of multisystemic disorders that arise as a result of various mitochondrial dysfunctions. Autosomal recessive aARS deficiencies represent a rapidly growing group of severe rare inherited mitochondrial diseases, involving multiple organs, and currently without curative option. They might be related to defects of mitochondrial aminoacyl t-RNA synthetases (mtARS) that are ubiquitous enzymes involved in mitochondrial aminoacylation and the translation process. Here, using NGS analysis of 281 nuclear genes encoding mitochondrial proteins, we identified 4 variants in different mtARS in three patients from unrelated Tunisian families, with clinical features of mitochondrial disorders. Two homozygous variants were found in KARS (c.683C>T) and AARS2 (c.1150-4C>G), respectively in two patients, while two heterozygous variants in EARS2 (c.486-7C>G) and DARS2 (c.1456C>T) were concomitantly found in the third patient. Bio-informatics investigations predicted their pathogenicity and deleterious effects on pre-mRNA splicing and on protein stability. Thus, our results suggest that mtARS mutations are common in Tunisian patients with mitochondrial diseases.

Potential dysfunctional effects of synonymous variants: Insights from an exhaustive in silico analysis of the ABCB4 gene.

The multiple drug resistance 3 (MDR3) protein is a canalicular phospholipid translocator involved in the bile secretion and encoded by the ABCB4 gene. Its deficiency is related to a large spectrum of liver diseases. Taking into account the increased evidence about the involvement of synonymous variants in inherited diseases, this study aims to explore the putative effects of silent genetic variants on the ABCB4 expression. We performed an exhaustive computational approach using ESE finder, RegRNA 2.0, MFOLD, SNPfold, and %MinMax software added to the measurement of the Relative Synonymous Codon Usage. This analysis included 216 synonymous variants distributed throughout the ABCB4 gene. Results have shown that 11 synonymous coding SNPs decrease the ESE activity, while 8 of them change the codon frequency. Besides, the c.24C>T variation, located 21 nucleotides downstream the start A (Adenine) U (Uracil) G (Glutamine) AUG causes an increase in the local stability. Moreover, the computational analysis of the 3'UTR region showed that six of the eight variants located in this region affected the Wild Type (WT) pattern of the miRNA targets sites and/or their proper display. The 26 sSNPs retained as putatively functional possessed a very low allele frequency, supporting their pathogenicity. In conclusion, the obtained results suggest that some synonymous SNPs in the ABCB4 gene, considered up to now as neutral, may be involved in the MDR3 deficiency.

First description of a novel mitochondrial mutation in the MT-TI gene associated with multiple mitochondrial DNA deletion and depletion in family with severe dilated mitochondrial cardiomyopathy.

Mitochondria are essential for early cardiac development and impaired mitochondrial function was described associated with heart diseases such as hypertrophic or dilated mitochondrial cardiomyopathy. In this study, we report a family including two individuals with severe dilated mitochondrial cardiomyopathy. The whole mitochondrial genome screening showed the presence of several variations and a novel homoplasmic mutation m.4318-4322delC in the MT-TI gene shared by the two patients and their mother and leading to a disruption of the tRNAIle secondary structure. In addition, a mitochondrial depletion was present in blood leucocyte of the two affected brother whereas a de novo heteroplasmic multiple deletion in the major arc of mtDNA was present in blood leucocyte and mucosa of only one of them. These deletions in the major arc of the mtDNA resulted to the loss of several protein-encoding genes and also some tRNA genes. The mtDNA deletion and depletion could result to an impairment of the oxidative phosphorylation and energy metabolism in the respiratory chain in the studied patients. Our report is the first description of a family with severe lethal dilated mitochondrial cardiomyopathy and presenting several mtDNA abnormalities including punctual mutation, deletion and depletion.

Cytochrome C oxydase deficiency: SURF1 gene investigation in patients with Leigh syndrome.

Leigh syndrome (LS) is a rare progressive neurodegenerative disorder occurring in infancy. The most common clinical signs reported in LS are growth retardation, optic atrophy, ataxia, psychomotor retardation, dystonia, hypotonia, seizures and respiratory disorders. The paper reported a manifestation of 3 Tunisian patients presented with LS syndrome. The aim of this study is the MT[HYPHEN]ATP6 and SURF1 gene screening in Tunisian patients affected with classical Leigh syndrome and the computational investigation of the effect of detected mutations on its structure and functions by clinical and bioinformatics analyses. After clinical investigations, three Tunisian patients were tested for mutations in both MT-ATP6 and SURF1 genes by direct sequencing followed by in silico analyses to predict the effects of sequence variation. The result of mutational analysis revealed the absence of mitochondrial mutations in MT-ATP6 gene and the presence of a known homozygous splice site mutation c.516-517delAG in sibling patients added to the presence of a novel double het mutations in LS patient (c.752-18 A > C/c. c.751 + 16G > A). In silico analyses of theses intronic variations showed that it could alters splicing processes as well as SURF1 protein translation. Leigh syndrome (LS) is a rare progressive neurodegenerative disorder occurring in infancy. The most common clinical signs reported in LS are growth retardation, optic atrophy, ataxia, psychomotor retardation, dystonia, hypotonia, seizures and respiratory disorders. The paper reported a manifestation of 3 Tunisian patients presented with LS syndrome. The aim of this study is MT-ATP6 and SURF1 genes screening in Tunisian patients affected with classical Leigh syndrome and the computational investigation of the effect of detected mutations on its structure and functions. After clinical investigations, three Tunisian patients were tested for mutations in both MT-ATP6 and SURF1 genes by direct sequencing followed by in silico analysis to predict the effects of sequence variation. The result of mutational analysis revealed the absence of mitochondrial mutations in MT-ATP6 gene and the presence of a known homozygous splice site mutation c.516-517delAG in sibling patients added to the presence of a novel double het mutations in LS patient (c.752-18 A>C/ c.751+16G>A). In silico analysis of theses intronic vaiations showed that it could alters splicing processes as well as SURF1 protein translation.

First report of an unusual novel double mutation affecting the transcription repression domain of MeCP2 and causing a severe phenotype of Rett syndrome: Molecular analyses and computational investigation.

Rett syndrome is an X-linked neurodevelopmental disorder that develops a profound intellectual and motor disability and affects 1 from 10 000 to 15 000 live female births. This disease is characterized by a period of apparently normal development until 6-18 months of age when motor and communication abilities regress which is caused by mutations occurred in the X-linked MECP2 gene, encoding the methyl-CpG binding protein 2. This research study reports a molecular analysis via an exhaustive gene sequencing which reveals an unusual novel double mutation (c.695 G > T; c.880C > T) located in a highly conserved region in MECP2 gene affecting the transcription repression domain (TRD) of MeCP2 protein and leading for the first time to a severe phenotype of Rett syndrome. Moreover, a computational investigation of MECP2 mutations demonstrates that the novel mutation c.695 G > T is highly deleterious which affects the MeCP2 protein showing also an adverse impact on MECP2 gene expression and resulting in an affected folding and decreased stability of MECP2 structures. Thus, the altered TRD domain engenders a disrupted process of MECP2 functions. Therefore, this is the first study which highlights a novel double mutation among the transcription repression domain (TRD) of MeCP2 protein in Rett patient with a severe clinical phenotype in North Africa region.

Clinical, Molecular, and Computational Analysis in two cases with mitochondrial encephalomyopathy associated with SUCLG1 mutation in a consanguineous family.

Deficiency of the mitochondrial enzyme succinyl COA ligase (SUCL) is associated with encephalomyopathic mtDNA depletion syndrome and methylmalonic aciduria. This disorder is caused by mutations in both SUCL subunits genes: SUCLG1 (α subnit) and SUCLA2 (ß subnit). We report here, two Tunisian patients belonging to a consanguineous family with mitochondrial encephalomyopathy, hearing loss, lactic acidosis, hypotonia, psychomotor retardation and methylmalonic aciduria. Mutational analysis of SUCLG1 gene showed, for the first time, the presence of c.41T > C in the exon 1 at homozygous state. In-silico analysis revealed that this mutation substitutes a conserved methionine residue to a threonine at position 14 (p.M14T) located at the SUCLG1 protein mitochondrial targeting sequence. Moreover, these analysis predicted that this mutation alter stability structure and mitochondrial translocation of the protein. In Addition, a decrease in mtDNA copy number was revealed by real time PCR in the peripheral blood leukocytes in the two patients compared with controls.

Hypoparathyroidism in children: a study of eight cases.

BACKGROUND: Hypoparathyroidism is a rare pediatric endocrine disease, which is caused by low circulating levels of PTH or insensitivity to its action in the target tissues. AIM: To report the clinical and biochemical characteristics and theoutcome of 8 patients with hypoparathyroidism. METHODS: We analyzed retrospectively the results of clinical, biochemical, radiological findings of patients with hypoparathyroidism diagnosed in pediatric department of Hedi Chaker Hospital during the period 1994-2013. RESULTS: Eight patients (5 females and 3 males) were diagnosed with hypoparathyroidism during 20 years's period. The median age at the onset of first symptoms was 17,5 months (15 days- 5 years and 10 months). Seizures were the most commonly presenting symptom and were seen in seven cases. Eight patients were diagnosed with hypoparathyroidism (Di-Georges syndrome: one case, Sanjad Sakati syndrome: 3 case, kearns sayre syndrome: 1 case, autoimmune polyendocrinopathy candidiasis- ectodermal dystrophy: one case, idiopathic hypoparathyroidism: two cases. Conventional treatment was based on calcium and vitamin D analogs. The average of follow up was 5 years. Nephrocalcinosis was noted in two patients. The death occurred in five patients; it was related to hypocalcaemia in one patient. CONCLUSION: The diagnosis of hyperparathyroidism is easy; it's established on the association of hypocalcaemia and hyperphosphatemia. Etiologic approach is based on molecular findings. Vitamin D analog treatment of hypoparathyroidism in children involves the challenge, of adjusting treatment dosage to minimize both symptomatic hypocalcemia and asymptomatic, but potentially kidney-damaging, hypercalciuria causing nephrocalcinosis and renal insufficiency.

Co segregation of the m.1555A>G mutation in the MT-RNR1 gene and mutations in MT-ATP6 gene in a family with dilated mitochondrial cardiomyopathy and hearing loss: A whole mitochondrial genome screening.

Mitochondrial disease refers to a heterogeneous group of disorders resulting in defective cellular energy production due to dysfunction of the mitochondrial respiratory chain, which is responsible for the generation of most cellular energy. Because cardiac muscles are one of the high energy demanding tissues, mitochondrial cardiomyopathies is one of the most frequent mitochondria disorders. Mitochondrial cardiomyopathy has been associated with several point mutations of mtDNA in both genes encoded mitochondrial proteins and mitochondrial tRNA and rRNA. We reported here the first description of mutations in MT-ATP6 gene in two patients with clinical features of dilated mitochondrial cardiomyopathy. The mutational analysis of the whole mitochondrial DNA revealed the presence of m.1555A>G mutation in MT-RNR1 gene associated to the m.8527A>G (p.M>V) and the m.8392C>T (p.136P>S) variations in the mitochondrial MT-ATP6 gene in patient1 and his family members with variable phenotype including hearing impairment. The second patient with isolated mitochondrial cardiomyopathy presented the m.8605C>T (p.27P>S) mutation in the MT-ATP6 gene. The three mutations p.M1V, p.P27S and p.P136S detected in MT-ATP6 affected well conserved residues of the mitochondrial protein ATPase 6. In addition, the substitution of proline residue at position 27 and 136 effect hydrophobicity and structure flexibility conformation of the protein.

Identification of compound heterozygous patients with primary hyperoxaluria type 1: clinical evaluations and in silico investigations.

BACKGROUND: Primary hyperoxaluria type 1 (PH1) is an autosomal recessive inherited disorder of glyoxylate metabolism in which excessive oxalates are formed by the liver and excreted by the kidneys. Calcium oxalate crystallizes in the urine, leading to urolithiasis, nephrocalcinosis, and consequent renal failure if treatment is not initiated promptly. Mutations in the AGXT gene which encodes the hepatic peroxisomal enzyme alanine:glyoxylate aminotransferase are responsible of PH1. In the present work, we aimed to analyze AGXT gene and in silico investigations performed in four patients with PH1 among two non consanguineous families. METHODS: Exhaustive gene sequencing was performed after PCR amplification of coding exons and introns boundaries. Bioinformatic tools were used to predict the impact of AGXT variants on gene expression as well as on the protein structure and function. RESULTS: Direct sequencing of all exons of AGXT gene revealed the emergence of multiple mutations in compound heterozygous state in the two studied families. Two patients were compound heterozygous for the c.731 T > C, c.32C > T, c.1020A > G and c.33_34insC and presented clinically with recurrent urinary tract infection, multiple urolithiasis and nephrocalcinosis under the age of 1 year and a persistent hyperoxaluria at the age of diagnosis. The two other patients presenting a less severe phenotypes were heterozygous for c.731 T > C and homozygous for the c.32C > T and c.1020A > G or compound heterozygous for c.26C > A and c.65A > G variants. CONCLUSION: In Summary, we provided relevance regarding the compound heterozygous mutations in non consanguineous PH1 families with variable severity.

Mutational analysis in patients with neuromuscular disorders: Detection of mitochondrial deletion and double mutations in the MT-ATP6 gene.

Mitochondrial diseases encompass a wide variety of pathologies characterized by a dysfunction of the mitochondrial respiratory chain resulting in an energy deficiency. The respiratory chain consists of five multi-protein complexes providing coupling between nutrient oxidation and phosphorylation of ADP to ATP. In the present report, we studied mitochondrial genes of complex I, III, IV and V in 2 Tunisian patients with mitochondrial neuromuscular disorders. In the first patient, we detected the m.8392C>T variation (P136S) in the mitochondrial ATPase6 gene and the m.8527A>G transition at the junction MT-ATP6/MT-ATP8 which change the initiation codon AUG to GUG. The presence of these two variations in such an important gene could probably affect the ATP synthesis in the studied patient. In the second patient, we detected several known variations in addition to a mitochondrial deletion in the major arc of the mtDNA eliminating tRNA and respiratory chain protein genes. This deletion could be responsible of an inefficient translation leading to an inefficient mitochondrial protein synthesis in P2.

Mutational screening in patients with profound sensorineural hearing loss and neurodevelopmental delay: Description of a novel m.3861A > C mitochondrial mutation in the MT-ND1 gene.

Mitochondrial diseases caused by mitochondrial dysfunction are a clinically and genetically, heterogeneous group of disorders involving multiple organs, particularly tissues with high-energy demand. Hearing loss is a recognized symptom of a number of mitochondrial diseases and can result from neuronal or cochlear dysfunction. The tissue affected in this pathology is most probably the cochlear hair cells, which are essential for hearing function since they are responsible for maintaining the ionic gradients necessary for sound signal transduction. Several mitochondrial DNA mutations have been associated with hearing loss and since mitochondria are crucial for the cellular energy supply in many tissues, most of these mtDNA mutations affect several tissues and will cause syndromic hearing loss. In the present study, we described 2 patients with sensorineural hearing loss and neurodevelopmental delay in whom we tested mitochondrial genes described to be associated with syndromic hearing loss. One of these patients showed a novel heteroplasmic mitochondrial mutation m.3861A > C (W185C) which lead to a loss of stability of the ND1 protein since it created a new hydrogen bund between the unique created cystein C185 and the A182 residue. In the second patient, we detected two novel heteroplasmic variations m.12350C > A (T5N) and m.14351T > C (E108G) respectively in the MT-ND5 and the MT-ND6 genes. The TopPred II prediction for the E108G variation revealed a decrease of the hydrophobicity in the mutated MT-ND6.

Mitochondrial DNA triplication and punctual mutations in patients with mitochondrial neuromuscular disorders.

Mitochondrial diseases are a heterogeneous group of disorders caused by the impairment of the mitochondrial oxidative phosphorylation system which have been associated with various mutations of the mitochondrial DNA (mtDNA) and nuclear gene mutations. The clinical phenotypes are very diverse and the spectrum is still expanding. As brain and muscle are highly dependent on OXPHOS, consequently, neurological disorders and myopathy are common features of mtDNA mutations. Mutations in mtDNA can be classified into three categories: large-scale rearrangements, point mutations in tRNA or rRNA genes and point mutations in protein coding genes. In the present report, we screened mitochondrial genes of complex I, III, IV and V in 2 patients with mitochondrial neuromuscular disorders. The results showed the presence the pathogenic heteroplasmic m.9157G>A variation (A211T) in the MT-ATP6 gene in the first patient. We also reported the first case of triplication of 9 bp in the mitochondrial NC7 region in Africa and Tunisia, in association with the novel m.14924T>C in the MT-CYB gene in the second patient with mitochondrial neuromuscular disorder.