Chahnez Triki

Molecular-clinical correlation in a family with a novel heteroplasmic Leigh syndrome missense mutation in the mitochondrial cytochrome c oxidase III gene.

Cytochrome c oxidase is an essential component of the mitochondrial respiratory chain that catalyzes the reduction of molecular oxygen by reduced cytochrome c. In this study, the authors report the second mutation associated with Leigh syndrome in the blood and buccal mucosa of 2 affected members of a Tunisian family. It was a novel heteroplasmic missense mitochondrial mutation at nucleotide 9478 in the gene specifying subunit III of cytochrome c oxidase substituting the valine at position 91 to alanine in a highly conserved amino acid. It was found with a high mutant load in tissues derived from endoderm (buccal mucosa) and mesoderm (blood). However, it was nearly absent in tissue derived from ectoderm (hair follicles). It was absent in 120 healthy controls, and PolyPhen analysis showed that the hydropathy index changed from +1.276 to +0.242, and the number of structures of the 3D protein decreased from 39 to 32.

Two new mutations in the MT-TW gene leading to the disruption of the secondary structure of the tRNATrp in patients with Leigh syndrome.

Leigh syndrome is a progressive neurodegenerative disorder occurring in infancy and childhood characterized in most cases by a psychomotor retardation, optic atrophy, ataxia, dystonia, failure to thrive, seizures and respiratory failure. In this study, we performed a systematic sequence analysis of mitochondrial genes associated with LS in Tunisian patients. We sequenced the encoded complex I units: ND2, ND3, ND4, ND5 and ND6 genes and the mitochondrial ATPase 6, tRNA(Val), tRNA(Leu(UUR)), tRNA(Trp) and tRNA(Lys) genes in 10 unrelated patients with Leigh syndrome. We revealed the presence of 34 reported polymorphisms, nine novel nucleotide variants and two new mutations (T5523G and A5559G) in the tested patients. These two mutations were localized in two conserved regions of the tRNA(Trp) and affect, respectively, the D-stem and the T-stem of the mitochondrial tRNA leading to a disruption of the secondary structure of this tRNA. SSP-PCR analysis showed that the T5523G and A5559G mutations were present with respective heteroplasmic rates of 66% and 43 %. We report here the first mutational screening of mitochondrial mutations in Tunisian patients with Leigh syndrome which described two novel mutations associated with this disorder.

Merosin-deficient congenital muscular dystrophy with mental retardation and cerebellar cysts, unlinked to the LAMA2, FCMD, MEB and CMD1B loci, in three Tunisian patients

We report three Tunisian patients affected by congenital muscular dystrophy with mental retardation and cerebellar cysts on cranial magnetic resonance imaging. The clinical features were characterized by hypotonia at birth, joint contractures associated with severe psychomotor retardation, absence of speech, inability to walk in three patients, but calf hypertrophy was noted only in two patients. Brain magnetic resonance imaging showed several cerebellar cysts and vermis hypoplasia in all of the patients. Abnormality of the white matter was present in two patients. The pattern of gyration was normal in all cases. Serum creatine kinase was elevated in all three cases and their muscle biopsy showed dystrophic changes compatible with congenital muscular dystrophy. The immunohistochemical analysis of the skeletal muscle revealed partial merosin deficiency, more pronounced for the N-terminal antibody. Linkage analysis excluded congenital muscular dystrophy loci on chromosomes 6q22, 9q31, 1p32 and 1q42. These patients constituted a particular form of congenital muscular dystrophy with a combination of severe motor delay, mental retardation, partial merosin deficiency and cerebellar cysts. Two patients showed white matter abnormalities on magnetic resonance imaging and hypertrophy of the calves. These cases, in addition to those reported previously, confirmed the large phenotypic variability in the group of secondary merosin deficiency congenital muscular dystrophy.

LAMA2 mRNA processing alterations generate a complete deficiency of laminin-α2 protein and a severe congenital muscular dystrophy

An increasing number of genomic variations are no more regarded as harmless changes in protein coding sequences or as genetic polymorphisms. Studying the impact of these variations on mRNA metabolism became a central issue to better understand the biological significance of disease. We describe here a severe congenital muscular dystrophy (CMD) with lumbar scoliosis and respiratory complications in a patient, who died at the age of 10. Despite a poor linkage to any form of CMD, total deficiency of laminin-alpha2 rather suggested the occurrence of an MDC1A form. Extensive analysis of LAMA2 gene revealed two novel mutations: a (8007delT) frameshift deletion in exon 57, and a de novo 7nt deletion in intron 17. Using an ex vivo approach, we provided strong evidence that the intron mutation is responsible for complete exon 17 skipping. The mutations are in trans and they each generate a nonsense mRNA potentially elicited to degradation by NMD. We further discuss the impact of mRNA alterations on the subtle phenotypic discrepancies.

The effects of 8 weeks of motor skill training on cardiorespiratory fitness and endurance performance in children with developmental coordination disorder

Interventions based on everyday motor skills have been developed to be effective in children with developmental coordination disorder (DCD). The purpose of the present study was to examine the effects of motor skill training on exercise tolerance and cardiorespiratory fitness in children with DCD. Children were assigned to 3 groups: an experimental training group comprising 14 children with DCD, a control nontraining group comprising 13 children with DCD, and a control nontraining group comprising 14 typically developed children. All participants were tested twice with an interval of 8-weeks on a cardiopulmonary exercise test, pulmonary function testing, and a 6-min walk test. After the training program the maximal power output was significantly increased for DCD group at anaerobic threshold (p < 0.05) and at peak level (maximal oxygen uptake, p < 0.001). Improvement in power output was more pronounced at the anaerobic threshold (t (13) = -5.21, p < 0.001) than at the maximal intensity (maximal oxygen uptake, t (13) = -3.08, p < 0.01) in the DCD training group. Children with DCD that participated in the training program improved their walking distance (t (13) = -9.08, p < 0.001), had a higher maximum heart rate (t (13) = -3.41, p < 0.01), and reduced perceived exertion (t (13) = 2.75, p < 0.05). The DCD nontraining group and the typically developed group did not change on any of the measures. In conclusion, training delayed reaching the anaerobic threshold and improved aerobic endurance and exercise tolerance in children with DCD.

A de novo mutation in the adenosine triphosphatase (ATPase) 8 gene in a patient with mitochondrial disorder

Mitochondrial DNA defects were known to be associated with a wide spectrum of human diseases and patients might present a wide range of clinical features in various combinations. In the current study, we described a patient with psychomotor and neurodevelopmental delay, mild hyperintensity of posterior periventicular white matter, generalized clonic seizures, leukodystrophy, and congenital deafness. He also had tetraplegia, with central blindness and swallowing difficulty. Brain magnetic resonance imaging (MRI) showed involvement of the interpeduncular nucleus and central tegmental tract, white matter abnormalities, and cerebellar atrophy. A whole mitochondrial genome screening revealed the presence of 19 reported polymorphisms and an undescribed A to G mutation at nucleotide 8411 (p.M16V) affecting a conserved region of the mitochondrial adenosine triphosphatase (ATPase) 8 protein. This de novo mutation was detected in heteroplasmic form (97%) and was absent in 120 controls. Thus, the m.8411A>G mutation could strongly be associated with the disease in the tested patient.

A Novel MECP2 Gene Mutation in a Tunisian Patient with Rett Syndrome

Patients with classical Rett show an apparently normal psychomotor development during the first 6-18 months of life. Thereafter, they enter a short period of developmental stagnation followed by a rapid regression in language and motor development. Purposeful hand use is often lost and replaced by repetitive, stereotypic movements. Rett syndrome (RTT) is an X-linked dominant disorder caused frequently by mutations in the methyl-CpG-binding protein 2 gene (MECP2). The aim of this study was to search for mutations in MECP2 gene in two Tunisian patients affected with RTT. The results of mutation analysis revealed mutations in exon 4 of MECP2 gene in the two patients. In one patient we identified a new mutation consisting of a deletion of four bases (c.810-813delAAAG), which led to a frame shift and generated a premature stop codon (p.Lys271Arg fs X15) in transcriptional repression domain-nuclear localization signal (TRD-NLS) domain of MeCP2 protein. With regard to the second patient, a previously described transition (c.916C>T) that changed an arginine to a cysteine residue (p.R306C) in TRD domain of MeCP2 protein was revealed. In conclusion, a new and a known de novo mutation in MECP2 gene were revealed in two Tunisian patients affected with RTT.

The effect of a motor skills training program in the improvement of practiced and non-practiced tasks performance in children with developmental coordination disorder (DCD)

The purpose of the present study was to examine the effect of a group-based task oriented skills training program on motor and physical ability for children with DCD. It was also investigated if there was an effect on fine motor and handwriting tasks that were not specifically practiced during the training program. Forty-one children aged 6-10years took part in this study. Children were assigned to three groups: an experimental training group consisting of 14 children with DCD, a control non-training group consisted of 13 children with DCD and a control non-training group consisting of 14 typically developed children. The measurements included were, the Movement Assessment Battery for Children (MABC), the Modified Agility Test (MAT), the Triple Hop Distance (THD), the 5 Jump-test (5JT) and the Handwriting Performance Test. All measures were administered pre and post an 8-week training program. The results showed that 10 children of the DCD training-group improved their performance in MABC test, attaining a score above the 15th percentile after their participation in the training program. DCD training-group showed a significant improvement on all cluster scores (manual dexterity (t (13)=5.3, p<.001), ball skills (t (13)=2.73, p<.05) and balance (t (13)=5.13, p<.001). Significant performance improvements were also found in MAT, THD, 5JT (t (13)=-4.55; p<.01), handwriting quality (t (12)=-2.73; p<.05) and speed (t (12)=-4.2; p<.01) after the training program. In conclusion, improvement in both practiced and non-practiced skills, in the training program, may reflect improvement in motor skill but also transfer to other skills.

A Novel Mutation in FGD4/FRABIN Causes Charcot Marie Tooth Disease Type 4H in Patients from a Consanguineous Tunisian Family

Charcot‐Marie‐Tooth (CMT) disease constitutes a clinically and genetically heterogeneous group of hereditary neuropathies characterized by progressive muscular and sensory loss in the distal extremities with chronic distal weakness, deformation of the feet, and loss of deep tendon reflexes. CMT4H is an autosomal recessive demyelinating subtype of CMT, due to mutations in FGD4/FRABIN, for which nine mutations are described to date. In this study, we describe three patients from a consanguineous Tunisian family, presenting with severe, early onset, slowly progressive, autosomal recessive demyelinating CMT, complicated by mild to severe kyphoscoliosis, consistent with CMT4H. In these patients, we report the identification of a novel homozygous frameshift mutation in FGD4: c.514_515insG; p.Ala172Glyfs*27. Our study reports the first mutation identified in FGD4 in Tunisian patients affected with CMT. It further confirms the important clinical heterogeneity observed in patients with mutations in FGD4 and the lack of phenotype/genotype correlations in CMT4H. Our results suggest that FGD4 should be screened in other early‐onset CMT subtypes, regardless of the severity of the phenotype, and particularly in patients of consanguineous descent. In Tunisians, as in other populations with high consanguinity rates, screening of genes responsible for rare autosomal recessive CMT subtypes should be prioritized.

Founder effect confirmation of c.241A>G mutation in the L2HGDH gene and characterization of oxidative stress parameters in six Tunisian families with L-2-hydroxyglutaric aciduria

L-2-hydroxyglutaric aciduria (L2HGA) is an autosomal recessive neurometabolic disorder characterized essentially by the presence of elevated levels of L-2-hydroxyglutaric acid (LGA) in plasma, cerebrospinal fluid and urine. L2HGA is caused by a deficiency in the L2-Hydroxyglutaric dehydrogenase (L2HGDH) enzyme involved in the oxidation of LGA to the alpha 2-ketoglutarate. LGA has been proposed as an endo- and exogenous cytotoxic organic acid that induces free radical formation and generation of reactive oxygen species (ROS). In this report, we analyzed 14 L2HGA patients belonging to six unrelated consanguineous families the south of Tunisia. The patients were diagnosed with L2HGA disease confirmed on the presence of high level of LGA in urine. We analyzed the L2HGDH gene in all probands and identified the same c.241A>G homozygous mutation, which was previously reported in Tunisia. We also used intragenic single nucleotide length polymorphisms (SNPs) and two extragenic microsatellites flanking the L2HGDH gene to confirm the founder effect of c.241A>G mutation in the 14 studied cases. In addition, we carried out the measurement of the oxidative stress parameters in the plasma of L2HGA patients which revealed a significant increase in the malondialdehyde levels (MDA), a biomarker of lipid peroxydation, and the reduced glutathione (GSH). A diminution of the antioxidant enzyme activities including superoxide dismutase (SOD), glutathione peroxidase (GPx), was also observed.