Review of SRD5A3 Disease-Causing Sequence Variants and Ocular Findings in Steroid 5α-Reductase Type 3 Congenital Disorder of Glycosylation, and a Detailed New Case

Steroid 5α-reductase type 3 congenital disorder of glycosylation (SRD5A3-CDG) is a severe metabolic disease manifesting as muscle hypotonia, developmental delay, cerebellar ataxia and ocular symptoms; typically, nystagmus and optic disc pallor. Recently, early onset retinal dystrophy has been reported as an additional feature. In this study, we summarize ocular phenotypes and SRD5A3 variants reported to be associated with SRD5A3-CDG. We also describe in detail the ophthalmic findings in a 12-year-old Czech child harbouring a novel homozygous variant, c.436G>A, p.(Glu146Lys) in SRD5A3. The patient was reviewed for congenital nystagmus and bilateral optic neuropathy diagnosed at 13 months of age. Examination by spectral domain optical coherence tomography and fundus autofluorescence imaging showed clear signs of retinal dystrophy not recognized until our investigation. Best corrected visual acuity was decreased to 0.15 and 0.16 in the right and left eye, respectively, with a myopic refractive error of -3.0 dioptre sphere (DS) / -2.5 dioptre cylinder (DC) in the right and -3.0 DS / -3.0 DC in the left eye. The proband also had optic head nerve drusen, which have not been previously observed in this syndrome.

Muscular dystrophies and myopathies: the spectrum of mutated genes in the Czech Republic

Inherited neuromuscular disorder (NMD) is a wide term covering different genetic disorders affecting muscles, nerves, and neuromuscular junctions. Genetic and clinical heterogeneity is the main drawback in a routine gene-by-gene diagnostics. We present Czech NMD patients with a genetic cause identified using targeted next-generation sequencing (NGS) and the spectrum of these causes. Overall 167 unrelated patients presenting NMD falling into categories of muscular dystrophies, congenital muscular dystrophies, congenital myopathies, distal myopathies, and other myopathies were tested by targeted NGS of 42 known NMD-related genes. Pathogenic or probably pathogenic sequence changes were identified in 79 patients (47.3%). In total, 37 novel and 51 known disease-causing variants were detected in 23 genes. In addition, variants of uncertain significance were suspected in 7 cases (4.2%), and in 81 cases (48.5%) sequence changes associated with NMD were not found. Our results strongly indicate that for molecular diagnostics of heterogeneous disorders such as NMDs, targeted panel testing has a high-clinical yield and should therefore be the preferred first-tier approach. Further, we show that in the genetic diagnostic practice of NMDs, it is necessary to take into account different types of inheritance including the occurrence of an autosomal recessive disorder in two generations of one family.

Novel mutations in the TAZ gene in patients with Barth syndrome

Barth syndrome is an X-linked recessive disorder that is caused by mutations in Taffazin gene (TAZ), leading to severe cardiolipin deficiency which results in respiratory chain dysfunction. Barth syndrome is characterized by cardiomyopathy, neutropenia, skeletal myopathy, growth deficiency and 3-methylglutaconic aciduria. In this paper, we present clinical, biochemical and molecular data of the first four Czech patients from four unrelated families diagnosed with this rare disease. The mean age of onset was 5.5 ± 3.8 months. One child suffered from sudden cardiac death at the age of 2 years, the age of living patients is between 3 and 13 years. Muscle hypotonia was present in all four patients; cardiomyopathy and growth retardation in three and neutropenia in two of them. Two patients manifested a dilated and one patient a hypertrophic cardiomyopathy. A characteristic laboratory abnormality was the intermittently increased excretion of 3-methylglutaconic acid. Three novel hemizygous mutations in the TAZ gene were found (c.584G>T; c.109+6T>C; c.86G>A). We conclude that Barth syndrome should be included in differential diagnosis of cardiomyopathy in childhood, especially in the cooccurrence of dilated cardiomyopathy and 3-methylglutaconic aciduria.

Lipoprotein lipase deficiency: clinical, biochemical and molecular characteristics in three patients with novel mutations in the LPL gene

Lipoprotein lipase (LPL) deficiency, caused by mutations in the LPL gene, is a rare autosomal recessive disorder manifesting in early childhood with recurrent abdominal pain, hepatosplenomegaly, acute pancreatitis, lipaemia retinalis and eruptive xanthomas. Typical laboratory findings are lactescent serum, extreme hypertriglyceridaemia and hypercholesterolaemia. The diagnostics is based on postheparin serum LPL assay and DNA analyses of the LPL gene. We report clinical, biochemical and molecular data of three children with LPL deficiency. One child manifested since the first week of life with recurrent abdominal pain (Patient 1), the second with abdominal distension and hepatosplenomegaly since the second month of life (Patient 3) and patient 2, asymptomatic younger brother of patient 1, was diagnosed in the first week of life. Lipaemia retinalis and splenomegaly were present in two symptomatic children, hepatomegaly in patient 3 and acute pancreatitis in patient 1. All children had lactescent serum, profound hypertriglyceridaemia (124 ± 25 mmol/l; controls < 2.2), hypercholesterolaemia (22.8 ± 7.3 mmol/l, controls < 4.2) and their LPL immunoreactive mass in serum did not increase after heparin injection. Molecular analyses revealed that both siblings are homozygous for novel mutation c.476C > G in the LPL gene changing the conserved amino acid of the catalytic centre. The third patient is a compound heterozygote for mutations c.604G>A and c.698A>G in the LPL gene, both affecting highly conserved amino acids. We conclude that LPL deficiency must be considered in neonates and young infants with abdominal pain and hypertriglyceridaemia because early treatment might prevent development of life-threatening acute pancreatitis.

Non-invasive screening of cytochrome c oxidase deficiency in children using a dipstick immunocapture assay

Cytochrome c oxidase (CIV) deficiency is among the most common childhood mitochondrial disorders. The diagnosis of this deficiency is complex, and muscle biopsy is used as the gold standard of diagnosis. Our aim was to minimize the patient burden and to test the use of a dipstick immunocapture assay (DIA) to determine the amount of CIV in non-invasively obtained buccal epithelial cells. Buccal smears were obtained from five children with Leigh syndrome including three children exhibiting a previously confirmed CIV deficiency in muscle and fibroblasts and two children who were clinical suspects for CIV deficiency; the smear samples were analysed using CI and CIV human protein quantity dipstick assay kits. Samples from five children of similar age and five adults were used as controls. Analysis of the controls demonstrated that only samples of buccal cells that were frozen for a maximum of 4 h after collection provide accurate results. All three patients with confirmed CIV deficiency due to mutations in the SURF1 gene exhibited significantly lower amounts of CIV than the similarly aged controls; significantly lower amounts were also observed in two new patients, for whom later molecular analysis also confirmed pathologic mutations in the SURF1 gene. We conclude that DIA is a simple, fast and sensitive method for the determination of CIV in buccal cells and is suitable for the screening of CIV deficiency in non-invasively obtained material from children who are suspected of having mitochondrial disease.

Two patients with clinically distinct manifestation of pyruvate dehydrogenase deficiency due to mutations in PDHA1 gene

The most common cause of pyruvate dehydrogenase complex (PDHc) deficiency is the deficit of the E1α-subunit. The aim of this study was to describe distinct course of the disease in two boys with mutations in PDHA1 gene and illustrate the possible obstacles in measurement of PDHc activity. Clinical data and metabolic profiles were collected and evaluated. PDHc and E1α-subunit activities were measured using radiometric assay. Subunits of PDHc were detected by Western blot. PDHA1 gene was analysed by direct sequencing. In patient 1, the initial hypotonia with psychomotor retardation was observed since early infancy. The child gradually showed symptoms of spasticity and arrest of psychomotor development. In patient 2, the disease manifested by seizures and hyporeflexia in the toddler age. The diagnosis was confirmed at the age of seven years after attacks of dystonia and clinical manifestation of myopathy with normal mental development. Brain MRI of both patients revealed lesions typical of Leigh syndrome. Enzymatic analyses revealed PDHc deficiency in isolated lymphocytes in the first but not in the second patient. The direct measurement of PDH E1-subunit revealed deficiency in this individual. In patient 1, a novel hemizigous mutation c.857C>T (Pro250Leu) was detected in the X-linked PDHA1 gene. Mutation c.367C>T (Arg88Cys) was found in patient 2. We present first two patients with PDHc deficit due to mutations in PDHA1 gene in the Czech Republic. We document the broad variability of clinical symptoms of this disease. We proved that normal PDHc activity may not exclude the disease.

Prolonged impairment of polymorphonuclear cells functions in one infant with transient zinc deficiency: a case report

BACKGROUND

Zinc is an essential trace element for the immune system. The zinc deficiency diminishes antibody- and cell-mediated responses in man. Lymphopenia and thymic atrophy are usually the early hallmarks of zinc deficiency. Surprisingly, only scarce data are available about polymorphonuclear cells (PMNs) functions in infants with zinc deficiency. We present the results of immunological analyses in one infant with transient zinc deficiency due to decreased zinc concentration in mother milk resulting in severe lactogenic acrodermatitis enteropathica.

MATERIAL/METHODS

Nine repeated examination of oxidative burst of PMNs and immunoglobulin levels using nitroblue tetrazolium dye test, chemiluminescence, flow cytometry and nephelometry were performed in the infant with severe zinc deficiency during 28 months period.

RESULTS

The unusual prolonged but transient impairment of PMNs respiratory burst accompanied with hypogammaglobulinaemia developed since the age of 2.5 months. Dramatic improvement of the skin was observed within days with total resolution of skin lesions on the 9th day of zinc therapy, but decreased PMNs respiratory burst persisted until the age of 23 months.

CONCLUSIONS

We conclude that zinc deficiency may lead to prolonged impairment of polymorphonuclear cells functions and hypogammaglobulinaemia.

The developmental changes in mitochondrial DNA content per cell in human cord blood leukocytes during gestation

The mitochondrial DNA (mtDNA) amount in cells as the basis for mitochondrial energy generating system, which produces ATP, plays an important role in the fetal development and postnatal morbidity. Isolated human cord blood leukocytes (HCBL) contribute very little to the overall metabolic turnover, but they may serve as easily available marker cells for the study of the mtDNA amount changes in cord blood during fetal development. The aim of our study was to analyze the mtDNA amount in HCBL. HCBL were isolated from cord blood samples of 107 neonates born between the 25th and 41st week of gestation. The mtDNA amount was analyzed by the real-time PCR method. The significant negative correlations were found between the relative mtDNA amount in HCBL and gestational age (r = -0.54, p<0.01) and birth weight (r = -0.43, p<0.01), respectively. The results revealed that the mtDNA content per cell decreases in HCBL with progressing fetal development. This may be explained by gradual shift of the hematopoiesis from fetal liver to bone marrow during the second half of pregnancy presumably accompanied by decreasing cell volume of HCBL as it was shown similarly in red blood cells.

Specific Properties of Heavy Fraction of Mitochondria from Human-term Placenta – Glycerophosphate-dependent Hydrogen Peroxide Production

Mitochondrial respiratory chain enzyme Complexes are present in placenta at proportion similar to other tissues with exception of glycerophosphate dehydrogenase (mGPDH) which is expressed at a very high rate. As shown by Western blot quantification and respiratory chain enzyme activity measurements, the specific content of mGPDH is similar to that of succinate dehydrogenase or NADH dehydrogenase. Using fluorometric probe dichlorodihydrofluorescein diacetate we found that placental mitochondria display high rate of glycerophosphate-dependent hydrogen peroxide production. This was confirmed by oxygraphic detection of glycerophosphate-induced, KCN- or antimycin A-insensitive oxygen uptake. Hydrogen peroxide production by mGPDH was highly activated by one-electron acceptor, potassium ferricyanide and it was depressed by inhibitors of mGPDH and by cytochrome c. Our results indicate that mGPDH should be considered as an additional source of reactive oxygen species participating in induction of oxidative stress in placenta.

[Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE)]

BACKGROUND

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a disorder with autosomal recessive inheritance caused by mutations in the gene encoding thymidine phosphorylase (TP). TP deficiency results in imbalance of mitochondrial pool of nucleotides leading secondary to multiple deletions and depletion of mitochondrial DNA (mtDNA) and impairment of oxidative phosphorylation system. The disease is clinically characterized by gastrointestinal dysmotility with symptoms of pseudo-obstruction, severe failure to thrive, ptosis, leukoencephalopathy, peripheral neuropathy and myopathy. We present results of the clinical, histochemical, biochemical and molecular analyses of the first Czech patient with MNGIE syndrome.

METHODS AND RESULTS

Man, 33-years old with twenty-year history of failure to thrive (height 168 cm, weight 34 kg) and progressive gastrointestinal dysmotility, external ophthalmoplegia, leucoencephalopathy and peripheral neuropathy was recommended to metabolic center. Histochemical analyses in muscle biopsy showed the presence of "ragged red fibers" with focal decrease of cytochrome c oxidase activity, but spectrophotometric analyses in isolated muscle mitochondria revealed normal activities of all respiratory chain complexes. Metabolic investigation revealed markedly increased plasma level of thymidine (6.6 micromol/l, controls <0.05 micromol/l) and deoxyuridine (15 micromol/l, controls <0.05 micromol/l). The activity of TP in isolated lymphocytes was low (0.02 micromol/hour/mg protein, reference range 0.78 +/- 0.18). Molecular analyses in muscle biopsy revealed multiple mtDNA deletions and homozygous mutation 1419G>A (Gly145Arg) was found in gene for TP. Both parents are heterozygotes.

CONCLUSIONS

MNGIE has to be considered in patients presenting with a combination of gastrointestinal and neurological symptoms. Plasma level of thymidine may serve as the best method for laboratory screening of MNGIE, but molecular analyses are necessary for genetic counselling and prenatal diagnosis in affected families.

Carnitine concentrations in term and preterm newborns at birth and during the first days of life

Carnitine plays an important role in energetic metabolism. The aim of the study was to characterize the carnitine status in term and preterm newborns with respect to gestational age, birth weight, haematocrit and red blood cell count (RBC). The effect of nutrition on carnitine levels in the first week of life was also studied. Total blood pool of free carnitine (FC), acylcarnitines (AC) and total carnitine (TC) were analysed in whole cord blood and postnatally in capillary blood obtained at the day 4-6 in 33 term newborns and at the day 7-10 in 27 preterm newborns using tandem mass spectrometry. Plasma level of carnitine in the cord blood was measured using radioenzymatic method. Cord plasma levels of FC, AC and TC were higher in preterm newborns in comparison with term newborns (p < 0.01), but the total blood pool of FC and TC in whole cord blood was lower in preterm newborns than in term newborns (p < 0.01) and positive correlation was found between FC and gestational age or birth weight (p < 0.05). In addition, positive correlation was found between AC and red blood cell count or haematocrit (p < 0.05). During the first week of life, blood pool of FC and TC in term newborns and AC and TC in preterm newborns decreased regardless of the type of enteral or parenteral nutrition. Our results indicate that preterm newborns are born with limited carnitine store. Interpretation of carnitine analyses in whole blood relies in addition to gestational age and birth weight on the haematocrit, especially in newborns with anaemia or blood hyperviscosity.

[Congenital disorder of type Ia protein glycosylation: clinical, biochemical and molecular characteristics in 2 siblings with cerebellar hypoplasia]

BACKGROUND

Congenital disorders of glycosylation (CDG syndrome) represent a newly delineated group of inherited diseases of glycoprotein synthesis. We present results of biochemical and molecular analyses in two Czech patients with CDG Ia syndrome.

METHODS AND RESULTS

Serum concentrations of the nonglycosylated and hypoglycosylated transferrin were measured using turbidimetric immunoassay. In positive patients, the isoelectric focusing of serum transferrin and molecular analyses of the gene for phosphomannomutase 2 were performed. The disease manifested in both children in infancy with failure to thrive, inverted nipples, strabismus, epilepsy, muscle hypotonia, microcephaly, psychomotor retardation and hypoplasia of the cerebellum. The biochemical investigation revealed elevated liver enzymes, low concentration of factor XI and protein S. In one child lower concentration of the antithrombin III and protein C were found. Activities of arylsulfatase A and beta-glucuronidase in serum were higher and activity of alpha-mannosidase in leucocytes was lower in comparison with controls. Molecular analyses revealed that both children are compound heterozygotes for the mutation 422G > A and 357C > A in gene for phosphomanomutase 2. Both siblings are also homozygotes for polymorfism IVS5 + 19 C-->T and heterozygygotes for polymorfism IVS5 + 22 T-->A.

CONCLUSIONS

The prognosis of children with CDG Ia is unfavourable. Enzymatic and/or molecular studies are necessary for genetic counselling and the prenatal diagnosis.

Polarographic evaluation of mitochondrial enzymes activity in isolated mitochondria and in permeabilized human muscle cells with inherited mitochondrial defects

Inherited disturbances of the mitochondrial energy generating system represent a heterogeneous group of disorders associated with a broad spectrum of metabolic abnormalities and clinical symptoms. We used the polarographic and spectrophotometric method for detection of mitochondrial disorders, because these two techniques provide a different insight into mitochondrial function. In six patients suspected of mitochondrial disease we found defects of complex I (two patients), complex III (one patient), complex IV (two patients) and a combination of defect of complex III and IV (one patient). Citrate synthase activity, used as the reference enzyme, was not changed. A comparison of the two methods showed several differences in evaluation of mitochondrial enzymes activity due to the fact that both methods used different conditions for enzyme activity measurements. In contrast to oxygen consumption measurements, where the function of the whole-integrated respiratory chain is characterized, spectrophotometric measurements characterize activities of isolated complexes in disintegrated membranes. However, it may be concluded from our experiments that both methods provide useful and complementary data about mitochondrial energetic functions. Whereas spectrophotometric data are suitable for evaluation of maximal enzyme activities of mitochondrial enzyme complexes, polarographic data provide better information about enzyme activities in cells with mitochondrial defects under in situ conditions.