CUX1-related neurodevelopmental disorder: deep insights into phenotype-genotype spectrum and underlying pathology

Heterozygous, pathogenic CUX1 variants are associated with global developmental delay or intellectual disability. This study delineates the clinical presentation in an extended cohort and investigates the molecular mechanism underlying the disorder in a Cux1+/- mouse model. Through international collaboration, we assembled the phenotypic and molecular information for 34 individuals (23 unpublished individuals). We analyze brain CUX1 expression and susceptibility to epilepsy in Cux1+/- mice. We describe 34 individuals, from which 30 were unrelated, with 26 different null and four missense variants. The leading symptoms were mild to moderate delayed speech and motor development and borderline to moderate intellectual disability. Additional symptoms were muscular hypotonia, seizures, joint laxity, and abnormalities of the forehead. In Cux1+/- mice, we found delayed growth, histologically normal brains, and increased susceptibility to seizures. In Cux1+/- brains, the expression of Cux1 transcripts was half of WT animals. Expression of CUX1 proteins was reduced, although in early postnatal animals significantly more than in adults. In summary, disease-causing CUX1 variants result in a non-syndromic phenotype of developmental delay and intellectual disability. In some individuals, this phenotype ameliorates with age, resulting in a clinical catch-up and normal IQ in adulthood. The post-transcriptional balance of CUX1 expression in the heterozygous brain at late developmental stages appears important for this favorable clinical course.

Cleft Palate as Distinguishing Feature in a Patient with GABRB3 Epileptic Encephalopathy

Mutations in GABA_A-receptor subunit genes are associated with a heterogeneous spectrum of epilepsies. Patients with epilepsy caused by mutations in a specific GABA_A-receptor (GABRA3) occasionally present with orofacial dysmorphism (e.g., cleft palates). While cleft palates have been described in Gabrb3 knockout mice and in humans with GABRB3 variants without epilepsy, the specific combination of epilepsy and cleft palate in humans with GABRB3 mutations has not yet been reported.We describe a patient with epileptic encephalopathy (EE) who presented with therapy-refractory neonatal-onset myoclonic seizures and severe developmental delay. Electroencephalogram showed burst suppression pattern at neonatal age and hypsarrhythmia at infantile age. Initial magnetic resonance imaging was unremarkable. As he additionally presented with a cleft palate, we were curious whether cleft palate and EE had the same genetic origin. Whole exome sequencing of the index patient revealed a novel pathogenic heterozygous de novo mutation in GABRB3 (c.899T > C; p.I300T). In consistency with Gabrb3 knockout mice data, this is the first report of cleft palate in a patient with GABRB3 associated EE.We suggest to add cleft palate to the phenotypic GABRB3 spectrum and to screen for mutations in GABA_A-receptors in patients with EE and orofacial dysmorphism.

Sandwich enzyme immunoassay of cystatin C in serum with commercially available antibodies

We developed a sandwich enzyme immunoassay for determining cystatin C in serum by using commercially available antibodies. We optimized each assay step (e.g., concentrations of coating rabbit anti-human cystatin C antibodies and horseradish peroxidase-conjugated antibodies) and studied the binding kinetics of antigen and antibodies. The within-assay CV was < 5%, the between-assay CV was 8.8%, the detection limit was 0.9 microgram/L, and the assay can be performed within 2 h. Cystatin C concentrations in sera from men were significantly higher than in women (mean and SD: 2.14 +/- 0.31 vs 1.78 +/- 0.26 mg/L). We studied the cystatin C concentrations in sera of 31 outpatients with suspected kidney damages to characterize the behavior of this low-M(r) protein as a possible indicator for estimating the glomerular filtration rate. The correlation with the values obtained by a standard isotopic method involving 99mTc-diethylenetriaminopentaacetic acid was rs = -0.89. The diagnostic sensitivity of cystatin C was 88.2% of that of the standard isotope clearance method and better than those of the conventional serum indicators of reduced kidney function, beta 2-microglobulin (64.7%) and creatinine (52.9%).

The genomic and clinical landscape of fetal akinesia

PURPOSE

Fetal akinesia has multiple clinical subtypes with over 160 gene associations, but the genetic etiology is not yet completely understood.

METHODS

In this study, 51 patients from 47 unrelated families were analyzed using next-generation sequencing (NGS) techniques aiming to decipher the genomic landscape of fetal akinesia (FA).

RESULTS

We have identified likely pathogenic gene variants in 37 cases and report 41 novel variants. Additionally, we report putative pathogenic variants in eight cases including nine novel variants. Our work identified 14 novel disease-gene associations for fetal akinesia: ADSSL1, ASAH1, ASPM, ATP2B3, EARS2, FBLN1, PRG4, PRICKLE1, ROR2, SETBP1, SCN5A, SCN8A, and ZEB2. Furthermore, a sibling pair harbored a homozygous copy-number variant in TNNT1, an ultrarare congenital myopathy gene that has been linked to arthrogryposis via Gene Ontology analysis.

CONCLUSION

Our analysis indicates that genetic defects leading to primary skeletal muscle diseases might have been underdiagnosed, especially pathogenic variants in RYR1. We discuss three novel putative fetal akinesia genes: GCN1, IQSEC3 and RYR3. Of those, IQSEC3, and RYR3 had been proposed as neuromuscular disease-associated genes recently, and our findings endorse them as FA candidate genes. By combining NGS with deep clinical phenotyping, we achieved a 73% success rate of solved cases.

Genotype-Phenotype Correlations in Charcot-Marie-Tooth Disease Due to MTMR2 Mutations and Implications in Membrane Trafficking

Charcot-Marie-Tooth type 4 (CMT4) is an autosomal recessive severe form of neuropathy with genetic heterogeneity. CMT4B1 is caused by mutations in the myotubularin-related 2 (MTMR2) gene and as a member of the myotubularin family, the MTMR2 protein is crucial for the modulation of membrane trafficking. To enable future clinical trials, we performed a detailed review of the published cases with MTMR2 mutations and describe four novel cases identified through whole-exome sequencing (WES). The four unrelated families harbor novel homozygous mutations in MTMR2 (NM_016156, Family 1: c.1490dupC; p.Phe498IlefsTer2; Family 2: c.1479+1G>A; Family 3: c.1090C>T; p.Arg364Ter; Family 4: c.883C>T; p.Arg295Ter) and present with CMT4B1-related severe early-onset motor and sensory neuropathy, generalized muscle atrophy, facial and bulbar weakness, and pes cavus deformity. The clinical description of the new mutations reported here overlap with previously reported CMT4B1 phenotypes caused by mutations in the phosphatase domain of MTMR2, suggesting that nonsense MTMR2 mutations, which are predicted to result in loss or disruption of the phosphatase domain, are associated with a severe phenotype and loss of independent ambulation by the early twenties. Whereas the few reported missense mutations and also those truncating mutations occurring at the C-terminus after the phosphatase domain cause a rather mild phenotype and patients were still ambulatory above the age 30 years. Charcot-Marie-Tooth neuropathy and Centronuclear Myopathy causing mutations have been shown to occur in proteins involved in membrane remodeling and trafficking pathway mediated by phosphoinositides. Earlier studies have showing the rescue of MTM1 myopathy by MTMR2 overexpression, emphasize the importance of maintaining the phosphoinositides equilibrium and highlight a potential compensatory mechanism amongst members of this pathway. This proved that the regulation of expression of these proteins involved in the membrane remodeling pathway may compensate each other's loss- or gain-of-function mutations by restoring the phosphoinositides equilibrium. This provides a potential therapeutic strategy for neuromuscular diseases resulting from mutations in the membrane remodeling pathway.

A novel mutation in sphingosine-1-phosphate lyase causing congenital brain malformation

INTRODUCTION

Recently recessive mutations in sphingosine-1-phosphate lyase (SGPL1) have been published as a cause of syndromic congenital nephrotic syndrome with adrenal insufficiency. We have identified a case with fetal hydrops and brain malformations due to a mutation in SGPL1.

CASE REPORT

We report a patient presenting with severe fetal hydrops, congenital nephrotic syndrome and adrenal calcifications. MRI imaging showed generalized cortical atrophy with simplified gyral pattern and hypoplastic temporal lobes as well as cerebellar hypoplasia and hyperintensity in the pons. The boy deceased at 6 weeks of age. Via whole exome sequencing, we identified a novel homozygous frameshift mutation c.1233delC (p.Phe411Leufs^∗56) in SGPL1.

CONCLUSION

In our patient, we describe a novel mutation in sphingosine-1-phosphate lyase (SGPL1) leading to severe brain malformation. Neurodevelopmental phenotypes have been reported earlier, but not described in detail. To this end, we present a review on all published SGPL1-mutations and genotype-phenotype correlations focusing on neurodevelopmental outcomes. We hypothesized on the severe neurological phenotypes, which might be due to disruption of neuronal autophagy. Mutations in SGPL1 shall be considered in the differential diagnosis of fetal hydrops as well as congenital brain malformations and neuropathies.

Molecular autopsy in maternal-fetal medicine

PurposeThe application of genomic sequencing to investigate unexplained death during early human development, a form of lethality likely enriched for severe Mendelian disorders, has been limited.MethodsIn this study, we employed exome sequencing as a molecular autopsy tool in a cohort of 44 families with at least one death or lethal fetal malformation at any stage of in utero development. Where no DNA was available from the fetus, we performed molecular autopsy by proxy, i.e., through parental testing.ResultsPathogenic or likely pathogenic variants were identified in 22 families (50%), and variants of unknown significance were identified in further 15 families (34%). These variants were in genes known to cause embryonic or perinatal lethality (ALPL, GUSB, SLC17A5, MRPS16, THSD1, PIEZO1, and CTSA), genes known to cause Mendelian phenotypes that do not typically include embryonic lethality (INVS, FKTN, MYBPC3, COL11A2, KRIT1, ASCC1, NEB, LZTR1, TTC21B, AGT, KLHL41, GFPT1, and WDR81) and genes with no established links to human disease that we propose as novel candidates supported by embryonic lethality of their orthologs or other lines of evidence (MS4A7, SERPINA11, FCRL4, MYBPHL, PRPF19, VPS13D, KIAA1109, MOCS3, SVOPL, FEN1, HSPB11, KIF19, and EXOC3L2).ConclusionOur results suggest that molecular autopsy in pregnancy losses is a practical and high-yield alternative to traditional autopsy, and an opportunity for bringing precision medicine to the clinical practice of perinatology.

Dropped head congenital muscular dystrophy caused by de novo mutations in LMNA

BACKGROUND

Dropped head syndrome is an easily recognizable clinical presentation of Lamin A/C-related congenital muscular dystrophy. Patients usually present in the first year of life with profound neck muscle weakness, dropped head, and elevated serum creatine kinase.

CASE DESCRIPTION

Two patients exhibited head drop during infancy although they were able to sit independently. Later they developed progressive axial and limb-girdle weakness. Creatine kinase levels were elevated and muscle biopsies of both patients showed severe dystrophic changes. The distinctive clinical hallmark of the dropped head led us to the diagnosis of Lamin A/C-related congenital muscular dystrophy, with a pathogenic de novo mutation p.Glu31del in the head domain of the Lamin A/C gene in both patients. Remarkably, one patient also had a central involvement with white matter changes on brain magnetic resonance imaging.

CONCLUSION

Lamin A/C-related dropped-head syndrome is a rapidly progressive congenital muscular dystrophy and may lead to loss of ambulation, respiratory insufficiency, and cardiac complications. Thus, the genetic diagnosis of dropped-head syndrome as L-CMD and the implicated clinical care protocols are of vital importance for these patients. This disease may be underdiagnosed, as only a few genetically confirmed cases have been reported.

Recessive PIEZO2 stop mutation causes distal arthrogryposis with distal muscle weakness, scoliosis and proprioception defects

The genetic work-up of arthrogryposis is challenging due to the diverse clinical and molecular etiologies. We report a-18^3/12-year-old boy, from a 2nd degree consanguineous family, who presented at 3^6/12 years with hypotonia, distal laxity, contractures, feeding difficulties at birth. He required surgery for progressive scoliosis at 16 years of age, and walked independently since then with an unstable gait and coordination defects. His latest examination at 18 years of age revealed a proprioceptive defect and loss-of-joint position sense in the upper limbs. Somatosensory evoked potentials supported bilateral involvement of dorsal column-medial lemniscal sensory pathways and nerve conduction studies revealed a mild axonal neuropathy. Muscle biopsy showed myopathic changes with neonatal myosin expression. Mendeliome sequencing led to the discovery of a recessive stop mutation in piezo-type mechanosensitive ion channel component 2 (PIEZO2, NM_022068, c.1384C>T, p.R462*). PIEZO2 is a nonselective cation channel, expressed in sensory endings of proprioceptors innervating muscle spindles and Golgi tendon organs. Dominant PIEZO2 mutations were described in patients with distal arthrogryposis type 5 and Marden-Walker syndrome. Sensory ataxia and proprioception defect with dorsal column involvement together with arthrogryposis, myopathy, scoliosis and progressive respiratory failure may represent a distinct clinical phenotype, and indicate recessive mutations in PIEZO2.

The ancient cell death suppressor BAX inhibitor-1

Bax inhibitor-1 (BI-1) was initially identified for its ability to inhibit BAX-induced apoptosis in yeast cells and is the founding member of a family of highly hydrophobic proteins localized in diverse cellular membranes. It is evolutionarily conserved and orthologues from plants can substitute for mammalian BI-1 in regard to its anti-apoptotic function suggesting a high degree of functional conservation. BI-1 interacts with BCL-2 and BCL-XL and, similar to these two anti-apoptotic proteins, the effect of BI-1 on cell death involves changes in the amount of Ca(2+) releasable from intracellular stores. However, BI-1 is also a negative regulator of the endoplasmic reticulum stress sensor IRE1 α, it interacts with G-actin and increases actin polymerization, enhances cancer metastasis by altering glucose metabolism and activating the sodium-hydrogen exchanger, and reduces the production of reactive oxygen species through direct interaction with NADPH-P450 reductase. In this contribution, we summarize what is known about the expression, intracellular localization and structure of BI-1 and specifically illuminate its effects on the intracellular Ca(2+) homeostasis and how this might relate to its other functions. We also present a thorough phylogenetic analysis of BI-1 proteins from major phyla together with paralogues from all BI-1 family members.

Early urinary markers of target nephron segments as studied in cadmium toxicity

A number of chemicals may adversely affect one or more of the anatomical structures of the kidney, such as the glomerulus, the tubular apparatus, the medullary, or interstitial cells. To recognize subclinical renal dysfunction, a battery of new, non-invasive tests was applied in comparison to established ones. The study on cadmium exposed subjects, performed within the framework of a collaborative European research project, exemplifies the concept of target selectivity within a nephron. One hundred seventy-two subjects were classified according to urinary cadmium excretion as controls (< 1.5 micrograms/g creatinine), or subjects with moderate or high cadmium body burden (1.5 to 5 micrograms/g creatinine, > 5 micrograms/g creatinine). Twenty-six urinary analytes (such as serum derived proteins, tubular enzymes, eicosanoids) and four plasma markers, related to the function or integrity of specific nephron segments, were investigated in a cross-sectional study. The group with the moderate cadmium body burden showed alterations of proximal tubular integrity, that is, increased excretion of tubular brush-border antigens. The group with higher cadmium body burden revealed an involvement of the whole nephron. The most prominent quantitative changes were found for the glomerular markers high molecular weight proteins, and thromboxane B2 and for the proximal tubular markers retinol binding protein, alpha 1-microglobulin, N-acetyl-beta-D-glucosaminidase, and the intestinal alkaline phosphatase. A diagnostic approach to screen for nephrotoxicity due to environmental hazards like cadmium should include proximal tubular markers (alpha 1-microglobulin and tubular enzymes, that is, intestinal alkaline phosphatase) but the measurement of glomerular markers is also advisable.

Changed excretion of urinary proteins and enzymes by chronic exposure to lead

Fifteen various serum and urine parameters were evaluated as indicators of renal alterations induced by lead in 82 male workers of a battery plant chronically exposed to lead (median of blood lead concentration: 2.03 mumol/l). The control group comprised 44 non-exposed healthy volunteers (0.34 mumol/l). High-molecular-mass proteins (transferrin, immunoglobulin G (IgG), (albumin)) were determined in urine as markers of glomerular integrity; low-molecular-weight proteins and parenchymal enzymes (alpha 1-microglobulin, beta 2-microglobulin, retinol-binding protein, lysozyme, ribonuclease, N-acetyl-beta-D-glucosaminidase (NAG), alanine aminopeptidase (AAP), alkaline phosphatase (AP), gamma-glutamyltransferase (GGT)) as indicators of changes in the proximal tubule; Tamm-Horsfall glycoprotein and kallikrein as markers of the distal tubule. There was a positive correlation between tubular indicators and blood lead concentration as well as the erythrocyte protoporphyrin (EPP). About 30% of the lead-exposed workers showed an increased excretion of alpha 1-microglobulin, NAG, ribonuclease, and/or Tamm-Horsfall protein, whereas the glomerular indicators remained unchanged. The combined determination of NAG and alpha 1-microglobulin in urine could be helpful in the early detection of lead-induced changes in the nephron.

Rapid screening of low molecular mass proteinuria: evaluation of the first immunochemical test strip for the detection of alpha 1-microglobulin in urine

A new semiquantitative immunochemical test strip for urinary alpha 1-microglobulin, a marker protein for tubular proteinuria, was assessed. This test strip has four colour zones, reflecting alpha 1-microglobulin concentrations of ca. 10, 25, 50, and 80 mg/l. alpha 1-Microglobulin concentrations were measured by means of the test strip and an immunonephelometric method in 330 samples collected as the second voided morning urine. The reading time of the test strip must be strictly observed. Reading one minute earlier or later than the 5 min stated in the instructions led to misclassification of over 70% of the results. Correlation between both methods was highly significant, with a Spearman rank correlation coefficient of rs = 0.84 (P < 0.001). There was a partial overlap of the test strip results in different concentration ranges. An elevation of alpha 1-microglobulin was defined as > 25 mg/l, calculated as the upper limit of the central 95% interval of alpha 1-microglobulin concentration in urine samples measured in a previous study of 304 healthy adults. Using this definition of alpha 1-microglobulin elevation, a sensitivity of 97.5%, specificity of 73.6%, a false-positive rate of 16.6%, and a false-negative rate of 0.9% of the test strip results were obtained. A fraction of 82.4% of the 330 samples investigated was correctly classified as having increased alpha 1-microglobulin concentration or not. Methodical improvements of the test strip are necessary to reduce overlapping results, in order to make the test suitable for screening purposes.

Sandwich enzyme immunoassay of cystatin C in serum with commercially available antibodies

We developed a sandwich enzyme immunoassay for determining cystatin C in serum by using commercially available antibodies. We optimized each assay step (e.g., concentrations of coating rabbit anti-human cystatin C antibodies and horseradish peroxidase-conjugated antibodies) and studied the binding kinetics of antigen and antibodies. The within-assay CV was < 5%, the between-assay CV was 8.8%, the detection limit was 0.9 microgram/L, and the assay can be performed within 2 h. Cystatin C concentrations in sera from men were significantly higher than in women (mean and SD: 2.14 +/- 0.31 vs 1.78 +/- 0.26 mg/L). We studied the cystatin C concentrations in sera of 31 outpatients with suspected kidney damages to characterize the behavior of this low-M(r) protein as a possible indicator for estimating the glomerular filtration rate. The correlation with the values obtained by a standard isotopic method involving 99mTc-diethylenetriaminopentaacetic acid was rs = -0.89. The diagnostic sensitivity of cystatin C was 88.2% of that of the standard isotope clearance method and better than those of the conventional serum indicators of reduced kidney function, beta 2-microglobulin (64.7%) and creatinine (52.9%).

Urinary proteins and enzymes as early indicators of renal dysfunction in chronic exposure to cadmium

We tested the diagnostic sensitivity of various urinary analytes for detecting cadmium-induced nephropathy at an early stage. We investigated 73 healthy persons (control group 1) and individuals exposed to cadmium, either environmentally (n = 36, risk group 2) or occupationally (n = 62, exposed group 3). All data were related to limits of the central 95% reference intervals of the control group. The serum creatinine and ribonuclease values, indicators of the glomerular filtration rate, were not different in the three groups. In the exposed persons (group 3), proximal tubular indicators (low-M(r) proteins lysozyme, ribonuclease, retinol-binding protein, and alpha 1-microglobulin) were more often increased than the glomerular indices (higher-M(r) proteins transferrin, IgG, and albumin). Both the low-M(r) proteins and tubular enzymes were differently altered in their excretion rates. Alanine aminopeptidase, alkaline phosphatase, and N-acetyl-beta-D-glucosaminidase increased even in the risk group 2. alpha 1-Microglobulin was increased in the exposed persons whose cadmium excretion was &lt; 5 mumol/mol creatinine. The combined determination of alpha 1-microglobulin and N-acetyl-beta-D-glucosaminidase exceeded the corresponding upper reference limits in 30% of group 2 and 39% of group 3. We recommend screening for these two analytes to detect cadmium-induced renal dysfunction at an early stage.

Urinary proteins and enzymes as early indicators of renal dysfunction in chronic exposure to cadmium

We tested the diagnostic sensitivity of various urinary analytes for detecting cadmium-induced nephropathy at an early stage. We investigated 73 healthy persons (control group 1) and individuals exposed to cadmium, either environmentally (n = 36, risk group 2) or occupationally (n = 62, exposed group 3). All data were related to limits of the central 95% reference intervals of the control group. The serum creatinine and ribonuclease values, indicators of the glomerular filtration rate, were not different in the three groups. In the exposed persons (group 3), proximal tubular indicators (low-M(r) proteins lysozyme, ribonuclease, retinol-binding protein, and alpha 1-microglobulin) were more often increased than the glomerular indices (higher-M(r) proteins transferrin, IgG, and albumin). Both the low-M(r) proteins and tubular enzymes were differently altered in their excretion rates. Alanine aminopeptidase, alkaline phosphatase, and N-acetyl-beta-D-glucosaminidase increased even in the risk group 2. alpha 1-Microglobulin was increased in the exposed persons whose cadmium excretion was < 5 mumol/mol creatinine. The combined determination of alpha 1-microglobulin and N-acetyl-beta-D-glucosaminidase exceeded the corresponding upper reference limits in 30% of group 2 and 39% of group 3. We recommend screening for these two analytes to detect cadmium-induced renal dysfunction at an early stage.

Development of an immunoenzymometric assay for alpha 1-microglobulin and measurement of its serum concentration in normal and HIV-infected persons

alpha 1-Microglobulin was purified from urine to a purity of 97.7% in a yield of 25.8%, and was used to produce antibodies in sheep. These antibodies, purified by affinity chromatography, were used to develop a rapid one-step and a two-step immunoenzymometric assay (IEMA). The equilibrium in the reaction between solid phase-adsorbed antibodies and antigen and between the antigen and enzyme-labelled antibodies was attained within 30 and 100 min, respectively. The one-step IEMA permits a good differentiation of low alpha 1-microglobulin concentrations after 30 min reaction time. Its detection limit is 0.35 micrograms/l, and its measurement range is between 0.5 and 100 micrograms/l. The IEMA correlates well with radial immunodiffusion (r = 0.973). The mean alpha 1-microglobulin serum concentration in women is insignificantly lower (33.2 mg/l) than in men (36.1 mg/l). In both sexes the alpha 1-microglobulin concentration increases with age. HIV-infected symptomless men have a significantly lower (15.9 mg/l) alpha 1-microglobulin concentration in serum than normal persons, whereas in AIDS patients it is significantly higher (45.5 mg/l).

A microalbuminuria assay using bromphenol blue

A simple microalbuminuria assay using bromphenol blue/glycine reagent is described. Urine samples were prepared using gel filtration on Sephadex G-50 minicolumns and absorbance was measured at 610 nm 20 s after mixing 10 parts of eluate and 1 part of reagent. The detection limit of this method was 3 mg/l; within-run and between-run precision was between 0.5 and 4.1% for borderline and raised albumin concentrations. The recovery of albumin added to samples was 98.7 +/- 2.5%. Results obtained by this method correlated closely with values obtained by radial immunodiffusion (r = 0.987). The test is cheap (reagent costs about 5 cents) and suitable for the non-specialist laboratory.

Production and characterization of monoclonal antibodies against human Cu/Zn superoxide dismutase and the establishment of a super-rapid enzyme-linked immunosorbent assay (SURALISA)

Murine monoclonal IgG1 antibodies directed against four different epitopes of human Cu/Zn superoxide dismutase (SOD) were produced by immunization with recombinant Cu/Zn SOD. The antibodies reacted well with the recombinant protein and Cu/Zn SOD purified from human erythrocytes, with binding constants ranging from 8.8 X 10(9) to 2.2 X 10(10) l/mol. When mixed, these antibodies completely prevented the binding of rabbit and sheep polyclonal antibodies raised against erythrocyte Cu/Zn SOD. Whereas one antibody was directed against a common homology region of bovine and human Cu/Zn SOD, all the other antibodies reacted exclusively or preferentially with human Cu/Zn SOD. Only one epitope on the human Cu/Zn SOD molecule was accessible at two different sites as demonstrated in a homologous two-site assay with one and the same antibody used as both capture and indicator antibody. In the indirect two-site assay with unlabelled monoclonal antibodies, and additive effect with a steeper dose-response curve was obtained by mixing antibodies against different epitopes. A super-rapid one-step two-site enzyme immunoassay (overall duration 20 min) was established with antibodies against two different epitopes. Its detection limit was 0.5 micrograms SOD/l.

Measurement of lysozyme in human body fluids: comparison of various enzyme immunoassay techniques and their diagnostic application

Three variants of the immunoenzymometric assay of human lysozyme with HRP-labeled antibodies were compared. The highest sensitivity (with a detection limit of 0.2 micrograms lysozyme/L) was achieved by a one-step assay lasting 2 h. Between-batch precision for the techniques was 6-11%. Lysozyme reference values were determined in serum, cerebrospinal fluid and urine. In serum they are age-dependent and in urine sex-dependent when related to creatinine excretion. Serum lysozyme is increased in only 57% of the patients with active rheumatoid arthritis and is also unreliable for indicating remission. In Crohn's disease the serum lysozyme reflects activity better, but it does not exceed the diagnostic value of alpha-1-acidic glycoprotein (orosomucoid). The lysozyme quantification in cerebrospinal fluid is useful in distinguishing between viral or bacterial meningitis.

Sialidase from different sources compared for electrophoretically separating serum alkaline phosphatase fractions from liver and bone

We compared sialidase (neuraminidase; EC 3.2.1.18) from Vibrio cholerae, Clostridium perfringens, and Arthrobacter ureafaciens, seeking to improve the electrophoretic separation of the liver and bone isoenzymes of alkaline phosphatase (EC 3.1.3.1) on cellulose acetate membranes. Resolution is decisively determined by the type and activity of sialidase used in the preincubation of serum sample. Sialidase from Arthrobacter ureafaciens is not suited for this method. For optimal separation of the two isoenzymes we recommend the use of sialidase from Vibrio cholerae, determination of its activity with a standard procedure such as described here (mucin or sialyl lactose as substrates), and a final concentration of sialidase activity of 2.0 or 2.9 U/L (measured with mucin or sialyl lactose) in the incubation mixture.

Sialidase from different sources compared for electrophoretically separating serum alkaline phosphatase fractions from liver and bone

We compared sialidase (neuraminidase; EC 3.2.1.18) from Vibrio cholerae, Clostridium perfringens, and Arthrobacter ureafaciens, seeking to improve the electrophoretic separation of the liver and bone isoenzymes of alkaline phosphatase (EC 3.1.3.1) on cellulose acetate membranes. Resolution is decisively determined by the type and activity of sialidase used in the preincubation of serum sample. Sialidase from Arthrobacter ureafaciens is not suited for this method. For optimal separation of the two isoenzymes we recommend the use of sialidase from Vibrio cholerae, determination of its activity with a standard procedure such as described here (mucin or sialyl lactose as substrates), and a final concentration of sialidase activity of 2.0 or 2.9 U/L (measured with mucin or sialyl lactose) in the incubation mixture.

Further evidence for tubular dysfunction in insulin dependent diabetes

There is evidence that increased excretion of urinary enzymes and low-molecular mass proteins indicate impaired tubular function. The excretion of N-acetyl-beta-D-glucosaminidase (NAG), lysozyme, and ribonuclease in Type I diabetic patients with (n = 19) and without (n = 17) persistent proteinuria (urinary protein excretion greater than 0.5 g/day) was investigated and compared with this excretion in 30 weight- and gender-matched nondiabetic subjects without renal disease. Urinary NAG excretion was significantly higher in diabetic patients with and without persistent proteinuria (1.16 +/- 0.09 and 3.19 +/- 1.2 Umol/L creatinine, respectively) compared to controls (0.37 +/- 0.03 Umol/L creatinine p less than 0.01). In addition, the urinary excretion of lysozyme and ribonuclease was significantly increased in diabetic patients. Urinary NAG was found to correlate positively with albuminuria and proteinuria (r = 0.95 and 0.93, respectively), as well as with ribonuclease and lysozyme (r = 0.93 and 0.60; p less than 0.01) in patients with persistent proteinuria. Furthermore, NAG excretion was significantly related to the duration of diabetes (r = 0.36; p less than 0.05). No relationship existed between urinary NAG and serum creatinine, beta-2-microglobulin, and degree of metabolic control (HbA7). The lysozyme excretion, but not NAG excretion, was significantly related to hypertension in patients with clinical proteinuria. In conclusion, our results suggest a relationship between the development of tubular dysfunction and the impairment of glomerular function in diabetic nephropathy. An increased excretion of NAG and low-molecular mass proteins may indicate early nephropathy

[The low molecular weight proteins ribonuclease, beta 2 microglobulin and lysozyme in the serum and urine of patients with chronic kidney diseases]

The diagnostical relevance of the low-molecular proteins ribonuclease, beta 2-microglobulin and lysozyme in serum and urine to detect a reduced glomerular filtration rate was examined in 52 patients with chronic renal diseases. The radioisotope clearance using 99mTc-DTPA was the base reference; the reference values of the low-molecular proteins were estimated in a control group. Ribonuclease was increased above the upper borderline value, if the glomerular filtration rate was lower than 1.24 ml s-1. Creatinine, beta 2-microglobulin and lysozyme remain yet in part in the normal range. The estimation of the ribonuclease in serum is suitable to detect an impaired glomerular filtration rate if the creatinine value is still not increased. Thereby, the diagnostics in renal diseases may be improved in the creatinine-blind area.

Urinary enzymes and low-molecular-mass proteins as indicators of diabetic nephropathy

We measured the excretion rates of six urinary enzymes that either originate from the proximal renal tubule, like alanine aminopeptidase (EC 3.4.11.2), alkaline phosphatase (EC 3.1.3.1), gamma-glutamyltransferase (EC 2.3.2.2), and N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30), or that are typical low-molecular-mass proteins, like lysozyme (EC 3.2.1.17) and pancreatic ribonuclease (EC 3.1.27.5). These rates were compared with those of total protein and albumin in urine of 36 insulin-dependent diabetic men and 30 healthy men. Seventeen of the diabetics had "clinical proteinuria," defined as excretion of more than 7.5 g of protein per mole of urinary creatinine (group B). Group A comprised the 19 diabetics without proteinuria. Except for gamma-glutamyltransferase, the excretions of enzymes and proteins were significantly higher in diabetics than in controls and were greater in group B than in group A. N-Acetyl-beta-D-glucosaminidase was the analyte most often increased in group A (89%), followed by albumin and alkaline phosphatase (each 32%). All patients in group B showed increased excretion of N-acetyl-beta-D-glucosaminidase. We conclude from the comparative data that this enzyme may be useful as an early predictor of diabetic nephropathy.

Urinary enzymes and low-molecular-mass proteins as indicators of diabetic nephropathy

We measured the excretion rates of six urinary enzymes that either originate from the proximal renal tubule, like alanine aminopeptidase (EC 3.4.11.2), alkaline phosphatase (EC 3.1.3.1), gamma-glutamyltransferase (EC 2.3.2.2), and N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30), or that are typical low-molecular-mass proteins, like lysozyme (EC 3.2.1.17) and pancreatic ribonuclease (EC 3.1.27.5). These rates were compared with those of total protein and albumin in urine of 36 insulin-dependent diabetic men and 30 healthy men. Seventeen of the diabetics had "clinical proteinuria," defined as excretion of more than 7.5 g of protein per mole of urinary creatinine (group B). Group A comprised the 19 diabetics without proteinuria. Except for gamma-glutamyltransferase, the excretions of enzymes and proteins were significantly higher in diabetics than in controls and were greater in group B than in group A. N-Acetyl-beta-D-glucosaminidase was the analyte most often increased in group A (89%), followed by albumin and alkaline phosphatase (each 32%). All patients in group B showed increased excretion of N-acetyl-beta-D-glucosaminidase. We conclude from the comparative data that this enzyme may be useful as an early predictor of diabetic nephropathy.

Diuresis-dependent excretions of low-molecular mass proteins in urine: beta 2-microglobulin, lysozyme, and ribonuclease

An investigation was carried out into how the low-molecular mass proteins beta 2-microglobulin, lysozyme, and ribonuclease were excreted over 8 h after high fluid intake (22 ml/kg of body weight in 15 min). With increasing urine flow rate the amount of lysozyme excreted per hour or per millimole creatinine increased more markedly than that of beta 2-microglobulin while at the same time the excretion rate of ribonuclease decreased. The effect of urinary flow upon the excretion rates of the various low-molecular mass proteins has to be considered as a preanalytical factor when these proteins are used as indicators of tubular dysfunction.

A rapid and sensitive enzyme immunoassay for Cu/Zn superoxide dismutase with polyclonal and monoclonal antibodies

An enzyme immunoassay for the quantification of human Cu/Zn SOD in serum, urine and erythrocytes was developed applying monoclonal and polyclonal antibodies. The one-step assay is completed within 30 min and enables the detection of 0.3 microgram Cu/Zn SOD per litre. A Cu/Zn SOD concentration of 46 +/- 21.5 micrograms/l and of 1 +/- 0.6 micrograms/mmol creatinine was determined in the serum and the urine, respectively, of healthy individuals. A content of 15 +/- 1.7 ng Cu/Zn SOD was found in 10(6) erythrocytes. Patients with Down's syndrome exhibited a 3.8-fold, a 2-fold and a 1.6-fold higher concentration of Cu/Zn SOD in their serum, urine and erythrocytes.

Diagnostic value of low-molecular mass proteins in serum for the detection of reduced glomerular filtration rate

The diagnostic value of the low-molecular mass proteins ribonuclease, beta 2-microglobulin, and lysozyme in serum for the detection of reduced glomerular filtration rates was evaluated. The values of these proteins and of serum creatinine investigated in 52 patients suffering from chronic renal diseases were plotted against 99m-Tc-diethylenetriaminopentaacetate clearance as an indicator of glomerular filtration rate. Log-transformed data showed a good fit of linearity. Considering the 95% confidence limits of the regression equations, ribonuclease increased above the normal range when the glomerular filtration rate was lower than 1.24 ml/s whereas the other analytes partly remained within their normal limits. Out of those 18 patients with glomerular filtration rates lower than 1.24 ml/s, all patients showed elevated ribonuclease levels. beta 2-Microglobulin, creatinine, and lysozyme were increased in 17, 14, and 12 cases, respectively. Ribonuclease and beta 2-microglobulin showed similar results when other diagnostic criteria (specificity, efficiency and predictive values) were taken into account. We recommend ribonuclease determination in serum for the detection of reduced glomerular filtration rate in the normal range of creatinine. The test is diagnostically powerful, cheap and easy to perform.

[Characteristic respiratory magnitude of isolated mitochondria of the rat kidney cortex in relation to measurement conditions]

Respiration speed, respiratory control index and ADP/O-quotient are important characteristics of mitochondria. Since their numerical values much differ in literature, the influence of the composition of the measuring medium on these parameters was established. In their value the parameters are particularly determined by the Mg2+ and the phosphate concentration as well as by the pH-value of the medium. For the investigation of the characteristics a medium of the following composition is recommended: 210 mmol/l saccharose, 10 mmol/l KCl, 10 mmol/l KH2PO4, 60 mmol/l tris(hydroxymethyl)aminomethan (pH 7.40), 0.5 mmol/l ethylene diamine tetra-acetic acid.

Influence of cyclosporin A on the respiration of isolated rat kidney mitochondria

In vitro exposure of isolated rat kidney mitochondria to cyclosporin A, a new immunosuppressive agent with serious nephrotoxic side-effects, leads to alterations of both succinate- and glutamate plus malate-supported respiration in a dose-related manner. ADP- and 2,4-dinitrophenol-stimulated respiration, respiratory control indices, and ADP/O ratios are decreased. The mitochondrial alterations are discussed as possible pathogenetic reasons of cyclosporin A nephrotoxicity.

Mitochondrial enzymes in human serum: comparative determinations of glutamate dehydrogenase and mitochondrial aspartate aminotransferase in healthy persons and patients with chronic liver diseases

We measured the activities of two mitochondrial enzymes, the mitochondrial form of aspartate aminotransferase (EC 2.6.1.1) and glutamate dehydrogenase (EC 1.4.1.2), in the serum of apparently healthy persons (n = 84) and patients suffering from chronic liver diseases (n = 43). The distribution of activities for glutamate dehydrogenase, but not mitochondrial aspartate aminotransferase, was sex-dependent. The upper limits of the reference intervals (99th percentile) at 37 degrees C were 3.2 U/L for mitochondrial aspartate aminotransferase, 6.4 U/L for glutamate dehydrogenase (women), and 11.0 U/L for glutamate dehydrogenase (men); there was a weak correlation between the activities of both mitochondrial enzymes (r = 0.439). In patients with chronic liver diseases we found a greater increase in the activity of glutamate dehydrogenase than of mitochondrial aspartate aminotransferase and the correlation between the two mitochondrial enzymes was stronger. The diagnostic sensitivity and specificity of either mitochondrial enzyme was less than that of total aspartate aminotransferase, alanine aminotransferase (EC 2.6.1.2), or gamma-glutamyltransferase (EC 2.3.2.2).

Mitochondrial enzymes in human serum: comparative determinations of glutamate dehydrogenase and mitochondrial aspartate aminotransferase in healthy persons and patients with chronic liver diseases

We measured the activities of two mitochondrial enzymes, the mitochondrial form of aspartate aminotransferase (EC 2.6.1.1) and glutamate dehydrogenase (EC 1.4.1.2), in the serum of apparently healthy persons (n = 84) and patients suffering from chronic liver diseases (n = 43). The distribution of activities for glutamate dehydrogenase, but not mitochondrial aspartate aminotransferase, was sex-dependent. The upper limits of the reference intervals (99th percentile) at 37 degrees C were 3.2 U/L for mitochondrial aspartate aminotransferase, 6.4 U/L for glutamate dehydrogenase (women), and 11.0 U/L for glutamate dehydrogenase (men); there was a weak correlation between the activities of both mitochondrial enzymes (r = 0.439). In patients with chronic liver diseases we found a greater increase in the activity of glutamate dehydrogenase than of mitochondrial aspartate aminotransferase and the correlation between the two mitochondrial enzymes was stronger. The diagnostic sensitivity and specificity of either mitochondrial enzyme was less than that of total aspartate aminotransferase, alanine aminotransferase (EC 2.6.1.2), or gamma-glutamyltransferase (EC 2.3.2.2).

Multiple forms of alanine aminopeptidase, alkaline phosphatase and gamma-glutamyltransferase in urine of healthy persons, patients suffering from kidney diseases and patients with kidney transplants

The catalytic activities of alanine aminopeptidase, alkaline phosphatase and gamma-glutamyltransferase were determined in the soluble and particulate fractions of urine, after ultracentrifugation. In healthy adults the fractional catalytic activities in the supernatants were 0.53, 0.56 and 0.24, respectively. Nearly the same proportions were found in children. In patients suffering from chronic kidney diseases there was a tendency for the proportion of catalytic activity in the soluble fraction to increase. However, the separation into the multiple forms gave no higher diagnostic reliability than the determination of total catalytic activity of the respective enzymes. The determination of multiple forms has no clinical significance in the detection of rejection episodes in renal transplant recipients.

Stability of enzymes in urine at 37 degrees C

The activity of alanine aminopeptidase, alkaline phosphatase, gamma-glutamyltransferase, lactate dehydrogenase and beta-N-acetyl-D-glucosaminidase in urine at 37 degrees C was investigated by a model simulating in vivo conditions. The stability of these urinary enzymes is influenced particularly by pH. At low pH values in urine (about pH 5.0) the four first-mentioned enzymes rapidly lose a considerable part of their activity, whereas beta-N-acetyl-D-glucosaminidase is inactivated at higher pH values in urine (about at pH 8.0). This inactivation effect is also time-dependent and can be modified by urinary substances such as creatinine, urea and electrolytes. To avoid misinterpretation of enzyme activity determinations in urine, the simultaneous measurement of urinary pH should be performed.

Influence of inorganic phosphate on the activity determination of isoenzymes of alkaline phosphatase in various buffer systems

The inhibitory effect of inorganic phosphate on the activity determination of isoenzymes of alkaline phosphatase (AP) in diethanolamine (DEA), glycine and 2-amino-2-methyl-1,3-propandiol (AMPD) buffer was studied. This effect depends on the buffer used and isoenzyme investigated. Especially the placental isoenzyme is inhibited; the inhibitory effect in DEA buffer is stronger than in the other buffers used. The requirement of purity for 4-nitrophenylphosphate with respect to its content of inorganic phosphate and conclusions for using control sera enriched with AP isoenzymes are discussed.

Suitability of commercial control sera for the quality control of activity determination of alkaline phosphatase

The suitability of thirteen commercially available control sera for measuring alkaline phosphatase (EC 3.1.3.1; orthophosphoric acid monoester phosphohydrolase, ALP) activity in human serum was tested. Apart from differences in ALP activity observed in some reconstituted commercial sera, the behaviour of control materials towards experimental variables such as the nature and concentration of the substrate, pH and type of buffer (or PO4-acceptor) together with the composition of the isoenzymes present in human serum highlights the problems and difficulties if commercial materials are to be used as control sera. The half-saturation constants in control sera were in all cases smaller than those of ALP isoenzymes from bone and liver. The shape of substrate activity curves and the pH optimum in most of control sera differed from that of human serum. The discrepant kinetic data of control materials and human serum may mask or suggest changes relevant to commercial quality control serum but not to samples of human serum.

Influence of Mg2+ ions on the activity measurement of isoenzymes of alkaline phosphatase

The activity of alkaline phosphatase isoenzymes from liver, bone and small intestine is differently influenced by Mg2+. The stimulation of isoenzymes from liver and bone is higher by Mg2+ ions than in the case of isoenzymes from small intestine. An obligatory preincubation of the serum sample in a buffer-Mg2+ mixture is necessary to avoid difficulties which may arise in the kinetic determination of alkaline phosphatase activity under extreme conditions, i.e. low Mg2+ concentration in serum, the necessity of dilution of the sample or the high isoenzyme content from liver or bone in the serum.