GDAP1 mutations in Italian axonal Charcot-Marie-Tooth patients: Phenotypic features and clinical course.

Mutations in the ganglioside-induced differentiation associated-protein 1 (GDAP1) gene have been associated with both autosomal recessive (AR) and dominant (AD) Charcot-Marie-Tooth (CMT) axonal neuropathy. The relative frequency of heterozygous, dominant mutations in Italian CMT is unknown. We investigated the frequency of dominant mutations in GDAP1 in a cohort of 109 axonal Italian patients by sequencing genomic DNA and search for copy number variations. We also explored correlations with clinical features. All cases had already been tested for variants in common axonal AD genes. Eight patients (7.3%) harbored five already reported heterozygous mutations in GDAP1 (p.Arg120Gly, p.Arg120Trp, p.His123Arg, p.Gln218Glu, p.Arg226Ser). Mutations had different penetrances in the families; the onset of symptoms is in the first decade and progression is slower than usually seen in GDAP1-related AR-CMT. We show that the relative frequency of mutations in GDAP was slightly higher than those observed in MFN2 and MPZ (7.3% vs 6.3% and 5.0%). The relatively milder clinical features and the quite indolent course observed are relevant for prognostic assessment. On the basis of our experience and the data reported here, we suggest GDAP1 as the first gene that should be analysed in Italian patients affected by CMT2.

Contribution of copy number variations in CMT1X: a retrospective study.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth disease type 1X (CMT1X) is an X-linked dominant hereditary motor-sensory peripheral neuropathy, which results from mutations in the Gap Junction B1 (GJB1) gene. In a few cases, gene deletions have been linked to the disease, but their relative contribution in the pathogenesis of CMT1X has not been assessed yet. Herein a retrospective study to establish the incidence of gene deletions is described. METHODS: Copy number variation analysis was performed by multiplex ligation-dependent probe amplification, whilst the breakpoints were defined by Sanger sequencing. RESULTS: A novel GJB1 deletion was identified in a family presenting with a classical CMT1X phenotype. The rearrangement includes the coding and the regulatory regions of GJB1. CONCLUSIONS: GJB1 deletions appear to be a rare but not insignificant cause of CMT1X and are associated with a typical disease phenotype. Accordingly, patients negative for point mutations whose pedigree and clinical records strongly suggest the possibility of CMT1X should be tested for GJB1 copy number variations.

DRD3 Ser9Gly variant is not associated with essential tremor in a series of Italian patients.

BACKGROUND: Essential tremor (ET) is the most common movement disorder worldwide. Three susceptibility loci on chromosomes 3q13, 2p24.1, and 6p23 have been reported, but no causative genes were found. The Ser9Gly variant of dopamine D3 receptor (DRD3) receptor was found associated to ET in a French and US population. METHODS: A case-control study to evaluate the association between the Ser9Gly variant and ET was performed in a cohort of 116 Italian patients with familial ET and in 158 normal controls. RESULTS: No significant difference in allele and genotype frequencies was found between the two groups. CONCLUSIONS: These results do not support an association between DRD3 Ser9Gly and susceptibility to ET in Italian patients.

A novel mutation of GDAP1 associated with Charcot-Marie-Tooth disease in three Italian families: evidence for a founder effect.

BACKGROUND: Mutations in a gene encoding a novel protein of unknown function-the ganglioside-induced differentiation-associated protein 1 gene (GDAP1)-are associated with the autosomal recessive Charcot-Marie-Tooth disease type 4A (CMT4A). OBJECTIVE: To investigate the role of GDAP1 mutations in causing autosomal recessive neuropathies in an Italian population. METHODS AND RESULTS: 76 patients with severe early onset polyneuropathy and possible autosomal recessive inheritance were screened for mutations. A T>G transversion (c.347 T>G) at codon 116 (M116R) was detected in four affected subjects from three apparently unrelated families. All patients had early onset of disease with pronounced foot deformities and impaired walking. Neurophysiological studies showed an extremely variable expression. Sural nerve biopsies revealed signs of both de-remyelination and axonal impairment, the most prominent feature being a severe loss of larger fibres. Haplotype analysis of the GDAP1 locus demonstrated a common disease haplotype. CONCLUSIONS: The association of the mutation with a common haplotype suggested a common ancestor.

Effect of endotoxin and cytokines on lipoprotein lipase activity in mice.

Endotoxin (lipopolysaccharide [LPS]) stimulates the production of cytokines, which mediate many of the metabolic effects associated with infection. In LPS-sensitive C57B1/6 mice, LPS doses as low as 0.01 micrograms per mouse decreased adipose tissue lipoprotein lipase (LPL) activity by greater than 50%. In LPS-resistant C3H/HeJ mice, which do not produce cytokines in response to LPS, doses of LPS as high as 10 micrograms per mouse did not affect LPL activity in adipose tissue. In muscle of C57Bl/6 mice, LPL activity was decreased by 27% after 10 micrograms of LPS, whereas in C3H/HeJ mice there was no effect. These results indicate that the LPS-induced decrease in both adipose and muscle LPL activity is mediated by cytokines. Tumor necrosis factor (TNF), interleukin (IL)-1, leukemia-inhibiting factor (LIF), interferon alfa, and interferon gamma all decreased adipose tissue LPL activity in intact mice. In skeletal and cardiac muscle, only IL-1 and interferon gamma decreased LPL activity, whereas TNF, LIF, and interferon alfa had no effect. Inhibition of TNF activity blocked the increase in serum triglycerides that is characteristically observed after LPS but did not affect the ability of LPS to decrease adipose tissue LPL activity. Inhibition of IL-1 activity with IL-1 receptor antagonist partially inhibited the increase in serum triglycerides; however, the ability of LPS to decrease LPL activity in either adipose or muscle tissue was not affected. These data indicate that although TNF and IL-1 play a role in mediating the increase in serum triglyceride levels, these cytokines do not play a crucial role in the inhibition of either adipose or muscle LPL activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic adenosine 3',5'-monophosphate and glucose stimulate thyroxine 5'-deiodinase type II in cultured mouse neuroblastoma cells.

Nutrient modulation increases mouse neuroblastoma (NB) T4-5'-deiodinase II (T4-5'-D II) activity. Carbohydrates are more potent than either amino acids or glycerol as nutrient sources. Glucose rapidly (2 to 4 hours) enhances NB enzyme activity and the response is dependent on new protein synthesis. The present study was performed to further characterize this glucose effect and explore its relationship to the cyclic adenosine monophosphate (cAMP) system in these cells. NB T4-5'-D II activity reached a maximum level (sixfold) in response to glucose (10 mmol/L) at 16 hours and thereafter remained constant up to 22 hours before reverting back to basal level between 24 and 30 hours. This pattern of response allowed the performance of detailed studies on maximum glucose activated NB T4-5'-D II under transient equilibrium conditions during the 16- to 22-hour period. Addition of dibutyryl cAMP (dbcAMP) (1 mmol/L) at this stage significantly increased enzyme activity (twofold at 2 hours and fourfold at 4 and 6 hours) compared with glucose alone. There was an additive response to dbcAMP under these maximum glucose-activated conditions. Nonactivated NB T4-5'-D II showed a twofold response to dbcAMP (1 mmol/L) at 4 hours in a glucose-free medium. Under these conditions, glucose (10 mmol/L) also increased enzyme activity twofold. Combined studies with dbcAMP and glucose increased enzyme activity fourfold at 4 hours. Subsequent studies were performed with forskolin (10 mumol/L) and cholera toxin (1 nmol/L), modulators of endogenous cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistence of the hypertriglyceridemic effect of tumor necrosis factor despite development of tachyphylaxis to its anorectic/cachectic effects in rats.

The administration of a single injection of tumor necrosis factor (TNF) produces a variety of acute and sustained biological effects, including hyperlipidemia, stimulation of hepatic lipogenesis, decreases in adipose tissue lipoprotein lipase activity, and anorexia with weight loss. Chronic administration of a fixed dose of TNF produces tachyphylaxis to the anorectic/cachectic effects of TNF. We now report that the hyperlipidemic effect of TNF persists during chronic TNF administration in the absence of any cachectic effect of TNF. Sprague-Dawley rats injected with TNF (250 micrograms/kg) show a significant decrease in weight over the next 24 h which can be accounted for by decreases in food and water intake accompanied by an increase in urine output. With subsequent daily injections of TNF, treated rats begin eating and rapidly regain weight. Hypertriglyceridemia persists for up to 10 days of daily injections of TNF. After three daily injections of TNF, no decreases were seen in lipoprotein lipase activity in a wide variety of tissues. De novo hepatic lipogenesis remained increased in TNF-treated animals after four daily injections, but by the fifth day hepatic lipogenesis returned to normal. After 5 days of TNF treatment the acute incorporation of labeled glycerol into serum triglycerides remained elevated. These data indicate that hyperlipidemia persists during multiple daily injections of TNF and that TNF induced hypertriglyceridemia is not inevitably linked to the syndrome of cachexia.

Effect of tumor necrosis factor (TNF) on lipid metabolism in the diabetic rat. Evidence that inhibition of adipose tissue lipoprotein lipase activity is not required for TNF-induced hyperlipidemia.

Tumor necrosis factor (TNF) administration produces an increase in plasma triglycerides that may be due to inhibition of adipose lipoprotein lipase activity and/or a stimulation of hepatic lipogenesis. We now report that TNF administration to insulinopenic diabetic rats increases serum triglycerides (2 h, 2.4-fold; 17 h, 4.3-fold). Adipose tissue lipoprotein lipase activity was markedly decreased in diabetic animals compared with controls and was not further inhibited by TNF. Incorporation of tritiated water into fatty acids in the liver was increased 45% 1-2 h after TNF and 87% at 16-17 h. These results indicate that the TNF-induced increase in circulating lipid levels can occur in the absence of a TNF-induced inhibition of adipose tissue lipoprotein lipase activity. Moreover, the clearance from the circulation of triglycerides in chylomicrons was similar in control and TNF-treated animals; these results provide further evidence that the removal of triglyceride-rich lipoproteins is not altered in the TNF-treated animals. Our data suggest that the TNF-induced stimulation of hepatic lipid synthesis may play an important role in the increase in serum triglycerides. In addition, TNF administration to diabetic animals leads to an elevation in serum glucose levels (73% at 17 h) without a change in serum insulin levels. Thus, TNF stimulation of hepatic lipogenesis is independent of changes in insulin.

Effect of tumor necrosis factor administration in vivo on lipoprotein lipase activity in various tissues of the rat.

When added to murine adipocytes in culture, tumor necrosis factor (TNF) decreases the levels of lipoprotein lipase (LPL). Semb et al (1987. J. Biol Chem. 262: 8390-8394) have shown that administration of murine TNF to rats decreases lipoprotein lipase (LPL) in the epididymal fat pad with maximal inhibition requiring several hours. We have now tested the effects of treatment of rats with TNF on LPL activity in a variety of tissues and find that few show decreases in LPL under conditions that acutely increase serum triglycerides. Ninety minutes after treatment of male rats with human TNF (25 micrograms/200 g, i.v.), serum triglycerides rose 2.2-fold but there was no decrease in LPL activity in epididymal fat. Sixteen hours after TNF treatment LPL activity had decreased by 44% in epididymal fat, consistent with the previously reported data. In contrast, in female rats, no significant decrease was seen in LPL activity in parametrial adipose tissue at either 90 min or 16 hr after TNF administration despite increases in serum triglycerides (1.8-fold and 1.5-fold, respectively). There was little change in LPL activity in most other adipose tissue sites of male or female rats at either time after TNF treatment. No effect of TNF was seen on heart or diaphragm muscle LPL at any time. TNF treatment of both male and female rats produces consistent increases in de novo hepatic lipogenesis in vivo under conditions that increase serum triglycerides. It is unlikely that the limited effects of TNF on LPL in vivo can account for the rapid and sustained increase in serum triglycerides.

Identification of proline-specific carboxypeptidase localized to brush border membrane of rat small intestine and its possible role in protein digestion.

A proline-specific carboxypeptidase (carboxypeptidase P, EC 3.4.12.-) was identified and partially characterized in the brush border membrane fraction of rat intestinal enterocytes and shown to be distinct from pancreatic proteases. The carboxypeptidase activity of isolated brush border membranes, with Z-Gly-Pro-Leu as substrate, was 43 nmol/min/mg protein representing a 16-fold purification when compared with mucosal cell homogenates. Activity was maximal in the middle region of the small intestine, and villus cells had twice the activity of crypt cells. Carboxypeptidase activity was maximal at pH 7.0, was stimulated by divalent cations, and was inhibited by metal chelating agents, suggesting that it is a metalloenzyme. The enzyme had the highest activity with synthetic peptides containing proline penultimate to the carboxy terminus. In vivo patterns of hydrolysis and absorption of amino acids from Z-Pro-Trp were examined using an intestinal perfusion technique. These studies indicate that brush border membrane carboxypeptidase may play an important role in the digestion of proline-containing peptides and proteins.

Carbohydrate reactivation of thyroxine 5'-deiodinase (type II) in cultured mouse neuroblastoma cells is dependent upon new protein synthesis.

The T3 concentration in brain predominantly reflects local production from T4 rather than T3 uptake from the circulating pool. We recently demonstrated that rat brain T3 content is increased by glucose feeding compared to chow feeding. One possible mechanism for this effect is an increase in brain T4 5'-deiodinase (5'-D) activity. Our recent preliminary studies of neuroblastoma (NB) cells demonstrate that renewal of RPMI-1640 medium stimulates T4 5'-D type II (NB T4 5'-D II) activity in these cells. The present studies were performed to determine the mechanism of this response. Studies were performed on NB cells supported in thyroid hormone-depleted (deficient) medium. This approach increased NB T4 5'-DII activity 4-fold compared to that in thyroid hormone-replete medium. Medium renewal further stimulated enzyme activity (7- to 9-fold; maximum at 6 h) in each group. The difference between the hypothyroid group and control was sustained over a 24-h period. Subsequent studies demonstrated that glucose (11 mM) was the specific medium ingredient mediating the medium renewal response. A progressive increase in NB T4 5'-DII activity was noted over 8 h during RPMI-1640 salt plus glucose (11 mM) incubation. This was equivalent to the effect of complete medium containing glucose (11 mM). Coincubation with insulin (10(-7)-10(-9) M) did not modify the enzyme response to glucose. In addition, fructose (10 mM) had a similar effect on enzyme activity. Glycerol and essential and nonessential amino acids also modestly increased NB T4 5'-DII activity compared to that in the control group (P less than 0.01). Actinomycin-D (1 microM), cycloheximide (100 microM), and puromycin (100 microM) significantly (P less than 0.001) decreased the glucose effect on T4 5'-DII by 5-, 9-, and 17-fold, respectively, after 6 h of incubation. In addition, puromycin (10-200 microM) inhibited both NB T4 5'-DII activity and [3H]amino acid incorporation during incubation in glucose. There was a significant correlation between these parameters (r = 0.8; P less than 0.001). The enzyme activity decay curves in the glucose-activated and control groups subsequent to puromycin (100 microM) addition at 8 h were parallel. The fractional turnover rate was 13%/h in the controls and 11%/h in the glucose groups. The calculated enzyme production rate was significantly higher (P less than 0.005) in the glucose group compared to that in the control group (17.4 vs. 6.8 fmol/mg protein.h).(ABSTRACT TRUNCATED AT 400 WORDS)

Carbohydrate feeding increases total body and specific tissue 3,5,3'-triiodothyronine neogenesis in the rat.

The glucose-fed rat, in contrast to the chow-fed animal, has a higher serum total T3 concentration and an increase in the hepatic content of T4 5'-deiodinase (type I) activity. The mechanism and significance of these glucose-induced changes in T3 metabolism are elucidated in this study. To focus on extrathyroidal thyroid hormone metabolism the kinetic parameters were determined in thyroidectomized T4-replaced rats (1.25 micrograms T4/100 g BW.day). Kinetics of T4 and T3 were studied separately by infusing labeled hormone to equilibrium. Glucose feeding for 72 h (G) significantly increased both the total and free serum T3 concentrations compared to the respective means in the chow-fed control group (P). The glucose-induced changes in serum T3 reflect the approximate doubling of T3 production to 14.7 +/- 0.6 ng/h.100 g in G rats compared to 7.6 +/- 0.7 ng/h.100 g in P rats. The higher T3 production rate in the G group is due to a significant increase in the fractional total body T4 to T3 conversion (0.33 +/- 0.02) compared to that in the P group (0.19 +/- 0.02). The tissue (liver, kidney, brain, and brown adipose tissue) concentration of T4 (nanograms per g wet wt) was significantly increased in the G group. The increase ranged from 54% in liver to 80% in kidney, brain, and brown adipose tissue. The tissue concentration of T3 (nanograms per g wet wt) was even more dramatically increased by glucose feeding than was T4. The glucose-induced increment in organ T3 ranged from 2.5-fold (kidney, muscle, and brain) to 5-fold (liver and white adipose tissue) to 12-fold (brown adipose tissue). These data indicate that the increase in serum total and free T3 concentrations associated with glucose feeding reflects augmented total body T3 production from T4. The effect of the enhanced T3 neogenesis was generalized, as the T3 content was increased in each organ studied. Thus, glucose feeding has unique effects on T3 metabolism.

Role of rat intestinal brush-border membrane angiotensin-converting enzyme in dietary protein digestion.

The role of rat intestinal angiotensin-converting enzyme (ACE; E.C 3.4.15.1) in the digestion and absorption of dietary protein was investigated. Enzyme activity was associated with the brush-border membrane fraction, with the highest activity in the proximal to midregion of the small intestine. Preliminary enzyme characterization studies were carried out using purified brush-border membrane preparations. When a variety of N-blocked synthetic peptides were used as potential substrates for ACE, activity was highest with those containing proline at the carboxy terminal position. The hydrolytic rates observed with these prolyl peptides were comparable to those observed when major digestive peptidases of the brush-border membrane such as aminopeptidase N and dipeptidyl aminopeptidase IV were assayed. When isolated rat jejunum was perfused in vivo with solutions of Bz-Gly-Ala-Pro, the dipeptide Ala-Pro was the main hydrolytic product detected in the perfusates. Absorption rates of the constituent amino acids, alanine and proline, depended on the concentration of peptide perfused. Captopril, an active site specific ACE inhibitor, significantly inhibited hydrolysis and absorption of constituent amino acids from Bz-Gly-Ala-Pro. These results show that intestinal brush-border membrane ACE functions as a digestive peptidase in addition to its role as a regulator of biologically active peptides in other tissues.

Brain lipoprotein lipase is responsive to nutritional and hormonal modulation.

Functional lipoprotein lipase activity was recently described in rat brain. The present study was performed to further characterize the biologic significance of brain lipoprotein lipase (heparin releasable component) and elucidate regulatory factors. Comparative studies were performed on tissue (brain, adipose, and heart) heparin releasable lipoprotein lipase in the fasted and diabetic (streptozotocin 100 mg/kg BW IP) rat. Both fasting (96 hours) and diabetes (ten days) significantly decreased brain (cortical) (P less than .05) and adipose (epididymal fat pad) (P less than .001) lipoprotein lipase activity. In contrast, heart muscle enzyme activity was significantly increased (P less than .001) in response to fasting and diabetes. Refeeding (Purina chow 96 hours) and insulin replacement (96 hours) reversed these changes in tissue lipoprotein lipase consequent to fasting and diabetes, respectively. There was a positive correlation between the changes in serum insulin concentration and adipose lipoprotein lipase, but there was no correlation between this parameter and brain or heart lipoprotein lipase. In addition, although T3 therapy normalized the low T3 state associated with both fasting and diabetes, it had no effect on the enzyme activity in the studied tissues. However, subsequent studies demonstrated that hypothyroidism (2 weeks post thyroidectomy) significantly decreased brain lipoprotein lipase activity (P less than .001) and increased both the adipose (P less than .025) and heart (P less than .025) enzyme activity. T3 replacement (0.8 micrograms/100 BW/d for 1 week) reversed the effects of hypothyroidism. However, the relationship between brain enzyme activity and serum T3 was nonlinear as hyperthyroidism tended to reduce brain LPL activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of alternation in patients treated for strabismic amblyopia.

Of a series of 57 formerly amblyopic patients who attained equal visual acuities (20/20 or better in each eye), only 29 were able to alternate after treatment. The oldest patient was 5 years old. The pattern visual-evoked response of the previously amblyopic eye in nonalternators showed a reduced amplitude as compared with that of the sound eye. This probably occurred because of a reduced number of cortical cells subserving the formerly amblyopic eye. Lack of alternation may be the result of cortical competition. More cortical cells are connected to the originally normal eye even after successful treatment of the amblyopic eye in the nonalternating patient.

Contrast sensitivity differences between strabismic and anisometropic amblyopia: objective correlate by means of visual evoked responses.

The visual evoked response transfer function of amblyopic subjects was studied. Strabismic amblyopes showed abnormalities only in the high spatial frequency range. Anisometropic amblyopes on the contrary, showed an abnormal function both in the low and high spatial frequency range. This is an objective correlate of functional differences between strabismic and anisometropic amblyopes.

The mechanism of the acute hypoglycemic action of phenformin (DBI).

The mechanisms by which biguanide (phenformin) acutely brings about a reduction in blood glucose in diabetic subjects has been studied with the aid of C-6 14C glucose. Six diabetic subjects were studied, each at three separate dose levels of phenformin. Two of these same subjects were studied with placebo. Consistent and increasingly pronounced effects of drug versus placebo were noted as the level of biguanide was increased. Biguanide consistently lowered hepatic glucose output while not significantly affecting the removal of glucose from the circulation. It was noted that glucogenesis from lactate was not significantly curtailed. However, a lack of stimulation in Cori Cycle activity in the presence of significant elevations of circulating lactate were taken as an indication of inhibition of glucogenesis from this substrate. On balance, it is concluded that the acute hypoglycemic action of this biguanide is mediated primarily through a restriction in the supply of glucose from the liver to the circulation. The data support the contention that these drugs inhibit hepatic glucogenesis even though Cori Cycle activity may be increased and also suggest that a portion of the decrease in hepatic glucose supply may be the result of impaired glycogenolysis.