Cystathionine Synthase Deficiency Research Articles

Short fourth metacarpal in homocystinuria.

Homocystinuria due to cystathionine synthase deficiency is an autosomal recessive multisystem disease which affects the eye, the cardiovascular system, the central nervous system, the skeleton and occasionally other organs. Archibald's metacarpal sign and Kosowicz's phalangeal sign were evaluated in 11 patients with homocystinuria. A short fourth metacarpal was demonstrated in four patients. Our study represents, to our knowledge, the first systematic evaluation of these skeletal signs in a rather large group of homocystinuric patients.

Improved identification of heterozygotes for homocystinuria due to cystathionine synthase deficiency by the combination of methionine loading and enzyme determination in cultured fibroblasts

Previous data on tentative identification of the carrier state for homocystinuria due to cystathionine synthase deficiency using methionine loading or measurement of cystathionine synthase activity in tissue extracts are conflicting. We studied the results of standardized oral methionine loading in 20 obligate heterozygotes and compared them with those of determination of cystathionine synthase activity in cultured fibroblasts. Special attention was devoted to our recently reported observation on the small but striking differences in methionine metabolism between healthy pre- and postmenopausal women and men. Fasting and after load peak levels of methionine in serum did not discriminate the carriers from the control subjects. The mean fasting level of total homocysteine was only significantly higher in the group of premenopausal heterozygotes than in the corresponding control group. Nevertheless, the individual values overlapped with the normal range in 4 of 12 premenopausal heterozygotes. After loading peak levels of total homocysteine in 18 out of the 20 obligate heterozygotes exceeded the upper limit of the ranges in the three control groups. Thus, this parameter discriminated 90% of the obligate carriers. Measurement of cystathionine synthase activity in cultured fibroblasts from a skin biopsy identified the obligate heterozygotes to a similar degree (85%). No significant correlation between the measurements of cystathionine synthase activity and the after load peak levels of total homocysteine in the individual heterozygotes was established. Combination of both methionine loading and determination of cystathionine synthase activity in cultured fibroblasts identified all of these carriers.

Pyridoxine treatment does not prevent homocystinemia after methionine loading in adult homocystinuria patients

Fasting homocystinemia in homocystinuria due to cystathionine synthase deficiency reportedly disappears on high-dose pyridoxine treatment. This does not necessarily reflect normal tolerance to methionine. The present study compares the effects of oral methionine loading on homocystine, cystine, and homocysteine-cysteine disulphide profiles in 8 adult homozygous homocystinuria patients on and off pyridoxine treatment and in 20 controls. Pyridoxine nearly normalized fasting serum amino acid levels. Nevertheless, with a similar methionine load the patient's homocystine levels on and off treatment rose and the cystine levels decreased, reflecting the ongoing formation of the homocysteine-cysteine disulphide in the presence of impaired transsulphuration of homocysteine. In the controls homocystinemia remained virtually absent and cystine transiently rose which indicates normal transsulphuration. On treatment methionine loading evoked a brisk rise of the homocysteine-cysteine disulphide levels to values equal to those off treatment, when these levels virtually plateaued after the load. Thus, pyridoxine treatment attenuates the biochemical abnormalities in the fasting patients but leaves their impaired capacity to handle major methionine loads essentially unchanged.

Electroencephalographic abnormalities in homocystinuria due to cystathionine synthase deficiency

Two patients with intraspinal extradural lipomas without associated spina bifida are presented. This type of lipoma is benign and uncommon. A summary of the relevant literature is given. The clinical and myelographic differential diagnoses are discussed and a few conclusions are drawn.

Homocystinuria (cystathionine synthase deficiency). Results of treatment in late-diagnosed patients.

The clinical outcome in 12 late-diagnosed patients with homocystinuria is reported. Three children died: all were mentally damaged and were never treated effectively. Eight children have been treated with pyridoxine--or with a low-methionine diet with supplemental L-cystine--for 2 to 9 years. Follow-up of these patients shows a striking improvement in behaviour and intellectual development in close correlation to the biochemical normalisation. No thromboembolic episodes occurred in adequately treated patients. However, in one child thrombosis of the retinal artery developed during dietary failure. In another patient the characteristic symptoms of an endangiitis obliterans completely disappeared. Both the reversibility and the improvement of some of the main sequelae in homocystinuria emphasize the need to treat all patients, regardless of their age at diagnosis.

Platelet function and morphology in homocystinuria

Platelet-function tests and morphological investigations by electron microscopy were performed in 8 patients with homocystinuria due to cystathionine synthase deficiency. In 3 patients, all pyridoxine-responders, the collagen-, ADP- and adrenalin-induced platelet aggregation was decreased before treatment; it returned to normal during treatment when homocystine disappeared from plasma. The platelet factor 3 availability, decreased before treatment, also became normal when pyridoxine was administered. The open canalicular system occupied 7.2 per cent of the total area of the platelets before treatment and decreased to 4.5 per cent 3 months later; the α-granules, on the other hand, increased from 7.2 to 11.1 per cent. Functional and morphological studies in the 5 patients already under treatment showed normal results. We conclude that the platelet alterations in untreated patients result from their refractory stage after a release reaction has taken place; the latter may be caused by the homocystine-induced endothelial lesions. In adequately treated patients, our data suggest that no additional administration of inhibitors of platelet aggregation is necessary.

Free amino acids in liver of patients with homocystinuria due to cystathionine synthase deficiency: Effects of vitamin B 6

Patients with homocystinuria due to cystathionine synthase deficiency do not have free homocystine in the liver when it is present in high concentrations in the plasma and the urine. The liver of these patients is capable of maintaining normal concentrations of cystine at a time when the plasma cystine concentration is severely reduced. There is an increase in the methionine concentration of the liver which is reduced to normal concentrations during pyridoxine therapy.

Skeletal abnormalities in homocystinuria

The skeletal changes of thirty-four patients with the biochemical and clinical features of cystathionine synthase deficiency are described. It is emphasized that there is clinical evidence of excessive bone growth and the formation for bone which is structurally weaker than normal. The similarities and differences between this condition and Marfan's syndrome are stressed and the possible nature of the connective tissue defect leading to the skeletal changes discussed. The most characteristic skeletal changes in homocystinuria are the skeletal disproportion (pubis-heel length greater than crown-pubis length), the abnormal vertebrae, sternal deformities, genu valgum and large metaphyses and epiphyses.

Homocysteine and cysteine loads in patients with homocystinuria due to cystathionine synthase deficiency: Effects of vitamin B-6

The metabolic response of patients with homocystinuria due to cystathionine synthase deficiency to oral loads of homocysteine indicates: that even severely affected patients with homocystinuria have pools of cystine in their tissues; that control of sulfur amino acid metabolism favors increased concentrations of methionine rather than homocystine in the plasma; and that even patients who apparently are not B-6-responsive respond differently to the loads of homocysteine when challenged during B-6-treatment compared with their response before B-6 treatment. Loading tests with homocysteine indicate that B-6 treatment be of some benefit even in individuals who do not have an obvious biochemical response to such therapy.

Platelet Survival and Morphology in Homocystinuria Due to Cystathionine Synthase Deficiency

In homocystinuria due to cystathionine synthase deficiency thromboembolism is a major cause of mortality and morbidity. Recent studies by others identified an abnormally shortened platelet survival and increased platelet vacuolization in patients with homocystinuria. When we studied six additional patients, however, we found the platelet survival to be within normal limits for each. The mean survival (+/-1 S.D.) was 9.75+/-0.94 days (normal, 9.27+/-1.06). In addition, platelets from five patients with homocystinuria and three obligate heterozygotes could not be distinguished from those of seven normal control subjects by electron microscopy. Specifically, no increased vacuolization was observed. Genetic heterogeneity, technical differences of differences in plasma homocystine concentrations could account for these descrepant results. The mechanism of thrombosis in homocystinuria remains an open question.

Homocystinuria due to cystathionine synthase deficiency. Studies of nitrogen balance and sulfur excretion.

Apparent nitrogen balances and urinary sulfur excretions were determined for normal subjects, seven cystathionine synthase-deficient patients, and a single cystathioninuric patient on semisynthetic diets containing low-adequate amounts of methionine and very low amounts of methionine and very low amounts (12 mg daily, or less) of cystine. The amounts of supplemental cystine required to prevent abnormally high nitrogen or sulfur losses were determined. The five cystathionine synthase-deficient patients who had low residual activities of this enzyme detected in fibroblast and/or liver extracts did not lose more nitrogen or sulfur on diets virtually devoid of cystine than did the normal subjects. These results suggest that the widely expressed opinion that cystine is an essential amino acid for cystathionine syntase-deficient patients requires modification. Residual enzyme activity of only a few percent of normal may obviate such a cystine requirement. These results are compatible with, and lend support to, the working hypothesis which states that the pyridoxine response in cystathionine synthase-deficient patients is mediated by an increase in the residual activity of the affected enzyme.

Free amino acids in extracts of cultured skin fibroblasts from patients with various amino acid metabolic disorders.

In the search for a simple screening test for prenatal diagnosis of amino acid metabolic disorders, we compared the free amino acid contents in the extract of cultured skin fibroblasts from normal individuals with that from patients with 10 metabolic disorders: maple-syrup urine disease; homocystinuria due to cystathionine synthase deficiency; homocystinuria due to N5, 10-methylene-tetrahydrofolate reductase deficiency; citrullinemia; argininosuccinic acidemia: propionic acidemia; hyperprolinemia Type II; non-ketotic hyperglycinemia; hydroxyprolinemia; and hyperonithinemia. An accumulation of abnormal metabolites was not found in any of the disorders except argininosuccinic aciduria. Argininosuccinic acid anhydrides were detected in cell extracts from all four patients only after the extract was boiled at acid pH for 2 1/2 h. Thus, it is concluded that the measurement of free amino acids in extracts from cultured fibroblasts is not a useful screening technique in the diagnosis of inborn errors of amino acid metabolism.

Folate-responsive homocystinuria and "schizophrenia". A defect in methylation due to deficient 5,10-methylenetetrahydrofolate reductase activity.

Homocystinuria and homocystinemia without hypermthioninemia, but with reccurent episodes of folate responseive schizophrenic-like behavior, was documented in a mildly retarded adolescent girl who lacked the habitus associated with cystathionine synthase deficiency. Enzymes involved in homocysteine-methionine metabolism were demonstrated to be normal. A defect in the ability to reducte N-5-10--methylenetetrahydrofolate to 5-methyltetrahydrofolate was demonstrated. Methylenetetrahydrofolate reductase was 18 per cent of control values. Methyltetrahydrofolate is used for the methylation of homocysteine to methionine, and a deficiency of this compound could explain the homocystinemia and homocystinuria.

Homocystinuria: Investigations of cystathionine synthase in cultured fetal cells and the prenatal determination of genetic status

CYSTATHIONINE SYNTHASE DEFICIENCY (Fig. 1), which is inherited in an autosomal recessive manner , results in the clinical syndrome of homocystinuria. The full clinical picture is distinct 1 and may include dislocation of the optic lenses, progressive skeletal changes, severe t h r o m b o e m b o l i c disease , and, of ten, var iable degrees of mental retardation. Synthase activity, and its absence in affected individuals, has been demonstrated in liver and brain2,3,7; more recently it has been found in cultured skin fibroblasts 4, 6 and phytohemagglutininstimulated lymphocytes, s Heterozygotes can now be distinguished from patients and from normal individuals by determinat ion of synthase activity in cultured skin fibroblasts. 6 The utilization of cultured skin fibroblasts in the diagnosis of numerous enzymatic disorders often has been followed by attempts a t spec i f ic prenatal diagnosis by assay of cultured amniotic fluid cells. However, in order to establish proper control data, it is essential to determine optimal assay conditions for cultured amniotic

Homocystinuria due to cystathionine synthase deficiency: clinical-roentgenologic correlations.

HOMOCYSTINURIA DUE TO CYSTATHIONINE SYNTHASE DEFICIENCY: CLINICAL-ROENTGENOLOGIC CORRELATIONSPAULA W. BRILL, M.D., HAROLD A. MITTY, M.D. and GERALD E. GAULL, M.D.Audio Available | Share

Methionine metabolism in mammals: The biochemical basis for homocystinuria

Three genetic disorders result in “homo-cystinuria”. Of these, cystathionine synthase deficiency is the most common. Impairment of N 5-methyltetrahydrofolate-homocysteine methyltransferase, due to either deficient coenzyme synthesis (derangement of B 12 metabolism) or to reduced substrate availability (methylenetetrahydrofolate reductase deficiency), is the basis for the other two forms. Analyses of the pathobiochemistry caused by these defects is essential for the development of rational and appropriate therapy. Such studies have the additional benefit of illuminating the pattern of methionine metabolism in the normal human.

A BEHAVIORAL STUDY IN RATS TREATED WITH AN EXPERIMENTAL DIET FOR HOMOCYSTINURIA

Patients with cystathionine (cy) synthase deficiency are unable to synthesize cy from homocysteine and serine. Wong et al. showed that they could form cy from homoserine and cyst(e)ine, and thus might correct cy deficiency. The effect of diets containing Jack Bean (JB) (with 2% homoserine) on Spraque-Dawley rats from weaning was tested in groups of 30 each as follows: A, Purina Chow, B, 44.5% corn + soya (so), C, 44.5% JB + so, D, 44.5% heated JB + so, E, 30% heated JB + so, F, 65.8% + so, G, 88.7% JB. All diets contained salts, vitamin, 1.3% cystine and 5% corn oil. G showed inanition but there was no significant difference in the mortality of other groups. From 101 to 111 days, all rats were tested by a novel computer-controlled behavioral system which required them to lever-press for standardized food pellets. Statistical analysis showed that C and F pressed for significantly more pellets that A. C, D and E pressed for significantly more pellets than B. 26% A, 70% C and 30% F “learned” to lever-press within 30 min (A vs C, p<0.001). C could “recall” significantly faster than B, Heating of JB (to destroy urease) did not produce any significant difference. This demonstrated a rapid, quantitative and reliable technique in evaluating “learning”, “recall” and “motivation” in toxicologic or behavioral studies, and revealed the superior performance in some groups of rats fed JB containing diets.

Homocystinuria due to cystathionine synthase deficiency: Enzymatic and ultrastructural studies

Enzymatic studies of liver extracts from patients with homocystinuria due to cystathionine synthase (synthase) deficiency gave evidence of genetic heterogeneity. Two B₆-unresponsive patients had no detectable synthase activity. Four B₆-responsive patients all had easily measurable activity prior to treatment; three of them had approximately fourfold increases in activity following treatment, the fourth showed no clear-cut increase in activity. A seventh patient for heterozygote), who presented an incomplete phenotype, had 15 per cent of mean control synthase activity, which increased twofold following a methionine load and fourfold after pyridoxine treatment. Four obligate heterozygotes had synthase activities of 21, 31, 29, and 46 per cent, respectively, of mean control, although the last was assayed after a methionine load. Hepatocytes from all the patients showed the abnormalities by electron microscopy previously described in unresponsive patients. The morphologic abnormalities were not significantly changed after treatment even in the B₆-responsive patients. Hepatocytes from the four obligate heterozygotes contained the same morphologic changes.

Cystathionine synthase deficiency: Heterozygote detection using cultured skin fibroblasta

An assay for cystathionine synthase in cultured fibroblasts, of high sensitivity and not rate-limited for substrate, is described. Enzymatic activity was found to be highest in controls (mean ± SEM = 20.97 ± 1.81 nmole cystathionine/mg protein/hour), intermediate in obligate heterozygotes for synthase deficiency (4.40 ± 0.92), and lowest in patients (0.77 ± 0.42), with no overlap between controls and heterozygotes. One clinically and biochemically atypical patient had a synthase activity at the low end of the heterozygote range. Thus, this method is effective for the detection of heterozygotes for cystathionine synthase deficiency.

Homocystinuria: studies in tissue culture.

Extract: Cystathionine synthase activities are reported for extracts of fibroblasts grown from 39 control subjects, 47 homocystinuric individuals, and 10 parents of cystathionine synthase-deficient patients. Among the group with homocystinuria, fibroblast extracts from 38 had specific activities of cystathionine synthase below the control range. A number of considerations indicate that these 38 patients excrete homocystine because of cystathionine synthase deficiency. Fibroblasts from nine patients with homocystinuria had specific activities of cystathionine synthase within the control range. This group of nine was shown to be comprised of two individuals with cystathionine synthase deficiency, three with deficient activity of methylenetetrahydrofolate reductase, three with deficient activity of N5-methyltetrahydrofolate-homocysteine methyl-transferase, and one in whom homocystine excretion found by others in earlier studies could not be confirmed during the present investigation. The specific activities in fibroblasts of parents of cystathionine synthase deficient patients in most cases fall near the low end of the control range. An assay of increased sensitivity was used to measure the cystathionine synthase activities in extracts of fibroblasts from cystathionine synthase-deficient patients at several concentrations of added pyridoxal phosphate. Of 25 cystathionine synthase-deficient patients judged to be clinically responsive to pyridoxine treatment, 24 had detectable cystathionine synthase activities in fibroblast extracts when the assays were performed without added pyridoxal phosphate. These activities ranged from approximately 0.1 % to 10% of the mean control value, and generally were stimulated no more by the addition of pyridoxal phosphate than were extracts from normal cells. Of 10 cystathionine synthase-deficient patients judged not to be responsive to pyridoxine, 9 had no cystathionine synthase activity in fibroblast extracts detected by the method employed. The cystathionine synthase in the cell extracts of the single nonresponsive patient with significant activity was stimulated much more by in vitro addition of pyridoxal phosphate than was control cystathionine synthase. Genetic heterogeneity in cystathionine synthase-deficient patients and some of the genetic implications of the demonstrated α2β2 subunit structure of mammalian cystathionine synthase are discussed. Speculation: Knowledge of enzyme activities, which includes cystathionine synthase, N5-methyl-tetrahydrofolate-homocysteine methyltransferase and methylenetetrahydrofolate reductase, in cultured fibroblasts is of diagnostic value in distinguishing between the several genetic abnormalities which may lead to excessive excretion of homocystine in the urine.