Low utilization of prenatal and pre-implantation genetic diagnosis in Huntington disease - risk discounting in preventive genetics.

Huntington disease (HD) is a late-onset, fatal neurodegenerative disorder caused by a (CAG) triplet repeat expansion in the Huntingtin gene that enlarges during male meiosis. In 1996 in this journal, one of us (J. D. S.) presented a methodology to perform pre-implantation genetic diagnosis in families at-risk for HD without revealing the genetic status of the at-risk parent. Despite the introduction of accurate prenatal and pre-implantation genetic testing which can prevent transmission of the abnormal HD gene in the family permanently, utilization of these options is extremely low. In this article, we examine the decision-making process regarding genetic testing in families with HD and discuss the possible reasons for the low uptake among this group.

The metabolism of amino acids, peptides, and disulfides in lysosomes of fibroblasts cultured from normal individuals and those with cystinosis.

The metabolism of amino acids, peptides, and disulfides has been investigates in cultured skin fibroblasts from normal individuals and patients with cystinosis. Human fibroblast lysosomes closely resemble the lysosomes of mouse peritoneal macrophages in having an apparent permeability barrier to amino acids and peptides with molecular weights of greater than 220-230. Cystinotic and normal cells behave similarly in this regard. Normal cells do not undergo lysosomal swelling when exposed to cysteine-penicillamine disulfides, while cystinotic cells are prominently vacuolized under these conditions. Normal lysosomes may have a specific mechanism for the disposal of cystine, and deficient activity of this mechanism in cystinotic lysosomes could result in cystine storage therein. The demonstration that human fibroblasts can be used conveniently to study lysosomal metabolism of small substrates may facilitate investigations of these aspects of lysosomal function in a variety of genetic diseases of man.

Cystinosis: selective induction of vacuolation in fibroblasts by L-cysteine-D-penicillamine disulfide.

In cultured fibroblasts from individuals with cystinosis vacuolation is induced by exposure to L-cysteine-D-penicillamine disulfide. Normal fibroblasts do not show vacuolation on such exposure. These observations provide direct evidence that cystinotic cells have deficient activity of a lysosomal system for disulfide metabolism or transport. Induction of vacuolation by the mixed disulfide in cystinotic but not in normal cells furnishes a histological marker for cystinotic fibroblasts.

Cystine: compartmentalization within lysosomes in cystinotic leukocytes.

The large amount of cystine compartmentalized in cystinotic leukocytes cosediments in isopycnic sucrose density gradients with dense lysosomal particles, within which it is presumably contained. Such cystine appears to be primarily noncrystalline in these organelles.

Cystine transport is defective in isolated leukocyte lysosomes from patients with cystinosis.

The activity of a cystine transport system in lysosomes prepared from the leukocytes of patients with cystinosis was found to be deficient. In normal subjects, this system was resistant to N-ethylmaleimide and demonstrated saturation kinetics. Lysosomes from individuals heterozygous for cystinosis demonstrated a reduced maximum velocity for cystine egress from lysosomes. The rate of cystine escape from normal lysosomes was enhanced by adenosine triphosphate. The availability of normal and mutant lysosomes provides a means of investigating mechanisms of amino acid transport across lysosomal membranes.

Reduction in oocyte number following prenatal exposure to a diet high in galactose.

When pregnant rats were fed a 50 percent galactose diet there was a striking reduction in oocyte number in the offspring. The most prominent effects were noted after exposure to galactose during the premeiotic stages of oogenesis. Prenatal exposure to galactose or its metabolites may contribute to the premature ovarian failure characteristic of human galactosemia.

Lesch-Nyhan syndrome: preventive control by prenatal diagnosis.

The Lesch-Nyhan syndrome was detected in a fetus at a time sufficiently early to allow termination of the pregnancy. The feasibility of a preventive program for control of a severe sex-linked neurological disease through prenatal diagnosis is thus demonstrated.

Membrane microviscosity is increased in the erythrocytes of patients with adrenoleukodystrophy and adrenomyeloneuropathy.

Adrenoleukodystrophy (ALD) and adrenomyeloneuropathy (AMN) are related X-linked disorders characterized by adrenal, gonadal, and nervous system dysfunction. While the pathologic finding common to these tissues appears to be the accumulation of excessive amounts of very long chain fatty acids, the mechanism leading to functional impairment in these tissues is unclear. Measurements of fluorescence polarization (P), using the lipid probe diphenylhexatriene, demonstrate a highly significant increase in the microviscosity of erythrocyte membranes in affected patients (P = 0.286 +/- 0.012) vs. normals (P = 0.239 +/- 0.020). Analyses of these membranes by gas-liquid chromatography revealed 1.9-, 1.6-, and 1.3-fold increases above normal values in the C25:0, C26:0, and C27:0 fatty acids, respectively. These observations are compatible with previously obtained data in animals that correlate membrane microviscosity with the number of hormone receptors in target tissues. The present data support the thesis that a decrease in responsiveness to trophic hormones in ALD and AMN is secondary to changes in the membrane microviscosity of the target tissues and suggest a mechanism by which adrenal and gonadal failure occur in such patients.

An inherited defect affecting the tricarboxylic acid cycle in a patient with congenital lactic acidosis.

Cultured skin fibroblasts from a 3 yr old girl with severe, diffuse neurologic disease and persistant lactic acidosis, oxidized radioactive citrate, palmitate, and pyruvate at less than one-third the rate of control cells. Her fibroblasts oxidized isocitrate and glutamate at rates comparable with controls. In disrupted cells from this patient, the activity of aconitate hydratase appeared normal. The binding of citrate to aconitate hydratase and the activities of the NAD- and NADP-linked isocitrate dehydrogenases were also normal, while the activity of citrate synthase was slightly below control values. A significant defect was, however, apparent in the activity of the pyruvate dehydrogenase complex although not in the thiamine-dependent first enzyme of that complex. This patient appears to have a partial genetic defect affecting the tricarboxylic acid cycle.

Biochemical heterogeneity in glutathione synthetase deficiency.

Two different clinical syndromes are associated with glutathione synthetase deficiency, one presenting with hemolytic anemia and 5-oxoprolinuria, the other with isolated hemolysis. We have differentiated these disorders on an enzymatic basis. In 5-oxoprolinuria, all cell types examined have grossly deficient enzyme activity and glutathione content. In contrast, in the nonoxoprolinuric variant, erythrocytes have decreased enzyme activity and glutathione content, whereas nucleated cells maintain substantial levels of both. The enzyme in this disorder is unstable in vitro and has shortened survival in intact erythrocytes. Nucleated cells appear able to maintain sufficient enzyme activity and concentrations of glutathione to suppress overproduction of 5-oxoproline.

The effect of ions and ionophores on cystine egress from human leucocyte lysosome-rich granular fraction.

This paper describes the stimulation of exodus of cystine from lysosome-rich granular fractions by potassium. Potassium permeability into lysosomes is low, but in the presence of an ionophore or permeable anion, the movement of K+ into lysosomes caused a large stimulation of cystine exodus. Lysosomal preparations from leucocytes of cystinotic patients, which lack carrier-mediated cystine transport, also manifested stimulation of cystine egress by valinomycin and K+. This suggests that potassium-dependent cystine egress involves a carrier different from that defective in cystinosis, or occurs through a non-carrier-mediated mechanism.

Progesterone production by cultured preantral rat granulosa cells? Stimulation by androgens.

Progesterone (P) production by isolated rat granulosa cells from preantral follicles was enhanced by addition of androgens to the tissue culture medium. Testosterone (T) at 10(-7), 10(-6), and 10(-4)M as well as 10(-6)M dihydrotestosterone (DHT) increased P production 400 to 700% over paired control cultures. Human chorionic gonadotropin (100 mIU/ml) and 17beta-estradiol (7.8 X 10(-10M) had no effect on P production. P was identified by both a specific radioimmunoassay and sephadex LH-20 column chromatography. The stimulatory influence of T and DHT on these preantral follicular cells is consistent with a direct role for androgens in granulosa cell differentiation.

Pituitary resistance to thyroid hormone in cystinosis.

Eleven children with nephropathic cystinosis without clinical features of hyperthyroidism or hypothyroidism had elevated serum levels of immunoreactive TSH. The mean TSH level (+/- SE) was 37.4 +/- 12.3 microM/ml. Serial determinations of thyroid function during 1 yr were: mean (+/- SE) serum T4, 10.8 +/- 0.7 microgram/dl; free T4, 2.1 +/- 0.2 ng/dl; and T3, 239 +/- 6 ng/dl. After 500 microgram TRH iv, the peak TSH level exceeded 100 microU/ml in 6 of 10 patients, whereas T3 responses were variable. Studies of parameters influenced by thyroid hormone, including red cell sodium content, serum cholesterol, and 24-h urinary hydroxylysine excretion, were consistent with euthyroidism. On the other hand, the mean pulse wave arrival time was significantly reduced, consistent with hyperthyroidism. Three control patients, 2 with Lowe's syndrome and 1 with benign cystinosis, had normal thyroid studies. Eight of the patients were given either exogenous L-T4 or T3 in doses which were increased at weekly intervals. The serum TSH concentrations were suppressed to normal only after elevation of serum levels of thyroid hormones and with high exogenous thyroid replacement doses. The data suggest abnormal pituitary resistance to feedback by thyroid hormone in patients with cystinosis. We believe this to be the first description of the association of a heritable metabolic disease with such pituitary resistance.

The fluctuation of plasma carotenoid concentrations by phase of the menstrual cycle: a controlled diet study.

This is the first controlled diet study to examine the fluctuation of plasma carotenoids, lipoproteins, and serum hormone concentrations by phase of the menstrual cycle. Nonsmoking, premenopausal women (n = 12) with confirmed ovulatory cycles were given a standard diet with 10 mg total carotenoids/d for two cycles under isoenergetic conditions. Blood was drawn for simultaneous measurement of carotenoids, lipoproteins, and hormones on menses days 1-2, 4-6, 11 through 1 d after the luteinizing hormone surge, and 7-8 d after the surge, representing the menses, early and late follicular, and midluteal phases, respectively. Regression modeling with adjustment for plasma cholesterol concentrations was used to compare mean individual and total plasma carotenoid concentrations by phase of the cycle. Plasma carotenoid concentrations were at their lowest at menses and significantly higher thereafter, except for alpha-carotene. Compared with plasma concentrations at menses, beta-carotene peaked (increased by 9%, P = 0.01) in the late follicular phase. Plasma lutein/zeaxanthin and anhydrolutein concentrations were higher by 8-11% (P < or = 0.006) and by 15-31% (P < or = 0.02), respectively, during the last three phases. Plasma lycopene and phytofluene concentrations peaked (increased by 12%, P = 0.004; and by 21%, P = 0.006, respectively) at the midluteal phase. This cyclic fluctuation may affect the estimation of the plasma carotenoid-disease relation in studies of premenopausal women.

Adrenoleukodystrophy: very long-chain fatty acid metabolism in fibroblasts.

We studied very long-chain fatty acid (VLFA) metabolism in cultured fibroblasts from patients with adrenoleukodystrophy (ALD). Total hexacosanoate (C26:0) content of ALD fibroblasts was sixfold higher than normal and did not return to normal when cells were grown in lipid-free medium. When normal or ALD fibroblasts were grown in medium containing 10% ALD serum (which is enriched in C26:0), there was no further increase in C26:0 content compared with cells grown in 10% normal human serum. Uptake and loss of 1-14C-palmitate (C16:0) and 1-14C-lignocerate (C24:0) by ALD fibroblasts were similar to normal fibroblasts. Catabolism of exogenous 3H-C26:0 to 3H2O was about 30% of normal. Oxidation of exogenous 1-14C-hexacosanoate, 1-14C-lignocerate, and 1-14C-palmitate in intact ALD fibroblasts was 42%, 27 +/- 13% (SD), and 73 +/- 47%, respectively, of normal. These results are consistent with, but do not conclusively prove, a VLFA oxidation defect in ALD fibroblasts.

Adrenoleukodystrophy: increased plasma content of saturated very long chain fatty acids.

With a new method we measured the saturated very long chain fatty acids in the plasma of adrenoleukodystrophy (ALD) hemizygotes, ALD heterozygotes, and controls. ALD hemizygotes showed increased levels of hexacosanoate (C26 fatty acid) which represented 0.081 +/- 0.0066% (SEM) of total fatty acids, compared to 0.015 +/- 0.0032% in the controls. C25, C24, and C23 fatty acids were also increased, but the C22 and C20 fatty acids were normal. C26 levels were also increased in most ALD heterozygotes, with a mean level 0.057 +/- 0.0063% of total fatty acids. The technique can be used for diagnosis and carrier identification, and in the evaluation of therapy.

Attempts at use of strychnine sulfate in the treatment of nonketotic hyperglycinemia.

In two cases of nonketotic hyperglycinemia treated from early ages with strychnine sulphate, the patients demonstrated persistent severe psychomotor retardation and seizures. Strychnine therapy improved tone and feeding, but did not seem to alter fundamentally the course of the disease in either patient.

Studies of the cause and treatment of hyperammonemia in females with ornithine transcarbamylase deficiency.

Assay of ornithine transcarbamylase (OTC) activity in multiple small bits of liver (approximately 5 mg) that were obtained from a single surgical biopsy in a patient with OTC deficiency revealed a 10- to 40-fold variation in enzyme activity. Similar studies with control autopsy liver specimens varied 2.5-fold at most. The greater variation in the patient with OTC deficiency probably is due to sampling of clusters of normal or abnormal hepatocytes that resulted from inactivation of either the abnormal or normal X chromosone. Enzyme activity assayed on small liver biopsy specimens may not be representative of the entire liver in female patients with OTC deficiency. The hyperammonemia in individuals heterozygous for OTC deficiency may be due in part to shunting of blood through multiple "metabolic portosystemic shunts." Treatment of a girl who has OTC deficiency with a low-protein diet, a low-protein diet supplemented with oral essential amino acids, and a low-protein diet plus oral ketoacids of essential amino acids, on a separate occasion, a low-protein diet was compared to a low-protein diet plus lactulose. The low-protein diet plus oral ketoacid supplementation resulted in the best metabolic control of the patient's disease. On the other hand, paradoxical transient hyperammonemia was observed after the intarvenous administration of ketoacids to two acutely ill female patients with OTC deficiency.

Use of tetrahydropterins in the treatment of hyperphenylalaninemia due to defective synthesis of tetrahydrobiopterin: evidence that peripherally administered tetrahydropterins enter the brain.

Substantial amounts of tetrahydrobiopterin and 6-methyltetrahydropterin can be detected in CSF when these pterins are given peripherally to patients with hyperphenylalaninemia due to defective biopterin synthesis. Results of this study suggest that administration of either of these pterins in proper doses may prove to be a treatment not only for the impaired peripheral phenylalanine metabolism, but also for the neurologic disorders that are characteristic of the variant forms of hyperphenylalaninemia due to defective tetrahydrobiopterin synthesis or metabolism.

Treatment of the embryo and the fetus in the first trimester: current status and future prospects.

An effective treatment is now available to prevent the masculinization of female fetuses with congenital adrenal hyperplasia. Some vitamin-responsive inborn errors of metabolism can be treated prenatally by cofactor administration. Maternal phenylketonuria and maternal diabetes mellitus and the prevention of recurrent neural tube defects are also areas where therapeutic advances are being made. It may be possible to carry out chorionic villi sampling before 8 weeks menstrual age if appropriate catheters and guidance systems (probably transvaginal ultrasound) are used. First trimester diagnosis and treatment of fetal cardiac arrhythmias could prove to be very important, as they are later in pregnancy. Future possibilities for progress include gene microinjection into zygotes, classification and treatment of fresh embryos, biopsy and frozen storage of genetically at risk embryos, and therapy of preimplantation embryos by chimera formation or gene introduction by retroviruses.