Jess G. Thoene

Cysteamine Therapy for Children with Nephropathic Cystinosis

We treated 93 children with nephropathic cystinosis with oral cysteamine (mean dose, 51.3 mg per kilogram of body weight per day) for up to 73 months. This agent is known to be effective in depleting cells of cystine. In our study, the mean cystine depletion from leukocytes was 82 percent. A historical control group of 55 children received either ascorbic acid (27 children) or placebo (28). At age six, 2 of 17 controls had a serum creatinine level less than 1.0 mg per deciliter, as compared with 17 of 27 patients treated with cysteamine for at least one year (odds ratio, 12.8; 95 percent confidence interval, 2.1 to 33.9). At the end of the study, creatinine clearance was higher in the cysteamine group than in the control group (38.5 vs. 29.7 ml per minute per 1.73 m2; 95 percent confidence limits on the difference, 1.8 and 15.8), even though the cysteamine group was on average 1.4 years older than the control group. Cysteamine also improved growth; those in the cysteamine group between two and three years of age grew at 93 percent of the normal velocity, as compared with 54 percent in the control group. Fourteen percent of the patients could not tolerate the taste and smell of cysteamine. Concurrent controls treated in a blinded fashion with a placebo were not included in this study. With this limitation in mind, we conclude that oral cysteamine, by depleting cells of cystine, helps maintain renal glomerular function, improves growth, and constitutes the current treatment of choice for nephropathic cystinosis.

The transport systems of mammalian lysosomes

X. Amino acid transport systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 A. Lysosomal cystine transport and cystinosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354 B. The cystine dimc~[~,yl esle~ selection technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 C. Cationic amino acid transport: lysosomal system c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 D. Cysteamine treatment of cystinosis and lysosomal transport system c . . . . . . . . . . . . . . . . . . 3568 E. Dicarboxylic amino acid transport: lysosomal system d . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 F. Transport of the small neutral amino acids: systems e,f, and p . . . . . . . . . . . . . . . . . . . . . . . 359 G. Transport of large neutral, hydrophobic amino acids: lysosomal system h . . . . . . . . . . . . . . . 360 H. The cysteine-specific lysosomal transport system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

Biotin-Responsive Carboxylase Deficiency Associated with Subnormal Plasma and Urinary Biotin

AN increasing number of patients have been diagnosed as having biotin-responsive multiple carboxylase deficiency.1 2 3 4 5 6 7 8 This genetic disorder involves defects in the metabolism of biotin a...

Ocular nonnephropathic cystinosis : Clinical, biochemical, and molecular correlations

Ocular nonnephropathic cystinosis, a variant of the classic nephropathic type of cystinosis, is an autosomal recessive lysosomal storage disorder characterized by photophobia due to corneal cystine crystals but absence of renal disease. We determined the molecular basis for ocular cystinosis in four individuals. All had mutations in the cystinosis gene CTNS, indicating that ocular cystinosis is allelic with classic nephropathic cystinosis. The ocular cystinosis patients each had one severe mutation and one mild mutation, the latter consisting of either a 928 G→A (G197R) mutation or an IVS10–3 C→G splicing mutation resulting in the insertion of 182 bp of IVS10 into the CTNS mRNA. The mild mutations appear to allow for residual CTNS mRNA production, significant amounts of lysosomal cystine transport, and lower levels of cellular cystine compared with those in nephropathic cystinosis. The lack of kidney involvement in ocular cystinosis may be explained by two different mechanisms. On the one hand (e.g. the G197R mutation), significant residual cystinosin activity may be present in every tissue. On the other hand (e.g. the IVS10–3 C→G mutation), substantial cystinosin activity may exist in the kidney because of that tissues specific expression of factors that promote splicing of a normal CTNS transcript. Each of these mechanisms could result in minimally reduced lysosomal cystine transport in the kidneys.

Increased Apoptosis in Cystinotic Fibroblasts and Renal Proximal Tubule Epithelial Cells Results from Cysteinylation of Protein Kinase Cδ

Cystinosis is a rare genetic disease characterized by defective lysosomal cystine transport and increased lysosomal cystine. How lysosomal cystine causes the lethal nephropathic phenotype is unknown. It was shown recently that cultured fibroblasts and renal proximal tubule epithelial cells whose lysosomes are cystine-loaded display a two-fold or greater increase in apoptosis after both intrinsic and extrinsic stimuli. The mechanism for the increased apoptosis is unknown. Protein kinase Cdelta (PKCdelta) is a proapoptotic protein kinase that has been shown in vitro to be activated via cysteinylation. This report now shows that PKCdelta forms disulfide bonds specifically with cystine that is released from lysosomes in cultured fibroblasts and renal proximal tubule epithelial cells during apoptosis. PKCdelta in cystinotic fibroblasts and renal proximal tubule epithelial cells have a four- to six-fold greater association with its substrate, lamin B, and a 2.5-fold increase in specific activity after TNF-alpha exposure. Both RNA inhibition and chemical inhibition of PKCdelta resulted in a significant decrease in apoptosis in cystinotic cells but not in normal cells. It is proposed that abnormally increased apoptosis plays a role in evolution of the cystinotic phenotype.

Course of nephropathic cystinosis after age 10 years

We identified 80 patients with nephropathic cystinosis older than age 10 years in the United States and Canada. The oldest reported individual was 26 years of age. Ninety percent of patients had received at least one renal allograft. Age at the time of first transplant varied between 7 and 17 years (mean 10.0 years). Almost three fourths of the patients required thyroid replacement, 27% had splenomegaly, and 42% had hepatomegaly. Photophobia was noted in 86% of patients, decreased visual acuity in 32%, and corneal ulcerations in 15%. Neurologic involvement, renal osteodystrophy, and diabetes mellitus were unusual. All these late complications of nephropathic cystinosis contribute to a description of the natural history of the disease and provide a rationale for the therapeutic use of cystine-depleting agents after renal transplantation.

Genetic and phenotypic heterogeneity suggest therapeutic implications in SCN2A-related disorders

Mutations in SCN2A, a gene encoding the voltage-gated sodium channel Nav1.2, have been associated with a spectrum of epilepsies and neurodevelopmental disorders. Here, we report the phenotypes of 71 patients and review 130 previously reported patients. We found that (i) encephalopathies with infantile/childhood onset epilepsies (≥3 months of age) occur almost as often as those with an early infantile onset (<3 months), and are thus more frequent than previously reported; (ii) distinct phenotypes can be seen within the late onset group, including myoclonic-atonic epilepsy (two patients), Lennox-Gastaut not emerging from West syndrome (two patients), and focal epilepsies with an electrical status epilepticus during slow sleep-like EEG pattern (six patients); and (iii) West syndrome constitutes a common phenotype with a major recurring mutation (p.Arg853Gln: two new and four previously reported children). Other known phenotypes include Ohtahara syndrome, epilepsy of infancy with migrating focal seizures, and intellectual disability or autism without epilepsy. To assess the response to antiepileptic therapy, we retrospectively reviewed the treatment regimen and the course of the epilepsy in 66 patients for which well-documented medical information was available. We find that the use of sodium channel blockers was often associated with clinically relevant seizure reduction or seizure freedom in children with early infantile epilepsies (<3 months), whereas other antiepileptic drugs were less effective. In contrast, sodium channel blockers were rarely effective in epilepsies with later onset (≥3 months) and sometimes induced seizure worsening. Regarding the genetic findings, truncating mutations were exclusively seen in patients with late onset epilepsies and lack of response to sodium channel blockers. Functional characterization of four selected missense mutations using whole cell patch-clamping in tsA201 cells-together with data from the literature-suggest that mutations associated with early infantile epilepsy result in increased sodium channel activity with gain-of-function, characterized by slowing of fast inactivation, acceleration of its recovery or increased persistent sodium current. Further, a good response to sodium channel blockers clinically was found to be associated with a relatively small gain-of-function. In contrast, mutations in patients with late-onset forms and an insufficient response to sodium channel blockers were associated with loss-of-function effects, including a depolarizing shift of voltage-dependent activation or a hyperpolarizing shift of channel availability (steady-state inactivation). Our clinical and experimental data suggest a correlation between age at disease onset, response to sodium channel blockers and the functional properties of mutations in children with SCN2A-related epilepsy.

Recent advances in the treatment of cystinosis

SummaryCysteamine bitartrate capsules (Cystagon) have been approved by the US Food and Drug Administration for use in patients with nephropathic cystinosis. Plasma cysteamine concentrations were virtually identical at various times following ingestion of either cysteamine hydrochloride or Cystagon capsules in 24 normal control subjects. A transfer study was done with eight cystinosis patients who had been receiving either cysteamine hydrochloride or phosphocysteamine for many years. The plasma cysteamine concentration was significantly higher 2h after Cystagon and the leukocyte cystine content was significantly lower at all times after Cystagon compared to older forms of the drug. These differences are probably the result of greater patient compliance in taking the capsules compared to the older, liquid forms of the drug. A new method for following the course of renal glomerular deterioration in diseases such as cystinosis has been published recently. This method was used to re-analyse data on the efficacy of cysteamine treatment and to re-analyse new data on treating cystinosis patients with either of two doses of cysteamine (1.30 g/m2 per day and 1.95 g/m2 per day). This new method agrees well with other methods and shows that both doses of drug are equally effective in maintaining glomerular function.

A comparison of the effectiveness of cysteamine and phosphocysteamine in elevating plasma cysteamine concentration and decreasing leukocyte free cystine in nephropathic cystinosis

ABSTRACT: Cysteamine (β-mercaptoethylamine, MEA) is currently used to treat children with nephropathic cystinosis. In this study MEA was compared to phosphocysteamine (MEAP), a phosphorothioester that tastes and smells better than MEA, with respect to its ability to elevate plasma MEA and deplete leukocytes of cystine. Studies were performed in six children with nephropathic cystinosis ranging in age from 2 to 10 yr. After equimolar oral doses of either MEA or MEAP plasma cysteamine was determined at various times for 6 h. MEA was determined by sodium borohydride reduction followed by high-performance liquid chromatography separation and electrochemical detection. Leukocyte cystine was measured before and 1 and 6 h after drug administration. Peak plasma MEA was obtained 30 min to 1 h after a dose and was not significantly different when MEA (48.6 ± 10.7, mean ± SD) or MEAP (54.1 ± 20.2) was given. Significant plasma MEA concentrations were seen as early as 15 min after an oral dose, indicating rapid absorption. Analysis of vomitus indicated that hydrolysis of the phosphate group of MEAP occurs in the stomach. The percent decrease in leukocyte cystine content obtained with MEA administration (61.9%) was not significantly different from the decrease observed when MEAP was administered (65.3%). MEA and MEAP appear to be equally effective in their cystine-depleting properties.

Cystinosis: Progress in a Prototypic Disease

Abstract Objective:To review the history, basic defect, pathogenesis, clinical manifestations, diagnosis, and treatment of nephropathic cystinosis. Design:Lysosomal membrane transport studies, clin...