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.

Normal leucocyte lysosome-rich granular fractions exhibited counter-transport of cystine, confirming that cystine transport across the lysosomal membrane is carrier-mediated. The trans-activation of cystine transport was temperature-dependent but relatively independent of the external Na+ or K+ concentration in phosphate buffer. Counter-transport, measured as uptake of exogenous [3H]cystine, increased with increasing intralysosomal cystine content up to approx. 3 nmol of half-cystine/unit of hexosaminidase activity. The amount of [3H]cystine entering lysosomes loaded with unlabelled cystine decreased when unlabelled cystine was added to the extralysosomal medium. Lysosomal cystine counter-transport was stereospecific for the L-isomer. Cystathionine, cystamine and cysteamine-cysteine mixed disulphide gave evidence of sharing the lysosomal cystine-transport system, although at lower activity than cystine. Other tested amino acids, including arginine, glutamate and homocystine, were inactive in this system. Nine leucocyte lysosome-rich preparations from eight different cystinotic patients displayed virtually no counter-transport of cystine, conclusively establishing that a carrier-mediated system for cystine transport is dysfunctional in cystinotic lysosomes.

Cystinotic lysosome-rich leucocyte granular fractions, loaded with [35S]cystine, were exposed to different cystine-depleting agents. During a 30 min incubation at 37 degrees C, untreated cystinotic granular fractions lost negligible [35S]cystine when corrected for lysosome rupture. Granular fractions exposed to 0.1 mM-cysteamine lost 64% of their initial cystine, and hexosaminidase activity was decreased by 10%. This was accompanied by the formation of high concentrations of [35S]cysteine-cysteamine mixed disulphide within the granular-fraction pellet, and, in the presence of N-ethylmaleimide, increasing amounts of [35S]cysteine-N-ethylmaleimide adduct outside the granular fraction. In separate experiments, [35S]cystine exited cystinotic leucocyte lysosomes at a negligible rate (half-times 199 and 293 min), but [35S]cysteine-cysteamine mixed disulphide exhibited substantial egress (half-times 66 and 88 min) and was recovered intact outside the granular-fraction pellet. We conclude that cysteamine depletes lysosomes of cystine by participating in a thiol-disulphide interchange reaction to produce cysteine and cysteine-cysteamine mixed disulphide, both of which traverse the cystinotic leucocyte lysosomal membrane.

OBJECTIVE-Hutchinson-Gilford progeria syndrome (HGPS) is a rare early-onset accelerated senescence syndrome. In HGPS, a recently identified de novo dominant mutation of the lamin A gene (LMNA) produces abnormal lamin A, resulting in compromised nuclear membrane integrity. Clinical features include sclerotic skin, cardiovascular and bone abnormalities, and marked growth retardation. Craniofacial features include "bird-like" facies, alopecia, craniofacial disproportion and dental crowding. Our prospective study describes dental, oral soft tissue, and craniofacial bone features in HGPS.METHODS-Fifteen patients with confirmed p.G608G LMNA mutation (1-17 years, 7 males, 8 females) received comprehensive oral evaluations. Anomalies of oral soft tissue, gnathic bones and dentition were identified.RESULTS-Radiographic findings included hypodontia (n=7), dysmorphic teeth (n=5), steep mandibular angles (n=11), and thin basal bone (n=11). Soft tissue findings included ogival palatal arch (n=8), median sagittal palatal fissure (n=7), and ankyloglossia (n=7). Calculated dental ages (9months-11y2m) were significantly lower than chronological ages (1y6m-17y8m) (p=0.002). Eleven children manifested a shorter mandibular body, anterior/posterior cranial base and ramus, but a larger gonial angle, compared to age/gender/race norms.CONCLUSION-Novel oral-craniofacial phenotypes and quantification of previously reported features are presented. Our findings expand the HGPS phenotype and provide additional insight into the complex pathogenesis of HGPS.

Primary hypothyroidism is a known complication of nephropathic cystinosis, a lysosomal storage disorder characterized by renal failure as well as deterioration of other organs. The drug cysteamine depletes lysosomes of cystine and helps preserve renal function and enhance growth in cystinosis patients. To determine whether cysteamine also prevents hypothyroidism, we retrospectively divided 101 patients into group A (n = 28; well treated), group B (n = 26; partially treated), and group C (n = 47; poorly treated). Lifetable analysis indicated a significantly higher probability of remaining free of L-T4 replacement in group A vs. group B (P = 0.09) or group C (P = 0.004). Cysteamine therapy also improved mean height z-scores (-2.17 in group A, -3.04 in group B, and -4.07 in group C) and reduced the bone age deficit (i.e. chronological age minus bone age) by 1.5 yr for every 10 yr of previous cysteamine therapy. We conclude that in addition to its other salutary effects, oral cysteamine therapy helps prevent hypothyroidism and enhances growth in patients with nephropathic cystinosis.