Adam J. Jonas

Asymptomatic maternal combined homocystinuria and methylmalonic aciduria (cblC) detected through low carnitine levels on newborn screening.

A symptom-free woman gave birth to a girl with a low carnitine level on newborn screening. The baby was unaffected, but the mother had biochemical abnormalities and mutations characteristic of the cblC defect of vitamin B(12) metabolism (late-onset form). This patient with cblC was detected through her infants newborn screening.

Hereditary multiple exostoses with spine involvement in a 4-year-old boy.

Hereditary multiple exostosis (HME) is an autosomal dominant disorder characterized by multiple osteochondromas. We describe a case of acute cervical spinal cord compression arising from an exostosis at the lamina of C7 and T1 in a 4‐year‐old Mexican‐American boy with HME. His affected sibling also displayed spinal cord compression because of a bony exostosis. Acute cervical spinal cord compression resulting from osteochondroma is a serious complication of HME.

Costello syndrome with pancreatic islet cell hyperplasia

A 3‐month‐old boy with Costello syndrome (CS) developed respiratory distress and fatal arrhythmias. An autopsy showed cardiac hypertrophy, mild coarctation of the aorta, and pancreatic islet cell hyperplasia. To our knowledge, this is the first report of a pancreatic abnormality in CS. Islet cell hyperplasia has also been observed in leprechaunism, Beckwith–Wiedemann (BWS), and Simpson–Golabi–Behmel syndromes. The syndromes are thought to involve abnormal insulin or insulin‐like growth factor (IGF) pathways. Clinical similarities among these disorders and CS, together with the finding of islet cell hyperplasia, suggest that they may be related.

Lysosomal sulfate transport: inhibitor studies.

Sulfate derived from the degradation of macromolecules is released from lysosomes via a carrier mediated process. In order to further characterize this process, recognized inhibitors of the erythrocyte band 3 anion transporter were examined for their effects on the lysosomal system. Studies with band 3 transport site inhibitors such as DIDS, SITS and phenylglyoxal indicated that, similar to the case for the band 3 protein, the lysosomal transporter has critical lysine and arginine residues. Band 3 translocation pathway or channel blocking inhibitors had mixed effects on the lysosomal system. 1,2-Cyclohexanedione, which covalently modifies a band 3 arginine residue distinct from that modified by phenylglyoxal, inhibited lysosomal sulfate transport. In contrast, the potent band 3 inhibitor dipyridamole had no effect on lysosomal sulfate transport indicating that there are some structural differences between the erythrocyte and lysosomal anion transporters. The band 3 translocation inhibitors niflumic acid and dinitrofluorobenzene were both effective inhibitors of the lysosomal system. Cupric ion inhibited sulfate transport while Ca2+, Co2+, Mg2+, Mn2+, and Zn2+ had no inhibitory effects. Exposure of intact lysosomes to trypsin largely ablated transport of sulfate. This information should be useful in efforts to further elucidate the structure and function of the lysosomal sulfate transporter.

RECONSTITUTION OF LYSOSOMAL SULFATE TRANSPORT IN PROTEOLIPOSOMES

As part of a strategy to purify the lysosomal sulfate transporter, we developed a method for reconstitution of transport in artificial membrane vesicles. Lysosomal membranes were prepared from Percoll density gradient purified rat liver lysosomes and membrane proteins were solubilized using the non-ionic detergent, Triton X-100. The solubilized proteins were mixed with liposomes prepared by sonication of egg yolk lecithin and the detergent was removed by passage of the mixture over Bio-beads XAD2. The resulting proteoliposomes exhibited saturable sulfate transport with characteristics that were very similar to those observed in lysosomal membranes. Transport in proteoliposomes had a Km of 155 microM, exhibited pH dependence and was sensitive to inhibition by DIDS. Reconstitution of transport in proteoliposomes may be useful as an assay for purification of the lysosomal sulfate carrier.

Lysosomal Sulfate Transport is Stimulated by Trivalent Cations

Objective: To study the regulatory roles of multivalent cations on lysosomal sulfate transport. Materials and Methods: Lysosomes were isolated and purified from Sprague-Dawley rat liver. Sulfate transport was measured using a filtration system and radioactive-labeled substrates. Results: Sulfate uptake by lysosomal membrane vesicles and intact lysosomes was markedly increased in the presence of trivalent cations such as lanthanum but was relatively unaffected by divalent cations such as calcium. The order of stimulatory potency of tested trivalent cations on sulfate transport was LaCl3＞AlCl3＞FeCl3＞CrCl3. Uptake of 100 μM sulfate increased between 4 and 8-fold in the presence of 100 μM lanthanum (K1/2=42 μM lanthanum) while uptake of glucose remained largely unchanged. Similar to previously reported characteristics of lysosomal sulfate transport, lanthanum-stimulated sulfate uptake was time dependent, pH-dependent, temperature-dependent, exhibited saturation kinetics (Km=90 μM) and was sensitive to inhibition by 4,4”-diisothiocyano-2,2-disulfonic acid stilbene (DIDS). Lanthanum stimulation of sulfate at pH 5.0 was greatest when sulfate and lanthanum were on the same side of the membrane. This was not the case for sulfate countertransport at pH 7.0 which was unaffected by the presence of lanthanum in the extra-vesicular buffer, consistent with an already maximal rate of transport. Lanthanum-stimulated sulfate uptake was inhibited by the protonophore, CCCP. Conclusion: It appears that lanthanum and other trivalent cations interact with the lysosomal membrane sulfate transporter to allow for enhanced function possibly by substituting for the effects of hydrogen ions.