Neurologic dysfunction and pancytopenia secondary to acquired copper deficiency following duodenal switch: case report and review of the literature.

The duodenal switch (DS) procedure is a type of restrictive-malabsorptive bariatric surgery that is typically reserved for severe morbidly obese people (body mass index >50 kg/m(2)) with obesity-related comorbidities, when diet, lifestyle changes, and pharmacologic therapy fail to achieve adequate weight loss. Patients who undergo the DS procedure are at risk for malabsorption, malnutrition, and nutrient deficiencies. Copper deficiency is a commonly reported long-term complication of Roux-en-Y gastric bypass (RYGB) surgery. However, data are limited on copper deficiency-associated complications and their treatment in DS patients. This article presents a case of a patient who developed hypocupremia with associated pancytopenia, myeloneuropathy, and leukoencephalopathy following DS and reviews the literature related to the pathophysiology of copper deficiency and copper replacement in bariatric surgery patients. When severe diarrhea was present, intravenous elemental copper 4 mg (as cupric chloride)/d in addition to daily oral copper gluconate was necessary to correct the hypocupremia and improve the hematologic indices and neurologic symptoms of copper deficiency. When diarrhea subsided, oral elemental copper 4 mg (as copper gluconate) 3 times daily maintained normal serum copper concentrations and avoided the relapse of severe neurologic dysfunction. Regular monitoring of serum copper and ceruloplasmin concentrations is recommended following DS surgery to detect any copper deficiency before irreversible neurologic damage occurs. Long-term copper supplementation is likely necessary to maintain normal copper status in DS patients.

Regulation of neurexin 1beta tertiary structure and ligand binding through alternative splicing.

Neurexins and neuroligins play an essential role in synapse function, and their alterations are linked to autistic spectrum disorder. Interactions between neurexins and neuroligins regulate inhibitory and excitatory synaptogenesis in vitro through a "splice-insert signaling code." In particular, neurexin 1beta carrying an alternative splice insert at site SS#4 interacts with neuroligin 2 (found predominantly at inhibitory synapses) but much less so with other neuroligins (those carrying an insert at site B and prevalent at excitatory synapses). The structure of neurexin 1beta+SS#4 reveals dramatic rearrangements to the "hypervariable surface," the binding site for neuroligins. The splice insert protrudes as a long helix into space, triggers conversion of loop beta10-beta11 into a helix rearranging the binding site for neuroligins, and rearranges the Ca(2+)-binding site required for ligand binding, increasing its affinity. Our structures reveal the mechanism by which neurexin 1beta isoforms acquire neuroligin splice isoform selectivity.