Systematic quantification of the anion transport function of pendrin (SLC26A4) and its disease-associated variants.

Thanks to the advent of rapid DNA sequencing technology and its prevalence, many disease-associated genetic variants are rapidly identified in many genes from patient samples. However, the subsequent effort to experimentally validate and define their pathological roles is extremely slow. Consequently, the pathogenicity of most disease-associated genetic variants is solely speculated in silico, which is no longer deemed compelling. We developed an experimental approach to efficiently quantify the pathogenic effects of disease-associated genetic variants with a focus on SLC26A4, which is essential for normal inner ear function. Alterations of this gene are associated with both syndromic and nonsyndromic hereditary hearing loss with various degrees of severity. We established HEK293T-based stable cell lines that express pendrin missense variants in a doxycycline-dependent manner, and systematically determined their anion transport activities with high accuracy in a 96-well plate format using a high throughput plate reader. Our doxycycline dosage-dependent transport assay objectively distinguishes missense variants that indeed impair the function of pendrin from those that do not (functional variants). We also found that some of these putative missense variants disrupt normal messenger RNA splicing. Our comprehensive experimental approach helps determine the pathogenicity of each pendrin variant, which should guide future efforts to benefit patients.

Cadherin 23-C Regulates Microtubule Networks by Modifying CAMSAP3's Function.

Cadherin-related 23 (CDH23) is an adhesive protein important for hearing and vision, while CAMSAP3/Marshalin is a microtubule (MT) minus-end binding protein that regulates MT networks. Although both CDH23 and CAMSAP3/Marshalin are expressed in the organ of Corti, and carry several protein-protein interaction domains, no functional connection between these two proteins has been proposed. In this report, we demonstrate that the C isoform of CDH23 (CDH23-C) directly binds to CAMSAP3/Marshalin and modifies its function by inhibiting CAMSAP3/Marshalin-induced bundle formation, a process that requires a tubulin-binding domain called CKK. We further identified a conserved N-terminal region of CDH23-C that binds to the CKK domain. This CKK binding motif (CBM) is adjacent to the domain that interacts with harmonin, a binding partner of CDH23 implicated in deafness. Because the human Usher Syndrome 1D-associated mutation, CDH23 R3175H, maps to the CBM, we created a matched mutation in mouse CDH23-C at R55H. Both in vivo and in vitro assays decreased the ability of CDH23-C to interact with CAMSAP3/Marshalin, indicating that the interaction between CDH23 and CAMSAP3/Marshalin plays a vital role in hearing and vision. Together, our data suggest that CDH23-C is a CAMSAP3/Marshalin-binding protein that can modify MT networks indirectly through its interaction with CAMSAP3/Marshalin.

Methicillin-resistant Staphylococcus aureus epidural abscess after transforaminal epidural steroid injection.

Transforaminal epidural steroid injections are provided frequently for patients with lumbar radiculopathy, having demonstrated efficacy and safety. We present a patient who developed methicillin-resistant Staphylococcus aureus epidural abscess 11 days after a transforaminal epidural steroid injection. The abscess required surgical intervention and intravenous vancomycin. Fortunately, the patient made a full recovery, and continues to do well one year later. The incidence, etiology and treatment of epidural injection-related infections are reviewed.

Effectiveness of transforaminal epidural steroid injections in low back pain: a one year experience.

Transforaminal epidural steroid injections under fluoroscopy are an alternative treatment for lower back pain with radiculopathy. We followed 82 patients with a standardized telephone questionnaire at 2, 6, and 12 months after the first injection, in order to assess their effectiveness. Ninety-two patients with radiculopathic back pain due to spinal stenosis, herniated discs, spondylolisthesis, and degenerated discs, underwent transforaminal epidural steroid injections under fluoroscopy. Eighty-two patients were followed with a standardized telephone questionnaire. The population was divided into four groups: Group I, previous back surgery (16%); Group II, discogenic abnormalities: herniations, bulges, or degeneration, (42%); Group III, spinal stenosis (32%); Group IV, those without MRI (11%). Age ranged between 24 to 99 years, mean 64.5. Forty-seven were female, 35 male. Thirteen patients (16%) underwent one procedure, 27 patients (33%) two, 37 patients (45%) three, and five patients (6%) four, an average 2.4 procedures per patient. The pain scores for all patients improved significantly at all three time points (2, 6 and 12 months) compared to the initial mean pain score of 7.3 to mean pain scores of 3.4, 4.5 and 3.9 respectively. After one year, 36 patients did not take any pain medications. Greater than 50% improvement after one year was seen in 23% of Group I; 59% in Group II; 35% in Group III and 67% in Group IV. Transforaminal epidural steroid injections can offer significant pain reduction up to one year after initiation of treatment in patients with discogenic pain and possibly in patients with spinal stenosis.

Neuropathic pain: Review of mechanisms and pharmacologic management.

Neuropathic pain is a challenge for clinicians because it is resistant to commonly prescribed analgesics, such as opioids and nonsteroidal antiinflammatory drugs. Fortunately, adjuvant analgesics, drugs not typically thought of as pain relievers, may be effective. It is helpful to classify adjuvant analgesics used to treat neuropathic pain into two broad categories: (1) membrane stabilizing agents, which inhibit ectopic discharges on damaged neural membranes, and (2) drugs that enhance dorsal horn inhibition, which may augment biogenic amine or GABAergic mechanisms in the dorsal horn of the spinal cord. Current evidence regarding efficacy generally does not support the use of one drug over another, and selection of a particular drug may depend on experience or expected side effects. The overall efficacy of tricyclic antidepressants for neuropathic pain is modest, and they may produce intolerable side effects. Based on current studies, gabapentin is a reasonable alternative to antidepressants, as initial monotherapy or add-on treatment, particularly for painful diabetic peripheral neuropathy and postherpetic neuralgia. From a practical standpoint, to optimize analgesia more than one drug may be necessary. Although polypharmacy is the result, this approach may improve therapy and minimize side effects. From a safety standpoint, medications generally should be started at low doses and titrated to effect. Although labor-intensive, this strategy can improve compliance and optimize patient care.