Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Example Input: Context: Restless leg syndrome (RLS) is a sensorimotor disorder. Clinical studies have implicated the dopaminergic system in RLS, while others have suggested that it is associated with insufficient levels of brain iron. To date, alterations in brain iron status have been demonstrated but, despite suggestions from the clinical literature, there have been no consistent findings documenting a dopaminergic abnormality in RLS brain tissue. In this study, the substantia nigra and putamen were obtained at autopsy from individuals with primary RLS and a neurologically normal control group. A quantitative profile of the dopaminergic system was obtained. Additional assays were performed on a catecholaminergic cell line and animal models of iron deficiency. RLS tissue, compared with controls, showed a significant decrease in D2R in the putamen that correlated with severity of the RLS. RLS also showed significant increases in tyrosine hydroxylase (TH) in the substantia nigra, compared with the controls, but not in the putamen. Both TH and phosphorylated (active) TH were significantly increased in both the substantia nigra and putamen. There were no significant differences in either the putamen or nigra for dopamine receptor 1, dopamine transporters or for VMAT. Significant increases in TH and phosphorylated TH were also seen in both the animal and cell models of iron insufficiency similar to that from the RLS autopsy data. For the first time, a clear indication of dopamine pathology in RLS is revealed in this autopsy study. The results suggest cellular regulation of dopamine production that closely matches the data from cellular and animal iron insufficiency models. The results are consistent with the hypothesis that a primary iron insufficiency produces a dopaminergic abnormality characterized as an overly activated dopaminergic system as part of the RLS pathology.
Question: Which deficiency is the cause of restless leg syndrome?
Example Output: iron

Example Input: Context: ESSENTIALS: When high probability of pulmonary embolism (PE), sensitivity of computed tomography (CT) is unclear. We investigated the sensitivity of multidetector CT among 134 patients with a high probability of PE. A normal CT alone may not safely exclude PE in patients with a high clinical pretest probability. In patients with no clear alternative diagnosis after CTPA, further testing should be strongly considered. Whether patients with a negative multidetector computed tomographic pulmonary angiography (CTPA) result and a high clinical pretest probability of pulmonary embolism (PE) should be further investigated is controversial. This was a prospective investigation of the sensitivity of multidetector CTPA among patients with a priori clinical assessment of a high probability of PE according to the Wells criteria. Among patients with a negative CTPA result, the diagnosis of PE required at least one of the following conditions: ventilation/perfusion lung scan showing a high probability of PE in a patient with no history of PE, abnormal findings on venous ultrasonography in a patient without previous deep vein thrombosis at that site, or the occurrence of venous thromboembolism (VTE) in a 3-month follow-up period after anticoagulation was withheld because of a negative multidetector CTPA result. We identified 498 patients with a priori clinical assessment of a high probability of PE and a completed CTPA study. CTPA excluded PE in 134 patients; in these patients, the pooled incidence of VTE was 5.2% (seven of 134 patients; 95% confidence interval [CI] 1.5-9.0). Five patients had VTEs that were confirmed by an additional imaging test despite a negative CTPA result (five of 48 patients; 10.4%; 95% CI 1.8-19.1), and two patients had objectively confirmed VTEs that occurred during clinical follow-up of at least 3 months (two of 86 patients; 2.3%; 95% CI 0-5.5). None of the patients had a fatal PE during follow-up. A normal multidetector CTPA result alone may not safely exclude PE in patients with a high clinical pretest probability.
Question: What can be predicted with the Wells criteria?
Example Output: pulmonary embolism

Example Input: Context: Evaluate efficacy and safety of tanezumab, a humanized monoclonal antibody against nerve growth factor, in neuropathic pain. Two randomized controlled trials. Patients with pain due to diabetic peripheral neuropathy (DPN) or postherpetic neuralgia (PHN). In the DPN study, patients received subcutaneous tanezumab 20 mg or placebo on Day 1 and Week 8. Evaluations included change from baseline in average DPN pain (primary endpoint), Patient's Global Assessment of DPN, and safety (including neuropathy assessments). Due to a partial clinical hold limiting enrollment and treatment duration, the prespecified landmark analysis was modified post hoc from Week 16 to Week 8. In the PHN study, patients received intravenous tanezumab 50 g/kg, tanezumab 200 g/kg, or placebo on Day 1. Evaluations included change from baseline in average daily pain (primary endpoint), Brief Pain Inventory-short form, Patient's Global Assessment of pain from PHN, and safety. Mean DPN pain reduction from baseline to Week 8 was greater with tanezumab vs placebo (P = 0.009); differences in Patient's Global Assessment of DPN were not significant (P > 0.05). Neither tanezumab dose resulted in significant differences vs placebo in efficacy in PHN (P > 0.05), although tanezumab 200 g/kg provided some benefit. Neuropathy assessments showed no meaningful changes. Tanezumab provided effective pain reduction in DPN. In PHN, only the highest tanezumab dose reduced pain; treatment differences were not significant. No new safety concerns were observed despite preexisting neuropathy.
Question: What is the target of tanezumab?
Example Output:
ngf