The activity of a damage-specific DNA-binding protein (DDB) is absent from a subset, Ddb ؊ , of cell strains from patients with xeroderma pigmentosum group E (XP-E). DDB is a heterodimer of 127-kDa and 48-kDa subunits. We have now identified single-base mutations in the gene of the 48-kDa subunit in cells from the three known Ddb ؊ individuals, but not in XP-E strains that have the activity. An A 3 G transition causes a K244E change in XP82TO and a G 3 A transition causes an R273H change in XP2RO and XP3RO. No mutations were found in the cDNA of the 127-kDa subunit. Overexpression of p48 in insect cells greatly increases DDB activity in the cells, especially if p127 is jointly overexpressed. These results demonstrate that p48 is required for DNA binding activity, but at the same time necessitate further definition of the genetic basis of XP group E.Xeroderma pigmentosum is a rare human hereditary disease, characterized by a high incidence of skin cancer upon exposure to ultraviolet (UV) light and by defective nucleotide excision repair (1). A damage-specific DNA binding (DDB) 1 activity is absent from cell strains from a minority of individuals carrying XP complementation group E (XP-E) (2-4). This activity has been purified from HeLa cells as a complex of a 127-kDa and a 48-kDa polypeptide (5, 6). Studies with duplex oligonucleotides containing unique UV-photoproducts identified a high affinity of DDB for trans-syn-, Dewar-and pyrimidine (6 -4) dimers (7). p127 alone appears to bind specifically to the UV-damaged DNA; however, the heterodimer binds with a different DNase I footprint, indicating that the heterodimer also binds specifically to damaged DNA (7). cDNA clones of DDB1 (p127) and DDB2 (p48) have been isolated from a diploid human fibroblast cDNA library and sequenced (6). While the p127 sequence is not related to any proteins of known function, the p48 sequence has 18% identity and 33% similarity to that of human CSA (Cockayne Syndrome Group A) (8).Evidence that DDB is involved in DNA repair is generally indirect (9 -12). However, microinjection of purified DDB protein into XP-E cells restores repair DNA synthesis to normal levels in XP-E Ddb Ϫ strains, while not affecting that of XP-E Ddb ϩ strains or of cells from other XP groups (13). A feasible explanation for these observations would be that while a mutation(s) in DDB is responsible for defective nucleotide excision repair in XP-E, Ddb Ϫ and Ddb ϩ strains have mutations in different subunits or different domains of a given subunit of DDB. p127 was the most likely candidate for the location of the mutations, since the large subunit alone apparently is capable of DNA binding (7, 12, 14 -16). In the present study, we sequenced cDNAs of both subunits of DDB, but observed mutations to be only in the p48 subunit of Ddb Ϫ XP-E strains. Individual and co-expression of the DDB subunits in insect cells demonstrated that p48 is required to obtain DNA binding activity. EXPERIMENTAL PROCEDURESCell Strains and Culture-Sf9 insect cells (CRL 1711) and IMR-90 norm...

Purpose: Conventional noncontrast CT (NCCT) is insensitive to hyperacute cerebral infarction in the first 3 h. Our aim was to determine if CT perfusion (CTP) can improve diagnostic accuracy over NCCT for patients presenting with stroke symptoms in the 3-hour window. Methods: Consecutive patients presenting to our emergency department with symptoms of ischemic stroke <3 h old and receiving NCCT and CTP as part of their triage evaluation were retrospectively reviewed. Patients with follow-up diffusion-weighted MRI (DWI) <7 days from ictus were included. Two readers rated the NCCT and CTP for evidence of acute infarct and its vascular territory. CTP selectively covered 24 mm of brain centered at the basal ganglia with low relative cerebral blood volume in a region of low cerebral blood flow or elevated time to peak as the operational definition for infarction. A third reader rated all follow-up DWI for acute infarct and its vascular territory as the reference standard. Sensitivity, specificity, and predictive values were calculated. An exact McNemar test and generalized estimating equations from a binary logistic regression model were used to assess the difference in detection rates between modalities. A two-sided p value <0.05 was considered significant. Results: 100 patients were included. Sixty-five (65%) patients had follow-up DWI confirmation of acute infarct. NCCT revealed 17 (26.2%) acute infarcts without false positives. CTP revealed 42 (64.6%) acute infarcts with one false positive. Of the 23 infarcts missed on CTP, 10 (43.5%) were outside the volume of coverage while the remaining 13 (56.5%) were small cortical or lacunar type infarcts (≤15 mm in size). CTP was significantly more sensitive (64.6 vs. 26.2%, p < 0.0001) and accurate (76.0 vs. 52%, p < 0.0001) and had a better negative predictive value (59.6 vs. 42.2%, p = 0.032) than NCCT. Conclusion: In a retrospective cohort of 100 patients with symptoms of hyperacute stroke in the 3-hour window, CTP provided improved sensitivity and accuracy over NCCT.

Case Presentation and EvolutionA 14-year-old Tongan male presented with a two-day history of tactile fevers and night sweats. He had a threeday history of dull right upper quadrant (RUQ) abdominal pain that extended to his upper back. The pain was intermittent in nature, characterized as five on a ten-point scale, occurred at least three times per day, was worse when laying on the right side, and slightly worse with eating, but not restrictive of dietary intake. The patient had no nausea or emesis or other symptoms. He had not consumed any uncooked or undercooked foods, nor had recent travel or camping. He had no prior hospitalizations, chronic medical problems or surgeries. His physical exam was only remarkable for localized and exquisite tenderness to palpation of his RUQ with no flank tenderness. The liver span was difficult to assess due to his pain, and he had no splenomegaly. There was no rebound or guarding.Laboratory tests revealed a white blood cell count of 10.2/mm 3 , hemoglobin 11.8 g/dl, and a platelet count 334,000/mm 3 . The differential included 80% neutrophils, 12% lymphocytes, and 7% monocytes. The total bilirubin was 1.6 mg/dl, direct bilirubin 0.6 mg/dl, aspartate aminotransferase 28 U/l, alanine aminotransferase 56 U/l, alkaline phosphatase 476 U/l, total protein 8.4 g/dl, albumin 2.3 g/dl, and lipase 149 U/l. His coagulation profile showed an international normalized ratio of 1.4, prothrombin time 16.3, and partial thromboplastin time 51.9. An abdominal ultrasound demonstrated multiple hypoechoic lesions in the right lobe of the liver, each measuring up to 3 cm.Given these findings, he was admitted to Lucile Packard Children's Hospital at Stanford. Tests for Entamoeba histolytica antibody, stool ova and parasites, and serology for Echinococcus were sent to the laboratory, and he was given intravenous clindamycin and cefipime for a potential bacterial process. A computed tomography (CT) scan of the abdomen demonstrated two large liver masses in the right lobe of the liver measuring 6.1 and 4.9 cm in largest diameter that were hypodense and heterogeneous in density without a well-defined capsule (Fig. 1). The distal appendix was dilated, measuring 1.4 cm in caliber, and contained an appendicolith near its tip. Given these findings, interventional radiology (IR) and surgery consultations were requested for the liver lesions and concern for acute appendicitis, respectively. The surgical team recommended observation, given his physical examination in combination with the absence of free fluid, stranding, and inflammation in the right lower quadrant on CT scan. In addition, his amebiasis evaluation was under way.A subsequent magnetic resonance imaging (MRI) scan demonstrated two pyogenic abscesses with no other hepatic lesions (Fig. 2). A branch off the anterior branch of the right portal vein demonstrated a thrombus (Fig. 3). The appendix was enlarged and hyperenhancing with an appendicolith and peri-appendiceal fluid consistent with appendicitis (Fig. 4). The same day the MRI was

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