The 2'-hydroxy group of flavin mononucleotide influences the catalytic function and promiscuity of the flavoprotein iodotyrosine dehalogenase.

The isoalloxazine ring system of the flavin cofactor is responsible for much of the catalytic power and diversity associated with flavoproteins. While the specificity of these enzymes is greatly influenced by the surrounding protein environment, the ribityl group of the cofactor may also participate in stabilizing transient intermediates formed by substrates and flavin. A conserved interaction between the phenolate oxygen of l-iodotyrosine and the 2'-hydroxy group of flavin mononucleotide (FMN) bound to iodotyrosine deiodianase (IYD) implied such a contribution to catalysis. Reconstitution of this deiodinase with 2'-deoxyflavin mononucleotide (2'-deoxyFMN) decreased the overall catalytic efficiency of l-iodotyrosine dehalogenation (kcat/Km) by more than 5-fold but increased kcat by over 2-fold. These affects are common to human IYD and its homolog from Thermotoga neapolitana and are best explained by an ability of the 2'-hydroxy group of FMN to stabilize association of the substrate in its phenolate form. Loss of this 2'-hydroxy group did not substantially affect the formation of the one electron reduced semiquinone form of FMN but its absence released constraints that otherwise suppresses the ability of IYD to promote hydride transfer as measured by a competing nitroreductase activity. Generation of IYD containing 2'-deoxyFMN also removed steric constraints that had previously limited the use of certain mechanistic probes. For example, l-O-methyl iodotyrosine could be accommodated in the active site lacking the 2'-hydroxy of FMN and shown to be inert to dehalogenation as predicted from a mechanism requiring ketonization of the phenolic oxygen. In the future, ancillary sites within a cofactor should now be considered when engineering new functions within existing protein architectures as demonstrated by the ability of IYD to promote nitroreduction after loss of the 2'-hydroxy group of FMN.

Breast Cancer Mortality among Women with a BRCA1 or BRCA2 Mutation in a Magnetic Resonance Imaging Plus Mammography Screening Program.

Annual breast magnetic resonance imaging (MRI) plus mammography is the standard of care for screening women with inherited BRCA1/2 mutations. However, long-term breast cancer-related mortality with screening is unknown. Between 1997 and June 2011, 489 previously unaffected BRCA1/2 mutation carriers aged 25 to 65 years were screened with annual MRI plus mammography on our study. Thereafter, participants were eligible to continue MRI screening through the high-risk Ontario Breast Screening Program. In 2019, our data were linked to the Ontario Cancer Registry of Cancer Care Ontario to identify all incident cancers, vital status and causes of death. Observed breast cancer mortality was compared to expected mortality for age-matched women in the general population. There were 91 women diagnosed with breast cancer (72 invasive and 19 ductal carcinoma in situ (DCIS)) with median follow-up 7.4 (range: 0.1 to 19.2) years. Four deaths from breast cancer were observed, compared to 2.0 deaths expected (standardized mortality ratio (SMR) 2.0, p = 0.14). For the 489 women in the study, the probability of not dying of breast cancer at 20 years from the date of the first MRI was 98.2%. Annual screening with MRI plus mammography is a reasonable option for women who decline or defer risk-reducing mastectomy.

Conversion of a Dehalogenase into a Nitroreductase by Swapping its Flavin Cofactor with a 5-Deazaflavin Analogue.

Natural and engineered nitroreductases have rarely supported full reduction of nitroaromatics to their amine products, and more typically, transformations are limited to formation of the hydroxylamine intermediates. Efficient use of these enzymes also requires a regenerating system for NAD(P)H to avoid the costs associated with this natural reductant. Iodotyrosine deiodinase is a member of the same structural superfamily as many nitroreductases but does not directly consume reducing equivalents from NAD(P)H, nor demonstrate nitroreductase activity. However, exchange of its flavin cofactor with a 5-deazaflavin analogue dramatically suppresses its native deiodinase activity and leads to significant nitroreductase activity that supports full reduction to an amine product in the presence of the convenient and inexpensive NaBH4 .

Oxygen flux reduces Cux1 positive neurons and cortical growth in a gestational rodent model of growth restriction.

BACKGROUND: The mammalian cerebral cortex forms in an inside-out manner, establishing deep cortical layers before superficial layers and is regulated by transcription factors which influence cell differentiation. Preterm birth interrupts the trajectory of normal neurodevelopment and adverse perinatal exposures have been implicated in cortical injury. We hypothesise that growth restriction (GR) and fluctuating hyperoxia (ΔO2) impair cortical laminar development. METHODS: Sprague-Dawley rats received 18% (non-restricted, NR) or 9% (growth restricted, GR) protein diet from E15-P7. Litters were reared in air or fluctuating hyperoxia (circa 10kPa) from P0 to P7. Cortical laminae were stained and measured. Neuronal subtypes were quantified using immunofluorescence for subtype-specific transcription factors (Satb2, Cux1, Ctip2, Tbr1). RESULTS: ΔO2 did not affect brain weight at P7 but reduced cortical thickness in both NR (p<0.05) and GR groups (p<0.001). ΔO2 resulted in superficial cortical thinning in both groups and in the deep layers of GR pups (p<0.001). Cell density was preserved. ΔO2 did not affect proportions of callosal, corticothalamic and corticospinal neurons but resulted in a reduction of neurons expressing Cux1 (p<0.01) implicated in dendritic branching and synapse formation. CONCLUSION: Postnatal ΔO2, a modifiable factor in neonatal care, impairs cortical development in a rodent model with preferential disadvantage to superficial neurons.

Pax6 exerts regional control of cortical progenitor proliferation via direct repression of Cdk6 and hypophosphorylation of pRb.

The mechanisms by which early spatiotemporal expression patterns of transcription factors such as Pax6 regulate cortical progenitors in a region-specific manner are poorly understood. Pax6 is expressed in a gradient across the developing cortex and is essential for normal corticogenesis. We found that constitutive or conditional loss of Pax6 increases cortical progenitor proliferation by amounts that vary regionally with normal Pax6 levels. We compared the gene expression profiles of equivalent Pax6-expressing progenitors isolated from Pax6⁺/⁺ and Pax6⁻/⁻ cortices and identified many negatively regulated cell-cycle genes, including Cyclins and Cdks. Biochemical assays indicated that Pax6 directly represses Cdk6 expression. Cyclin/Cdk repression inhibits retinoblastoma protein (pRb) phosphorylation, thereby limiting the transcription of genes that directly promote the mechanics of the cell cycle, and we found that Pax6 inhibits pRb phosphorylation and represses genes involved in DNA replication. Our results indicate that Pax6's modulation of cortical progenitor cell cycles is regional and direct.

Differences in natural history between breast cancers in BRCA1 and BRCA2 mutation carriers and effects of MRI screening-MRISC, MARIBS, and Canadian studies combined.

BACKGROUND: It is recommended that BRCA1/2 mutation carriers undergo breast cancer screening using MRI because of their very high cancer risk and the high sensitivity of MRI in detecting invasive cancers. Clinical observations suggest important differences in the natural history between breast cancers due to mutations in BRCA1 and BRCA2, potentially requiring different screening guidelines. METHODS: Three studies of mutation carriers using annual MRI and mammography were analyzed. Separate natural history models for BRCA1 and BRCA2 were calibrated to the results of these studies and used to predict the impact of various screening protocols on detection characteristics and mortality. RESULTS: BRCA1/2 mutation carriers (N = 1,275) participated in the studies and 124 cancers (99 invasive) were diagnosed. Cancers detected in BRCA2 mutation carriers were smaller [80% ductal carcinoma in situ (DCIS) or ≤10 mm vs. 49% for BRCA1, P < 0.001]. Below the age of 40, one (invasive) cancer of the 25 screen-detected cancers in BRCA1 mutation carriers was detected by mammography alone, compared with seven (three invasive) of 11 screen-detected cancers in BRCA2 (P < 0.0001). In the model, the preclinical period during which cancer is screen-detectable was 1 to 4 years for BRCA1 and 2 to 7 years for BRCA2. The model predicted breast cancer mortality reductions of 42% to 47% for mammography, 48% to 61% for MRI, and 50% to 62% for combined screening. CONCLUSIONS: Our studies suggest substantial mortality benefits in using MRI to screen BRCA1/2 mutation carriers aged 25 to 60 years but show important clinical differences in natural history. IMPACT: BRCA1 and BRCA2 mutation carriers may benefit from different screening protocols, for example, below the age of 40.

Peritraumatic distress: its relationship to posttraumatic stress and complicated grief symptoms in sudden death survivors.

Although sudden death has been linked to posttraumatic stress disorder (PTSD), its role in complicated grief (CG) and sudden death survivors is unknown. This questionnaire study investigated the role of peritraumatic distress in PTSD and CG symptoms in adults (n = 125) an average of 28.37 months (SD = 3.12) after a loved one's sudden death. The Peritraumatic Distress Inventory, Impact of Event Scale-Revised, and Inventory of Complicated Grief were administered to assess symptoms of peritraumatic distress, PTSD, and CG, respectively. Peritraumatic distress was the strongest correlate of both PTSD (ß = .42, p < .001) and CG (ß = .39, p < .001) symptoms, in a model containing current distress (Hopkins Symptom Checklist-21). Peritraumatic distress may be a key mechanism in the development of both PTSD and CG, therefore suddenly bereaved individuals reporting higher peritraumatic distress may be at risk of both adverse trauma and grief reactions.

Is ductal carcinoma in situ with "possible invasion" more predictive of invasive carcinoma than pure ductal carcinoma in situ?

OBJECTIVES: To compare the underestimation of ductal carcinoma in situ (DCIS) vs DCIS with "possible invasion" at breast biopsy and to determine if any factors related to clinical indication, imaging abnormality, biopsy, or DCIS-grade affected the likelihood of underestimation. METHODS: Of 3836 consecutive lesions that were biopsied by using a 14-gauge needle, 117 lesions revealed DCIS. Surgical pathology results of invasive carcinoma were compared with needle biopsy results of DCIS or DCIS with possible invasion. Clinical indication, imaging abnormality, biopsy guidance modality, sample number, and histologic grade were recorded. Yates corrected χ(2) and Fisher exact tests were used to determine differences between groups. RESULTS: A total of 101 lesions were DCIS and 16 were DCIS with possible invasion at biopsy. Thirty-six of 117 lesions (31%) revealed invasive carcinoma at resection pathology. Invasive carcinoma was present more often when DCIS with possible invasion was diagnosed compared with pure DCIS (7/16 [44%] vs 29/101 [29%], P = .36). No factor, including clinical indication, imaging abnormality, biopsy guidance method, sample number, or grade, was found to significantly affect the likelihood of underestimation for lesions diagnosed as DCIS vs DCIS with "possible invasion." The likelihood of pure DCIS underestimation significantly increased when lesions were high grade compared with either intermediate or low grade (18/44 [41%] vs 9/44 [21%] vs 2/10 [20%], P = .03). CONCLUSION: For lesions biopsied by using a 14-gauge needle, there is a trend towards underestimation of the presence of invasive carcinoma when pathology reveals DCIS with possible invasion compared with pure DCIS. High-grade DCIS was significantly more likely to be underestimated.

Psychological impact of recall on women with BRCA mutations undergoing MRI surveillance.

OBJECTIVE: The addition of magnetic resonance imaging (MRI) to mammography for surveillance of women with BRCA mutations significantly increases sensitivity but lowers specificity. This study aimed to examine whether MRI surveillance, and particularly recall, is associated with increased anxiety, depression, or breast cancer worry/distress. METHODS: Women with BRCA mutations in an MRI surveillance study were invited to complete: Hospital Anxiety and Depression Scale (HADS), Lerman's Breast Cancer Worry Scale, Breast Cancer Worry Interference Scale, and a quality of life rating at 3 time points: 1-2 weeks before (T1), 4-6 weeks after (T2) and 6 months after their annual surveillance (T3). Repeated measures analyses were performed over the 3 time points for recalled and non-recalled women. RESULTS: 55 women (30 BRCA1, 25 BRCA2) completed study instruments at T1 and T2, and 48 at T3. Eighteen women (32%) were recalled for additional imaging. At T1, 27 women (49%) were above HADS threshold for "possible cases" for anxiety (score≥8). Recalled (but not non-recalled) women had a significant increase of HADS anxiety at T2 which dropped to below baseline by T3. No group differences were observed in terms of change over time in other quantitative psychological measures. CONCLUSIONS: While breast MRI surveillance did not have a detrimental psychological impact on women with a BRCA1 or BRCA2 mutation, recalling these very high-risk women for further imaging after a false positive MRI scan temporarily increased their global anxiety.

The role of Pax6 in forebrain development.

Pax6 encodes a highly conserved transcriptional regulator with two DNA-binding motifs, a paired domain and a paired-like homeodomain. Humans carrying PAX6 loss-of-function mutations suffer from abnormal development of the eyes (congenital aniridia) and brain. Small eye mice carrying Pax6 loss-of-function mutations provide a good model for these human conditions. Their analysis has demonstrated the critical importance of this transcription factor in multiple cell types and at several key stages of forebrain development. In the forebrain, Pax6 is critical for the establishment of the pallial-subpallial boundary, which separates dorsal (future cerebral cortex) and ventral (future striatum) telencephalic regions. Levels of Pax6 expression are critically important for cortical progenitor proliferation and its presence in a rostro-lateral(high) to caudo-medial(low) gradient in the cortex is necessary to establish rostro-lateral identities. Furthermore, axon guidance is disrupted in Pax6⁻/⁻ mutants: the majority of thalamocortical axons fail to enter the ventral telencephalon and those that do are unable to innervate their cortical targets. The extent to which the effects of Pax6 later in development are secondary to its effects in early patterning and proliferation remains largely unknown. This is likely to be clarified by future studies on the molecular mechanisms of action of Pax6 and, in particular, the identification of its downstream target genes. Such studies should also help generate an increasingly coherent understanding of how this pleiotropic transcription factor becomes involved in so many facets of neural development.

Pax6 is required at the telencephalic pallial-subpallial boundary for the generation of neuronal diversity in the postnatal limbic system.

During embryogenesis, the pallial-subpallial boundary (PSB) divides the two main progenitor domains in the telencephalon: the pallium, the major source of excitatory neurons, and the subpallium, the major source of inhibitory neurons. The PSB is formed at the molecular interface between the pallial (high Pax6+) and subpallial (high Gsx2+) ventricular zone (VZ) compartments. Initially, the PSB contains cells that express both Pax6 and Gsx2, but during later stages of development this boundary is largely refined into two separate compartments. In this study we examined the developmental mechanisms underlying PSB boundary formation and the postnatal consequences of conditional loss of Pax6 function at the PSB on neuronal fate in the amygdala and olfactory bulb, two targets of PSB-derived migratory populations. Our cell fate and time-lapse imaging analyses reveal that the sorting of Pax6+ and Gsx2+ progenitors during embryogenesis is the result of a combination of changes in gene expression and cell movements. Interestingly, we find that in addition to giving rise to inhibitory neurons in the amygdala and olfactory bulb, Gsx2+ progenitors generate a subpopulation of amygdala excitatory neurons. Consistent with this finding, targeted conditional ablation of Pax6 in Gsx2+ progenitors results in discrete local embryonic patterning defects that are linked to changes in the generation of subsets of postnatal excitatory and inhibitory neurons in the amygdala and inhibitory neurons in the olfactory bulb. Thus, in PSB progenitors, Pax6 plays an important role in the generation of multiple subtypes of neurons that contribute to the amygdala and olfactory bulb.

Improvement in DCIS detection rates by MRI over time in a high-risk breast screening study.

Although magnetic resonance imaging (MRI) is much more sensitive than mammography for detecting early invasive breast cancer, in many high-risk screening studies MRI was less sensitive than mammography for detecting ductal carcinoma in situ (DCIS). We reviewed our experience detecting DCIS in our single center study of annual MRI, mammography, ultrasound and clinical breast examination (CBE) for screening very high-risk women. All cases of DCIS±microinvasion and invasive cancer were compared in two time frames: before (period A) and after (period B) July 2001-when we acquired expertise in the detection of DCIS with MRI-with respect to patient demographics, method of detection, and rates of detection of invasive cancer and DCIS. In period A there were 15 cases (3.1% of 486 screens) in 223 women, of which 2 (13%) were DCIS-one with microinvasion-neither detected by MRI. In period B there were 29 cases (3.3% of 877 screens) in 391 women, of which 10 (34%) were DCIS±microinvasion (p=0.04), all 10 detected by MRI but only one by mammography. No DCIS cases were detected by ultrasound or CBE. Specificity was lower in period B than in period A but acceptable. The ability to detect DCIS with screening MRI improves significantly with experience. MRI-guided biopsy capability is essential for a high-risk screening program. In experienced centers the increased sensitivity of MRI relative to mammography is at least as high for DCIS as it is for invasive breast cancer.

The generation of superficial cortical layers is regulated by levels of the transcription factor Pax6.

The ventricular zone (VZ) of the embryonic dorsal telencephalon is a major site for generating cortical projection neurons. The transcription factor Pax6 is highly expressed in apical progenitors (APs) residing in the VZ from the earliest stages of corticogenesis. Previous studies mainly focused on Pax6(-/-) mice have implicated Pax6 in regulating cortical progenitor proliferation, neurogenesis, and formation of superficial cortical layers. We analyzed the developing cortex of PAX77 transgenic mice that overexpress Pax6 in its normal domains of expression. We show that Pax6 overexpression increases cell cycle length of APs and drives the system toward neurogenesis. These effects are specific to late stages of corticogenesis, when superficial layer neurons are normally generated, in cortical regions that express Pax6 at the highest levels. The number of superficial layer neurons is reduced in postnatal PAX77 mice, whereas radial migration and lamina specification of cortical neurons are not affected by Pax6 overexpression. Conditional deletion of Pax6 in cortical progenitors at midstages of corticogenesis, by using a tamoxifen-inducible Emx1-CreER line, affected both numbers and specification of late-born neurons in superficial layers of the mutant cortex. Our analyses suggest that correct levels of Pax6 are essential for normal production of superficial layers of the cortex.

Preoperative breast magnetic resonance imaging: controversies arising in the quest to evaluate clinical benefit.

Breast magnetic resonance imaging (MRI) is indisputably the highest sensitivity test available to detect breast cancer, revealing more extensive cancer in the ipsilateral and otherwise occult cancer in the contralateral breasts when used before surgery. The use of preoperative breast MRI has become somewhat controversial, because the clinical benefit of the heightened detection provided by MRI has been questioned in the context of multidisciplinary breast cancer treatment, relatively low local recurrence, and metachronous contralateral cancer rates. Also, MRI detection rates have been compared with the high rates reported in the pathology literature. The emerging clinical outcome literature is showing conflicting results to demonstrating actual overall benefit. Critical review of this literature reveals several misconceptions about MRI detection rates and limitations of many of the published outcome studies to date, which render the results not necessarily generalizable to contemporary optimized breast MRI practices. This article addresses some of the misconceptions raised by critics, provides a critical review of the clinical outcome literature, reviews patient subgroups anticipated to have the highest yield when using preoperative MRI, makes recommendations for optimizing breast MRI practice, and suggests areas for potential future research.

[Colorectal cancer in the elderly: which surgical approach?]. / Carcinoma colo-rettale nell'anziano: quale approccio chirurgico?

Single-operator case studies of 135 patients undergoing surgery for colon rectal carcinoma (CRC) between June 2004 and April 2008 in our Institute. Patients were divided into two groups (A: < 70 years old, n = 44, - = 27 U = 17, B: ≥ 70 years old, n = 91, - = 49 U = 42) and were compared clinical, pathological and surgical data. In particular, were analyzed age range and average age, ASA score, post-operative complications (major and minor), mortality at 30 days. Surgical procedure with radical intent (R0) was achieved in 41 (93%) and 76 (83%) patients respectively in group A and B; Given the more than double the number in group B than in group A is easy to imagine that for equal numbers in both groups might have observed an almost equal R0 resections in both groups; Despite the uneven number of groups A and B, it was noted that age is not a factor in determining the surgical therapeutic strategy in the CRC, as well as the clinical conditions of patients.

Preliminary in vivo validation of a dedicated breast MRI and sonographic coregistration imaging system.

OBJECTIVE: Sonographic correlation of breast MRI findings is often challenging. We present a preliminary in vivo feasibility study evaluating the degree of error of a new MRI-sonography coregistration system for showing MRI and sonographically visible breast lesions. CONCLUSION: In 10 patients with 13 lesions, the system was found to be an accurate means for targeting sonography to MRI of the same breast lesions.

Is mammography adequate for screening women with inherited BRCA mutations and low breast density?

BACKGROUND: Several observational studies have shown that magnetic resonance imaging (MRI) is significantly more sensitive than mammography for screening women over age 25 at high risk for hereditary breast cancer; however, MRI is more costly and less specific than mammography. We sought to determine the extent to which the low sensitivity of mammography is due to greater breast density. METHODS: Breast density was evaluated for all patients on a high-risk screening study who were diagnosed with breast cancer between November 1997 and July 2006. Density was measured in two ways: qualitatively using the four categories characterized by the Breast Imaging Reporting and Data System and quantitatively using a computer-aided technique and classified as (a) 50% density. Comparison of sensitivity of mammography (and MRI) for each individual density category and after combining the highest two and lowest two density categories was done using Fisher's exact test. RESULTS: A total of 46 breast cancers [15 ductal carcinoma in situ (DCIS) and 31 invasive] were diagnosed in 45 women (42 with BRCA mutations). Mean age was 48.3 (range, 32-68) years. Overall, sensitivity of mammography versus MRI was 20% versus 87% for DCIS and 26% versus 90% for invasive cancer. There was a trend towards greater mammographic sensitivity for invasive cancer in women with fattier breasts compared with those with greater breast density (37-43% versus 8-12%; P = 0.1), but this trend was not seen for DCIS. CONCLUSION: It is necessary to add MRI to mammography for screening women with BRCA mutations even if their breast density is low.

BRCA1 mutation and young age predict fast breast cancer growth in the Dutch, United Kingdom, and Canadian magnetic resonance imaging screening trials.

PURPOSE: Magnetic resonance imaging (MRI) screening enables early detection of breast cancers in women with an inherited predisposition. Interval cancers occurred in women with a BRCA1 mutation, possibly due to fast tumor growth. We investigated the effect of a BRCA1 or BRCA2 mutation and age on the growth rate of breast cancers, as this may influence the optimal screening frequency. EXPERIMENTAL DESIGN: We reviewed the invasive cancers from the United Kingdom, Dutch, and Canadian MRI screening trials for women at hereditary risk, measuring tumor size at diagnosis and on preceding MRI and/or mammography. We could assess tumor volume doubling time (DT) in 100 cancers. RESULTS: Tumor DT was estimated for 43 women with a BRCA1 mutation, 16 women with a BRCA2 mutation, and 41 women at high risk without an identified mutation. Growth rate slowed continuously with increasing age (P = 0.004). Growth was twice as fast in BRCA1 (P = 0.003) or BRCA2 (P = 0.03) patients as in high-risk patients of the same age. The mean DT for women with BRCA1/2 mutations diagnosed at ages < or =40, 41 to 50, and >50 years was 28, 68, and 81 days, respectively, and 83, 121, and 173 days, respectively, in the high-risk group. Pathologic tumor size decreased with increasing age (P = 0.001). Median size was 15 mm for patients ages < or =40 years compared with 9 mm in older patients (P = 0.003); tumors were largest in young women with BRCA1 mutations. CONCLUSION: Tumors grow quickly in women with BRCA1 mutations and in young women. Age and risk group should be taken into account in screening protocols.

Incidental MRI detection of BRCA1-related solitary peritoneal carcinoma during breast screening--A case report.

BACKGROUND: The reported cumulative risk of developing primary peritoneal carcinoma (PPC) one to 20 years after prophylactic bilateral oophorectomy is 3.5% to 4.3%. Virtually all reported cases have been stage III or IV. CASE: During MRI screening of the breasts, an incidental mass on the surface of the liver was identified in a 56-year-old BRCA1 mutation carrier who had undergone prophylactic bilateral salpingo-oophorectomy several years previously with no evidence of malignancy. After four cycles of chemotherapy a localized, grade 3 serous papillary adenocarcinoma was resected followed by further chemotherapy and radiation. She remains disease-free 3 years post-treatment. CONCLUSION: The literature on PPC after prophylactic oophorectomy is reviewed. To the best of our knowledge, this is the first description of an apparently localized case of BRCA related PPC outside the pelvis.

[Cholecysto-gastric fistulas: case report and literature revision]. / Le fistole colecisto-gastriche. Descrizione di un caso e revisione della letteratura.

Authors report a recent case of cholecysto-gastric fistula. On the basis of their own experience and of the literature, authors discuss the pathogenesis of the cholecysto-enteric fistulas and underline the relative non frequent of fistulas with the stomach. Authors stress the available diagnostic and therapeutic features and believe that this disease deserves, whenever possible, a surgical correction.