Performance of commercial blood tests for the diagnosis of latent tuberculosis infection in children and adolescents.

BACKGROUND: The accurate diagnosis of latent tuberculosis infection reduces the risk of progression to severe disseminated disease. However, in young children, a major limitation of the standard tuberculin skin test is that false-negative results cannot be detected. The new interferon-gamma release assays QuantiFERON-TB Gold (Cellestis Carnegie Victoria, Australia), QuantiFERON-TB In-Tube (Cellestis), and T-SPOT.TB (Oxford Immunotec, Abingdon, United Kingdom) show promise of greater accuracy, but they may also be affected by impaired cellular immunity, resulting in indeterminate results (ie, insufficient response in positive-control wells). OBJECTIVE: To evaluate the impact of age on the performance of interferon-gamma release assays when used in a routine hospital setting among children tested for suspected active or latent TB infection. METHODS: We retrospectively studied 496 children 0 to 19 years of age who had been tested with the tuberculin skin test and at least 1 interferon-gamma release assay: 181 with QuantiFERON-TB Gold and 315 with QuantiFERON-TB In-Tube. In 154 of the children, paired interferon-gamma release assay testing was available: 87 with QuantiFERON-TB Gold/T-SPOT.TB and 67 with QuantiFERON-TB In-Tube/T-SPOT.TB. RESULTS: Compared with T-SPOT.TB, the rates of indeterminate results were significantly higher for both QuantiFERON-TB Gold and QuantiFERON-TB In-Tube. QuantiFERON-TB Gold and QuantiFERON-TB In-Tube also gave indeterminate results more frequently in children <4 years of age than in those >/=4 years of age. Indeterminate results were associated with younger age for both QuantiFERON-TB Gold and QuantiFERON-TB In-Tube but not for T-SPOT.TB. Considering age as a binary variable (<4 and >/=4 years of age), a significantly higher concentration of phytohaemagglutinin-produced interferon-gamma was observed in older children with both QuantiFERON-TB Gold and QuantiFERON-TB In-Tube. CONCLUSIONS: Different blood tests for the diagnosis of latent tuberculosis infection in children seem to perform differently, because both QuantiFERON-TB tests were more likely than T-SPOT.TB to give indeterminate results in children <4 years of age.

Short stature homeoboxcontaining gene and idiopathic short stature.

The term idiopathic short stature (ISS) refers to patients who are short due to various unknown reasons. Although it is clear that multiple factors contribute to final height, genetic factors play a crucial role. Mutations of a human homeobox gene, short stature homeobox-containing (SHOX) gene, have been shown to be associated with the short stature phenotype in patients with Turner syndrome, most patients with Leri-Weill dyschondrosteosis and some cases of ISS. The prevalence of SHOX anomalies in subjects previously recognized as having ISS has been estimated at 2.4% in a large series of ISS individuals. This review focuses on the functional properties of the SHOX gene and its linkage to ISS.

Intestinal inflammation in nursing infants: different causes and a single treatment ... but of protected origin.

Three case histories of nursing infants suffering from different forms of intestinal problems, who underwent special dietary therapy in order to solve situations that would be difficult to deal with using the special artificial milk varieties on the market, are presented. These children were administered a homemade food consisting ofParmigiano Reggiano cheese seasoned for at least 36 months, rice or maize custard and tapioca, sugar, maize oil. In the first case the diagnosis of "widespread nonspecific acute colitis" was made compatible with "antibiotic-associated colitis" and Clostridium difficile was isolated from the feces. The second case, under the suspicion of cow's milk allergy, was fed by soya and hydrolyzed milk with persitent disturbed alvus with greenish feces and mucus. The third case was represented by a nursing child with persistent diarrhoic alvus after an acute episode with subsequent intolerance to rice milk. After the introduction of the food based on Parmigiano Reggiano cheese, all cases showed a rapid and progressive improvement of symptoms and alvus characteristics and were discharged with increased weight. The Parmigiano Reggiano cheese shows a high concentration of easily absorbed amino acids and oligopeptides like a hydrolyzed proteic preparation. As regards the lipoid component the medium and short chain fatty acids are directly absorbed in the bowel and immediately usable as a significant source of energy. Finally, another relevant characteristic of Parmigiano Reggiano cheese is the complete absence of lactose. The use of Parmigiano Reggiano cheese as a dietary therapy is appropriate not only for its high nutritional value, but also for its characteristics as a functional food that produces beneficial effects on health with regards to the gastrointestinal tract and the inflammatory problems resulting from alimentary intolerance, post-therapeutic antibiotic dismicrobism, or post-infective conditions. Moreover, its efficay on these pathologic conditions is further improved by the prebiotic and probiotic effects resulting from the oligosaccharides and the bacterial flora of this natural food product, only derived from the nature and the work of skilled artisans closely tied to tradition.

Thirty-year persistence of obesity after presentation to a pediatric obesity clinic.

BACKGROUND: Few large, long-term studies are available on the relationship between childhood and adult obesity. AIM: The present study examined the 30-year association between childhood and adult obesity in a large sample of girls with essential and uncomplicated obesity. SUBJECTS AND METHODS: 318 girls who had visited our Pediatric Obesity Clinic between January 1972 and December 1974 were re-contacted between January 2002 and December 2005. All had undergone an assessment of weight, height and pubertal status at the baseline visit. Anthropometry was performed again on those who agreed to take part in the follow-up visit. The women's general practitioners were also asked to compile a health questionnaire. Hypertension, hypercholesterolemia, hypertriglyceridemia and diabetes were defined according to current guidelines. Rates are expressed as number of cases per 1000 person-years (PY). Multivariable Poisson regression was used to identify predictors of persistent obesity. RESULTS: 224 (70%) of the 318 girls took part to the 30-year follow-up study. They had the same baseline anthropometry of those not available at follow-up. Sixteen per cent of them were still obese at the 30-year follow-up, giving a persistence rate of obesity of 5.2 x 1000 PY. Tanner stages > or = 1 [rate = ratios (RR) from 4.73 to 7.74 for different stages, p < or = 0.021] and Z-score of BMI (RR = 2.72 for one SDS, p = 0.019) were independent predictors of obesity persistence. Having a university degree vs. an elementary degree was instead protective (RR = 0.32, p = 0.009). The most prevalent complication was hypertriglyceridemia (8.8 x 1000 PY), followed by hypercholesterolemia (rate = 8.4 x 1000 PY), hypertension (rate = 5.2 x 1000 PY) and diabetes mellitus (rate = 1.0 x 1000 PY). CONCLUSION: The study reinforces the notion that obesity should be prevented at an early age and shows that adolescents with severe obesity and low educational degree are at greater risk of becoming obese adults.

Long-term course of chronic hepatitis C in children: from viral clearance to end-stage liver disease.

BACKGROUND & AIMS: The natural course of chronic hepatitis C (CHC) in children is not well understood. The aim of this study was to assess the long-term course of CHC in a large sample of otherwise healthy children. METHODS: From 1990 to 2005, 504 consecutive antihepatitis C virus (HCV)-positive children were enrolled at 12 centers of a national observatory and were followed up retrospectively/prospectively. RESULTS: Putative exposure was perinatal in 283 (56.2%) cases, parenteral in 158 (31.3%), and unknown in 63 (12.5%). At baseline, 477 (94.6%) cases were HCV RNA seropositive, 118 (24.7%) of which were treated with standard interferon alpha. Ten years after putative exposure, the outcome in 359 HCV RNA-positive, untreated patients was (1) undetectable viremia in 27 (7.5%) (by Cox regression analysis, spontaneous viral clearance was independently predicted by genotype 3 [hazard ratio 6.44; 95% confidence interval: 2.7-15.5]) and (2) persistent viremia in 332 (92%) cases. Six of these 332 cases (1.8%) progressed to decompensated cirrhosis (mean age, 9.6 years). This latter group included 5 Italian children perinatally infected with genotype 1a (4 of the mothers were drug users). Thirty-three (27.9%) treated patients achieved a sustained virologic response. CONCLUSIONS: Over the course of a decade, few children with chronic HCV infection cleared viremia spontaneously, and those who did were more likely to have genotype 3. Persistent viral replication led to end-stage liver disease in a small subgroup characterized by perinatal exposure, maternal drug use, and infection with HCV genotype 1a. Children with such features should be considered for early treatment.

Homeostatic cytokines and expansion of regulatory T cells accompany thymic impairment in children with Down syndrome.

Down syndrome (DS), the most common chromosomal abnormality in humans, is characterized by precocious immunologic aging that results, among other things, in alterations of B and T lymphocyte subsets and natural killer cells, defective phagocytosis, and chemotaxis of polymorphonuclear leukocytes. We studied 30 children affected by DS, compared them to 29 healthy controls, and evaluated the functionality of the thymus (by measuring the amount of lymphocytes that express the signal-joint T cell receptor rearrangement excision circles [sj-TREC+]), the plasma levels of interleukin (IL)-7 and IL-15, the proliferative T cell response to these cytokines, the expression of the alpha chain of the IL-7 receptor (CD127), the extrathymic differentiation of T lymphocytes, and the presence of natural regulatory T cells (Tregs) in peripheral blood. We found that DS children had a significantly lower number of sj-TREC+ lymphocytes, the levels of which were strongly correlated with age. We found higher plasma levels of IL-7 and IL-15 than in healthy controls, and a higher proliferative T cell response to IL-15. DS children also showed a lower percentage of CD4(+) cells and profound alterations of T cell differentiation, along with increased amount of Tregs and of cells expressing markers of apoptosis. We can thus hypothesize that the precocious thymic involution occurring in DS is mirrored by a high production of IL-7 and IL-15, which is crucial for cell survival and proliferation. The complex alterations present in the periphery are likely the result of a compensatory mechanism: the overproduction of homeostatic cytokines could be a reaction to the impaired intrathymic production of T lymphocytes and/or to the expansion of Treg in the periphery, and could be required to allow the survival of T cells.

Low-density lipoprotein oxidizability in children with chronic renal failure.

BACKGROUND: In childhood, dyslipidemia and low-density lipoprotein (LDL) oxidation play an important role in the development of atherosclerosis. Alterations of these factors have been shown in adult uremic patients. METHODS: Nine children affected by chronic renal failure (CRF; urinary tract malformation, n = 8; polycystic kidney disease, n = 1) were studied to investigate the abnormalities of plasma lipoprotein concentration and composition and to assess the susceptibility of LDL to oxidation. All patients with CRF were on conservative treatment and, after informed consent, underwent the evaluation of (i) quantitative and qualitative plasma lipid profile; (ii) lipoprotein oxidation in vitro; and (iii) lipoprotein anti-oxidant content. These results were compared to those of an age-matched control group of eight healthy children. RESULTS: Total cholesterol, LDL and triglycerides were significantly higher in CRF than in the control group. The composition of lipoproteins was different in the two groups: the amount of anti-oxidant factors (alpha-, gamma-tocopherol and carotenoids) was different in CRF and normal controls children, while LDL susceptibility to oxidation was significantly higher in uremic children than in controls. CONCLUSIONS: CRF patients, already before dialysis, have a higher LDL oxidizability due to an altered lipoprotein composition and a low anti-oxidant content; therefore they have higher risk factors for atherosclerosis. On the basis of these data, supplementation with anti-oxidants might be useful in CRF children, but further studies are needed to evaluate the efficacy and safety of this therapeutic intervention.

Approaches to dyslipidemia treatment in children and adolescents.

Atherosclerosis represents a disease that begins in childhood, and alterations in lipid concentration play a fundamental role in the development of this condition. Children and adolescents with high cholesterol levels are more likely than their peers in the general population to present with dyslipidemia in adulthood. Precocious identification of dyslipidemias associated with premature cardiovascular disease is crucial during childhood to delay or prevent the atherosclerotic process. The National Cholesterol Education Program has established guidelines for the diagnosis and treatment of dyslipidemia during pediatric age. It has been suggested that a heart-healthy diet should begin at 2 years of age, and no adverse effects on psychological aspects, growth, pubertal development and nutritional status in children and adolescents limiting total and saturated fat intake have been demonstrated. Pharmacotherapy should be considered in children aged 10 years or older when low-density lipoprotein cholesterol concentrations remain very high despite dietary therapy, especially when multiple risk factors are present. The lipid-lowering drugs recommended for childhood and adolescence are resins and statins. The increasing use of statins is dependent on their effectiveness and safety. Ezetimibe, a selective cholesterol absorption inhibitor, may provide a similar cholesterol-lowering effect as that reached with statin treatment. This review provides an update on recent advances in the therapy of dyslipidemia, especially hypercholesterolemia, during pediatric age and adolescence.

Clinical phenotype of lathosterolosis.

Lathosterolosis (LS) is a defect of cholesterol biosynthesis due to the deficiency of the enzyme sterol-C5-desaturase. Only two patients have been described to date, both presenting with multiple malformations, mental retardation, and liver involvement. In addition in one of them pathological examination revealed mucolipidosis-like inclusions on optic microscopy analysis, and peculiar lysosomal lamellar bodies on electron microscopy analysis. This study is focused on a better characterization of the clinical phenotype of LS. We describe a further case in a fetus, sibling of the first patient reported, presenting with neural tube defect, craniofacial and limb anomalies, and prenatal liver involvement. The fetal phenotype suggests the possible occurrence of significant intrafamilial variability in LS, and expands the phenotypic spectrum of the disease. Histological examination of autopsy samples from the fetus and skin fibroblasts from the living sibling suggested that the mucolipidosis-like picture previously reported is not a constant feature of LS, being possibly associated with the most severe biochemical defects, but confirmed the ultrastructural finding of lamellar inclusions. The LS phenotype appears to be characterized by the distinctive association of a recognizable pattern of congenital anomalies, involving axial and appendicular skeleton, liver, central nervous and urogenital systems, and lysosomal storage. This condition partially overlaps with other defects of sterol metabolism, suggesting intriguing pathogenic links among these conditions.

Unusual concurrent detection by polymerase chain reaction of Bartonella henselae and parvovirus b19 in an immunocompetent child with erythema nodosum and hepatic granulomatous disease.

We report an unusual case of documented Bartonella henselae genotype I from hepatic tissue in an Italian immunocompetent girl presenting with erythema nodosum and hepatic granulomata. Polymerase chain reaction (PCR) was performed on biopsied liver sample to confirm the etiologic role of B. henselae and to identify the genetic variant of this organism. A PCR on the same liver biopsy for parvovirus B19 was also positive, but the clinical meaning of this was not clear.

Mitochondrial alterations and tendency to apoptosis in peripheral blood cells from children with Down syndrome.

Different types of cells from subjects with Down syndrome (DS) have an increased susceptibility to cell death. We have studied apoptosis and mitochondrial (mt) membrane potential (DeltaPsi(m)) in peripheral blood mononuclear cells (PBMC) from DS children and age-matched healthy donors after in vitro treatment with apoptogenic molecules, along with mtDNA content. We found that PBMC from DS and healthy controls had a similar tendency to undergo apoptosis and a similar amount of mtDNA. However, in cells from DS subjects, mitochondria showed a higher loss of DeltaPsi(m), underlying the presence of an increasing susceptibility of these organelles to damaging agents.

Growth hormone impaired secretion and antipituitary antibodies in patients with coeliac disease and poor catch-up growth after a long gluten-free diet period: a causal association?

INTRODUCTION: Coeliac disease (CD) is usually associated with impaired growth in children. A gluten-free diet (GFD) induces a catch-up growth with the recovery of height in about 2 years. AIM AND DISCUSSION: The lack of the height improvement has been related to growth hormone (GH) secretion impairment. CD is an autoimmune disease often associated with other endocrine and non-endocrine autoimmune disease. The aim of this study was to evaluate antipituitary autoantibodies (APA) and antihypothalamus autoantibodies in CD children with poor clinical response to a GFD and growth hormone deficiency (GHD). We diagnosed CD on the basis of specific antibodies and endoscopic biopsies in 130 patients aged 1-15 years. Seven CD children, without catch-up growth after at least 12-months GFD, were tested for GH secretion and, in five out of seven patients, the diagnosis of GHD was made in the absence of metabolic and systemic diseases. RESULTS: APA and antihypothalamus antibodies were detected by the indirect immunofluorescence method in the seven CD children without catch-up growth factor and in 25 CD children without growth impairment matched for sex and age, and in 58 healthy children as control groups. APA resulted positive at high titres in four out of five CD-GHD patients and were also positive at low titres (<1:8) in three of only CD children and in two out of 58 controls. Hypothalamic-pituitary magnetic resonance imaging (MRI) was normal in all patients except in one with cystic pineal. APA have been previously detected not only in adults with GHD, but also in idiopathic GHD children, suggesting the occurrence of an autoimmune hypophysitis in these patients. CONCLUSION: In our study, the presence of APA in CD children without catch-up growth after GFD seems to be able to identify an autoimmune form of hypophysitis involving the somatotrophs cells.

Genetic polymorphisms of Fas (CD95) and Fas ligand (CD178) influence the rise in CD4+ T cell count after antiretroviral therapy in drug-naïve HIV-positive patients.

Fas and Fas ligand (FasL) are the main genes that control cell death in the immune system. Indeed, they are crucial for the regulation of T lymphocyte homeostasis because they can influence cell proliferation. A strong debate exists on the importance of Fas/FasL system during HIV infection, which is characterized by the loss of CD4+ T cells directly, or indirectly, caused by the virus. To investigate whether the genetic background of the host plays a role in the immunoreconstitution, we studied the influence of different Fas and FasL polymorphisms on CD4+ T lymphocyte count and plasma viral load following initiation of highly active antiretroviral therapy (HAART) in drug-naïve HIV+ patients. We studied 131 individuals, who were compared to 136 healthy donors. Statistical analysis was performed by using Chi2 test, Fischer's Exact Test, and analysis for repeated measurements. The group of HIV+ patients had an unexpected lower frequency of FasLnt169 polymorphism (delT allele) than healthy controls (p = 0.039). We then observed no significant differences in the immune reconstitution, in terms of CD4+ T cell increase, when the influence of single alleles of the gene Fas or FasL was considered. However, the combination of some polymorphisms of Fas or FasL significantly influenced CD4+ T cell production and viral load decrease, showing that these genes can play a role in the immunoreconstitution triggered by antiretroviral therapy.

Direct analysis of thymic function in children with Down's syndrome.

BACKGROUND: Down's syndrome (DS) is characterized by several immunological defects, especially regarding T cell compartment. DS is considered the best example of accelerated ageing in humans. Direct observations of the thymus have shown that in DS this organ undergoes severe histological and morphological changes. However, no data on its capacity to generate T cells are present in the literature. Here, using a new technology based upon real time PCR, we have investigated the capacity of the thymus to produce and release newly generated T lymphocytes (the so called "recent thymic emigrants", RTE) in children with DS. METHODS: We studied 8 children affected by DS, aged 2-7 years, compared with 8 age- and sex-matched healthy controls. Flow cytometry was used to determine different lymphocytes subsets. Real time PCR with the Taqman system was used to quantify the amount of RTE, i.e. peripheral blood lymphocytes that express the T cell receptor rearrangement excision circles (TREC). RESULTS: In comparison with control children, those with DS had a significant lower number of TREC+ peripheral blood cells. Moreover, in DS children but not in controls, a strong negative correlation between age and the levels of TREC+ cells was found. CONCLUSIONS: The direct measure of thymic output indicates that the impairment of the organ results in a reduced production of newly generated T cells. This observation could suggest that cytokines able to modulate thymic function, such as interleukins, could be useful to improve the functionality of the organ and to treat the immunodeficiency present in DS subjects.

Acute hepatitis in course of rotavirus gastroenteritis: a case report.

We report a case of an immunocompetent child with acute rotavirus gastroenteritis who developed an acute liver damage during infection. Acute rotavirus-related hepatitis has been previously described in immunodeficient children, but never in a normal child.

The De Barsy syndrome.

BACKGROUND: In 1968, De Barsy reported on a girl exhibiting an aged aspect, 'dwarfism, oligophrenia, and degeneration of the elastic tissue in cornea and skin'. The disorder was recognized as a subgroup of cutis laxa syndrome and termed De Barsy-Moens-Dierckx syndrome. The pathogenesis of the disorder is unknown. METHODS: To improve the comprehension of the pathogenetic mechanisms involved in the De Barsy syndrome, we performed an ultrastructural, morphometric, immunocytochemical study on a skin biopsy of a boy with the De Barsy phenotype, who has been clinically followed for 12 years from birth. Moreover, the lysyl oxidase activity was measured on skin fibroblasts cultured in vitro. RESULTS: Light and electron microscopy, morphometry, and immunocytochemical observations showed a significant reduction of the elastic fibers in the papillary and in the reticular dermis of patient compared to an age-matched control (p < 0.05). By contrast, the collagen structure, content, and the distribution were normal, as well as lysyl oxidase activity in the medium of in vitro fibroblasts (12,323 DPM/10(6) cells). The immunoreaction for antibodies recognizing fibrillin-1, neutrophilic elastase, and tumor necrosis factor-alpha was stronger, whereas that for antibodies against transforming growth factor-beta was less pronounced in the dermis of the De Barsy boy compared to control. CONCLUSIONS: Clinical, phenotypic, and structural data were consistent with the diagnosis of De Barsy syndrome. This is the first case described in Italy. Clinical and structural data confirm that the elastic component is mostly affected in this disorder. Moreover, ultrastructural and immunochemical findings suggest that both elastic fiber degradative and very likely synthetic processes are involved.

Hypobetalipoproteinemia with an apparently recessive inheritance due to a "de novo" mutation of apolipoprotein B.

Familial hypobetalipoproteinemia (FHBL) is a co-dominant disorder either linked or not linked to apolipoprotein (apo) B gene. Abetalipoproteinemia (ABL) is a recessive disorder due to mutations of microsomal triglyceride transfer protein (MTP) gene. We investigated a patient with apparently recessive hypobetalipoproteinemia consistent with symptomatic heterozygous FHBL or a "mild" form of ABL. The proband had fatty liver associated with LDL-cholesterol (LDL-C) and apo B levels <5th percentile but no truncated apo B forms detectable in plasma. MTP gene sequence revealed that he was a carrier of the I128T polymorphism and an unreported amino acid substitution (V168I) unlikely to be the cause of hypobetalipoproteinemia. Apo B gene sequence showed that he was heterozygous for two single base substitutions in exon 9 and 22 resulting in a nonsense (Q294X) and a missense (R1101H) mutation, respectively. Neither of his parents carried the Q294X; his father and paternal grandmother carried the R1101H mutation. Analysis of polymorphic genetic markers excluded non-paternity. In conclusion, the proband has a "de novo" mutation of apo B gene resulting in a short truncated apo B form (apo B-6.46). Sporadic cases of FHBL with an apparently recessive transmission may be caused by "de novo" mutations of apo B gene.

Endocrine aspects of coeliac disease.

Coeliac disease (CD) is a permanent intolerance to gluten that results in damage of the small intestinal mucosa, and it is one of the common causes of chronic malabsorption in children. It is well known that patients with CD are at great risk of malignant complications, but in patients with CD many other disorders have been recognized. Autoimmunity diseases, such as type 1 diabetes mellitus, thyroid diseases, and autoimmune polyglandular syndromes are known to be associated with CD, and they seem to be related to gluten exposure. Growth, bone metabolism, and fertility can be affected in patients with CD, especially if they are not on a gluten-free diet. We review the literature on endocrine aspects of CD, because patients with CD are at great risk of developing endocrine disorders.

Fibrosis in chronic hepatitis C acquired in infancy: is it only a matter of time?

OBJECTIVE: The natural history of chronic hepatitis C acquired in infancy is not well understood. The progression of fibrosis was analyzed in untreated children with chronic hepatitis C virus infection and no other hepatotoxic cofactors. METHODS: A total of 112 pediatric patients (13 with paired liver biopsies) were considered. Fibrosis was assessed by METAVIR score (i.e., stage F1 to F4). The ratio between the stage of fibrosis (METAVIR units) and the presumed duration of infection represented the "estimated" rate of fibrosis progression per year. In patients with paired biopsies, the "observed" rate of fibrosis progression was defined as the difference between the stage of fibrosis in the two biopsies divided by the time interval between them. RESULTS: Both age of patients at biopsy and duration of infection correlated with stage of fibrosis (p < 0.002 and p < 0.0005, respectively). Stage of fibrosis differed significantly between patients with infection lasting less or more than 10 yr (p < 0.0006). Sex, hepatitis C virus genotype, and route of infection did not correlate with stage of fibrosis. Among the 13 patients with paired biopsies, stage of fibrosis increased in seven and did not change in six; the median rate of estimated fibrosis progression per year was 0.142. The difference between estimated and observed fibrosis progression rates was significant (coefficient of determination, r(2) = 0.031), which demonstrated that the prediction of the fibrosis progression was unreliable in 97% of patients. CONCLUSIONS: Chronic hepatitis C acquired in childhood is a progressive, slow-moving, fibrotic disease. Fibrosis progression inferred on the basis of linear mathematical models should be critically evaluated in the clinical practice.