Developmental Neuropathology and Neurodegeneration of Down Syndrome: Current Knowledge in Humans

Individuals with Down syndrome (DS) suffer from developmental delay, intellectual disability, and an early-onset of neurodegeneration, Alzheimer’s-like disease, or precocious dementia due to an extra chromosome 21. Studying the changes in anatomical, cellular, and molecular levels involved may help to understand the pathogenesis and develop target treatments, not just medical, but also surgical, cell and gene therapy, etc., for individuals with DS. Here we aim to identify key neurodevelopmental manifestations, locate knowledge gaps, and try to build molecular networks to better understand the mechanisms and clinical importance. We summarize current information about the neuropathology and neurodegeneration of the brain from conception to adulthood of foetuses and individuals with DS at anatomical, cellular, and molecular levels in humans. Understanding the alterations and characteristics of developing Down syndrome will help target treatment to improve the clinical outcomes. Early targeted intervention/therapy for the manifestations associated with DS in either the prenatal or postnatal period may be useful to rescue the neuropathology and neurodegeneration in DS.

Exploring polymorphisms and effects of candidate genes on milk fat quality in dairy sheep

The aim of the present study was to investigate the genetic control of the fatty acid (FA) composition in milk from 3 breeds of sheep: Altamurana, Gentile di Puglia, and Sarda. Single nucleotide polymorphisms within genes, encoding enzymes putatively involved in the synthesis and metabolism of milk fat, were selected for analysis, and the allele substitution effects were determined for 16 genes, which were polymorphic in the 3 sheep breeds, upon the milk fat composition. Four genes (alpha-1-antichymotrypsin-2; diacylglycerol O-acyltransferase homolog-2; propionyl Coenzyme A carboxylase, beta polypeptide; and insulin-like growth factor-I) play a role in the desaturation of stearic FA into polyunsaturated fatty acids. Furthermore, 2 genes (growth hormone receptor and zona pellucida glycoprotein-2) affect the variability of the total fat content in addition to the butyric and stearic FA profile, and the fatty acid synthetase gene has an influence on the medium-chain FA. Milk FA profiles play an important role in dairy sheep farming because they have a large effect on cheese characteristics and also because sheep milk may be marketed as a source of nutraceuticals because it contains higher levels of conjugated linoleic acid than milk from other ruminants. The current study evaluated the global effects of a large number of single nucleotide polymorphisms and haplotypes on traits that are not commonly investigated in sheep but that are potentially very useful for improving milk quality.

Laboratory markers for COPD in “susceptible” smokers

Smoking is the major risk factor for the development of chronic obstructive pulmonary disease. Apart from the important preventive steps of smoking cessation, there are no other specific treatments for COPD that are as effective in reversing the condition. However, only a relatively small proportion of smokers-about 15%-will develop clinically relevant COPD. Allergy, airway hyper-responsiveness (AHR) to methacholine, and gender differences have been proposed to identify individuals susceptible to the development of COPD. However, variable response to cigarette smoke clearly suggests genetic susceptibility. Among the COPD candidate genes are those (a) that effect the production of proteases and antiproteases, (b) modulate the metabolism of toxic substances in cigarette smoke, (c) are involved with mucocilliary clearance, and (d) that influence inflammatory mediators. Recently, sputum cells from smokers with and without COPD were tested for Microsatellite DNA Instability (MSI) with positive results. This finding suggests that MSI can be a useful marker of genetic susceptibility and thereby indicate destabilization of the genome in the "susceptible" smoker. Nevertheless, COPD lacks established viable biomarkers to predict and monitor disease progression and outcome variables. Such monitoring tools may be induced sputum, exhaled air condensate, peripheral blood, urine, bronchial biopsies, and bronchoalveolar lavage fluid (BALF). This review summarizes recent research on potential laboratory markers in smokers and subsequent COPD development.

Few smokers develop COPD. Why?

COPD is a common disease and its major risk factor, cigarette smoking, has been identified. However, only a minority of smokers develop clinically relevant disease. Although, the current understanding of the pathogenesis includes an "abnormal inflammation" as a response to various noxious agents, its various pathways are not clear. Oxidative stress, inflammation, tissue damage and tissue repair (remodeling) are parts of the complex procedure leading to COPD. This is a review of the available literature concerning the "susceptible" smoker. An epidemiological model is discussed, putting emphasis on the timing of the exposure to cigarette smoke. There are evidences that respiratory adenoviral infection in early life could be also an important factor. Differences in nutrition could also play a role in protecting against the oxidative stress. Airway hyperresponsiveness failed to clarify the whole picture and is still open for debate. Genetic differences are the most likely explanations to describe the "susceptible" smoker. However, the only well-established genetic risk factor is the alpha-l-antitrypsin. Other candidate genes were reviewed, alpha-l-antichymotrypsin, blood group antigens, vitamin-D binding protein, a2-macroglobulin, immunoglobulin deficiency, extracellular superoxide dismutase, secretory leukocyte proteinase inhibitor, cathepsin G, tumor necrosis factor-a gene and others. Microsatellite DNA instability in COPD could be a useful tool to identify the locus of genetic alterations leading to COPD. Thus, in addition to exposure to exogenous factors, host factors, most likely several genes, are involved and affect various pathways of the pathogenesis of COPD.

Inherited metabolic diseases of the liver

Many inherited metabolic diseases affect the liver in neonates, children, or adults. The histopathologic changes are diverse and may be acute or chronic. They can be considered primary (when the injury is from the cytopathic effect of an accumulated metabolite) or secondary (e.g., an infection caused by an immune deficiency). All forms of liver disease are described: for example, intrahepatic cholestasis, neonatal hepatitis with giant-cell transformation, paucity of bile ducts, steatosis, steatohepatitis, necroinflammatory diseases (acute or chronic), fibrosis, cirrhosis, and neoplasms (benign or malignant). Familiarity with the morphologic changes is important in clinicopathologic correlation, diagnosis, and understanding of pathogenetic mechanisms.

Phenotype of CF and the effects of possible modifier genes

Cystic fibrosis is an inherited multi-system disease, characterised by progressive lung disease and pancreatic insufficiency that is classically attributed to the dysfunction of a single gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR). The widely diverse phenotypic expression of CF is likely influenced by other genetic traits separate from the CFTR locus or modifier genes. Many of the genes currently under study as potential modifiers of CF, particularly those which influence the severity of lung disease, are involved in the control of infection, immunity and inflammation. Some of these include HLA class II antigens, mannose-binding lectin, alpha(1)-antitrypsin and alpha(1)-antichymotrypsin, glutathione-S-transferase, nitric oxide synthase type I, TNF-alpha, TGF-beta, IL-1beta and IL-1Ra.

Syndecans, heparan sulfate proteoglycans, maintain the proteolytic balance of acute wound fluids

An imbalance between proteases and antiproteases is thought to play a role in the inflammatory injury that regulates wound healing. The activities of some proteases and antiproteases found in inflammatory fluids can be modified in vitro by heparin, a mast cell-derived glycosaminoglycan. Because syndecans, a family of cell surface heparan sulfate proteoglycans, are the major cellular source of heparin-like glycosaminoglycan, we asked whether syndecans modify protease activities in vivo. Syndecan-1 and syndecan-4 ectodomains are shed into acute human dermal wound fluids (Subramanian, S. V., Fitzgerald, M. L., and Bernfield, M. (1997) J. Biol. Chem. 272, 14713-14720). Moreover, purified syndecan-1 ectodomain binds cathepsin G (Kd = 56 nM) and elastase (Kd = 35 nM) tightly and reduces the affinity of these proteases for their physiological inhibitors. Purified syndecan-1 ectodomain protects cathepsin G from inhibition by alpha1-antichymotrypsin and squamous cell carcinoma antigen 2 and elastase from inhibition by alpha1-proteinase inhibitor by decreasing second order rate constants for protease-antiprotease associations (kass) by 3700-, 32-, and 60-fold, respectively. Both enzymatic degradation of heparan sulfate and immunodepletion of the syndecan-1 and -4 in wound fluid reduce these proteolytic activities in the fluid, indicating that the proteases in the wound environment are regulated by interactions with syndecan ectodomains. Thus, syndecans are shed into acute wound fluids, where they can modify the proteolytic balance of the fluid. This suggests a novel physiological role for these soluble heparan sulfate proteoglycans.

Serine protease inhibitors in patients with chronic viral hepatitis

BACKGROUND/AIMS

This study aimed to determine whether deficiency of the major serine protease inhibitors (alpha1-antitrypsin (AAT) or alpha1-antichymotrypsin (ACT)) is associated with increased risk for chronic hepatitis B or C virus (HBV or HCV) infection.

METHODS

We studied 709 adults with chronic liver disease who had undergone liver biopsy during the 14-year period 1978-92. Anti-HCV testing was carried out with second-generation ELISA and immunoblot assays (RIBA 2). HBV markers were tested with commercially available radioimmunoassays. ACT and AAT concentrations in plasma were measured with electroimmunoassay and immune nephelometry. Plasma samples were screened for the AAT PiZ deficiency with ELISA technique and phenotyped by isoelectric focusing. The 229Pro-->Ala mutation for ACT deficiency was identified by PCR techniques.

RESULTS

Of the 709 patients, 132 (18.6%) were positive for anti-HCV according to RIBA 2. PiZ AAT deficiency was found in 44 (6.2%) of patients (one PiZZ, 38 PiMZ, and PiSZ), while subnormal ACT levels were found in 33 (4.6%) patients, frequencies that were higher than expected in the general population (p=0.0375 and p<0.0001, respectively). Of the PiZ-carriers, 8/44 (18%) were found to be anti-HCV positive according to RIBA 2, as compared to 123/662 (19%) non-PiZ-carriers (p>0.05). One of these patients had cirrhosis, four chronic active hepatitis, and three chronic persistent hepatitis. In contrast, 17/33 (51.5%) of the patients with subnormal ACT were anti-HCV positive (OR=5.2, CI=2.6-10.6; p<0.0001). No relationship was found between HBV infection and AAT deficiency or subnormal ACT levels. Only one patient with subnormal ACT levels was heterozygous for the 229Pro-->Ala mutation of ACT deficiency. There was no significant difference in the histological findings when the patients with subnormal ACT levels or PiZ allele were subgrouped according to HCV status.

CONCLUSIONS

There is no overrepresentation of chronic HBV or HCV in heterozygous AAT deficiency, although an association with more severe liver disease in such patients cannot be excluded. In contrast, low plasma levels of ACT that may be acquired or hereditary, due to mutations other than 229Pro-->Ala, are frequent in HCV infection.

Serum alpha 1-antichymotrypsin level as a marker for Alzheimer-type dementia

Excessive alpha 1-antichymotrypsin (ACT) in brain has been postulated to play a role in the pathogenesis of Alzheimer's disease (AD). We measured serum ACT by radial immunodiffusion in 57 patients with presumed AD, 110 healthy controls (24 children; 86 adults), 67 non-AD patients from a geriatric private practice and a VA nursing home, and 136 asthmatics (56 adults; 80 children) as an inflammatory disease control group. Serum ACT was significantly higher in AD (73.1 +/- 22 mg/dl) than in healthy controls (47.9 +/- 8.1 mg/dl) or non-AD patients (61.8 +/- 23.9 mg/dl). A level of 60 mg/dl best separated AD patients from controls or non-AD patients. Serial measurements served to distinguish elevations of ACT level in AD from non-AD inflammatory conditions; the ACT level in the latter returned to normal with therapy or time, but the levels in AD remained elevated. A measure of serum ACT by radial immunodiffusion can be used to support a diagnosis of AD disease but not necessarily as a screening test due to the potentially large number of false positives (26% in the population studied) should malignancy or inflammatory disease be concurrent.

The molecular basis of alpha 1-antichymotrypsin deficiency in a heterozygote with liver and lung disease

Alpha 1-antichymotrypsin (alpha 1-ACT) is a serine proteinase inhibitor (serpin) with cathepsin G, mast cell chymase and chymotrypsin as target enzymes. We present the case of a middle-aged man with low plasma levels of alpha 1-ACT, asthma with progression to emphysema, and chronic HCV positive liver disease with selective accumulation of alpha 1-ACT in hepatocytes. This secretory defect is analogous to that seen in Pi Z alpha 1-antitrypsin deficiency. The molecular basis of alpha 1-ACT deficiency in this patient has been characterized by direct sequencing of the alpha 1-ACT genes from the patient and his father. A C-->G transversion in exon III causing a 229Pro-->Ala substitution is proposed to cause a conformational change resulting in abnormal transport through the RER. This mutation was found in one of 20 additional tested patients with chronic obstructive lung disease, but in no control. Two additional polymorphisms of the gene have been identified in unrelated healthy individuals with normal plasma alpha 1-ACT levels. The alpha 1-ACT deficiency state may predispose to obstructive lung disease and influence the course of liver disease. Identification of a specific mutation allows identification of heterozygotes for this deficiency allowing future evaluation of its clinical significance.

Hepatic endoplasmic reticulum storage diseases

Endoplasmic Reticulum Storage Diseases (ERSD) represent a novel group of inborn errors of metabolism affecting secretory proteins and resulting in hepatocytic storage and plasma deficiency of the corresponding protein. The hepatocellular storage is due to a molecular abnormality hindering the translocation of the abnormal protein from the rough (RER) to the smooth endoplasmic reticulum (SER). The molecular abnormality is genetically determined; hence it is hereditary, congenital, familial and permanent. The storage is selective and exclusive for the mutant protein and predisposes to the development of chronic cryptogenic liver disease. ERSD include alpha-1-antitrypsin deficiency, fibrinogen storage and alpha-1-antichymotrypsin deficiency. Basically, the diagnosis of ERSD is a morphological one: immunohistochemistry and electron microscopy are essential tools for their identification.

Improved phenotyping of alpha 1-antichymotrypsin (ACT) by isoelectric focusing and immunoprinting: first demonstration of a deficient protein variant in the ACT system

Genetic variation of human alpha 1-antichymotrypsin (ACT) was investigated in sera using thin-layer polyacrylamide gel isoelectric focusing (pH range 4.0-6.5) followed by immunoprinting with a monospecific anti-human ACT antibody. Sialidase-treated samples showed a microheterogeneous banding pattern which consisted of two major and several additional minor components with isoelectric points between pH 5.0 and 5.3. A population study of 200 unrelated individuals from southern Germany revealed no genetic variation. In a clinical investigation, however, we found a unique banding pattern in a female patient suffering from chronic obstructive pulmonary disease. In comparison with the monomorphic normal type the detected variant phenotype shows two additional bands that have lower intensities and are located cathodically to their major bands. Inheritance of the deficient IEF variant "ACT Bochum" was confirmed by a family study. To our knowledge this is the first genetic ACT mutant to be observed at the protein level.

Partial deficiency of alpha 1-antichymotrypsin is associated with chronic cryptogenic liver disease

alpha 1-Antichymotrypsin (ACT) and alpha 1-antitrypsin (AAT) are two closely related antineutrophil proteinase inhibitors. Whereas AAT deficiency is clearly linked to liver disease, an association between liver disease and partial ACT deficiency has not been established. In a previous study we noted an increased prevalence of liver abnormalities among subjects with heterozygous ACT deficiency. To study a possible association between partial ACT deficiency and liver disease, we screened 316 consecutive patients with biopsy-verified liver disease for partial ACT deficiency and compared the prevalence with that of an unselected adult population in a case-control study. In all, 9 of 316 patients had partial ACT deficiency, which is more than expected (prevalence ratio (PR), 2.46 (1.15-5.27), P less than 0.05). The prevalence of partial ACT deficiency was highest in the chronic active hepatitis (5 of 40; PR, 12.0 (5.33-27.0] and the cryptogenic cirrhosis (3 of 24; PR, 12.0 (4.38-32.9] subgroups. In the chronic active hepatitis subgroup two patients (PR, 8.16 (2.25-29.5] were ACT deficiency heterozygotes, thus partly explaining the high prevalence of partial ACT deficiency among patients with chronic liver disease. The majority (6 of 9) of the patients with partial ACT deficiency lacked autoimmune and viral markers and were thus cryptogenic. The present findings show that partial ACT deficiency and chronic cryptogenic liver disease are associated. To some extent (the true magnitude of which is at present unknown) partial ACT deficiency is caused by a rare trait, heterozygous ACT deficiency, which in parallel with heterozygous alpha 1-antitrypsin deficiency (PiMZ) also seems to be associated with chronic cryptogenic liver disease.

Structure determination of the glycans of human-serum alpha 1-antichymotrypsin using 1H-NMR spectroscopy and deglycosylation by N-glycanase

alpha 1-Antichymotrypsin purified from normal human serum was separated by affinity chromatography into th ree microheterogeneous forms on a concanavalin-A-Sepharose column: a pass-through (peak 1), a retarded (peak 2) and a bound form (peaks 3 + 4). For each form the asparagine-linked carbohydrate chains were liberated as oligosaccharides by hydrazinolysis, submitted to reduction with NaBH4 after re-N-acetylation and further separated by affinity chromatography on a concanavalin-A-Sepharose column. The complete primary structure of the glycans was determined by high-resolution 1H-NMR spectroscopy. The results indicated the presence of disialyl diantennary and of trisialyl triantennary type glycanic structures, the latter being accompanied by traces of disialylated triantennary oligosaccharide. The N-glycanase was used for the deglycosylation of the unfractionated alpha 1-antichymotrypsin; the successive removal of the N-linked complex-type oligosaccharide side chains of alpha 1-antichymotrypsin was studied in the presence of detergents. From these experiments it is concluded that alpha 1-antichymotrypsin carries four oligosaccharide side chains. Moreover our results show that the peak 1 contains four triantennary glycans, the peak 2 three triantennary and one diantennary glycans while the bound peaks 3 + 4 possess, on average, about one triantennary and three diantennary glycans per molecule. Since we showed that the peak 4 contains mostly diantennary glycans, it can be deduced that in peak 3 there are molecules carrying two triantennary and two diantennary glycans and others carrying one triantennary and three diantennary glycans.

Heterozygous alpha 1-antichymotrypsin and PiZ alpha 1-antitrypsin deficiency. Prevalence and clinical spectrum in asthmatic children

In a case-control study we compared the prevalence of heterozygous deficiency of two closely related anti-neutrophil protease inhibitors, alpha 1-antitrypsin and alpha 1-antichymotrypsin, in 172 consecutive children with asthma. In a cohort study the clinical spectrum and severity were compared. On the basis of family studies 5/172 (2.9%) were classified as heterozygotes for alpha 1-antichymotrypsin deficiency, a high prevalence compared with that of an unselected adult population (prevalence ratio 4.5 (1.7-11.9), P less than 0.005). This finding suggests that the carrier state of this rare allele (prevalence 0.64%) may predispose to asthma in children. Among these heterozygous patients the prevalence of positive RAST tests for foodstuffs was significantly increased (prevalence ratio 4.8 (1.7-13.2), P less than 0.005) and 2/5 manifested food allergy with Quincke oedema. Either the PiMZ or SZ phenotype of alpha 1-antitrypsin deficiency was found in 12 (7.0%) of the 172 patients, a prevalence similar to that of a normal population (prevalence ratio 1.3 (0.67-2.6), P = 0.44). However, the asthma was more severe among the Z allele carriers, judged by the number of hospital admissions, compared with the non-Z asthmatic children (mean 2.92 vs. 1.72, P less than 0.05). The results indicate that heterozygous deficiency of protease inhibitors directed against neutrophil proteases may affect the severity and clinical spectrum of childhood asthma, and to some degree be predisposing.

Hepatocyte inclusions of alpha 1-antichymotrypsin in a patient with partial deficiency of alpha 1-antichymotrypsin and chronic liver disease

We present a case of chronic liver disease with selective and exclusive hepatocyte endoplasmic reticulum storage of alpha 1-antichymotrypsin in the form of granules, detected by specific immunohistochemistry at the light microscopy level and corresponding to material found in dilated endoplasmic reticulum of hepatocytes by electron microscopy. The patient had intermediate deficiency of alpha 1-antichymotrypsin. Thus, the hepatocyte accumulation of alpha 1-antichymotrypsin may indicate the presence of an export block resembling that of a closely-related protein, namely PiZ alpha 1-antitrypsin. It is proposed that hepatocyte storage of alpha 1-antichymotrypsin may be an expression of an inborn error of metabolism bearing the characteristics of endoplasmic reticulum storage diseases such as PiZ alpha 1-antitrypsin deficiency and hereditary hypofibrinogenaemia.

Asthma and heterozygous alpha 1-antichymotrypsin deficiency: a possible association

During studies of families with alpha 1-antichymotrypsin deficiency heterozygotes, an apparently increased prevalence of asthma among first degree relatives was noticed. In a case control study, the prevalence of asthma among first degree relatives of 12 women with heterozygous alpha 1-antichymotrypsin deficiency was compared with that of first degree relatives of 58 matched controls. Secondly, the strength of association between asthma and low or subnormal plasma ACT concentration, in first and second degree relatives to heterozygotes, was assessed. The prevalence of asthma among first degree relatives of women with heterozygous alpha 1-antichymotrypsin deficiency was significantly higher [prevalence ratio 3.22 (1.06-9.83), P = 0.04]. Among heterozygotes, the prevalence of asthma in first and second degree relatives with low plasma alpha 1-antichymotrypsin concentration was higher than in relatives with normal plasma ACT concentration, but the difference in prevalence did not reach statistical significance [prevalence ratio 3.1 (0.96-9.83), P = 0.059]. The findings are in agreement with previous studies and suggest a possible association between asthma and heterozygous alpha 1-antichymotrypsin deficiency.

The microheterogeneity of desialylated alpha 1-antichymotrypsin: the occurrence of two amino-terminal isoforms, one lacking a His-Pro dipeptide

ACT (alpha 1-antichymotrypsin), a serine antiproteinase with specificity against neutrophil cathepsin G, is homologous with alpha 1-antitrypsin, plasminogen activator inhibitor and angiotensinogen, all with known amino-terminal microheterogeneity. Here we report that the two predominant isoforms of desialylated ACT obtained on isoelectric focusing correspond to a microheterogeneity at the amino terminus of ACT: one isoform (His-Pro-Asn-Ser-Pro-) and a two residues shorter isoform (Asn-Ser-Pro-). The relative occurrence of the two isoforms was comparable both in normal plasma, acute-phase plasma and plasma from subjects with heterozygous familial ACT deficiency. When desialylated ACT, isolated by affinity chromatography from ACT-deficient, normal or acute-phase plasma, was compared with regard to mass and charge microheterogeneity, we found no significant differences in either respect. Nor was the isoform pattern of desialylated plasma from patients with rheumatoid arthritis different. Although the occurrence of heterozygous familial ACT deficiency implies genotypic variation, isolated ACT from patients with the trait was not found to exhibit any phenotypic variation detectable by standard electrophoretic methods.

Cloning of the human alpha 1 antichymotrypsin gene and genetic analysis of the gene in relation to alpha 1 antitrypsin deficiency

Deficiency of alpha 1 antitrypsin (Pi) is clinically heterogeneous and the unpredictability of the clinical manifestation in a person of phenotype PiZ, which may vary from severe childhood liver disease to normal health, is a problem in genetic counselling. This problem may increase as couples at risk who have not had an affected child are identified in screening programmes. One possibility is that genetic variation of other protease inhibitors may influence the prognosis. With this in mind we report the isolation of the human gene for alpha 1 antichymotrypsin (AACT) on a series of cosmid clones, with restriction mapping of about 70 kb around the gene. A probe pACE3.4 derived from the 5' end of the gene defines sequences which have been assigned to chromosome 14 using somatic cell hybrids and has been used to show a common TaqI polymorphism with allele frequencies of AACT6 = 0.7 and AACT3 = 0.3 in Europeans. pACE3.4 is closely linked to alpha 1 antitrypsin (maximum lod score in males +2.29 at theta = 0; in females Z = +6.11 at theta = 0.032). Analysis of Pi-AACT haplotypes in 31 families ascertained through PiZ or PiSZ subjects did not show any linkage disequilibrium. The distribution of AACT6 and AACT3 alleles in 16 unrelated PiZ patients presenting with childhood liver disease and five unrelated PiZ patients with adult chest disease did not differ significantly from each other. These results suggest that if genetic variation at the AACT locus does influence the outcome of alpha 1 antitrypsin deficiency, such variation is not in linkage disequilibrium with the AACT polymorphism reported here.