Identification of ETV6-RUNX1-like and DUX4-rearranged subtypes in paediatric B-cell precursor acute lymphoblastic leukaemia

Fusion genes are potent driver mutations in cancer. In this study, we delineate the fusion gene landscape in a consecutive series of 195 paediatric B-cell precursor acute lymphoblastic leukaemia (BCP ALL). Using RNA sequencing, we find in-frame fusion genes in 127 (65%) cases, including 27 novel fusions. We describe a subtype characterized by recurrent IGH-DUX4 or ERG-DUX4 fusions, representing 4% of cases, leading to overexpression of DUX4 and frequently co-occurring with intragenic ERG deletions. Furthermore, we identify a subtype characterized by an ETV6-RUNX1-like gene-expression profile and coexisting ETV6 and IKZF1 alterations. Thus, this study provides a detailed overview of fusion genes in paediatric BCP ALL and adds new pathogenetic insights, which may improve risk stratification and provide therapeutic options for this disease.

Genomic profiling and directed ex vivo drug analysis of an unclassifiable myelodysplastic/myeloproliferative neoplasm progressing into acute myeloid leukemia

Myelodysplastic/myeloproliferative neoplasms, unclassifiable (MDS/MPN-U) are rare genetically heterogeneous hematologic diseases associated with older age and a poor prognosis. If the disease progresses into acute myeloid leukemia (AML), it is often refractory to treatment. To gain insight into genetic alterations associated with disease progression, whole exome sequencing and single nucleotide polymorphism arrays were used to characterize the bone marrow and blood samples from a 39-year-old woman at MDS/MPN-U diagnosis and at AML progression, in which routine genetic diagnostics had not identified any genetic alterations. The data revealed the presence of a partial tandem duplication of the MLL gene as the only detectable copy number change and 11 non-silent somatic mutations, including DNMT3A R882H and NRAS G13D. All somatic lesions were present both at initial MDS/MPN-U diagnosis and at AML presentation at similar mutant allele frequencies. The patient has since had two extramedullary relapses and is at high risk of a future bone marrow relapse. A directed ex vivo drug sensitivity analysis showed that the patient's AML cells are sensitive to, for example, the MEK inhibitor trametinib and the proteasome inhibitor bortezomib, indicating that she may benefit from treatment with these drugs. © 2016 Wiley Periodicals, Inc.

The landscape of somatic mutations in infant MLL-rearranged acute lymphoblastic leukemias

Infant acute lymphoblastic leukemia (ALL) with MLL rearrangements (MLL-R) represents a distinct leukemia with a poor prognosis. To define its mutational landscape, we performed whole genome, exome, RNA and targeted DNA sequencing on 65 infants (47 MLL-R and 18 non-MLL-R) and 20 older children (MLL-R cases) with leukemia. Our data demonstrated infant MLL-R ALL to have one of the lowest frequencies of somatic mutations of any sequenced cancer, with the predominant leukemic clone carrying a mean of 1.3 non-silent mutations. Despite the paucity of mutations, activating mutations in kinase/PI3K/RAS signaling pathways were detected in 47%. Surprisingly, however, these mutations were often sub-clonal and frequently lost at relapse. In contrast to infant cases, MLL-R leukemia in older children had more somatic mutations (a mean of 6.5/case versus 1.3/case, P=7.15×10⁻⁵) and contained frequent mutations (45%) in epigenetic regulators, a category of genes that with the exception of MLL was rarely mutated in infant MLL-R ALL.

Integrated genetic and epigenetic analysis of childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the commonest childhood malignancy and is characterized by recurring structural genetic alterations. Previous studies of DNA methylation suggest epigenetic alterations may also be important, but an integrated genome-wide analysis of genetic and epigenetic alterations in ALL has not been performed. We analyzed 137 B-lineage and 30 T-lineage childhood ALL cases using microarray analysis of DNA copy number alterations and gene expression, and genome-wide cytosine methylation profiling using the HpaII tiny fragment enrichment by ligation-mediated PCR (HELP) assay. We found that the different genetic subtypes of ALL are characterized by distinct DNA methylation signatures that exhibit significant correlation with gene expression profiles. We also identified an epigenetic signature common to all cases, with correlation to gene expression in 65% of these genes, suggesting that a core set of epigenetically deregulated genes is central to the initiation or maintenance of lymphoid transformation. Finally, we identified aberrant methylation in multiple genes also targeted by recurring DNA copy number alterations in ALL, suggesting that these genes are inactivated far more frequently than suggested by structural genomic analyses alone. Together, these results demonstrate subtype- and disease-specific alterations in cytosine methylation in ALL that influence transcriptional activity, and are likely to exert a key role in leukemogenesis.

An Inv(16)(p13.3q24.3)-encoded CBFA2T3-GLIS2 fusion protein defines an aggressive subtype of pediatric acute megakaryoblastic leukemia

To define the mutation spectrum in non-Down syndrome acute megakaryoblastic leukemia (non-DS-AMKL), we performed transcriptome sequencing on diagnostic blasts from 14 pediatric patients and validated our findings in a recurrency/validation cohort consisting of 34 pediatric and 28 adult AMKL samples. Our analysis identified a cryptic chromosome 16 inversion (inv(16)(p13.3q24.3)) in 27% of pediatric cases, which encodes a CBFA2T3-GLIS2 fusion protein. Expression of CBFA2T3-GLIS2 in Drosophila and murine hematopoietic cells induced bone morphogenic protein (BMP) signaling and resulted in a marked increase in the self-renewal capacity of hematopoietic progenitors. These data suggest that expression of CBFA2T3-GLIS2 directly contributes to leukemogenesis.

IDH1 and IDH2 mutations in pediatric acute leukemia

To investigate the frequency of isocitrate dehydrogenase 1 (IDH1) and 2 (IDH2) mutations in pediatric acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL), we sequenced these genes in diagnostic samples from 515 patients (227 AMLs and 288 ALLs). Somatic IDH1/IDH2 mutations were rare in ALL (N=1), but were more common in AML, occurring in 3.5% (IDH1 N=3 and IDH2 N=5), with the frequency higher in AMLs with a normal karyotype (9.8%). The identified IDH1 mutations occurred in codon 132 resulting in replacement of arginine with either cysteine (N=3) or histidine (N=1). By contrast, mutations in IDH2 did not affect the homologous residue but instead altered codon 140, resulting in replacement of arginine with either glutamine (N=4) or tryptophan (N=1). Structural modeling of IDH2 suggested that codon 140 mutations disrupt the enzyme's ability to bind its substrate isocitrate. Accordingly, recombinant IDH2 R140Q/W were unable to carry out the decarboxylation of isocitrate to α-ketoglutarate (α-KG), but instead gained the neomorphic activity to reduce α-KG to R(-)-2-hydroxyglutarete (2-HG). Analysis of primary leukemic blasts confirmed high levels of 2-HG in AMLs with IDH1/IDH2 mutations. Interestingly, 3/5 AMLs with IDH2 mutations had FLT3-activating mutations, raising the possibility that these mutations cooperate in leukemogenesis.

The impact of climate change on winter road maintenance and traffic accidents in West Midlands, UK

Winter weather can be a significant cause of road traffic accidents. This paper uses UKCIP climate change scenarios and a temporal analogue to investigate the relationship between temperature and severe road accidents in the West Midlands, UK. This approach also allows quantification of the changes in the severity of the winter season over the next century in the region. It is demonstrated that the predicted reduction in the number of frost days should in turn reduce the number of road accidents caused due to slipperiness by approximately 50%. However, the paper concludes by warning against complacency in winter maintenance regimes. A warmer climate may result in budget cuts for highway maintenance which in turn may well reverse declining accident trends.

Neutralizing IL-21 and IL-15 inhibits pro-inflammatory cytokine production in rheumatoid arthritis

Interleukin IL-21 and IL-15 belong to the common gamma-chain receptor family. IL-15 represents a novel therapeutic target in rheumatoid arthritis (RA), whereas less is known about the role of IL-21 in human inflammatory diseases. We have analysed the effects of blocking IL-21 and IL-15 on spontaneous production of pro-inflammatory cytokines in RA synovial cell cultures. RA synovial membrane cells were cultured in the presence of an IL-21R-Fc chimera or a neutralizing IL-15 antibody and production of tumour necrosis factor (TNF)alpha, IL-6 and IL-1beta was measured by enzyme-linked immunosorbent assay (ELISA). Expression of IL-21 and IL-15 in RA synovium was measured by RT-PCR and ELISA. mRNA for IL-21 and IL-21R was detected in the culture cell lysates. Protein for IL-15 was found at detectable levels in the cell lysates. Both the IL-21R-Fc chimera and anti-IL-15 antibody inhibited cytokine release, although substantially more IL-21R-Fc was needed. IL-21R-Fc at the highest dose (100 microg/ml) significantly reduced TNFalpha production by 50%, IL-6 by 57% and IL-1beta by 81%. Anti-IL-15 antibody (5 microg/ml) significantly inhibited TNFalpha release by 51%, IL-6 by 37% and IL-1beta by 82% in line with previous published observations. The data confirm that IL-15 plays a role in RA and suggests that IL-21 is also involved in driving the pro-inflammatory cytokine response in RA.

Recent developments in the immunobiology of rheumatoid arthritis

Progress into the understanding of immunopathology in rheumatoid arthritis is reviewed in the present article with regard to pro-inflammatory cytokine production, cell activation and recruitment, and osteoclastogenesis. Studies highlight the potential importance of T helper 17 cells and regulatory T cells in driving and suppressing inflammation in rheumatoid arthritis, respectively, and highlight other potential T-cell therapeutic targets. The genetic associations of the HLA shared epitope alleles with antibodies to citrullinated peptides in rheumatoid arthritis patients indicate that T cells are providing help to B cells to produce autoantibodies, and there is increasing evidence that these autoantibodies are pathogenic in rheumatoid arthritis.

Alteration of the cortisol–cortisone shuttle in leprosy type 1 reactions in leprosy patients in Hyderabad, India

Regulation of inflammation in leprosy may be influenced by local concentrations of active cortisol and inactive cortisone, whose concentrations are regulated by enzymes in the cortisol-cortisone shuttle. We investigated the cortisol-cortisone shuttle enzymes in the skin of leprosy patients with type 1 reactions (T1R), which are characterised by skin and nerve inflammation. Gene expression of the shuttle enzymes were quantified in skin biopsies from 15 leprosy patients with new T1R before and during prednisolone treatment and compared with levels in skin biopsies from 10 borderline leprosy patients without reactions. Gene expression of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 2, which converts cortisol to cortisone, is down-regulated in skin from T1R lesions. However expression levels of 11beta-HSD type 1, which converts cortisone to cortisol, were similar in skin with and without reactions and did not change during anti-leprosy drug treatment. Prednisolone treatment of patients with reactions is associated with an upregulation of 11beta-HSD2 expression in skin. The down regulation of 11beta-HSD2 at the beginning of a reaction may be caused by pro-inflammatory cytokines in the leprosy reactional lesion and may be a local attempt to down-regulate inflammation. However in leprosy reactions this local response is insufficient and exogenous steroids are required to control inflammation.

Nitric oxide contributes to cytokine-induced apoptosis in pancreatic beta cells via potentiation of JNK activity and inhibition of Akt

AIMS/HYPOTHESIS

Pro-inflammatory cytokines cause beta cell secretory dysfunction and apoptosis--a process implicated in the pathogenesis of type 1 diabetes. Cytokines induce the expression of inducible nitric oxide (NO) synthase (iNOS) leading to NO production. NO contributes to cytokine-induced apoptosis, but the underlying mechanisms are unclear. The aim of this study was to investigate whether NO modulates signalling via mitogen-activated protein kinases (MAPKs) and Akt.

MATERIALS AND METHODS

MAPK activities in INS-1 cells and isolated islets were determined by immunoblotting and in vitro kinase assay. Apoptosis was determined by ELISA measurement of histone-DNA complexes present in cytoplasm.

RESULTS

Apoptosis in INS-1 cells induced by IL-1beta plus IFNgamma was dependent on NO production as demonstrated by the use of the NOS blocker NG-methyl-L-arginine. Accordingly, an NO donor (S-nitroso-N-acetyl-D, L-penicillamine, SNAP) dose-dependently caused apoptosis in INS-1 cells. SNAP activated c-Jun N-terminal kinase (JNK) and p38 MAPK, but suppressed the activity of extracellular signal-regulated kinase MAPK. In rat islets, NOS inhibition decreased JNK and p38 activities induced by a 6-h exposure to IL-1beta. Likewise, IL-1beta-induced JNK and p38 activities were lower in iNOS(-/-) mouse islets than in wild-type islets. In human islets, SNAP potentiated IL-1beta-induced JNK activation. The constitutive level of active, Ser473-phosphorylated Akt in INS-1 cells was suppressed by SNAP. IGF-I activated Akt and protected against SNAP-induced apoptosis. The anti-apoptotic effect of IGF-I was not associated with reduced JNK activation.

CONCLUSIONS/INTERPRETATION

We suggest that NO contributes to cytokine-induced apoptosis via potentiation of JNK activity and suppression of Akt.

Lactate induces tumour necrosis factor-alpha, interleukin-6 and interleukin-1beta release in microglial- and astroglial-enriched primary cultures

Hyperammonaemia has deleterious effects on the CNS in patients with liver dysfunction. Cellular mechanisms underlying the effects of hyperammonaemia are largely unknown, although astrocytes have been the main target of interest. This study investigated how treatment with NH4Cl and lactate, which increase in the brain as a consequence of hyperammonaemia, affects cells in primary rat cultures enriched in either astrocytes or microglia. Morphological changes were studied over time using light microscopy. Release of the proinflammatory cytokines tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-6 and IL-1beta was measured using ELISA. NH4Cl was found to induce vacuole formation in both culture systems. Lactate treatment altered astrocytic appearance, resulting in increased space between individual cells. Microglia adopted a round morphology with either NH4Cl or lactate treatment. Lactate, but not NH4Cl, induced release of TNF-alpha and IL-6 in both astroglial- and microglial-enriched cultures, while IL-1beta was released only in microglial cultures. Cytokine release was higher in the microglial- than in the astroglial-enriched cultures. Additionally, the astroglial-enriched cultures containing approximately 10% microglial cells released more cytokines than cultures containing about 5% microglial cells. Taken together, our data suggest that most TNF-alpha, IL-6 and IL-1beta release comes from microglia. Thus, microglia could play an important role in the pathological process of hyperammonaemia.

Effects of prednisolone treatment on cytokine expression in patients with leprosy type 1 reactions

Leprosy type 1 reactions (T1R) are due to increased cell-mediated immunity and result in localized tissue damage. The anti-inflammatory drug prednisolone is used for treatment, but there is little good in vivo data on the molecular actions of prednisolone. We investigated the effect of prednisolone treatment on tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-10, and transforming growth factor beta1 (TGF-beta1) mRNA and protein expression in blood and skin biopsies from 30 patients with T1R in India. After 1 month of prednisolone treatment the sizes of the skin granulomas were reduced, as were the grades of cells positive for TNF-alpha and IL-10 in skin lesions. Increased production of TGF-beta1 was seen in skin lesions after 6 months of prednisolone treatment. Expression of mRNA for TNF-alpha, IL-1beta, and TGF-beta1 was reduced, whereas no change in IL-10 mRNA expression was detected during treatment. The circulating cytokine profiles were similar in patients with and without T1R, and prednisolone treatment had no detectable effects on cytokine expression in the blood. The data emphasize the compartmentalization of pathology in T1R and the importance of the immune response in the skin. Clinical improvement and cytokine expression were compared. Surprisingly, patients with improved skin and nerve function and patients with nonimproved skin and nerve function had similar cytokine profiles, suggesting that clinical improvement is not directly mediated by the cytokines studied here. This in vivo well-controlled study of the immunosuppressive effects of prednisolone showed that the drug does not switch off cytokine responses effectively.

Human glutathione transferase A1-1 demonstrates both half-of-the-sites and all-of-the-sites reactivity

A study of the kinetics of a heterodimeric variant of glutathione transferase (GST) A1-1 has led to the conclusion that, although the wild-type enzyme displays all-of-the-sites reactivity in nucleophilic aromatic substitution reactions, it demonstrates half-of-the-sites reactivity in addition reactions. The heterodimer, designed to be essentially catalytically inactive in one subunit due to a single point mutation (D101K), and the two parental homodimers were analyzed with seven different substrates, exemplifying three types of reactions catalyzed by glutathione transferases (nucleophilic aromatic substitution, addition, and double-bond isomerization reactions). Stopped-flow kinetic results suggested that the wild-type GST A1-1 behaved with half-of-the-sites reactivity in a nucleophilic aromatic substitution reaction, but steady-state kinetic analyses of the GST A1-D101K heterodimer revealed that this was presumably due to changes to the extinction coefficient of the enzyme-bound product. In contrast, steady-state kinetic analysis of the heterodimer with three different substrates of addition reactions provided evidence that the wild-type enzyme displayed half-of-the-sites reactivity in association with these reactions. The half-of-the-sites reactivity was shown not to be dependent on substrate size, the level of saturation of the enzyme with glutathione, or relative catalytic rate.

Melatonin protects against streptozotocin, but not interleukin-1beta-induced damage of rodent pancreatic beta-cells

In the present study, we examined whether melatonin can protect rodent pancreatic islets against streptozotocin (STZ) and interleukin-1beta (IL-1beta)-induced suppression of beta-cell function. Formation of free radicals, DNA damage and extensive DNA repair leading to depletion of intracellular nicotinamide adenine dinucleotide (NAD) may mediate STZ toxicity. Activation of inducible nitric oxide synthase and nitric oxide (NO) formation may cause IL-1beta -induced beta-cell impairment. We also studied the effect of melatonin against STZ-induced hyperglycemia in C57BL/Ks mice. For in vitro studies, cultured rat islets were exposed to melatonin (100 microM-1 mM) 30 min prior to STZ (0.5 mM) or IL-1beta (25 U/mL) addition. After an additional 30 min incubation with STZ, islet function and NAD content were analyzed either acutely or after 18 hr of recovery in fresh culture medium. For IL-1beta experiments, islets were incubated for 48 hr with the cytokine before evaluation of islet function. We found that melatonin counteracted STZ-induced inhibition of glucose metabolism and insulin release in cultured rat islets after 18 hr of recovery. Moreover, NAD levels were higher in the melatonin-treated group at this time point. Melatonin had no effect on IL-1beta-induced islet inhibition of glucose oxidation or NO formation. Diabetes induced by STZ (140 mg/kg body weight; i.v.) was effectively prevented by administration of melatonin (100 mg/kg body weight; i.p.) 30 min before STZ injection. We conclude that the protective effects of melatonin against beta-cell damage may be related to interference with DNA damage and poly(ADP-ribose) polymerase (PARP) activation rather than through effects on NO generation pathways.

Cytokine-induced inhibition of insulin release from mouse pancreatic beta-cells deficient in inducible nitric oxide synthase

Cytokines may participate in islet destruction during the development of type 1 diabetes. Expression of inducible nitric oxide synthase (iNOS) and subsequent NO formation induced by IL-1 beta or (IL-1 beta + IFN-gamma) may impair islet function in rodent islets. Inhibition of iNOS or a deletion of the iNOS gene (iNOS -/- mice) protects against cytokine-induced beta-cell suppression, although cytokines might also induce NO-independent impairment. Presently, we exposed wild-type (wt, C57BL/6 x 129SvEv) and iNOS -/- islets to IL-1 beta (25 U/ml) and (IL-1 beta (25 U/ml) + IFN-gamma (1000 U/ml)) for 48 h. IL-1 beta and (IL-1 beta + IFN-gamma) induced a significant increase in NO formation in wt but not in iNOS -/- islets. Both IL-1 beta and (IL-1 beta + IFN-gamma) impaired glucose-stimulated insulin release and reduced the insulin content of wt islets, while (IL-1 beta + IFN-gamma) reduced glucose oxidation rates and cell viability. IL-1 beta exposure to iNOS -/- islets impaired glucose-stimulated insulin release, increased insulin accumulation and reduced the insulin content, without any increase in cell death. Exposure to (IL-1 beta + IFN-gamma) had no effect on iNOS -/- islets except reducing the insulin content. Our data suggest that IL-1 beta may inhibit glucose-stimulated insulin release by pathways that are not NO-dependent and not related to glucose metabolism or cell death.

Defects in TCIRG1 subunit of the vacuolar proton pump are responsible for a subset of human autosomal recessive osteopetrosis

Osteopetrosis includes a group of inherited diseases in which inadequate bone resorption is caused by osteoclast dysfunction. Although molecular defects have been described for many animal models of osteopetrosis, the gene responsible for most cases of the severe human form of the disease (infantile malignant osteopetrosis) is unknown. Infantile malignant autosomal recessive osteopetrosis (MIM 259700) is a severe bone disease with a fatal outcome, generally within the first decade of life. Osteoclasts are present in normal or elevated numbers in individuals affected by autosomal recessive osteopetrosis, suggesting that the defect is not in osteoclast differentiation, but in a gene involved in the functional capacity of mature osteoclasts. Some of the mouse mutants have a decreased number of osteoclasts, which suggests that the defect directly interferes with osteoclast differentiation. In other mutants, it is the function of the osteoclast that seems to be affected, as they show normal or elevated numbers of non-functioning osteoclasts. Here we show that TCIRG1, encoding the osteoclast-specific 116-kD subunit of the vacuolar proton pump, is mutated in five of nine patients with a diagnosis of infantile malignant osteopetrosis. Our data indicate that mutations in TCIRG1 are a frequent cause of autosomal recessive osteopetrosis in humans.

Novel experimental strategies to prevent the development of type 1 diabetes mellitus

Type 1 diabetes is an autoimmune disease leading to extensive destruction of the pancreatic beta-cells. Our research focusses on the role of beta-cells during the course of the disease, aiming at finding novel strategies to enhance beta-cell resistance against the cytotoxic damage inflicted by the immune system. Special attention has been paid to the possibility that cytokines released by the immune cells infiltrating the pancreatic islets can directly suppress and kill beta-cells. Certain cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma) either alone or in combination, are able to activate signal transduction pathways in beta-cells leading to transcription factor activation and de novo gene expression. In this context, it has been found that induction of inducible nitric oxide synthase mediates an elevated production of nitric oxide, which impairs mitochondrial function and causes DNA damage eventually leading to apoptosis and necrosis. However, other induced proteins SUCH AS heat shock protein 70 and superoxide dismutase may reflect a defense reaction elicited in the beta-cells by the cytokines. Our strategy is to further seek for proteins involved in both destruction and protection of beta-cells. Based on this knowledge, we plan to apply gene therapeutic approaches to increase expression of protective genes in beta-cells. If this is feasible we will then evaluate the function and survival of such modified beta-cells in animal models of type 1 diabetes such as the NOD mouse. The long-term goal for this research line is to find novel approaches to influence beta-cell resistance in humans at risk of developing type 1 diabetes.

Calpains in lens epithelium from patients with cataract

Lens epithelium from patients with cataract was obtained during surgery and frozen. The samples were subjected to SDS-electrophoresis and Western blotting. Calpains were quantified using polyclonal antibodies against m- and mu-Calpain could be detected but not the isoenzyme mu-calpain, indicating that m-calpain is the significant most important calpain in human lens epithelium. Quantification of m-calpain showed no relationship to age or gender, but there were significant differences between different types of cataract.

Changes in the soluble protein of the human vitreous in vitreoretinal disease

Samples of the vitreous were analysed in order to identify changes of soluble proteins in vitreo-retinal disease. The soluble proteins of the vitreous were separated on an anion exchange column (Mono-Q). The degree of neutral proteolytic activity in vitreous body was also measured. The vitreous from cataract cases without vitreoretinal disease was characterized by its low content of soluble proteins equivalent to about 1% of that of serum. Albumin and transferrin were the major identified components and their concentrations were approximately 0.85 and 0.03 g/l, respectively. In cases with vitreoretinal disease the vitreous showed changes of total soluble protein and the appearance of additional protein peaks. In patients with PVR the albumin concentration in the vitreous was found to be three times higher as compared to the control group consisting of patients with cataract. Neutral proteolytic activity in the vitreous was relatively low in both normal and pathological vitreous.

A longitudinal study of a population based sample of astigmatic children. I. Refraction and amblyopia

The refraction changes in 310 children with astigmatism greater than or equal to 1.0 D in at least one eye at one year of age were followed during a period of 3 years. At the age 4 years amblyopia was found in 23 children (7%). The refraction data of these children were compared to the rest of the sample. We found that an increasing astigmatism during the test period was associated with an increased risk to develop amblyopia. The majority of children (n = 280) showed a decrease of their astigmatism, whereas all cases with a marked amblyopia (V.A. less than 0.5) or binocular amblyopia, except one, had an increasing or unchanged astigmatism during the age period 1 to 4 years. Strabismus and oblique astigmatism at any time during the test period was also strongly related to amblyopia. The incidence of strabismus (1%) was unexpectedly low. The study also showed that independent of age there was no simple relationship between amblyopia and refraction errors measured at a single test session. The main conclusion of this study is that failure of emmetropization may play an important role in visual development.