Sickle cell disease: Clinical presentation and management of a global health challenge.

Sickle cell disease is an autosomal recessive, multisystem disorder, characterised by chronic haemolytic anaemia, painful episodes of vaso-occlusion, progressive organ failure and a reduced life expectancy. Sickle cell disease is the most common monogenetic disease, with millions affected worldwide. In well-resourced countries, comprehensive care programs have increased life expectancy of sickle cell disease patients, with almost all infants surviving into adulthood. Therapeutic options for sickle cell disease patients are however, still scarce. Predictors of sickle cell disease severity and a better understanding of pathophysiology and (epi)genetic modifiers are warranted and could lead to more precise management and treatment. This review provides an extensive summary of the pathophysiology and management of sickle cell disease and encompasses the characteristics, complications and current and future treatment options of the disease.

Characterization of a polymorphism in the 3' part of the chicken vitellogenin gene.

An allele giving rise to a polymorphism within the 3' part of the chicken vitellogenin gene was cloned, sequenced, and compared to the previously cloned allele. The polymorphism is formed by a perfect copy of 343 bp from intron 32 in tandem array with a perfect copy of 244 bp from intron 33; this 587-bp element is inserted in a head-to-tail arrangement in intron 33. We propose a mechanism in which an unequal crossing-over resulted in a vitellogenin gene with two exons 33, one of which was subsequently deleted. Thus, intron 33 was enlarged by the tandem repeats without affecting the protein-encoding sequence of the gene. At the boundaries of the repeated elements, two short direct repeats are found that resemble the recombination signals of immunoglobulin genes. They may have had a key role in the formation of the new allele.

In vivo footprinting of the estrogen-inducible vitellogenin II gene from chicken.

Protein-DNA interactions in the promoter region of the chicken vitellogenin II gene were analyzed by in vivo dimethylsulphate footprinting with expressing and non-expressing tissues. The reactivity of G-residues is essentially the same in erythrocytes, oviduct and control liver, not expressing the gene. In the expressing estrogen-induced liver we find a number of G-residues with altered reactivities. These G's are located within distinct sequences: the estrogen responsive elements, a sequence resembling the NF-1 recognition motive, and several elements which are conserved between yolk protein genes. The expression-dependent binding of proteins to these sites was confirmed by DNaseI footprinting applied to nuclei isolated from estrogen-induced and control liver. Estradiol appears to establish a transcription complex comprising a number of distinct proteins bound to different sites in the 5' flanking region of the vitellogenin II gene.

Estrogen-inducible binding of a nuclear factor to the vitellogenin upstream region.

The estrogen-dependent binding of a protein to the upstream region of the chicken vitellogenin gene was detected by using in vivo dimethyl sulfate, genomic DNase I, and in vitro exonuclease III footprinting. The site is located between base pairs -848 and -824, and its sequence resembles that of the nuclear factor I binding site. The results suggest that a nuclear factor binding to this site is involved in the regulation of the vitellogenin gene.

Tissue-specific and steroid-dependent interaction of transcription factors with the oestrogen-inducible apoVLDL II promoter in vivo.

Using in vivo dimethylsulphate footprinting, we have analysed protein--DNA interactions within the promoter region of the oestrogen-inducible gene encoding chicken apo very low density lipoprotein II (apoVLDL II). Most of the guanosine--protein contacts found, are located within the 230-bp DNA 5' flanking the gene and can be grouped into separate protein-binding sites. Two of these sites resemble the oestrogen-responsive element (ERE) which is the target site for the oestrogen receptor. A third site has some features in common with the chicken ovalbumin upstream promoter element binding the COUP transcription factor. All protein contacts identified are present in the apoVLDL-II-expressing liver exclusively, and are not found in the hormone-naive liver, in erythrocytes or the oviduct tubular gland. Our results demonstrate the binding in vivo of a protein, presumably the oestrogen receptor, to the ERE and suggest that the hormone activates transcription by establishing a transcription complex comprising several factors at the apoVLDL II promoter.

Expression-linked demethylation of 5-methylcytosines in the chicken vitellogenin gene region.

We have studied the methylation status of the estradiol-controlled chicken vitellogenin (Vtg) gene, which is expressed in the liver. A 30-kb region was investigated, containing 17 HpaII and 18 HhaI sites, of which 21 are in the 22-kb gene. Of these 21 sites, 9 were found to be demethylated in laying-hen liver relative to immature chicken liver. Outside the transcribed region, only one site was found to be relatively undermethylated in laying-hen liver. This site, at 0.6 kb in front of the gene, is, as shown earlier, also demethylated in rooster or immature chicken liver upon primary hormone stimulation, as well as in the non-expressing estradiol target organ oviduct. In this respect, this site sharply contrasts with those in the transcribed region, which appear to become demethylated only upon prolonged transcription of the gene.

Methylation of the chicken vitellogenin gene: influence of estradiol administration.

The degree of methylation of the chicken vitellogenin gene has been investigated. Upon induction by administration of estradiol to a rooster, methyl groups at specific sites near the 5'-end of the gene are eliminated. The process of demethylation is slower than the activation of the gene. Demethylation is therefore probably not a prerequisite to gene transcription. At least two other sites in the coding region of the gene are methylated in the liver of estrogenized roosters, but not in the liver of a laying hen, where the gene is naturally active.