The haemoglobinopathies are the commonest single-gene disorders known, almost certainly because of the protection they provide against malaria, as attested by a number of observations. The geographical distributions of malaria and haemoglobinopathies largely overlap, and microepidemiological surveys confirm the close relationship between them. For two of the commonest disorders, haemoglobin S and alpha(+)-thalassaemia, there is also good clinical evidence for protection against malaria morbidity. However, not all the evidence appears to support this view. In some parts of the world malaria and haemoglobinopathies are not, and never have been, coexistent. It is also difficult to explain why the majority of haemoglobinopathies appear to be recent mutations and are regionally specific. Here we argue that these apparent inconsistencies in the malaria hypothesis are the result of processes such as genetic drift and migration and of demographic changes that have occurred during the past 10,000 years. When these factors are taken into account, selection by malaria remains the force responsible for the prevalence of the haemoglobinopathies.

The frequency of alpha+-thalassaemia, but not other unlinked DNA polymorphisms, exhibits an altitude- and latitude-dependent correlation with malaria endemicity throughout Melanesia, supporting the hypothesis that protection against this parasitic disease is the major factor responsible for the high frequencies of haemoglobinopathies in many parts of the world.

No abstract

BackgroundThere is current expansion of newborn screening (NBS) programs to include lysosomal storage disorders because of the availability of treatments that produce an optimal clinical outcome when started early in life.ObjectiveTo evaluate the performance of a multiplex-tandem mass spectrometry (MS/MS) enzymatic activity assay of 6 lysosomal enzymes in a NBS laboratory for the identification of newborns at risk for developing Pompe, Mucopolysaccharidosis-I (MPS-I), Fabry, Gaucher, Niemann Pick-A/B, and Krabbe diseases.Methods and ResultsEnzyme activities (acid α-glucosidase (GAA), galactocerebrosidase (GALC), glucocerebrosidase (GBA), α-galactosidase A (GLA), α-iduronidase (IDUA) and sphingomyeline phosphodiesterase-1 (SMPD-1)) were measured on ~43,000 de-identified dried blood spot (DBS) punches, and screen positive samples were submitted for DNA sequencing to obtain genotype confirmation of disease risk. The 6-plex assay was efficiently performed in the Washington state NBS laboratory by a single laboratory technician at the bench using a single MS/MS instrument. The number of screen positive samples per 100,000 newborns were as follows: GAA (4.5), IDUA (13.6), GLA (18.2), SMPD1 (11.4), GBA (6.8), and GALC (25.0).DiscussionA 6-plex MS/MS assay for 6 lysosomal enzymes can be successfully performed in a NBS laboratory. The analytical ranges (enzyme-dependent assay response for the quality control HIGH sample divided by that for all enzyme-independent processes) for the 6-enzymes with the MS/MS is 5- to 15-fold higher than comparable fluorimetric assays using 4-methylumbelliferyl substrates. The rate of screen positive detection is consistently lower for the MS/MS assay compared to the fluorimetric assay using a digital microfluidics platform.

These results are different from the published results on which the NICE guidelines were based; however, the evidence base in children is small. There is currently insufficient evidence to support the use of ultrasound guidance for central venous catheterization in children.

No abstract

Allelic sequence polymorphism at the 13-globin locus was investigated in a group of 36 Melanesians.A 3-kilobase fragment containing the gene and its flanking regions was sequenced in 60 normal (HA) and 12 thalassemic (intron 1, position 5, G -* C) chromosomes. Haplotype relationships between linked polymorphisms were derived by allele-specific PCR amplification and sequencing. Seventeer nucleotide polymorphisms and 2 length variants were identified, and these sites segregated as 17 sequence haplotypes in the normal chromosomes. This haplotype diversity is higher than that expected on the basis of the nucleotide polymorphism observed and is probably due to recombination and gene conversion. Nucleotide diversity at synonymous sites in the sample is 0.14%, suggesting an average age of sequence divergence of =450,000 years, consistent with that expected for a neutrally evolving human nuclear locus.Molecular population genetic analysis of nuclear loci was pioneered by Kreitman in a study of the alcohol dehydrogenase (Adh) locus in Drosophila melanogaster (1). That survey of 11 alleles revealed extensive nucleotide polymorphism, which has since been shown to reflect the effects of both recombination (2) and balancing selection (3) on the Adh gene. Although allelic sequencing is the ideal approach to investigating both molecular mechanisms and population genetic questions, the stratagem of using isochromosomal species lines to simplify analysis of diploid loci is not applicable to humans. Studies ofhuman DNA polymorphism have therefore been mostly limited to sequence analysis of haploid mitochondrial DNA (mtDNA) and to scoring of restriction fragment length polymorphisms (RFLPs) at nuclear loci (4). Allelic sequence analysis of nuclear genes has remained, largely for technical reasons, an elusive aim. The polymerase chain reaction (PCR) (5) and accompanying innovations have made rapid sequencing ofgenomic DNA commonplace, but because PCR simultaneously amplifies both alleles of diploid loci, linkage relationships in compound heterozygotes are obscured. In most instances, amplified DNA must be subcloned, a time-consuming procedure with the potential for introducing sequence errors that are unacceptable in population-genetic analyses. We have used allelespecific PCR amplification (6) to circumvent these difficulties and extend the analysis of human nuclear genes by determining allelic sequence variation in a 3-kilobase (kb) region surrounding the human ,3globin locus.The 3globin locus has been one of the most intensively studied of all human loci, not least because of its association with severe inherited hemoglobinopathies such as sickle cell anemia and 3thalassemia, some of the commonest genetic diseases in the world. The earliest examples of prenatal diagnosis of these disorders using DNA analysis relied on

Tandem-repetitive highly variable loci in the human genome (minisatellites) have been used in gene mapping and as DNA "fingerprints", but they have not yet found much application in population genetics. We have investigate the capacity of six minisatellites to discriminate between four populations in Oceania. We find that in comparison to Melanesians, Polynesians have a significant loss of heterozygosity (or gene diversity), not noted using more traditional markers. We show also that the number of alleles, the allele distribution and the mutation rates at the Polynesian minisatellite loci do not deviate from those predicted by the neutral mutation/infinite allele model. The low gene diversity is therefore likely to be a result of the maintenance of small population sizes and bottleneck effects during the colonization of the Pacific.