Alpha-thalassaemia, one of the most monogenic disorders in
humans, is the result of defective production of the alpha chain of
haemoglobin [1]. The primary causes of alpha-thalassaemia involve
deletions of one or both of the alpha-globin genes in the telomeric
region of chromosome 16 (16p 13.3) on chromosome 16 [2]. Deletions
leading to alpha-thalassaemia are more common than nucleotide variations,
otherwise known as “nondeletion” alpha-thalassaemia variants.
Defects due to either type of mutation that leads to dysfunction of one
or two alpha genes may cause slight reduction in erythrocyte volume
and size but are not clinically relevant. Loss of function of three alpha
genes leads to Hb H disease, a chronic moderate anaemia associated
with a picture of alpha-thalassaemia intermedia [3]. Complete deletion
of all four alpha-globin genes results in severe anaemia in utero and a
condition known as Hb Barts hydrops foetalis. Definition of alpha
globin genotypes in potential carriers is useful to predict prognosis
and management options, due to the strong correlation of phenotype
and genotype in Hb H disease patients [4–7]. For identification of
nondeletion variants in alpha globin gene, Sanger sequencing is the reference
method. However, in routine laboratories, the detection of
known thalassaemiamutations and globin chain variants in populations
with specificmutation spectrums is mainly performed using traditional
well-established methods such as restriction enzyme analysis of PCR
amplicons (RE-PCR), allele-specific amplification using the amplification
refractorymutation system (ARMS), allele-specificmutation detection
of amplified DNA based on hybridization of PCR products to allelespecific
oligonucleotide probes (ASO) in either forward or reverse ASO
approach [8]. More recently, pyrosequencing, involving sequencing by
synthesis [9] and high resolution melting analysis without the need
for post-PCR sample manipulation [10], have been proposed for the
rapid genotyping or screening of “nondeletion” HBA mutations
In this paper, we report a method that facilitates direct detection by
the naked eye of the 13most common “nondeletion” alpha-globin gene
mutations in populations around the Mediterranean and Middle East
using a dipstick biosensor in a dry-reagent format. The method
comprises PCR amplification of a single fragment for each HBA1 and
HBA2 gene flanking all mutations, using any conventional thermal
cycler, multiplex primer extension (PEXT) reaction of just 10 cycles
followed by the visual detection of the reaction productswithin minutes
by the multi-allele dipstick biosensor. Specialized instrumentation is
precluded, and the requirements for highly qualified technical personnel
are minimized.