The Maltese Population

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The genetic component within a population is strongly affected by its history and demography. The genetic pool of a population is affected by mutations, population admixture as well as by random genetic drift that occurs most often due to catastrophic events that result in a major decrease in the population (Wright et al., 1999; Harpending et al., 1998). Genetically isolated populations (by geography and/or culture) that recently expanded from a very small number of founders with occasional interbreeding with other ethnic groups are more likely to share haplotypes identical by descent (IBD) over longer genetic distances (Wright et al., 1999; Kruglyak, 1999a).

The first inhabitants of the Maltese islands were thought to have came from Southern Italy approximately 7,000 years ago. From that time on the inhabitants of the islands mixed with a series of occupants and traders including the Phoenicians, Romans and Arabs. In an article published in National Geographic Magazine a link between the Maltese and the Phoenicians was reported from a study of the Y-chromosome, where it was suggested that the Phoenicians might have completely replaced the original inhabitants of Malta (Franklin-Barbajosa, 2004). In a previous study, it was observed that the frequencies of haplotypes on the Y chromosome were different in Greeks and Italians when compared to Asians and Slavs, suggesting a possible common origin from sea-faring people such as the Phoenicians rather than from Neolithic European farmers (Mitchell et al, 1997). Recent analysis of Y-chromosome STRs in several populations from the Mediterranean basin revealed that Malta forms part of the Central-East Mediterranean cluster being closest to north western Sicilians, with southern Italy, Cyprus and Turkey also in the same group (Capelli et al., 2005). The authors reported that these results could show the correctness when saying that near eastern populations are evidence of the Neolithic expansion from the Middle East towards Europe. The distribution of LD between Y-linked alleles is larger when compared to the X chromosome which in turn has a wider LD than autosomes, mainly because of lower recombination rates (Pritchard & Przeworski, 2001; Devlin et al., 2001). For the Y-chromosome recombination during meiosis only occurs in males at the pseudoautosomal region with the X chromosome.  In a recent study, Y chromosome haplogroup analysis also showed that there is a marked degree of genetic heterogeneity in the Sicilian population especially between western and eastern regions, although it seems that the main contribution was coming from Greek settlers (especially on the Eastern side) while haplogroup analysis showed that mostly on the western part, African/Phoenician populations contributed to approximately 6% of the gene pool (Di Gaetano et al., 2008).  

 

 

 

The present Maltese population, although geographically (but not genetically) isolated, is thought to have expanded exponentially from a much smaller population during the last four hundred years with a possibility of a number of founder effects introduced due to admixture with other populations coming from Sicily, eastern Mediterranean and northern Africa (Wettinger, 2002). Founder effects were reported in the Maltese population including a mutation (R1160X) found in the NPHS1 gene coding for nephrin that causes nephrotic syndrome (Koziell et al., 2002) and the 68G>A mutation within the quinoid dihydropteridine reductase gene that causes a rare form of hyperphenylalaninaemia and phenylketonuria (Farrugia et al., 2007). A recent study using autosomal STRs performed in the present population living on the Maltese islands showed closest genetic relationship with the Sicilian population (Cassar et al., 2008). The Sicilian population used in our study was coming from the western part of Sicily from a small town in the Palermo province, called Alia. Y-chromosome haplogroups and gene flow at Northwestern part of Sicily were observed to be more of African/Phoenician origin, thought that these were introduced by a number of trans-Mediterranean migrations from northern Africa (Carthage) (Di Gaetano et al., 2008). So our study although using autosomal STRs agreed with previous and current observations using Y-STRs. Also as shown in the figure below we showed closer genetic relationship between the Greeks and a southern Italian population from Campania region (south of Napoli) a region that was mainly colonised by Greeks. Our observations using autosomal STRs agreed with other observations using Y-STRs which are less prone to change from one generation to the next. STR allele frequences in the Maltese population can be downloaded from here.

 

Phylogenic tree from analysis of 5 STRs between different populations

 

During the years there were major fluctuations in population growth due to a number of historical events, including constant attacks on the Maltese islands by Turks in the mid sixteenth century. During the sixteenth and seventeenth centuries, when the Knights of St John ruled the islands, there was a constant contact between Maltese people and Sicilians who were mainly mariners and traders especially in harbour areas. Italian influence on the Maltese population is supported by the number of surnames of Italian origin and also from linguistics which was more Italianised in port areas and Semitic in rural villages.  Other fluctuations in the population were brought about by emigration of the Maltese due to fear from further attacks by the Turks, death by famine and the plague. The plague struck Malta several times between the fourteenth and nineteenth centuries with the latest epidemic being that of 1813. Every outbreak resulted in the death of a significant percentage of the population ranging from 9% during the 1592 outbreak to 4% in the latest outbreak of 1813, where in the latter the population was of nearly 116,000. Other sources mentioned that during the outbreak of 1675 approximately 8,000 to 11,000 individuals perished from a population of approximately 50,000. These events might indicate that the present Maltese population is not as old as one might have thought but it increased from a much smaller population during the last four hundred years, structured by a number of population bottlenecks and admixture.

 

More about Genetic Studies in the Maltese Population (disease related)

 

 References

Additional references are:

Cassar M., Farrugia C., Vidal C. (2008) Allele frequencies of 14 STR loci in the population of Malta. Legal Medicine 10: 153 - 156.

Di Gaetano C., Cerutti N., Crobu F et al. (2008) Differential Greek and northern African migrations to Sicily are supported by genetic evidence from the Y chromosome. European Journal of Human Genetics (in press)

 

 

 
 
 
 
 

 

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