MJD has been reported from Africa and in a few families of African descent in the USA. To the best of our knowledge, these are the first MJD patients described in Sudan. Quite surprisingly, and unlike all other MJD African families analysed, this family shows the same exact (“pure”) Machado lineage, as the MJD families originating from Portugal (primarily central mainland and the Azorean island of São Miguel).
At the phenotypical level, however, onset (both in the proband and his examined brother) was at a relatively early age (24 and 20 years old), and time of disease evolution was short (only 14 and 7 years, respectively). In the Portuguese-Azorean islands of São Miguel and Flores (homelands of the Machado and Joseph families), as well as in Portuguese migrants in the USA and Canada, there is a well-established difference in AO and disease duration: onset occurs later and disease course is more protracted in the Machado family and others from São Miguel and in the east coast of the USA; mean AO ± SD was 43.2 ± 13.5 in patients from São Miguel (versus 35.3 ± 15.2 in Flores) (Sequeiros 1989). Accordingly, MJD subphenotypes 3 and 1 were predominantly observed in Machado and Joseph original families, respectively (Coutinho 1992; Nakano et al. 1972; Rosenberg et al. 1976; Sequeiros 1989); our current knowledge on the distinct haplotype backgrounds of these two families sheds light on what could have been one of the first phenotype-genotype studies in MJD. Still nowadays, such correlations are scarce and difficult to perform since (1) a precise clinical examination is required with patients observed for more than seven years, once types 1 and 3 are considered to be defined; and (2) sometimes, more than one subtype is found within the same family, mainly across generations. The Sudanese brothers analysed in this study showed earlier onset and a more severe and rapid disease progression, relatively to the Portuguese kindreds of the Machado lineage. This would be unlikely explained by cis-factors in the immediate proximity of the (CAG)n, in the 15 kb region analysed; other cis or trans-acting modifiers present in their population background, and/or environmental or stochastic factors could account for it.
The MJD Machado lineage had only been observed in Portugal and in a few countries with well documented connections to Portugal (as nearby Spain, and migrants’ descendants in Brazil and North-America), even if only three or six SNPs were typed in those studies (Gaspar et al. 2001; Martins et al. 2007). Now, we genotyped 30 intragenic SNPs and 7 STRs flanking the expanded (CAG)n, in this Sudanese family and in the other 93 MJD families sharing its Machado ancestral origin. The analysis of phylogenetic relationships among STR haplotypes, supported also a Portuguese ancestry for the Machado lineage. Nevertheless, dispersal routes responsible for the presence of MJD in Sudan are difficult to trace, since no intermediate STR haplotypes were found. When comparing STR haplotypes among all families with the Machado lineage, we see 4 STRs downstream to be highly conserved, with only one single-step mutation at AC_21 (H10) and two recombination events (H11 and H12). This reinforces a single recent mutational origin for all, rather than a predisposing haplotype; accordingly, two alleles of the ancestral haplotype H1 are extremely rare in European and Asian control populations or even absent among Africans. Thus, assuming H1 as the ancestral STR haplotype, 5 branches diverge from it in the most parsimonious network. Origin of H4 and H5 by recombination from H1 is also the best explanation, as the alternative of their evolution by the many stepwise mutations required (on the 3 STRs upstream) seems more unlikely.
The fact that most Portuguese families with this lineage share the ancestral haplotype H1, strongly suggests that a major founder effect contributed to the high frequency of MJD in Portugal, as previously suggested (Martins et al. 2007). The main founder Machado haplotype seems to coincide with the ancestral background where a de novo expansion might have occurred.
In spite of our extensive search in many other populations, the full picture of the Machado mutational origin may yet be incomplete, as MJD could still being underdiagnosed in some populations from Africa and elsewhere. If that were the case, the age of 3,210 ± 693 years, as now anticipated for the ancestral origin of this lineage, would be an underestimate. In any case, as previously postulated (Martins et al. 2007), the mutational origin of the Machado lineage must be much more recent than the worldwide-spread Joseph lineage (5,774 ± 1,116y (Martins et al. 2007), 16,335 ± 1,966y (Li et al. 2018)), or the Joseph-like sublineages (11,837 ± 1,871y, 9,272 ± 1,352y, 9,254 ± 1,411y, all estimations in the Chinese population (Li et al. 2018); and 7,191 ± 1,252y for the reported Joseph-Groote sublineage found in several Asian families (Martins et al. 2012)). The use of the information provided by the genotyping of Ancestry Informative Markers in this genomic region could provide useful clues to clarify the origin of these lineages in terms of their continental birthplaces.