William Arias

Admixture in Latin America: Geographic Structure, Phenotypic Diversity and Self-Perception of Ancestry Based on 7,342 Individuals

The current genetic makeup of Latin America has been shaped by a history of extensive admixture between Africans, Europeans and Native Americans, a process taking place within the context of extensive geographic and social stratification. We estimated individual ancestry proportions in a sample of 7,342 subjects ascertained in five countries (Brazil, Chile, Colombia, México and Perú). These individuals were also characterized for a range of physical appearance traits and for self-perception of ancestry. The geographic distribution of admixture proportions in this sample reveals extensive population structure, illustrating the continuing impact of demographic history on the genetic diversity of Latin America. Significant ancestry effects were detected for most phenotypes studied. However, ancestry generally explains only a modest proportion of total phenotypic variation. Genetically estimated and self-perceived ancestry correlate significantly, but certain physical attributes have a strong impact on self-perception and bias self-perception of ancestry relative to genetically estimated ancestry.

Genetic make up and structure of Colombian populations by means of uniparental and biparental DNA markers

Colombia is a country with great geographic heterogeneity and marked regional differences in pre-Columbian native population density and in the extent of past African and European immigration. As a result, Colombia has one of the most diverse populations in Latin America. Here we evaluated ancestry in over 1,700 individuals from 24 Colombian populations using biparental (autosomal and X-Chromosome), maternal (mtDNA), and paternal (Y-chromosome) markers. Autosomal ancestry varies markedly both within and between regions, confirming the great genetic diversity of the Colombian population. The X-chromosome, mtDNA, and Y-chromosome data indicate that there is a pattern across regions indicative of admixture involving predominantly Native American women and European and African men.

A novel Cys212Tyr founder mutation in parkin and allelic heterogeneity of juvenile Parkinsonism in a population from North West Colombia

We report the molecular characterization of three multiplex families and a sporadic case of juvenile Parkinsonism identified in the province of Antioquia (Colombia). Linkage and haplotype analysis using markers in 6q25.2-27 indicated that Parkinsonism in the pedigrees is linked to the parkin gene (maximum LOD-score of 3.85) but that they carry two different mutant haplotypes. Sequence analysis revealed a novel G to A transition in exon 6 at position 736 (G736A) of parkin. This change results in a non-conservative cysteine for tyrosine substitution. All affected individuals from two families were homozygous for this mutation, which was not detected in 100 normal controls. Patients from the family carrying the second haplotype and the sporadic case were homozygous for a GT insertion in exon 3. This mutation has been previously identified in French families with juvenile Parkinsonism. The concomitant presence of founder effects and allelic heterogeneity in Antioquia might relate to the founding admixture at the origin of this population.

A genome-wide association scan implicates DCHS2 , RUNX2 , GLI3 , PAX1 and EDAR in human facial variation

We report a genome-wide association scan for facial features in ∼6,000 Latin Americans. We evaluated 14 traits on an ordinal scale and found significant association (P values<5 × 10−8) at single-nucleotide polymorphisms (SNPs) in four genomic regions for three nose-related traits: columella inclination (4q31), nose bridge breadth (6p21) and nose wing breadth (7p13 and 20p11). In a subsample of ∼3,000 individuals we obtained quantitative traits related to 9 of the ordinal phenotypes and, also, a measure of nasion position. Quantitative analyses confirmed the ordinal-based associations, identified SNPs in 2q12 associated to chin protrusion, and replicated the reported association of nasion position with SNPs in PAX3. Strongest association in 2q12, 4q31, 6p21 and 7p13 was observed for SNPs in the EDAR, DCHS2, RUNX2 and GLI3 genes, respectively. Associated SNPs in 20p11 extend to PAX1. Consistent with the effect of EDAR on chin protrusion, we documented alterations of mandible length in mice with modified Edar funtion.

A genome-wide association scan in admixed Latin Americans identifies loci influencing facial and scalp hair features

We report a genome-wide association scan in over 6,000 Latin Americans for features of scalp hair (shape, colour, greying, balding) and facial hair (beard thickness, monobrow, eyebrow thickness). We found 18 signals of association reaching genome-wide significance (P values 5 × 10−8 to 3 × 10−119), including 10 novel associations. These include novel loci for scalp hair shape and balding, and the first reported loci for hair greying, monobrow, eyebrow and beard thickness. A newly identified locus influencing hair shape includes a Q30R substitution in the Protease Serine S1 family member 53 (PRSS53). We demonstrate that this enzyme is highly expressed in the hair follicle, especially the inner root sheath, and that the Q30R substitution affects enzyme processing and secretion. The genome regions associated with hair features are enriched for signals of selection, consistent with proposals regarding the evolution of human hair.

A genome-wide association study identifies multiple loci for variation in human ear morphology

Here we report a genome-wide association study for non-pathological pinna morphology in over 5,000 Latin Americans. We find genome-wide significant association at seven genomic regions affecting: lobe size and attachment, folding of antihelix, helix rolling, ear protrusion and antitragus size (linear regression P values 2 × 10−8 to 3 × 10−14). Four traits are associated with a functional variant in the Ectodysplasin A receptor (EDAR) gene, a key regulator of embryonic skin appendage development. We confirm expression of Edar in the developing mouse ear and that Edar-deficient mice have an abnormally shaped pinna. Two traits are associated with SNPs in a region overlapping the T-Box Protein 15 (TBX15) gene, a major determinant of mouse skeletal development. Strongest association in this region is observed for SNP rs17023457 located in an evolutionarily conserved binding site for the transcription factor Cartilage paired-class homeoprotein 1 (CART1), and we confirm that rs17023457 alters in vitro binding of CART1.

A genetic cluster of early onset Parkinson's disease in a Colombian population†

We previously identified in two families with early onset Parkinsons Disease (PD) from the isolated population of Antioquia (Colombia), a parkin Cys212Tyr substitution caused by a G736A mutation. This mutation was subsequently observed in a Spanish family, suggesting that it could have been taken to Antioquia by Spanish immigrants. Here we screened for the G736A mutation in additional Antioquian early onset PD cases and used haplotype analysis to investigate the relationship between Spanish and Antioquian G736A chromosomes. We confirmed the occurrence of an extensive founder effect in Antioquia. Thirteen individuals (10 homozygotes) from seven nuclear families were identified with the G736A mutation. Genealogical investigations demonstrated the existence of shared ancestors between six of these families four to five generations ago and no evidence of Spanish ancestry during this period. A second parkin mutation (a duplication of exon 3), was detected in the three G736A heterozygote carriers. Haplotype data exclude a recent common ancestry between the Spanish and Antioquian patients studied here and is consistent with the introduction of the G736A mutation in Antioquia during early colonial times (about 16 generations ago).

Language Deficits as a Preclinical Window into Parkinson’s Disease: Evidence from Asymptomatic Parkin and Dardarin Mutation Carriers

OBJECTIVES The worldwide spread of Parkinsons disease (PD) calls for sensitive and specific measures enabling its early (or, ideally, preclinical) detection. Here, we use language measures revealing deficits in PD to explore whether similar disturbances are present in asymptomatic individuals at risk for the disease. METHODS We administered executive, semantic, verb-production, and syntactic tasks to sporadic PD patients, genetic PD patients with PARK2 (parkin) or LRRK2 (dardarin) mutation, asymptomatic first-degree relatives of the latter with similar mutations, and socio-demographically matched controls. Moreover, to detect sui generis language disturbances, we ran analysis of covariance tests using executive functions as covariate. RESULTS The two clinical groups showed impairments in all measures, most of which survived covariation with executive functions. However, the key finding concerned asymptomatic mutation carriers. While these subjects showed intact executive, semantic, and action-verb production skills, they evinced deficits in a syntactic test with minimal working memory load. CONCLUSIONS We propose that this sui generis disturbance may constitute a prodromal sign anticipating eventual development of PD. Moreover, our results suggest that mutations on specific genes (PARK2 and LRRK2) compromising basal ganglia functioning may be subtly related to language-processing mechanisms. (JINS, 2017, 23, 150-158).

Alteraciones cognitivas en Parkinson Juvenil causado por la mutación C212Y en el gen Parkin.

In Antioquia, Colombia, four families have been reported with juvenile Parkinson´s disease and carrying the C212Y mutation in the Parkin gene. Many cognitive alterations associated with idiopathic, late-onset Parkinson´s disease have been described; however, little attention has been paid to the description of neuropsychological profiles in families carrying mutations in genes associated with juvenile Parkinson´s disease. For this study we selected a group of ten homozygous carriers of Parkin mutation C212Y with the clinical and a group of molecular diagnosis of Parkinson´s disease, and ten healthy relatives as controls. The neuropsychological evaluation revealed statistically significant differences between the two groups (p < 0.05) in Minimental State Examination and in tests evaluating working memory and attention in which prolonged execution times and marked slowing down of information processing were observed. We suggest that the observed alterations could be considered as neuropsychological features of patients with the C212Y mutation in the Parkin gene, the phenotypic expression of which seems to be associated in this population with slow evolution, mild cognitive impairment and functional involvement.