Francisco J. Perea

Hb D-Los Angeles Associated with Hb S or β-Thalassemia in Four Mexican Mestizo Families

Twenty-five individuals were studied from four unrelated Mexican Mestizo families with Hb D-Los Angeles. We observed five compound heterozygotes: four for Hb S and Hb D, and one for Hb D and beta-thalassemia (beta(0) 39 nonsense mutation); 16 heterozygotes: four for Hb S, seven for Hb D, and five for beta-thalassemia, while the remaining four were normal. The four Hb S/Hb D patients had severe hemolytic anemia, while in the Hb D/beta-thalassemia patient, the anemia was similar to that of a beta-thalassemia heterozygote; therefore, Hb D is clinically harmful when it is associated with Hb S. The beta(S) chromosomes were associated with the Benin haplotype in two families and Bantu in one family, while the beta(D) and beta(0) 39 mutations were associated with haplotype 1 [+ - - - - + +]. The Bantu and Benin haplotypes have been found with high frequency in Hb S individuals from the East Coast and Northwestern Mexico. The beta(D) chromosomes from Italy were also shown to be associated with haplotype 1, the most frequently observed haplotype in the world; there are no haplotype studies on beta(D) chromosomes from India or China where Hb D-Los Angeles is most common. Thus, the true origin of this mutation observed in these Mestizo families remains to be elucidated.

Centromere–telomere (12;8p) fusion, telomeric 12q translocation, and i(12p) trisomy 1

The concurrence of a short arm isochromosome and a translocation of the entire long arm of the same chromosome to a telomere of another chromosome, implying trisomy for 4p, 5p, 7p, 9p, 10p or 12p, has been described in 13 patients. We have now used fluorescence in situ hybrization (FISH) to better characterize one of these rearrangements in which 12q was translocated to 8pter, whereas 12p was converted into an isochromosome. An alphoid centromere‐12 repeat gave a strong signal on the i(12p) and a weak but distinct signal at the breakpoint junction of the der(8), whereas the pantelomeric probe revealed three clear hybridization sites on the der(8): one at each end and another at the breakpoint junction. These findings suggest that the prime event was a post‐fertilization centric fission of chromosome 12 leading to the 12q translocation via a real centromere–telomere fusion and the i(12p). Alternatively, the crucial event may have been a centromere–telomere recombination. An interstitial telomere has been documented by means of FISH at the breakpoint junction of the sole derivative usually present in 20 constitutional translocations including eight with a jumping behavior. In addition, six other telomeric translocations defined by banding methods, including another case of 12q translocation/i(12p), have also been jumping ones. These telomeric translocations have been de novo events and their proneness to exhibit a jumping behavior appears to be independent of the involved chromosomes, size of the translocated segments, and concomitant abnormalities.

β-Thalassemia and βA globin gene haplotypes in Mexican mestizos

Abstractβ-globin haplotypes of 20 β-thalassemia (β-thal) and 87 βA Mexican mestizo chromosomes were analyzed to ascertain the origin of the β-thal alleles and the frequencies and distribution of the βA haplotypes among northwestern Mexican mestizos. Sixteen β-thal chromosomes carried six Mediterranean alleles [five codon 39 C→T; two IVS1:1 G→A; two IVS1:5 G→A; three IVS1:110 G(A; one codon 11 (–T) and three (δβ)°-thal]; the remaining four were linked to three rare alleles (two –28 A→C and one each: –87 C→T and initiation codon ATG→GTG). Among the 87 βA chromosomes, 17 different 5′ haplotypes with frequencies for 1, 3, 2 and 5 of 39.0%, 17. 2%, 9.2% and 6.9%, respectively, were observed. The β-haplotype analysis showed that 13 out of 16 Mediterranean chromosomes could easily be explained by gene migration; however, one codon 39 associated with haplotype 4 (– – – – + + –), one IVS1:1 with haplotype 1(+ – – – – + +) and one IVS1:5 G→A, may represent separate mutational events. Analysis of the rare alleles showed that the –28 A→C mutation was associated with the commonest βA haplotype in Mexican mestizos, Mediterraneans and the total world population; therefore an independent origin cannot be ruled out. The –87 C→T and initiation codon ATG→GTG were found with β-haplotypes different from the reported ones, suggesting an indigenous origin.

βA globin gene haplotypes in Mexican Huichols: Genetic relatedness to other populations

The haplotypes of 97 βA independent chromosomes from a Mexican Huichol Native American group were analyzed. The analysis also included 87 βA chromosomes from a Mexican Mestizo population previously studied. Among Huichols, eight different 5′ β haplotypes (5Hps) were observed, with types 1(+ − − − −), 13(+ + + − +) and 2(− + + − +) at frequencies of 0.794, 0.093, and 0.041, respectively. In Mestizos, 17 5Hps were found, types 1, 3(− + − + +), 2, 5(− + − − +) and 9(− − − − −) being the most common at frequencies of 0.391, 0.172, 0.092, 0.069, and 0.046, respectively. 3′ haplotype (3Hps) frequency distributions were 0.443(+ +), 0.083(+ −), and 0.474(− +) in Huichols and 0.563(+ +), 0.149(+ −), and 0.287(− +) in Mestizos. Pairwise comparison for both haplotype distributions between the two populations showed significant differences. Pairwise distributions of 3Hps for Huichols were compared with nine worldwide populations, three African, two Asian, two Melanesian, one Caucasian, and one United States Native American. The distributions of the Huichol were different (P < 0.05) from all populations except the Native American. Neis genetic distances showed the Huichols to be closer to the Native Americans, followed by Melanesians from Vanuatu and Asians; Africans were the farthest. The 5Hp distributions in Mexicans were also compared with 23 worldwide populations (including African, Native American, Asian, Caucasian, and Pacific Islanders). Huichol distributions were different (P < 0.05) from all other populations except Koreans. The Mestizo distribution was also different from the others, except three Caucasian groups. Neis genetic distance between the same populations disclosed that the Huichols are in relatively close proximity to five out of six Asian populations considered. The same analysis with grouped worldwide populations showed Native Americans as population closest to the Huichols, followed by Pacific Islanders and Asians. Present observations are consistent with an important Asian contribution to the Huichol genome in this chromosomal region. Am. J. Hum. Biol. 12:201–206, 2000.

Diversity of the 5′ β-Globin Haplotype of Four β-Thalassemia Mutations in the Mexican Population

β-Globin haplotypes have been used to investigate the origin and spread of β-globin mutations such as Hb S [β6(A3)Glu→Val, GAG>GTG], Hb E [β26(B8)Glu→Lys, GAG>AAG], and β-thalassemia (β-thal). Molecular analyses revealed the presence of 17 β-thal mutations in the Mexican population; the most frequent of these are the nonsense codon 39 (C>T), IVS-I-1 (G>A), IVS-I-110 (G>A), and −28 (A>C). To improve our knowledge about their origin, we analyzed the 5′ haplotypes by restriction fragment length polymorphism. The codon 39 mutation (n = 17) was observed with five 5′ haplotypes: 1 (59%), 2 (23%), and 4, 6, and 9 (6% each). The IVS-I-1 mutation (n = 15) was found with five 5′ haplotypes: 1 (73.6%), 2, 3, 5, and 11 (6.6% each), whereas the IVS-I-110 (n = 9) and −28 mutations (n = 1) were only associated with haplotype 1. In the population studied, the codon 39 and IVS-I-1 mutations show a multicentric origin, whereas the IVS-I-110 and −28 mutations have an apparent single origin. Further investigation is required for the analysis of the polymorphisms surrounding the β-globin gene.

Analysis of the SLC4A1 gene in three Mexican patients with hereditary spherocytosis: report of a novel mutation

We analyzed the SLC4A1 gene in three Mexican patients with Hereditary Spherocytosis (HS). The promoter and all 20 exons were investigated through heteroduplex analysis and DNA sequencing. No DNA changes were detected in one of the three patients. Two well-known polymorphisms, Memphis I and the Diego-a blood group, were detected in another one. In the third, the HS phenotype could be explained by the novel 1885_1888dupCCGG mutation found in heterozygosis. This frameshift mutation is predicted to result in a truncated and unstable protein lacking normal functions.

Haplotype analysis of the Mexican frameshift Cd 11 (−T) and −28 A→C β‐thalassemia alleles

The origins of the −28 A→C and frameshift Cd 11 −T (Fs Cd 11 −T) alleles were investigated by β‐globin cluster haplotype analysis. These alleles were found in a Mexican mestizo family with β‐thalassemia (β‐thal). The ‐28 A→C mutation was described previously in Kurdish Jews linked to the most common haplotype in the world (+−−−−++), the same haplotype observed in this Mexican family. Therefore, it is not possible to assess a new origin of the −28 A→C mutation in our population. The Fs Cd 11 −T allele, not reported to date in any other populations, was linked to the −++−−+− haplotype (sixth in frequency in the world). This haplotype has not been reported in association with any β‐thal mutant, suggesting a Mexican origin for the Cd 11 −T mutation.

Characterization of the 5′ and 3′ Breakpoints of the Spanish (δβ)0-Thalassemia Deletion in Mexican Patients

We studied five unrelated Mexican carriers of the Spanish (δβ)0-thalassemia [(δβ)0-thal] mutation to characterize the size of the deletion, the 5′ and 3′ breakpoints and the 5′ β-globin haplotype. Sequence analysis revealed the presence of an 89,548 bp deletion. The δ- and β-globin genes, two olfactory receptor genes (OR51V1 and OR52A1) and two pseudogenes (OR52Z1P and OR51A1P) were deleted. The 5′ breakpoint was located at the same position as previously reported, and the 3′ breakpoint was situated 7.0 kb downstream of OR52A1 and 11.7 kb upstream of OR52A5. The Spanish (δβ)0-thal allele was associated with the 5′ haplotype 2 [– + + – +] in the studied patients. Because this mutation is relatively frequent in Spain, and the Mexican population contains a high level of Spanish genetic background, we propose that the mutation in both populations share a common ancestral origin.

A Frameshift at Codons 77/78 (–C): A Novel β‐Thalassemia Mutation

We identified and characterized a novel β‐thalassemia (β‐thal) mutation due to a deletion of cytosine at codons 77/78 (–C) [CAC(His) CA– or CTG(Leu)→–TG] found in a heterozygous state in four members of a Mexican family. The β haplotype analysis performed on the family revealed that the frameshift at codons 77/78 (–C) mutation in this family is associated with haplotype V [– + – – – +] and framework 2. Ten β‐thal alleles with a cytosine deletion are described at the Globin Gene Server, two of which are very near codon 77. The molecular pathology of β‐thal in the Mexican population has been shown to be heterogeneous, because some Mediterranean, Asian, private and rare alleles have been observed, a similar fact as has been observed in populations with a low frequency of β‐thal.

Hb COLIMA [β49(CD8)Ser→Cys]: A NEW HEMOGLOBIN VARIANT

Hb Colima was found in a 52-year-old Mexican Mestizo female, who was born in Colima, Mexico. This variant was observed during a population screening for the main hemoglobinopathies in the state of Colima, performed at the Centro de Investigación Biomédica de Occidente, Instituto Mexicano del Seguro Social, Guadalajara, Mexico. The hematological data of the proband, obtained by an electronic ABX-VEGA counter, were as follows: RBC 4.29610=L, Hb 13.6 g=dL, MCV 96.9 fL, MCH 32.0 pg, RDW 13.3%, and the reticulocyte count was normal. Biochemical analysis was done by conventional methods: Hb F 1.1%, Hb A2 3.4%, and Hb X 29.3%, that migrated faster than Hb A and Hb Fannin-Lubbock on cellulose acetate electrophoresis at pH 8.6. Hb X was quantified by DEAE cellulose chromatography of the stored hemolysate (at 15 C for two weeks). The isopropanol and butanol stability tests were normal. Isoelectrofocusing (IEF) was performed on a PhastSystem using PhastGel (Amersham Biosciences, Piscataway, NJ, USA) IEF media 5–8, and showed an X band that focused towards the anode from Hb A. DNA was extracted from the buffy coat by the salting-out method. Direct DNA sequencing of the b-globin gene showed a C!G substitution at codon 49 (Fig. 1), that results in the replacement of the serine residue by a cysteine in the b-globin chain. The entire b-globin gene was sequenced by ABI PRISM BigDye Terminator chemistry on an Applied BioSystems 3100 sequencer (Applied BioSystems, Foster City, CA, USA). The heterozygosity for the C!G