[Identifying deletions in the dystrophin gene and detecting carriers in families with Duchenne's/Becker's muscular dystrophy]. / Identificación de deleciones en el gen de la distrofina y detección de portadoras en familias con distrofia muscular de Duchenne/Becker.

INTRODUCTION: Between 60 and 65% of the mutations that cause Duchenne's/Becker's muscular dystrophy (DMD/BMD) are deletions in the dystrophin gene. Identifying deletions confirms the diagnosis and allows carriers to be detected with precision, which is the main preventive resource. The frequency and distribution of deletions in the DMD gene is unknown in south-east Mexico. AIMS: To identify deletions in the DMD gene and to detect carriers in families with DMD/BMD in south-east Mexico. PATIENTS AND METHODS: The study involved 26 families that showed clinical signs of DMD/BMD: Deletions were determined in the DNA of 40 males by means of the multiple polymerase chain reaction (PCR) in 22 segments of the gene. Detection of carriers was applied to 33 female relatives using PCR-restriction fragment length polymorphism of the polymorphic markers Pert 87.8/Taq 1, pERT 87.15/Bam H1, and single PCR for VNTR MP1P by linkage analysis. RESULTS: Deletions were identified in 67.5% of patients with DMD and they were located in the 5' end and in the central region, exons 44 to 52, of the gene. In the detection of carriers, 73.33% of the families were informative. The markers 87.8/Taq 1 and MPIP yielded the greatest information power, with 26.67 and 33.33%, respectively. Of a total of 33 females, 21 (63.64%) were carriers, one (3.03%) was a non-carrier and 11 (33.33%) were not informative. CONCLUSIONS: The frequency of deletions was 67.5%. Carrier status was determined in 66.67% of the females who were analysed. The markers pERT 87.8/Taq 1 and MP1P yielded the greatest information power.

[Spectrum of congenital malformations observed in neonates of consanguineous parents]. / Espectro de malformaciones congénitas observadas en recién nacidos de progenitores consanguíneos.

INTRODUCTION: Consanguineous unions occur in all populations around the world. Couples related as second cousins or closer have been observed with deleterious effect. Among the clinical effects of parental consanguinity, the incidence of offspring with congenital malformations (CM) increases approximately two-fold. MATERIALS AND METHODS: A hospital database of neonates with CM was searched to select neonates with parental consanguinity and two control groups. One control group consisted of healthy neonates and the other control group consisted of neonates with CM but without parental consanguinity. Both control groups consisted of the first neonate of the same sex to be born after a consanguineous neonate with CM. Family, sociodemographic and anthropometric variables, as well as the severity of the malformations, were compared between the two groups with CM. Neonates with CM were grouped into five categories: Major multiple CM, minor multiple CM, isolated major CM, isolated minor CM, and specific diseases. The indigenous Mayan subpopulation was also analyzed. RESULTS: Among 1117 neonates with CM, parental consanguinity was found in 21. Parental consanguinity was also found in 8 neonates in the group of healthy controls (OR 2.4 [1.05-5.95]). The most common form of consanguinity was between second cousins and was more frequent in the Mayan subpopulation. Major multiple CM were more frequent among consanguineous than among nonconsanguineous couples. No association was found between the severity of CM and the degree of relationship. CONCLUSIONS: The prevalence of consanguinity found in neonates with CM and healthy controls (1.9 % and 0.8 %) was similar to that found in other Latin populations. A higher prevalence was found in the Mayan population. Mayor multiple CM were more frequent among the neonates of consanguineous than among nonconsanguineous couples.

Forensic potential of the STR DXYS156 in Mexican populations: inference of X-linked allele null.

The pentanucleotide STR (TAAAA)n DXYS156 offers advantages for genetic identity testing. In addition to establish the gender, DXYS156 expands the DNA profile and is able to indicate the possible geographic origin of the individual. We analyzed DXYS156 in 757 individuals of both sexes from Mexican populations. We studied the cosmopolitan Mestizo population and six Mexican ethnic groups: Tarahumaras, Purépechas, Nahuas, Mayas, Huicholes and Mezcala Indians. The six shorter (4-10) and the three larger alleles (11-13) were specific for the X and Y-chromosomes, respectively. A random distribution of alleles into genotypes was observed in males and females from each population. We estimated the power of exclusion for paternity testing according to the son's gender, and the power of discrimination in forensic casework. In addition, we detected a relatively high frequency of an X-linked allele null, principally in Mexican-Mestizos (3.6%), which must be considered when DXYS156 be applied for identification purposes.

Frequency of the thermolabile variant C677T in the MTHFR gene and lack of association with neural tube defects in the State of Yucatan, Mexico.

The C677T variant in the MTHFR gene is considered to be an associated risk factor for neural tube defects. However, the association has not been found in some ethnic groups. In order to assess the association between neural tube defects and the C677T variant, we determined the frequency of this variant in the MTHFR gene in the State of Yucatan, Mexico, where neural tube defects are highly prevalent. The study was performed on 65 subjects with spine bifida, 60 of their mothers and 110 control subjects. The presence of the C677T variant was determined by amplification and digestion with HinF1 of each subject's DNA. Genotypic and allelic frequencies were calculated for all groups. We did not observe any statistically significant difference in the genotypic or allelic frequencies between cases and controls for any of the groups studied (p > 0.05), suggesting that the thermolabile variant C677T is not an associated risk factor neither for the development of neural tube defects nor for mothers to have affected offspring in the population from Yucatan. Interestingly, the frequency of the C677T variant (54%) obtained in the Yucatan population is one of the highest reported (p < 0.01) and confirmed the high frequency of this allele throughout Mexico.

[Cytogenetic research in couples with recurrent spontaneous gestational losses]. / Investigación citogenética en parejas con péridadas gestacionales espontáneas recurrentes (PGER).

The most common complication of pregnancy is fetal wastage in any of its manifestations. One of the causes of these reproductive losses is the presence of parental chromosomal aberration. The diagnosis of this cause permits appropriate specific risk for the couple reproduction. In this study, cytogenic analysis were performed to a group of couples with fetal wastage of unknown, to know whether some parental chromosomic aberrations were the etiologic cause of them. Were included 173 couples with two or more reproductive failures. In all couples, metaphase chromosome analysis of peripheral blood was performed, with trypsin-Giemsa banding and C standing. In five women (2.9%) it was found some chromosomal aberration. In all the men and in 168 women the karyotype was normal. In 2.8% of all the subjects it was found some polimorphic chromosome. Routinary chromosomal survey realized to couples with pregnancy looses of unknown cause is important to identify individuals carrying some chromosomal aberration.

Chromosomic findings in patients with paroxysmal nocturnal hemoglobinuria.

The chromosomes of 14 patients (9 males, 5 females) suffering from paroxysmal nocturnal hemoglobinuria in Merida, Mexico between April 1989 and July 1992 were analyzed. Four of the patients were children (range, 3-15 years old) and 9 were adults (range, 19-62 years old). None of the patients had any evidence of leukemic transformation and 9 of them had antecedent insecticide exposure. In 50%, the clinical presentation was anemia plus hemorrhagic syndrome. Only 1 case had thrombosis. The lapse between the beginning of the disease and the karyotypic analysis was 14.5 months on average (range, 1-172 months). In all cases we found a normal chromosomic complement. In addition, 5 patients had an acentric fragment in only 1 metaphase and one of these had a mar and Cq chromatid break in another metaphase, but neither could be considered as specific chromosomal abnormality for paroxysmal nocturnal hemoglobinuria.

TAR-like syndrome in a consanguineous Mayan girl.

We report on a 3-month-old girl with a TAR-like syndrome. Her older brother died with a similar disorder at 3 months of unknown causes. The parents are second cousins of Mayan ancestry. The infant also had, in addition to the usual abnormalities of TAR syndrome, depressed nasal bridge, cataracts, glaucoma, megalocorneae, and blue sclerae.