Gerardo Vaca

Centric fission, centromere‐telomere fusion and isochromosome formation: a possible origin of a de novo 12p trisomy

A 5‐month‐old girl had a typical 12p trisomy syndrome due to a monocentric i(12p) present in a 46‐chromosome complement that also included the translocation of all 12q onto the 8p telomere; i.e., her complex karyotype could be written as 46.XX, – 8,–12,+ der(8),t(8;12)(p23.3;cen), + i(12p). The present concurrence of a whole‐arm q translocation and an i(p) for a single chromocome, along with six previous similar instances involving chromosomes 4, 5 and 9, suggests the following origin for such a special rearrangement: a centric fission in Gl initially yielding two telocentrics; at the next replication, the tel(q) translocates onto a nonhomologous telomere (centromere‐telomere fusion), whereas the tel(p) becomes an i(p). This mechanism can be either meiotic or postzygotic and surmises that the translocated long arm retains a partial centromere, which subsequently is inactivated and loses its staining properties.

Red blood cell sorbitol dehydrogenase deficiency in a family with cataracts

SummarySorbitol dehydrogenase (SORD) was quantitatively assayed in a family in which four out of five brothers and their father had bilateral cataracts. Three sibs (two of them with cataracts) and both their father and paternal grandfather had SORD activity of about 25% of the reference values; of the other two affected sibs one had about 50% and the other had 75%; the mother and two paternal uncles had about 75%. These results do not define a clear cataract-SORD deficiency etiopathogenic relationship, nevertheless, they strongly suggest activity polymorphism in human red cell SORD, which would be highly relevant not only to the study of cataracts but of other major complications in diabetes.

G-6-PD Guadalajara. A new mutant associated with chronic nonspherocytic hemolytic anemia

SummaryThis paper describes a new G-6-PD variant designated Guadalajara, which was found in a Mexican boy suffering from chronic hemolytic anemia. The red cell enzyme activity of the subject is about 14%. The mutant enzyme showed rapid electrophoretic mobility, slightly increased affinity for glucose-6-phosphate, slightly decreased affinity for NADP+, moderately elevated utilization of substrate analogues, and normal heat stability, pH curve, and inhibition by NADPH. G-6-PD Guadalajara differs from all previously reported variants and is the first variant associated with chronic hemolysis found in Mexico.

Meiotic arrest at first spermatocyte level: A new inherited infertility disorder

SummaryThree 46,XY phenotypically male, azoospermic brothers out of thirteen sibs from a consanguineous marriage were studied and found to have a unique pattern of testicular histology with arrest of spermatogenesis at the pachytene stage of primary spermatocytes. Endocrinological evaluation showed elevated plasma luteinizing (LH) and normal to elevated follicle-stimulating (FSH) hormones, positive gonadotropin pituitary response to luteinizing hormone-releasing hormone, depletion of LH and FSH levels by exogenous testosterone (T) administration, normal levels of T and dihydrotestosterone hormones, and elevation of T after stimulation with human chorionic gonadotropin hormone. Electrophoretic assay of lactic dehydrogenase isozymes did not reveal band C4 in semen or testicular tissue. These traits seem to constitute a hitherto undescribed form of infertility in which spermatogenesis arrest at the first spermatocyte level is the main feature. The parental consanguinity suggests autosomal recessive inheritance.

Glucose-6-phosphate dehydrogenase (G-6-PD) mutations in Mexico: four new G-6-PD variants

Screening for mutations at the G-6-PD gene by PCR-SSCP combined with restriction enzyme analysis and DNA sequencing was performed in nine G-6-PD deficient individuals with negative results for the presence of the most frequent G-6-PD mutations previously observed in Mexican population. The variants G-6-PD Valladolid(406T), G-6-PD Durham(713G), and G-6-PD Viangchan(871A) and four new G-6-PD mutant alleles were identified. The new mutations are located at cDNA nt 376 A --> T (126 Asn --> Tyr), nt 770 G --> T (257 Arg --> Leu), nt 1094 G --> A (365 Arg --> His), and nt 1285 A --> G (429 Lys --> Glu) and they were named G-6-PD San Luis Potosi, G-6-PD Zacatecas, G-6-PD Veracruz, and G-6-PD Yucatán, respectively. To date, a total of 18 different G-6-PD variants have been observed in Mexico and several of them are common in Africa, South Europe, and Southeast Asia.

Mutational analysis of the LDL receptor and APOB genes in Mexican individuals with autosomal dominant hypercholesterolemia.

The goal of this project was to identify families with autosomal dominant hypercholesterolemia (ADH) to facilitate early detection and treatment and to provide genetic counselling as well as to approximate the mutational diversity of ADH in Mexico. Mutational analysis of the LDLR and APOB genes in 62 index cases with a clinical and/or biochemical diagnosis of ADH was performed. Twenty-five mutations (24 LDLR, 1 APOB) were identified in 38 index cases. A total of 162 individuals with ADH were identified using familial segregation analysis performed in 269 relatives of the index cases. In addition, a novel PCSK9 mutation, c.1850 C>A (p.Ala617Asp), was detected. The LDLR mutations showed the following characteristics: (1) four mutations are novel: c.695 -1G>T, c.1034_1035insA, c.1586 G>A, c.2264_2273del; (2) the most common mutations were c.682 G>A (FH-Mexico), c.1055 G>A (FH-Mexico 2), and c.1090 T>C (FH-Mexico 3); (3) five mutations were identified in 3 or more apparently unrelated probands; (4) three mutations were observed in a true homozygous state; and (5) four index cases were compound heterozygous, and one was a carrier of two mutations in the same allele. These results suggest that, in Mexico, ADH exhibits allelic heterogeneity with 5 relatively common LDLR mutations and that mutations in the APOB gene are not a common cause of ADH. This knowledge is important for the genotype-phenotype correlation and for optimising both cholesterol lowering therapies and mutational analysis protocols. In addition, these data contribute to the understanding of the molecular basis of ADH in Mexico.

G-6-PD Jalisco and G-6-PD Morelia: Two new Mexican variants

SummaryTwo new G-6-PD variants designated G-6-PD Jalisco and G-6-PD Morelia were identified in two unrelated Mexican families. An additional G-6-PD variant was found in each family: G-6-PD trinacria and G-6-PD A-. In both families compound heterozygotes were identified. G-6-PD Jalisco and G-6-PD Morelia belong to Classes 3 and 4, respectively. G-6-PD Morelia is the first variant from its class with a high Km for NADP and a low Ki for NADPH.

Los Angeles variant of galactose-1-phosphate uridyltransferase (EC 2.7.7.12) in a Mexican family.

SummaryEnzymatic activity and electrophoretic mobility of galactose-1-phosphate uridyltransferase (EC 2.7.7.12) were assayed in a Mexican family (8 sibs and their parents) with two galactosemic members. Normal, galactosemic and Los Angeles enzyme variants were identified. A survey of the ethnological backgrounds of the individuals reported to date with the Los Angeles variant showed multiple origins that could be explained by an ancient and widespread gene mutation or, more probably, by further biochemical heterogeneity.

Partial mispairing and crossing-over between β0 and δ genes as the origin of the δ β0 thalassemia gene

SummaryTwo double heterozygous β0/δβ0 thalassemic sibs of Mexican descent were studied. The father had a β0/β0 genotype, while the mother, one sib and several maternal relatives were β0/δβ0 heterozygotes. Parental consanguinity and an apparently low frequency of thalassemia among Mexicans suggested a possible common origin of both β0 and δβ0 genes. A hypothesis to explain such a possibility is proposed on the basis of a partial mispairing between β0 and δ genes followed by a crossing-over which would results in a δβ0 recombinant gene. This hypothesis could also be extended to explain the β 22 glu→ala, δ 22 ala→glu and δ 116 arg→his Hb variants as recombinants from double crossing-over between β and δ mispaired genes for which the name “interstitial-Lepore” is proposed.