A fragile X family with high penetrance in females: risk heterogeneity?

A fragile X family is described which shows two interesting features. In a sibship of seven, the two males and four of the five females are affected with mental retardation. Since the only normal daughter is not a carrier, the penetrance of the fragile X mutation in carrier daughters is 100%. Nevertheless, the penetrance of this syndrome in affected daughters of normal mothers has been estimated at a third. Also, DNA typing analysis of flanking RFLP markers revealed a higher than expected number of crossing-overs. We also include the molecular study of the mutation in the (CGG)n repeat of the FMR-1 gene.

Recombinant X chromosome in a prenatal diagnosis

The prenatal cytogenetic study of an amniotic fluid sample of a 39-year-old female showed one X chromosome with a fragment of extra material in the short arm. The G-band pattern suggested that the extra material could be the long arm of an X chromosome. Several complementary studies were performed in order to better clarify the origin of the material. These studies included parental karyotypes, microsatellite typing and comparative genomic hybridization (CGH). The results obtained allowed us to conclude that the derivative chromosome arose de novo as a recombinant X chromosome with duplication of Xq and partial deletion of Xp. Once informed, the parents decided to continue with the pregnancy, after which a healthy girl was born with no apparent disorders.

Trisomy rescue by postzygotic unbalanced (X;14) translocation in a girl with dysmorphic features

In this report we present the clinical features and molecular and cytogenetic findings in a female with partial trisomy 14q. Molecular and cytogenetic studies allowed us to determine that the extra 14q material (of paternal origin) was translocated postzygotically onto the maternal X chromosome. Consequently, only the derivative X chromosome was inactivated, although inactivation apparently did not spread over the entire chromosome 14q. This partial inactivation makes the present case unusual, giving rise to phenotypic features absent in other patients with partial trisomy 14q, typically restricted to the distal part of the chromosome.

Chromosome 11 abnormalities in myelodysplastic syndromes

Cytogenetic studies were performed in 140 patients with myelodysplastic syndrome (MDS) at diagnosis. Chromosome 11 anomalies were found in 7 cases (5%); 2 of these patients had refractory anemia (RA), 2 had refractory anemia with excess of blasts (RAEB), 1 had RAEB in transformation (RAEB-t), and 2 had chronic myelomonocytic leukemia (CMMoL) according to the French-American-British (FAB) Cooperative Group criteria. The chromosome 11 abnormalities comprised trisomy 11 (2 patients), monosomy 11 (1 patient), del(11)(q23) (2 patients), add(11)(p15) (1 patient), and der(11) t(3;11)(p21;q23) (1 patient). Abnormalities involving band q23 of chromosome 11 occurred in 3 cases and were the most common alteration. However, specific chromosomal alterations were not associated with any FAB classification group. These findings and their implications in the biology of MDS are discussed.

A novel TP53 germ-line mutation identified in a girl with a primitive neuroectodermal tumor and her father

A search of TP53 mutations was undertaken in a series of 51 pediatric brain tumors. The only germ-line mutation was detected in a 9-year-old girl with a PNET. Her family history was unremarkable for neoplastic disease, except for the paternal grandfather, who died of a gallbladder carcinoma at an advanced age. The mutation was a thymine deletion at the first base of codon 241, leading to termination codon at position 246 that has not previously been reported. This mutation was found to be inherited from the proband's father, who was healthy at age 40. In the tumoral sample, loss of heterozygosity in several 17p markers was found, the only TP53 allele preserved in the tumor was the mutated one. The presence of two short tandem repeats and two different palindromic sequences spanning the deletion lead us to propose the predisposition of this region to forming a complex secondary structure during replication. Consequently, it could have facilitated the present deletion. Furthermore, six other short deletions affecting--partially or totally--the region implicated in the folding model that we propose have been described in the literature. These findings confirm that this sequence represents a hotspot of deletion in the TP53 gene.

Pediatric brain tumors: loss of heterozygosity at 17p and TP53 gene mutations

Cytogenetic and molecular analyses of primitive neuroectodermal tumors (PNETs) of the central nervous system (CNS) have demonstrated material losses of 17p, the region that contains the TP53 gene, as the most frequent abnormality. Mutations in the TP53 gene are, however, very rare in these tumors. These findings strongly suggest that another, as yet unidentified, gene on 17p may be involved. We performed a search for loss of heterozygosity (LOH) on 17p by microsatellite markers on 26 childhood CNS tumors as well as TP53 gene mutations (exons 5-8) by single-strand conformational polymorphism analysis on 41 pediatric brain tumor samples of distinct histologic types. LOH was detected in 10 cases: 7 PNET, 2 astrocytomas, and 1 glioblastoma multiforme. In 4 of the PNETs the losses were limited to more distal markers. On the other hand, TP53 mutations were detected in 6 of 41 samples studied. Our results not only confirm the low penetrance of the TP53 gene on pediatric CNS tumors, but also provide further evidence of a putative tumor suppressor gene distal to TP53, between markers (D17S938, D17S926) and 17pter, specifically taking part in the development of PNET.

Translocation (12;14)(q13;q32) in myelodysplastic syndrome

We report a patient diagnosed with refractory anemia with excess blasts in transformation (RAEB-t) who underwent an evolution to a nonlymphocytic acute leukemia (ANLL-M5a). Initial cytogenetic study showed a diploid karyotype; however, when ANLL-M5a was diagnosed, the bone marrow (BM) cells showed a t(12;14)(q13;q32), which to our knowledge has not been described previously in a myelodysplastic syndrome (MDS).

[Genetic analysis of Friedreich's ataxia using polymorphic DNA markers]

Friedreich's ataxia (FA) is a progressive degenerative disease involving both central and peripheral nervous system. It is an autosomal recessive hereditary disorder, which begins around puberty and has an unknown genetic basis and biochemical defect. The recent mapping of FA locus in human chromosome 9 by means of the analysis of the molecular genetic linkage has permitted to evaluate FA genetics with polymorphic genetic markers (RFLPs) that are secreted linked with the FA gene. The normal and mutant allele secretion of FA was evaluated in ten Spanish families with one or two members with FA by means of several cloned probes (MCT112, DR47, D9S1 and HHH220), localized in chromosome 9 and strongly linked to FA gene, with the aim of achieving a predictive diagnosis of relatives in the pediatric age and to detect healthy carriers. In 9 out of 10 families some totally or partially informative RFLP were found. In 5 of 6 relatives in pediatric age the future development of the disease could be ruled out. By contrast, the carrier status could only be identified in three relatives. In a family with two affected children a genetic recombinant for D9S1 was found. Remarkably, one of them had a better clinical evolution and preserved tendon reflexes in lower limbs.

Nucleolus organizer regions (NORs) inserted in 6q15

We studied a family in which three of the members present one chromosome 6 with an isochromatid gap at the band 6q15 level. Studies of the chromosomes by various banding techniques suggested that the secondary constriction represents a stalk from an acrocentric chromosome inserted into 6q15. The possible influence of the abnormal localization is considered.

Trisomy of the long arm of chromosome 1 in patients with hematologic malignancies and solid tumors: report of six cases

Complete or partial trisomy of the long arm of chromosome #1 was observed in six patients with malignant disorders. Four patients suffered from hematologic diseases (two cases of refractory anemia with excess of blasts and one case each of acute myeloblastic leukemia and Burkitt lymphoma), and two had solid tumors (retinoblastoma and Ewing's sarcoma). In all cases the excess material included the distal part of chromosome #1. Such material was translocated to chromosomes #16 (three patients), #3, #9, and Y (one patient each), and this was accompanied by additional cytogenetic changes in five of the six patients. The present and other previously published observations support the hypothesis of the localization of genes responsible for malignant growth in the distal segments of chromosome #1.

X-linked dysmorphic syndrome with mental retardation

We present a dysmorphic syndrome in eight males of the same family (four brothers, three cousins and one uncle) that is characterised by: mental retardation, facial dysmorphia, abnormal growth of teeth, skin dimple at the lower back, clinodactyly, patella luxation, malformation of lower limbs, abnormalities of the fundus of the eye and subcortical cerebral atrophy. These physical defects do not correspond to any previously described syndrome, which suggests that it is a new syndrome. According to the model of heredity this syndrome could be due to a mutant gene situated in the X-chromosome.

Refractory anemia with monosomy 2 and a double minute chromosome

We present a case of refractory anemia with monosomy 2 in the 41 cells of the bone marrow studied and a double minute chromosome (dmin) in 68% of these cells. The illness developed over a period of 3 years and the patient died of cerebral hemorrhage without developing leukemia.

Trisomy 4: another specific anomaly in acute nonlymphocytic leukemia

We present herein a case of acute nonlymphocytic leukemia, type M2 of the FAB classification, in which the cytogenetic study of the bone marrow cells showed a trisomy 4 as the only alteration. This case was detected from among 118 cases of acute nonlymphocytic leukemia under cytogenetic study.

Translocation (11;22) in Ewing's sarcoma

A cytogenetic study carried out by a direct method on the tumor of a patient with Ewing's sarcoma showed a t(11;22) in the six cells studied. The fact that this structural alteration was detected by a direct method indicates that the translocation is present in Ewing's sarcoma cells and that this alteration, when detected in established cell lines and short-term cultures, is not an alteration induced by the conditions of culture.

Pericentric inversions of chromosome 12 in two families

Two cases of pericentric inversion of chromosome 12 are presented, one 46,XX,inv(12)(p13;q11) and the other was also a heterozygotic carrier of the inversion. These inversions were detected among 4035 cytogenetic analyses carried out in patients with psychosomatic retardation and/or malformations (357 with a Down phenotype) and in patients with histories of miscarriages, sterility, or growth failure. In cases studied from a review of the literature together with our own we found that among 3235 cases of Down syndrome there were 7 patients with trisomy 21 and inherited balanced reciprocal translocation involving chromosomes other than pair 21. The frequent participation of some chromosomes in these balanced reciprocal translocations, above all those of group A (1-3), suggests that these and probably other rearrangements could make the segregation of chromosome 21 easier.