Delineation of the critical deletion region for congenital heart defects, on chromosome 8p23.1

Deletions in the distal region of chromosome 8p (del8p) are associated with congenital heart malformations. Other major manifestations include microcephaly, intrauterine growth retardation, mental retardation, and a characteristic hyperactive, impulsive behavior. We studied genotype-phenotype correlations in nine unrelated patients with a de novo del8p, by using the combination of classic cytogenetics, FISH, and the analysis of polymorphic DNA markers. With the exception of one large terminal deletion, all deletions were interstitial. In five patients, a commonly deleted region of approximately 6 Mb was present, with breakpoints clustering in the same regions. One patient without a heart defect or microcephaly but with mild mental retardation and characteristic behavior had a smaller deletion within this commonly deleted region. Two patients without a heart defect had a more proximal interstitial deletion that did not overlap with the commonly deleted region. Taken together, these data allowed us to define the critical deletion regions for the major features of a del8p.

Length polymorphism of heterochromatic segment of the Y chromosome in boys with acute leukemia

The extent of length polymorphisms of the heterochromatic and euchromatic segment of the human Y chromosome were investigated in 15 boys with acute leukemia and were compared with 15 normal controls. A greater value of the Yh/F index in relation to controls was established (P < 0.05). The length of the euchromatic segment was also shorter in the patients than the controls (P < 0.05).

Interferon system defects in malignant T-cells

Deletions of chromosome 9p21-22 occur in acute lymphocytic leukemia (ALL), melanoma and glioma. With some exceptions, these deletions include the alpha- and beta-interferon (IFN) genes. In this study, the frequency of alpha- and beta-IFN gene deletions was investigated in 17 T-cell lines, and losses of IFN genes were related to other aspects of the IFN system. Deletions of alpha-/beta-IFN genes were observed in 7/17 cell lines. In two cases the deletions were homozygous for both loci. In most cases aberrations of chromosome 9 were also apparent on cytogenetic analysis. An increased proportion (40% as compared to the expected 13%) of the remaining ten cell lines showed homozygosity for all five common polymorphic alpha-/beta-IFN markers, possibly implicating allelic deletion by loss of heterozygosity (LOH) in some of these clones. The cell lines showed a large variability in IFN production, IFN-alpha receptor number, susceptibility to IFN measured as induction of the enzyme 2',5' oligoadenylate synthetase and cell growth inhibition. No correlations between loss of IFN genes and IFN-producing capacity, or susceptibility to IFN, were found. Of the seven cell lines with a normal IFN-gene dosage and heterozygosity for the alpha- and beta-IFN genes, three had a deficiency in their IFN-producing capacity and one was also insensitive to growth inhibition by IFN. All IFN-producing cell lines predominantly produced beta-IFN.

Multiple genetic events involving RB1 gene deletion and amplification of chromosome 21 in a case of acute lymphocytic leukemia

A patient with acute lymphocytic leukemia was found to have a hyperdiploid karyotype, characterized by hexasomy 21 and del(7)(p15). It was shown that the four extra copies of chromosome 21 were all derived from only one of the homologous chromosomes. Molecular analysis showed that the patient had a deletion of both alleles of the retinoblastoma (RBI) gene. These results suggest that multiple events, including loss of RBI gene function and amplification of a key gene(s) on chromosome 21, have contributed to the leukemic transformation.

Deletions of the short arm of chromosome 9, including the interferon-alpha/-beta genes, in acute lymphocytic leukemia. Studies on loss of heterozygosity, parental origin of deleted genes and prognosis

A restriction fragment length polymorphism (RFLP) analysis of the alpha- and beta-interferon (IFN) genes was performed in malignant cells from 52 patients with acute lymphocytic leukemia (ALL). Normal cell DNA was available for comparison in 23 of the patients. Ten patients were found to have gross alterations of their alpha- and beta-IFN genes. Leukemic cells from 2 ALL patients showed a complete loss of alpha- and beta-IFN genes. Seven patients had a hemizygous loss of one of the alpha- and beta-IFN alleles, as shown by RFLP analysis and/or loss of signal intensity. In one other patient the malignant clone was reduced to homozygosity with regard to the alpha- and beta-IFN genes, without loss of signal intensity. In patients without hemizygous deletions, the overall incidence of complete homozygosity for the alpha- and beta polymorphisms was higher than expected. Analysis of the data indicates that the total frequency of ALL clones with gross alterations of the IFN-loci is around 30%. A 9p24 probe detected hemizygous deletions in 2 cases of IFN gene deletions. In the other tested cases the deletions were interstitial. No deletions of 9p24 were detected in patients without allelic losses of IFN genes. In 5 cases of allelic IFN gene deletions, DNA from parents was available for comparison. In 4 cases the deleted allele was derived from the mother, whereas in the fifth it originated from the father. Pediatric ALL patients with IFN-gene deletions or homozygosity for all polymorphisms in the IFN-loci had a significantly worse prognosis than heterozygotes. We conclude that deletion of alpha- and beta-IFN genes is a relatively common event in ALL and that RFLP analysis of the IFN genes may provide additional prognostic information in childhood ALL. Whether or not the IFNs act as tumor-suppressor genes in this disease is not yet known.

Prader-Willi syndrome in a brother and sister without cytogenetic or detectable molecular genetic abnormality at chromosome 15q11q13

We report on a 12-year-old boy and his 7-year-old sister with the Prader-Willi syndrome. They both had severe initial hypotonia with feeding problems and later developed an increasing appetite. Both sibs have almond-shaped eyes, triangular mouth, hypogonadism, retarded growth, and mental retardation. An older brother suffered from severe hypotonia and died at 7 days of age. The children have normal chromosomes by high-resolution technique and have inherited the same chromosomes 15 short arm polymorphisms from their parents. The family was informative for one of four DNA markers specific for the 15q11q13 region. No deletion was found using this marker. The parents were healthy and unrelated. Autosomal recessive inheritance or a paternally inherited submicroscopic deletion are possible explanations for the sib occurrence in this family.

Interferon system in primary acute lymphocytic leukemia cells with or without deletions of the alpha-/beta-interferon genes

Various aspects of the interferon (IFN) system were studied in malignant cells from 37 unselected patients with acute lymphocytic leukemia (ALL). It was found that leukemic cells from two of 37 patients had a complete loss of alpha- and beta-IFN genes, whereas cells from four of 37 had lost one of the alpha-/beta-IFN alleles. In 25 cases, viable cells were also available for functional studies. Cell clones with loss of one of the alpha-/beta-IFN alleles produced low amounts of IFN after virus induction in vitro. Some clones with an apparently normal set of IFN genes were unable to produce detectable amounts of IFN. All clones studied were found to carry high-affinity alpha-IFN receptors. In clones carrying deletions of IFN genes, the cells were sensitive to IFN in vitro as measured by alpha-IFN-induced enhancement of 2',5'-oligoadenylate synthetase (2',5'-A synthetase). Cells from four patients with an apparently normal set of IFN genes were insensitive to this effect of IFN. We conclude that of the 17 patients in which IFN genes, IFN production, alpha-IFN receptors, and IFN-induced enhancement of 2',5'-A synthetase were studied, nine (53%) showed some abnormality in their IFN system. This finding may add some support to the hypothesis that defects in the IFN system could be a step on the path to malignant transformation in ALL. Moreover, patients whose malignant cells carry IFN gene deletions or other defects in their IFN-producing capacity, but are still sensitive to exogenous IFN, could represent a subgroup of ALL with a greater likelihood of responding to IFN therapy.

Prenatal investigation of a 45,X/46,X,r(?) karyotype in amniocytes using fluorescence in situ hybridization with an X-centromeric probe

The karyotype of cultured amniotic fluid cells obtained on the indication of advanced maternal age was shown to be a mosaic 45,X/46,X,r(?). The small size and banding pattern made it difficult to determine whether the ring was derived from and X or a Y chromosome, or even from an autosome. By using an X-centromeric probe and fluorescence in situ hybridization (FISH), we demonstrated the ring to have an X centromere. Thus, a more complete genetic counselling was possible. This confirms the usefulness of FISH in identifying and characterizing this and other chromosome rearrangements in prenatal diagnosis.

Middle-aged women with Turner's syndrome. Medical status, hormonal treatment and social life

A study of 49 middle-aged (greater than 35 years old) women with Turner's syndrome was performed to evaluate medical status, hormonal treatment and social life. Most of the women lived a normal social life in stable relationships and all were employed. Some had adopted children and 4 had children of their own. They had all been informed about Turner's syndrome at time of diagnosis, but after the induced puberty they did not know who to turn to with their variety of medical problems. They were healthy except for reduced hearing, which in many cases required hearing aid. Elevated liver enzymes were found in almost all the women. The mechanism behind this finding is unclear, but it does not seem to imply severe liver damage why the indicated estrogen therapy should not be withdrawn from these women. Today amniocentesis and chorionic villus biopsies are commonly used to detect chromosome abnormalities. It is our duty as counsellors to give adequate information on the prognosis of a specific finding in the fetus to help future parents in their decision.

Extra small marker chromosome associated with normal phenotype due to 3:1 disjunction of t(14;22) in a parent. Implications for the origin of marker chromosomes

A family with segregation of a translocation t(14;22) (q31;q11) is is reported. The proband was ascertained by chromosome analysis after repeated spontaneous abortions in his wife. His normal sister was found to have the karyotype 47,XX,+ der (22). The small size and banding pattern of chromosome 22 make it difficult to determine the breakpoint with certainty, but it was judged to be at q11. This small marker chromosome could thus be similar to the one found in the cat eye syndrome, and further studies may cast light on gene(s) involved in this syndrome.

Molecular analysis of 4p deletion associated with Wolf-Hirschhorn syndrome moving the "critical segment" towards the telomere

We report molecular studies in 2 patients with Wolf-Hirschhorn syndrome, probing genomic DNA from the patients and their parents with markers that have been mapped to 4p16.3. One of the patients was heterozygous for alleles detected by probe F5.53, which maps to the centromeric end of the D4S10 locus, but hemizygous for loci located more distally. The region in common, which was deleted in both these patients, is within 4p16.3. This observation suggests that the gene(s) for Wolf syndrome may be contained within this region, and that the "critical segment" is located more distally than previous cytogenetic observations have suggested. Furthermore, we found that the deletion was of maternal origin in one patient, and of paternal origin in the other.

Deletion of alpha-, beta-, and omega-interferon genes in malignant cells from children with acute lymphocytic leukemia

Scanning densitometry and restriction fragment length polymorphism analysis were used to study the alpha-, beta-, gamma-, and omega-interferon (IFN) genes in malignant cells from 11 children with acute lymphocytic leukemia and in one cell line of T-cell origin. In the malignant cells of one patient there was a complete loss of alpha-, beta-, and omega-IFN genes, whereas in another patient one of the alleles of these genes had been deleted. Cytogenetic analysis revealed a deletion of the short arm of chromosome 9, i.e., the region containing the alpha-, beta-, and omega-IFN genes, in the latter patient. The normal cells of the patients with IFN gene deletions had two alleles of the alpha-, beta-, and omega-IFN genes. In cells from none of the patients could deletions or rearrangements of the gamma-IFN genes be detected. We conclude that in 2 of 11 patients with acute lymphocytic leukemia the malignant transformation is accompanied by loss of material on one or both chromosomes 9 and that the alpha-, beta-, and omega-IFN genes are included in these deletions.

Partial monosomy 8p with minimal dysmorphic signs

A female patient with a 46,XX,del(8)(p23----pter) karyotype is presented. She was mentally retarded and showed a few dysmorphic features. Her red cell glutathione reductase level was within normal limits. This terminal deletion, on the short arm of chromosome 8, appears to be the smallest segment hitherto reported.