Prenatal diagnosis of beta-thalassemia: the experience of the Center of Rome.
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Biomedical subjects
Publications and source records attributed to B Dallapiccola.
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The activity of four enzymes, including GOT-1, has been investigated in he erythrocytes of a 10q to 24 qter trisomic fetus. Analyses have been performed on a feto-maternal blood mixture sampled by fetoscopy and on red cells obtained by cardiac puncture, following therapeutic abortion. The demonstration of a 40 per cent increase of GOT-1 activity, as compared to normal fetuses of similar gestational age, suggests that gene dosage studies may be a useful confirmatory technique in prenatal diagnosis of unbalanced chromosomal aberrations. Practical application of a similar diagnostic approach is conditioned by (1) precise characterization of fetal chromosome imbalance; (2) confirmed assignment of the gene locus coding for the gene product under investigation; (3) evidence of a linear proportionality between gene dose and concentration of the gene product in patients with the same chromosome imbalance detected in the fetus; (4) knowledge of the range of normal variation at different weeks of gestation of the enzyme activity to be tested in the fetus; (5) safety of fetal sampling procedure.
A terminal deletion of the long arm of one chromosome 21 at band q21 was found in two patients with acute leukemia and a low platelet count: one case of acute myelomonocytic leukemia and one case of acute lymphocytic leukemia. The segment deleted from chromosome 21 could not be found translocated to any other chromosome of the complement. The results indicate that the 21q- marker chromosome may be due to a true deletion and that the marker is no specific for primary thrombocythemia or other myeloproliferative disorders associated with thrombocytosis.
The quantitative expression of GALT and galactose utilization have been investigated in two patients with 9p deletion. Case 1 had a distal deletion of the band 9p22 leads to pter, while case 2 had an interstitial deletion of the region 9p133 leads to p23. In the former patient GALT activity and galactose utilization were found to be normal: in the latter decreased GALT activity and a significant decrease of galactose utilization were present. The above findings suggest that the GALT locus is in the 9p21 band.
Chromosome banding pattern of bone marrow cells, cell morphology according to the FAB classification, and clinical finding were compared in two groups of adult patients with acute nonlymphocytic leukemia (ANLL): 52 patients occupationally exposed to chemical solvents, insecticides, or petrol products, and 110 patients with no history of occupational exposure to potential mutagenic/carcinogenic agents. Striking differences were found between the two groups: (1) Clonal chromosomal aberrations were present in 75% of exposed patients compared with only 32% in the nonexposed group. (2) Of the patients exposed to solvents and insecticides 92% had abnormal chromosomes, whereas only 29% of patients exposed to petrol products showed abnormalities; in the total material 10/13 exposed patients with normal chromosomes were exposed to petrol products. (3) The relationship between chromosomal abnormality and exposure was evident in both females and males. However, only 29% of women with an abnormal karyotype were exposed, whereas 70% of males with an abnormal karyotype were exposed. (4) The incidence of certain characteristic karyotypic abnormalities, i.e., -5/5q-, 7/7q-, +8, +21, t(8;21), and t(9;22), were decidedly more common in exposed than in nonexposed patients. At least one of these changes were present in 92% of exposed patients with aberrations, whereas in the nonexposed group the incidence was only 60%. (5) The monocytic varieties of ANLL (M4 + M5) were more common in the nonexposed patients, whereas erythroleukemia (M6) was more common in the exposed group. The predominance of abnormal karyotypes in the exposed compared to the nonexposed patients was similar in leukemia types M1 + M2 and in M4 + M5. (6) There was no difference in survival time between the two groups and the same correlation was obvious in both exposed and nonexposed patients: patients who had only abnormal metaphases had poorer prognosis than those with normal bone marrow metaphases only (6 vs 1.5 months). This correlation was obvious in patients classified as acute myeloid leukemia (AML) as well as in the monocytic varieties of ANLL.
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Quantitative evaluation of six red cell enzymes in a patient with trisomy 10p syndrome showed significantly increased activity levels of HK 1. These results are in agreement with the evidence derived from another similar patient and strongly support the idea of gene dosage effect of HK1 in the erythrocytes of 10p trisomics. It is suggested that the HK 1 structural locus may be in the 10 pter leads to p13 region.
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Five unrelated patients with a supernumerary chromosome derivative of chromosome 15 are described. The clinical findings in the present series of cases show a gross concordance with the data previously reported in subjects with similar aberrations and allow the delineation of a distinct syndrome. Although undetermined variation in the structure of these extra chromosomes may contribute significantly to phenotypic heterogeneity, the patients display a rather common constellation of findings, which include: absence of major malformations, mental and developmental retardation, seizures, hypotonia, behavioural disturbances, and reduced total ridge count on fingertips. Patients with partial trisomy 15q- resulting from dicentric chromosomes bear little resemblance to patients carrying 15q- chromosomes arising de novo or due to unbalanced translocations.
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A 45,X/46,X,r(X) mosaicism was found in a mother and daughter. Characterisation of the ring by banding studies showed that breakpoints had occurred at bands Xp13 and Xq27. It is confirmed that women heterozygotes for partial deficiencies of the short arm of an X chromosome are fertile. Although the mother developed secondary amenorrhoea at the age of 29, it is suggested that fertility per se may not be affected by deficiencies of the distal part of Xq.
A de novo tandem duplication 1q32--q42 was observed in a 7-month-old mentally retarded and malformed male infant. Karyotype-phenotype correlation in other similar unbalanced trisomies has shown psychomotor retardation, micro- or retrognathia or both, and low set or malpositioned ears to be the most common features associated with this newly recognised syndrome. However, after reviewing patients with duplication of regions 1q2, 3, and 4 and 1q2 and 3, it was concluded that similar non-specific clinical features are also present in these 1q imbalances. On the whole, a rather wide range in phenotypical expression has been observed in different cases. Thus it is concluded that, at present, it is impossible to delineate the profile of the syndromes resulting from partial 1q trisomies.
A male infant with dup (1) (q32 leads to q43) constitution is reported. He had mental and physical retardation and a constellation of dysmorphisms, which are considered characteristic of trisomics for the distal one-third of the long arm of chromosome 1. The assay for guanylate kinase 1 (GUK 1) activity showed a gene dosage effect and confirmed the regional assignment of this marker in the chromosomal region indicated by data derived from somatic hybrids.
A 33p+ chromosome in the lymphocytes of an infant with mental deficiency and congenital malformations was found to be a de novo translocation that could not be characterized by banding methods. The demonstration of a dosage effect for four enzymes--TPI, GAPHD, LDHB, and ENO2--in the infant's erythrocytes was consistent with trisomy 12p. The observation demonstrates the usefulness of information provided by the human gene map in the characterization of small chromosome imbalances which defy accurate identification by available banding techniques.
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A 3 1/2-year-old male with partial trisomy of the long arm of chromosome 16 resulting from a maternal balanced translocation is described. Karyotype: 46,XY,--22,der(22),t(16;22)(q21;p12)mat.
A de novo 16q- trisomy was found in a patient with severe mental retardation and mild physical abnormalities. A preliminary delineation the clinical features characteristic of trisomy 16q- is proposed, based upon comparison of the two cases identified so far. The mild phenotypical effects of this chromosome imbalance suggest that the alleged lethality of partial chromosome 16 aneuploidies should be reconsidered.