Familial paracentric inversion of the short arm of chromosome 3.

A paracentric inversion of the short arm of chromosome number 3 is reported in three generations of a family. The index patient presented with slight psychomotor retardation. The literature on this subject is briefly reviewed.     

Cytogenetic recombinants from a female carrying a paracentric inversion of the short arm of chromosome number 5

Summary We present a family, identified through a girl with Cri-du-chat syndrome, in which two different types of recombinants exist [del(5)(qterp14:) and dup(5)(p13)]. They are due to a 5p paracentric inversion of maternal origin [inv(5) (pter p13)]. We discuss the relationship between the breakpoints and segregation of the inversion carrier, as well as the origin and the identification of the recombinants.     

Three large Danish families with a paracentric inversion in the short arm of chromosome N. 5

A paracentric inversion in the short arm of chromosome 5 [inv(5p)] was segregating through at least four generations in three large danish families. All inversion carriers were phenotypically normal, and no adverse effects on reproduction were observed.     

A recombinant X chromosome in a short statured girl resulting from a maternal pericentric inversion

Summary a 73/4-year-old girl with short stature was found to have a recombinant (X), dup q chromosome resulting from an apparently unique pericentric inversion (X)(p11.2q26) present in her mother and maternal grandmother. The recombinant X chromosome was shown to be late replicating and the inversion X chromosome to be randomly inactivated. This appears to be only the eighth report (7 female, 1 male) of a recombinant resulting from an X pericentric inversion despite all diagnosed females having mild clinical abnormalities. Reasons for the rarity of such recombinant X chromosomes in man are examined.     

Partial deletion of the long arm of chromosome 18

Summary A female infant with mental retardation and multiple somatic anomalies is described. The karyological analysis disclosed the partial deletion of the long arm of chromosome 18 in cells of probands peripheral blood culture. Repeated investigations of probands mothers peripheral blood cultures disclosed the presence of various chromosomal aberrations in 25–70% of cells.     

A second case of (de novo) paracentric inversion of the short arm of the X chromosome

A de novo paracentric inversion of the short arm of an X chromosome (p11.2p22.1) was observed in a 17-year-old girl studied because of primary amenorrhea and a Turner phenotype. To our knowledge this is only the second case of a paracentric inversion of the X chromosome short arm reported, the first having been briefly described in 1982, in a young lady with the Turner phenotype. In spite of its balanced appearance, there is little doubt that this rearrangement is the cause of the phenotypic anomalies of the patient, probably as the result of gene(s) modification(s) at the breakpoints on the X chromosome, or because the inverted gene sequence resulted in modifications by position effect. It has become increasingly difficult to recognize obvious phenotype-genotype correlations in Turner syndrome, given the multiplicity of chromosome rearrangements--some of them quite subtle--which are associated with ovarian dysgenesis.     

Tiny interstitial duplication of proximal 7q in association with a maternal paracentric inversion

Summary Paracentric inversion of chromosome 7 was found in a female infant with multiple malformations and in her phenotypically normal mother. Examination of prometaphase chromosomes revealed an additional small dark band on the inverted chromosome 7 of the girl. It was assumed that an unequal crossing over at the base of a meiotic loop of chromosome 7 had occurred in the mother and resulted in a tiny interstitial duplication in the girl.     

Recurrent proximal 18p monosomy and 18q trisomy in a family with a maternal pericentric inversion of chromosome 18

We report a recurrent partial monosomy of 18p10-->11.2 and proximal partial trisomy of 18q10-->21.3 caused by a maternal pericentric inversion of chromosome 18, involving breakpoints p11.2 and q21q21.3 Based on cytogenetics and FISH analysis, we speculate that the recurrent chromosome abnormality in the proband and in the fetus was the result of a translocation, possibly in a germ cell or germ cell precursor, between the maternal normal 18 and her inverted 18, resulting in maternal germinal mosaicism, i.e. 46,XX,inv(18)/46,XX,t[18;inv(18)][q10;q10]. The unbalanced karyotype of the proband and the fetus is 46,XY,+18,der[18;inv(18)][q10;q10]. To the best of our knowledge, there are no reports of this combination of proximal 18p monosomy and proximal 18q trisomy. The other interesting observation was association of Hirschsprung's disease in the proband.     

Genetic control of chromosome synapsis in mice heterozygous for a paracentric inversion

Frequencies of formation of inversion loops and their relative sizes were studied in laboratory mice heterozygous at paracentric inversion In1(1)Rk in chromosome 1, depending on the genetic background. Homozygotes In1/In1 were crossed with mice from five inbred strains (A/HeJ, BALB/cJ, C3H/HeJ, C57BL/6J, DBA2/J). The frequency of formation of inversion loops, their relative sizes, and the dependence of these parameters on the stage of pachitene were analyzed on electron-microscopic slides of spread spermatocytes in first-generation hybrids. It was shown that the genetic background and cross direction statistically significantly influenced the duration of individual pachitene stages and the frequency of inversion loops, but not relative loop size. Using a database on SNP distribution in the inbred strains examined, we carried out in silico mapping of genes affecting the genotype-dependent characters. We have found that the efficiency of synapsis in the inversion does not depend on interstrain differences in homology of the chromosome 1 region involved in the inversion. Genes controlling the inversion loop frequency in the inversion heterozygotes were mapped to chromosome 7, and genes controlling the duration of individual pachitene stages, to chromosomes 2 and 5.     

Duplication-deficiency of chromosome 18, resulting from recombination of a paternal pericentric inversion,with a note for genetic counselling

Summary A fifth case of rec(18) resulting from recombination of a paternal pericentric inversion is described. The propositus' complement includes a chromosome 18 with partial deletion of the long arm, and partial duplication of the short. The recombination risk is evaluated at 5%. The eventuality of deleterious effects of pericentric inversions is discussed.     

Acute leukaemia and the same chromosome abnormality in monozygotic twins

Summary Monozygotic twin girls, both of whom had acute undifferentiated leukaemia and a 47,XX,+19 karyotype, are described. The case is discussed in terms of childhood leukaemia and the hypothesis that a single transformation event in utero may be responsible for leukaemia in twins.     

Identification of a large submetacentric X chromosome as pericentric inversion of an isochromosome of the long arm

Summary A large submetacentric and late-replicating X chromosome in a patient with Turner stigmata was identified as pericentric inversion of an isochromosome of the long arm by means of the G-banding pattern.     

A duplication-deficiency X chromosome in a girl with severe mental retardation

Summary An identical pair of twins with the tetraphocomelia-cleft palate syndrome is presented. It is hypothesized that Roberts' syndrome and the pseudothalidomide syndrome, previously reported as separate entities, represent different manifestations of the same autosomal, recessively inherited malformation pattern.     

"Cri-du-chat" syndrome in a patient born to a mother with a paracentric inversion of chromosome 5q

We report the case of a female child presented at birth with hypotonia, growth retardation and respiratory distress. Chromosome study from peripheral blood showed a 46,XX,del(5)(p14pter) karyotype. Parental chromosome studies revealed that the mother carried an apparently balanced paracentric inversion of long arms of one chromosome 5, giving the karyotype 46,XX,inv(5)(q12q32), whereas paternal karyotype was normal. The maternal abnormality was confirmed by fluorescence in situ hybridization (FISH) and was not present in the daughter's metaphases. Microsatellite analysis in the proposita and her parents permitted us to conclude that the deleted chromosome 5 was paternal in origin, as usually described. Therefore, as might have been expected, maternal paracentric inversion of chromosome 5q and "cri-du-chat syndrome" presented by the daughter were not related.