Pericentric inversion in chromosome no. 2 as a de novo mutation

Angelman Syndrome-Affected Individual with a Numerically Normal Karyotype and Isodisomic Paternal Uniparental Disomy of Chromosome 15 due to Maternal Robertsonian Translocation (14;15) by Monosomy Rescue

Angelman syndrome (AS) is a neurodevelopmental disorder caused by deletion of the maternally inherited 15q11q13 region, paternal uniparental disomy 15 [upd(15)pat], an imprinting defect of the maternal chromosome region 15q11q13, or a pathogenic mutation of the maternal UBE3A allele. Predisposing factors for upd(15)pat, such as nonhomologous robertsonian translocation involving chromosome 15, have been discussed, but no evidence for this predisposition has been published. In the present study, chromosomal analysis was performed in a child with AS, both parents, and the maternal grandparents. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) was employed on DNA of the index individual, and microsatellite analysis was carried out on DNA of the index individual and his parents. The cytogenetic analysis showed that the mother and maternal grandfather are carriers of a rob(14;15). The index individual has a numerically normal karyotype, but MS-MLPA and microsatellite analyses confirmed the clinical diagnosis of AS and revealed a pattern highly suggestive of isodisomic upd(15)pat. This is the first report of an AS-affected individual with isodisomic upd(15)pat and a numerically normal karyotype that most likely results from a rob(14;15)-associated meiotic error in the maternal germline followed by monosomy 15 rescue in the early embryo.

Pericentric inversions in man: personal experience and review of the literature

The Leuven cytogenetic centre experience on pericentric inversion in man is discussed with exclusion of the pericentric inversions of the heterochromatic blocks of chromosomes 1 and 9. In a total of 51,500 patients, referred for constitutional chromosome analysis during the period 1970-1985, pericentric inversions were found in 24 index patients. The breakpoints detected in these different pericentric inversions are summarized and compared to those found in previous reports. Bands 2p13, 2q21, 5q31, 6q21, 10q22, and 12q13 were shown to be repeatedly involved in the different studies and, furthermore, breakpoints at bands 2q11, 5p13, 5p15, 5q13, 7q11, 11q25, and 14p11 were present in this study as well as in our previous review on reciprocal autosomal translocations. In 13 familial pericentric inversions, even after exclusion of all inversion carrier probands, a 1.6:1 excess of pericentric inversion carriers versus karyotypically normal progeny was observed. While chromosomally unbalanced offspring represent 3.5% of all chromosomally investigated liveborns of the present study, 7.1% of all liveborn inversion carrier offspring presented with a mental retardation and/or multiple congenital anomalies (MR/MCA) problem. Additional chromosomal abnormalities, i.e. a 21 trisomy and an accessory small ring chromosome were observed in two pericentric inversion carriers. These data and results are discussed and compared to the data available in the literature.

Antenatal diagnosis of a de novo paracentric inversion of chromosome 11

A de novo paracentric inversion of chromosome 11 identified through antenatal diagnosis is described along with long-term follow-up information on the child and discussion of reported experiences with de novo inversions.

The significance of pericentric inversions of chromosome 2

Thirteen new cases of a pericentric inversion 2 collected from different laboratories are reported. In addition 41 cases of a pericentric inversion 2 were reviewed from the literature. The pooled data were analysed using Weinberg's proband method to evaluate the risk of a carrier for either children with congenital anomalies or reproductive wastage. In the "corrected" sample of 166 lifeborn offspring of carriers of a pericentric inversion 2 there were five who showed phenotypic anomalies and two died a few hours after delivery. The reported anomalies are heterogeneous and probably reflect the basic risk of any couple for abnormal lifeborn offspring. There has been no observation of a lifeborn who inherited an unbalanced recombination of a parental pericentric inversion 2. A carrier of a pericentric inversion 2 obviously has an increased risk for reproductive wastage. This is indicated by (1) an increase of the rate of spontaneous abortions and (2) an increase of the rate of index patients ascertained because of previous miscarriages. The risk of a carrier of a pericentric inversion 2 for a spontaneous abortion or a stillbirth may be about twice the basic risk of the general population.

Inversion of chromosome 2 (p11p13): frequency and implications for genetic counselling

Two cases of a pericentric inversion of chromosome 2 were found amongst 3619 blood specimens referred for karyotypic analysis. An additional three cases were identified within 1820 pregnancies presenting for genetic amniocentesis because of late maternal age. The implications for management in these cases are discussed.

Pericentric inversions. Problems and significance for clinical genetics

A review is given of the incidence, cytogenetics, and biologic relevance of pericentric inversions (pii). In 251 cases in the literature and our patients, 96 different inversion forms with different breakpoints are found. Eighteen of these cases have been observed several times in unrelated families; they are classified as types. The problem of pii in the heterochromatic regions of chromosomes 1 and 9 is especially emphasized and the investigations required are pointed out. The significance of the individual pii is checked with regard to their behavior in meiosis and their phenotypical relevance. An approximately 1:1 segregation is found. Fertility, stillbirth, and rates of abortion are not statistically altered. The gonadal findings available at present in man are reported and commented on. The occurrence of aneusomic recombinants among the live offspring of carriers shows a marked dependence on the length of the relative inversion segments. Since these are distinctly below average in inversion types, they only result in recombinants in exceptional cases. Certain pointers to an above-random common occurrence of other chromosomal aberrations are not found in families with pii. A correlation between pii and clinical symptoms likewise cannot be detected. However, in this connection it is pointed out that trisomic mosaics were observed jointly with pii(9) and pii(22). The review is completed by a brief examination of the literature concerning the significance of pii in evolution.