A cytogenetic study of recurrent abortion

Familial pericentric and paracentric inversions of chromosome 1

We investigated 33 individuals (21 carriers) from one family with a pericentric inversion involving a large part of chromosome 1 (1p36.1----1q32). In addition, we investigated 15 individuals (10 carriers) from another family with a paracentric inversion of a small part of chromosome 1 (1p32----1p36.1). In each family, the index patient was ascertained because three miscarriages had occurred. Each carrier of these inversions was phenotypically normal. If the miscarriages of the index patients are excluded, the frequency of recognized miscarriages among the carriers of childbearing age was 9% (4 of 46) for the family with pericentric inversion and 17% (4 of 23) for the family with paracentric inversion. One of the pericentric inv(1) carriers had had a stillborn daughter. The carriers of the pericentric inversion who were of childbearing age had 41 children; carriers of the paracentric inversion who were of childbearing age had 19 children. No live-born children with birth defects were observed in either family. This evidence, together with the low frequency of miscarriages, suggests that crossover within the inversion loop occurs much less frequently than might be expected from the large size of this inversion. Our investigation suggests that the risk of recognized miscarriages, stilbirths, and live-born children with recombinant chromosomes who have birth defects may be much lower for inv(1) carriers than previously reported. The risk of having a malformed child because of a recombinant chromosome is probably less than 3% for carriers of the pericentric inversion and less than 6% for the carriers of the paracentric inversion.

Recurrent pregnancy losses and parental chromosome abnormalities: a review

A compilation of the cytogenetic results taken from 79 published surveys of couples with two or more pregnancy losses (comprising 8208 women and 7834 men) showed an overall prevalence of major chromosome abnormalities of 2.9%. This is five to six times higher than that of the general adult population. In every group of chromosome abnormalities in the parents a predominance of female to male affected was noted (2:1). Approximately 50% of all chromosome abnormalities detected were balanced reciprocal translocations, 24% were Robertsonian translocations, 12% were sex chromosomal mosaicisms in females, and the rest consisted of inversions and other sporadic abnormalities. Parents with two or more idiopathic pregnancy losses should be karyotyped to aid in management and counselling. When a translocation or other abnormality (e.g. X chromosomal mosaicism) predisposing to an abnormal zygote is found, prenatal diagnosis is indicated in future pregnancies. Even when parental karyotypes are normal, prenatal diagnosis should be considered in subsequent pregnancies of parents with two or more pregnancy losses because of the high incidence of chromosome abnormalities in spontaneous abortions. For the same reason, if a single previous pregnancy loss is known to have been chromosomally aneuploid, parental karyotypes may have to be examined (depending upon the finding in the pregnancy loss), and prenatal diagnosis should also be considered in subsequent pregnancies.

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.

Familial inv(1) (p3500q21.3) associated with azoospermia

An inv(1) (p3500q21.3) was found in an azoospermic man, his mother and two other maternal relatives. Although the mechanisms involved are still unclear, it is stressed that pericentric inversions of chromosome 1 in which the inverted chromosome becomes submetacentric (centromeric index less than or equal to 0.324) apparently impair spermatogenesis.

Cytogenetic findings in 318 couples with repeated spontaneous abortion: a review of experience in British Columbia

We studied G-banded chromosome complements on 318 couples with 2 or more spontaneous abortions. Seven chromosome abnormalities were detected. Three women and one man were identified as carriers of balanced Robertsonian translocations, t(13;14), t(13;14), t(13;21), and t(14;22), respectively. Aneuploidy: 47,XXX; 47,XX, + marker; and 45,X/46,XX/47,XXX were found in the other 3 women. The overall aberration frequency was 2.2% of couples. When a stringent criterion of greater than or equal to 3 consecutive spontaneous abortions was used, the frequency was 4.2%. In this series no chromosome aberrations were identified in couples with 2 spontaneous abortions and a live-born child with congenital anomalies; 1 of 22 couples with 2 spontaneous abortions and a still-born infant showed a chromosomal abnormality. Findings from the recent literature are compared with those from this study.

Chromosomal findings in 164 couples with repeated spontaneous abortions: with special consideration to prior reproductive history

The cytogenetic evaluation of 164 couples who experienced repeated spontaneous abortions revealed 11 chromosomal abnormalities (10 translocations and 1 sex chromosome mosaic, 6.70%). An apparent positive relationship between the frequency of chromosome anomalies and the number of spontaneous abortions was observed. Couples with at least one normal liveborn child, in addition to the spontaneous abortions, had a significant increase in chromosomal abnormalities (17.85%) when compared with those with no liveborn offspring (4.41%) (P less than 0.005). Similarly, couples whose fetal wastage consisted of only first trimester spontaneous abortions had a greater increase in the frequency of chromosomal abnormalities (8.03% vs 0.00%).

Chromosome analyses in couples with repeated pregnancy loss

Cytogenetic investigations were undertaken on 120 couples in Newcastle with repeated pregnancy loss for which no anatomical or other obvious reason could be established. The level of major chromosome anomalies was high, with 6·7% of couples showing one member with an abnormal karyotype. One major anomaly occurred in a control series of 240 random newborns. The couples also showed an elevated incidence of chromosomal heteromorphisms. Similar studies in the literature are reviewed. It seems that major chromosome anomalies make an appreciable contribution to repeated reproductive loss, but proof of the involvement of minor chromosome variants though suspected is less clear.

Structural differences in pericentric inversions. Application to a model of risk of recombinants

The potential chromosomal imbalance in offspring of pericentric inversion heterozygotes can be evaluated by measuring (% of haploid autosomal length, % HAL) the chromosomal segments distal to the breakpoints in the inversion. These distal segments were measured in presently reported and published cases of pericentric inversions, divided into two ascertainment groups: (I) those ascertained through recombinant offspring and (II) those ascertained through balanced heterozygotes. The distal segments in group II inversions were significantly larger than those of group I, i.e., the potentially larger chromosomal imbalances were not observed in full-term offspring. These results are discussed in relation to the model of risk of abnormal offspring in the progeny of heterozygotes for structural rearrangements (the chromosome imbalance size--viability model). The mean distal segment sizes for group I and group II pericentric inversions were respectively not significantly different from the mean interchange segment size for a sample of reciprocal translocations divided into the same two ascertainment groups. It was concluded that the restrictions on the size (% HAL) of chromosomal imbalance in offspring surviving until term are similar whether this imbalance arises from reciprocal translocations or pericentric inversions.

Chromosomal analysis of couples with repeated spontaneous abortions

Chromosome banding studies were carried out on both partners of 182 consecutive couples with a history of two or more spontaneous abortions. Seventeen abnormal karyotypes were detected. This represents a frequency of 4.67 per cent, which is higher than hitherto reported. The pregnancy outcome in 105 couples with normal and abnormal karyotype was compared and no significant difference was found.

Familial pericentric inversion of chromosome 1 with a note on reproductive risks

An inversion of chromosome 1 was found in three normal members of a two generation family. G- and C-banding studies revealed inv(1)(p13q23). The problems encountered in counseling such normal carriers are discussed.

Association of D/D translocations with fetal wastage and aneuploidy. A report of four families

Four families are described with a t(13q14q) segregating. Two of them were identified through index cases with Down's syndrome; their karotypes revealed the unusual 46,XY, -13, -14, +t(13q14q), +21. The other two families were identified through a chromosomal study of parents with repeated spontaneous abortions. Analysis of data on 3 of these 4 families and on 7 other from the published reports showed no evidence of increased fetal wastage among 13/14 carriers. However, the risk of producing offspring with various types of aneuploidy may be greater among carriers than among persons with a normal chromosome pattern. Qualitative and quantitative differences in D/D translocations may account for the observed variation in clinical findings. These differences add to the problem of determining genetic risks from an analysis of grouped data.

A 22/22 translocation carrier with recurrent abortions demonstrated by a Giemsa banding technique,

A 22/22 Robertsonian translocation has been identified in a woman with recurrent abortions by a Giemsa banding technique. Cytogenetic studies of the embryonic tissue derived from one of her spontaneous abortions have demonstrated that the aborted fetus had a 46,XX,-22,+t(22q22q) karyotype.