Down's syndrome at young maternal age: cytogenetical and genealogical study of eighty-one families

Margareta Mikkelsen

Margareta Mikkelsen, a well-known Danish cytogeneticist, started to research autosome aberrations in 1959 and built the first chromosome laboratory at the University of Copenhagen with Anders Frøland. In 1968, she developed a fully functional chromosome laboratory from scratch at the John F. Kennedy Institute (JFKI). Not only the laboratory performed diagnoses all over Denmark, but also it is a sole place among all the departments of human genetics to train Danes to be clinical geneticists. A generation of Danish geneticists grew up under Dr. Mikkelsen's wing. Dr. Mikkelsen played a pioneering role in research on Down syndrome (DS) and exploring the source of the extra chromosome 21 remains her main interest. She performed the first case of prenatal diagnosis by amniocentesis in Denmark and since then, she was active in this field. The JFKI also committed to research on the fragile X syndrome. Dr. Mikkelsen took on many public responsibilities in Denmark and in Europe. She was on the board of many Danish scientific organizations and an active member of the European Society of Human Genetics (ESHG). She was efficient in public education with communication in lay language. After her retirement, she was more dynamic in medical ethics. Born as Irmtraud Wieser in Munich, Dr. Mikkelsen walked through the hardship of pre-war Germany, the inferno of the World War II, the trauma brought by her two husbands' alienation, the obstacles in work, and physical ailment to fulfill her unwavering commitment to human genetics.

Advanced grandmaternal age on the mother's side--a risk of giving rise to trisomy 21

The age distribution of maternal grandmothers of children with Down syndrome was compared with paternal grandparents of the same group and with grandparents of healthy children (controls). The significant advanced maternal grandmaternal age was found in cases of Down syndrome caused by first meiotic error in the maternal oogenesis. The advanced maternal grandmaternal age was found independent of maternal age. No differences were found between the ages of grandfathers of Down syndrome and of controls.

Recurrence rate for de novo 21q21q translocation Down syndrome: a study of 112 families

Recurrence of de novo GqGq Down syndrome (DS) in nine reported families and the low frequency of this chromosome abnormality in the population prompted this multicenter study to examine recurrence rate. Pedigrees and cytogenetic findings were analyzed from 112 families ascertained by a DS child with de novo GqGq translocation. Four of 112 sets of parents had abnormal cytogenetic findings. One mother and two fathers had a low proportion of mosaicism for trisomy 21 in peripheral lymphocytes. In one of these fathers, fibroblast studies confirmed the mosaicism (others not similarly studied). Two of these three families have one additional child each, both being normal. In the fourth family, the mother is heterozygous for a pericentric inversion of chromosome 21. Ninety of the 112 probands had a total of 130 full sibs and 34 half sibs. None of these 164 sibs was affected; the recurrence rate could still be as high as 2% (with 95% confidence based upon calculation of a one-tailed confidence interval). Because of the latter, the nine reports of recurrence in the literature, and the abnormal cytogenetic findings in peripheral lymphocytes in 4/112 sets of parents (3.6%), we think that caution should be exercised when counseling that the recurrence risk of this event is remote.

Down's syndrome in Western Australia: cytogenetics and incidence

235 cases of Down's syndrome were ascertained in a 10-year study of Down's syndrome in Western Australia. Although cytogenetic studies performed on 222 subjects confirmed that 95% of cases were trisomic due to nondisjunction, 4% were trisomic due to translocation, and 1% were mosaic, the ratio of inherited/sporadic translocations differed from that usually reported. Comparison of the results with those of an earlier Australian survey of Down's syndrome demonstrated a real fall in the incidence of Down's syndrome in Australia but no significant change in maternal age-specific incidences.

A variant chromosome 17 in a mother with repeated abortions and a 46, XY/47, XXY Klinefelter son

A female with a satellited chromosome 17 is presented. She had suffered repeated abortions and later gave birth to a 46,XY/47,XXY Klinefelter boy. The significance of the variant chromosome 17 in the etiology of the mother's reproductive failure is discussed. The mental and physical development of her now 8-year-old 46,XY/47,XXY son has been checked regularly since birth. The boy showed a significant deviation in behaviour pattern and development of body habitus already from early infancy.

Human karyotype polymorphism. III. Routine ank fluorescence microscopic investigation of chromosomes in normal adults and mentally retarded children

The results of a routine and fluorescence microscopic investigation of chromosomes are presented in 208 normal adults and 141 mentally retarded children (80 with diagnosis of "mental retardation of unknown etiology" and 61 with Down's syndrome). The occurence of both real chromosome aberrations and chromosome variants are presented, with special attention being paid to the chromosome variants. The data obtained show that in all groups studied there is considerable polymorphism of heterochromatic regions that appears to be dependent on sex and connected with the origin of some pathologic conditions.

Familial 21/22 translocation

A family is described with 21/22 translocation, where chromosome segregation appeared to follow theoretical expectations, rather than empirical risk figures, in male and female carriers alike. The usefulness of prenatal genetic studies in genetic counseling is also demonstrated.

A prospective, cytogenetic study of recurrent abortion

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Down's syndrome with familial G-G translocation

Cytogenetic examinations of a 7/12-year-old girl and her parents revealed a familial G/G translocation.

46 chromosomes in the mitoses of the mongoloid child and only 45 chromosomes in those of the apparently normal father could be observed. The analysis of karyotypes revealed a balanced G/G translocation in the father and a G/G translocation mongolism in the probanda. Dermatoglyphic patterns of both the child and her father showed some features characteristic of Down's syndrome.

The mother's karyotype proved to be normal (46, XX).