Section 16 — Human Cytogenetics 



was an increase in the incidence of drumsticks 

 with an increase in nuclear lobe number from 

 1 to 5, but the frequency of drumsticks in cells 

 of any given lobe number showed wide varia- 

 tions in different women. This difference could 

 be demonstrated on repeated occasions. 



In the patients with chromosomal abnormali- 

 ties, but not the mentally defective non-mongol 

 girls, there was a decrease in the average number 

 of polymorphonuclear lobes and a lower in- 

 cidence of drumsticks. Moreover, the frequency 

 of drumsticks per cell of constant lobe number 

 was less than in the normal women. 



It is suggested that chromosomal abnormalities 

 tend to lower the segmentation of the polymor- 

 phonuclear nuclei and that this is associated 

 with an even more marked reduction in the 

 number of drumsticks. 



16.16. (D.) Monozygotic Twins of Different Sex. 



T. Dent and J. H. Edwards (Birmingham, 

 Great Britain). 



A case of Turner's syndrome, presenting with 

 amenorrhoea and dwarfism, was noted to have 

 a twin brother. The brother appeared to be a 

 normal male. Blood and serum groups showed 

 no evidence of dizygosity, and the palm prints 

 were strikingly similar. Chromosome analysis 

 from lymphocyte and fibroblast cultures showed 

 that both twins were preponderately XO in 

 constitution. 



The male twin had marked difference in eye 

 colour, one eye being blue-green, the colour of 

 his sister's eyes, and the other brown. This sug- 

 gests the possibility of a locus on the Y chro- 

 mosome related to eye colour. 



The origin of this chromosomal error was 

 presumably mitotic non-disjunction at a stage 

 before the cell lines determining either twin 

 were defined. The remarkably normal pheno- 

 type of the boy suggests that, if his tissues are 

 preponderately XO, then the stigmata of Tur- 

 ner's syndrome may be related to endocrine 

 abnormality rather than to defective responses 

 of structural tissues to directives relating to 

 growth. 



16.17. Lethal Chromosome Constitutions in Man. 



K. Patau, S. L. Inhorn, and E. Therman 

 (Madison, U.S.A.). 



The word "lethal" is here restricted to condi- 

 tions that invariably prevent birth of a live child. 

 Evidently, polyploidy is lethal. In a study of 



placental and fetal tissues from early abortions 

 a new case of triploidy was found, the first 

 with XXX and no Y. Among mechanisms that 

 may cause triploidy, fertilization by a giant 

 sperm should also be considered. Precise mea- 

 surements showed these to contain twice the 

 DNA content of haploid sperm. Nullosomy for 

 the X is undoubtedly lethal, and so is mono- 

 somy for any autosome. Viable trisomy is known 

 only for three autosomes; Di, 18, and the mon- 

 golism chromosome. Di and 18 trisomies may 

 have a high pre-natal mortality, but it is at least 

 as likely that their rarity, compared with 

 mongolism, reflects much lower non-disjunction 

 rates. There are reasons for believing that 

 numerous genes are involved in trisomy effects 

 and that trisomy for any human autosome inter- 

 feres in many ways with development. It is con- 

 cluded that trisomy for all, or almost all, but 

 the three above mentioned autosomes is lethal. 

 In the abortion study, no trisomies have turned 

 up as yet, but at least two cases of monosomy 

 for a C chromosome were found. In one, there 

 was an admixture of female diploid cells, but 

 in both cases the sex chromatin count was so 

 high that the lacking chromosome must have 

 been an autosome. In a third case of C mono- 

 somy no sex chromatin data could be obtained. 



16.18. Abnormalities of the Acrocentric Chromo- 

 somes. Kurt Hirschhorn (New York, 

 U.S.A.). 



A significant number of reports have appeared 

 during the past few years dealing with various 

 abnormalities of the acrocentric chromosomes. 

 These have included conditions recognized as 

 definitely associated with pathological states 

 (trisomies, deletions), as potentially pathological 

 (translocations), and finally, as of purely mor- 

 phological interest (for example, satellite struc- 

 ture, distribution, and inheritability). We would 

 like to discuss several new morphological va- 

 riants. Three patients and members of their 

 family were found to possess additional material 

 in the short arms of either the long acrocentrics, 

 the short acrocentrics, or both. 



The first patient, a 19-year-old unmarried fe- 

 male with primary amenorrhea, no other clinical 

 abnormalities, and an excellent response to 

 exogenous hormonal therapy, had one long acro- 

 centric chromosome whose short arms were 2-3 

 times as long as those of the other long acro- 

 centrics. The same chromosome has been found 

 in the patient's asymptomatic brother, sister, 

 mother, and uncle. The second patient, a one- 

 year-old male child with congenital heart dis- 



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