Amer J Hum Genet 25:77-81, 1973

Identification by Fluorescent Microscopy of theAbnormal Chromosomes Associated with the

G-Deletion Syndromes

RICHARD J. WARREN,' DAVID L. RIMOIN,2 AND ROBERT L. SUMMITT3

In 1970 Warren and Rimoin [1] reported two patients with identical chromosomalabnormalities, ring G chromosomes, but with distinctly different clinical phenotypes.A review of the previously published cases of deletions involving the G-groupchromosomes revealed that most cases could be placed in one of two categories.Weleber et al. [2] were the first to suggest that these were two distinct syndromescaused by abnormalities of the individual pairs of G chromosomes; they have beendesignated G-deletion syndrome I and G-deletion syndrome II [1]. Subsequently,at least five more reports of deleted G chromosomes have appeared, three with aphenotype of G-deletion syndrome I and two with G-deletion syndrome II [3-6].

G-deletion syndrome I is characterized by a phenotype that in some respects isantithetical to Down's syndrome. Lejeune and co-workers [7] first described thisas "le contretype" of mongolism, and it has since been referred to as "antimongol-ism." The "antimongolism" concept comes from the hypothesis that the samechromosome which if present in triplicate causes mongolism (pair no. 21) causes"antimongolism" if deleted. In concurrence with this hypothesis is the suggestionby Warren and Rimoin [1] that G-deletion syndrome II is the result of a deletedno. 22 chromosome.

Proof of these hypotheses could not be obtained until cytogenetic techniqueswere developed which could distinguish between chromosomes 21 and 22. Now,using fluorescent techniques, chromosomes 21 and 22 can be readily distinguishedby their characteristic banding patterns [8, 9]. We have used fluorescence tech-niques to provide laboratory support for Lejeune's "antimongolism" hypothesis and

Received June 12, 1972; revised August 28, 1972.Presented in part at the Fourth International Congress of Human Genetics, Paris, September

1971.Supported by H.E.W. Health Services and Mental Health Administration, Maternal and Child

Health Services, Project 903 (Miami) and Project 900 (Memphis); U.S. Public Health Serviceresearch grant HD 05624; and Clinical Research Center grant RR-00425 (Torrance).

1 Mailman Center for Child Development, Department of Pediatrics, University of Miami,P.O. Box 6, Biscayne Annex, Miami, Florida 33152. Address reprint requests to R. J. Warren.

2 Division of Medical Genetics, Harbor General Hospital-UCLA School of Medicine, Torrance,California 90509.

3 Genetics Section, Department of Pediatrics, University of Tennessee, Memphis, Tennessee38103.© 1973 by the American Society of Human Genetics. All rights reserved.

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to show that the two clinical syndromes associated with ring G chromosomes have acytologic basis. One syndrome, G-deletion syndrome I, is the result of a deleted orring no. 21 chromosome and the other, G-deletion syndrome II, is caused by adeleted or ring no. 22 chromosome.

SUBJECTS AND METHODS

SubjectsAll three patients in the present study have previously been reported [1, 6].Case 1. R. B. is a 2-year-old male with features of G-deletion syndrome I. In addition

to being mentally retarded, he has microcephaly, a high arched palate, low-set ears,hypertonia, downward-slanting eyes, prominent nasal bridge, micrognathia, growth re-tardation, skeletal abnormalities, and inguinal hernia (fig. 1).

FIG. 1.-Case 1 (R. B.), showing microcephaly, low-set abnormal ears, downward-slantingeyes, prominent nasal bridge, micrognathia.

Case 2. S. S. is a 9-year-old female with features of G-deletion syndrome II. She ismentally retarded, has epicanthic folds, ptosis, and is hypotonic (fig. 2, left).

Case 3. J. S. is a 2-year-old male with features of G-deletion syndrome II. He ismentally retarded, has bilateral epicanthal folds and ptosis, and is very hypotonic (fig. 2,right).

MethodsPeripheral lymphocytes were cultured with phytohemagglutinin and prepared for anal-

ysis by standard techniques.Quinacrine mustard was a generous gift of the Sterling-Winthrop Research Institute.

The staining technique was essentially that of H. A. Lubs (personal communication).

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A~~~~~~LFIG. 2.-Case 2 (S. S.), left, and case 3 (J. S.), right, showing epicanthal folds and ptcsis.

RESULTS

Quinacrine staining of the chromosomes of cultured peripheral lymphocytes re-vealed that the abnormal ring chromosome in all three cases could be identified aseither a no. 21 or no. 22 by the process of elimination. Case 1 (G-deletion syn-drome I) had a ring 21 chromosome (fig. 3)-. The chromosomes of pair 22 wereboth present, but only one brightly fluorescing chromosome 21 was evident alongwith a smaller but brightly fluorescent ring. The Y chromosome in this patient wasconsistently larger and fluoresced in its characteristic fashion, making it easilydiscernible from chromosomes 21 and 22.

Cases 2 and 3 (G-deletion syndrome II) had ring 22 chromosomes (fig. 3). Inboth instances a brightly fluorescent pair of no. 21 chromosomes was visible alongwith one characteristic no. 22 and the ring chromosome. The Y chromosome incase 3 was identified by its characteristic bright fluorescence. The ring chromosomein these cases also fluoresced brightly.

DISCUSSION

The concept of monosomy and trisomy of the same chromosome producingopposite phenotypes dates back to the work of Bridges in 1916 [10]. This "contre-type" principle was first introduced to human genetics by Lejeune et al. [7] andhas since been proposed by others for syndromes associated with monosomy andtrisomy of chromosomes 13 and 18 [11, 12], both of which have been identifiableby autoradiography.

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FIG. 3.-Partial karyotypes revealing the abnormal (ring) chromosomes from case 1 (top),case 2 (bottom), and case 3 (middle).

Proof of any "contretype" postulate depends on the accurate identification ofthe chromosomes involved. Chromosomes 21 and 22 were not distinguishable beforethe advent of fluorescence techniques in human cytogenetics. These techniquesprovide the tools for testing Lejeune's "antimongolism" postulate and, concurrently,for ruling on the postulates by Weleber et al. [2] and Warren and Rimoin [1]that a deleted no. 22 chromosome is responsible for the abnormalities in thosepatients who are not "antimongols" but who also have a ring G chromosome.The findings reported in this paper provide strong support for Lejeune's hypoth-

esis, that is, that "antimongolism" is caused by the partial monosomy of chromo-somal material which in triplicate causes mongolism. Furthermore, partial monosomyof chromosome 22 resulting in a second G-deletion syndrome, as suggested byWeleber et al. [2] and documented by Warren and Rimoin [1], is likewise sup-ported. Case 1, who has the typical clinical features of "antimongolism," was foundto have a ring 21 chromosome, whereas cases 2 and 3, who have the clinical featuresof G-deletion syndrome II, have ring 22 chromosomes. Thus, G-deletion syndrome

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I ("antimongolism") is associated with a deletion of chromosome 21, whereas G-deletion syndrome II is associated with a deletion of chromosome 22.

SUMMARY

Fluorescence microscopy of quinacrine-stained chromosomes has been used toidentify the chromosomes involved in the G-deletion syndromes. G-deletion syn-drome I ("antimongolism") is the phenotype that results when chromosome 21exists as a ring, while G-deletion syndrome II is caused by a ring chromosome 22.

ACKNOWLEDGMENTSWe are grateful to Drs. Robert L. Kaufman, Jerry D. Williams, Peter J. Chauvel, and

Warren R. Dammers, as well as Mrs. Dorothy Chesnut for assistance in obtaining distantsamples. Expert technical assistance was rendered by P. Martens, R. Fernandez, andC. Norman.

Note added in proof: Since the completion of this manuscript, Crandall et al.[13] and Magenis et al. [14] have reported identical findings.

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drome? Amer J Dis Child 115:489-494, 19683. ARMENDARES S, BUENTELLO L, CANTU-GARZA JM: Partial monosomy of a G-group

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10. LEJEUNE J: Type et contretypes, in Journe'es parisiennes de pediatrie, Paris,Flammarion, 1966, pp 78-83

11. DE GROUCHY J: The 18p-, 18q- and 18r syndromes. Birth Defects: OriginalArticle Series 5(5): 74-87, 1969

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13. CRANDALL BF, WEBER F, MULLER HM, et al: Identification of 21 and 22r chromo-somes by quinacrine fluorescence. Clin Genet 3: 264-2 71, 1972

14. MAGENIS RE, ARMENDARES S, HECHT F, et al: Identification by fluorescence oftwo G rings: (46,XY,21r) G deletion syndrome I and (46,XX,22r) G deletionsyndrome II. Ann Genet. In press, 1972

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