American Journal of Medical Genetics 2:233-240 ( 1 9 7 8 )
Spreading of Inactivation in an (X;14) Translocation Penelope W. Allderdice, Orlando J. Miller, Dorothy A. Miller, and Harold P. Klinger Department of Human Genetics and Development [P. W.A., O.J.M., D.A.M.), and Department of Obstetrics and Gynecology (O.J.M.), College of Physicians and Surgeons, Columbia University, Mew York; and Department of Genetics (H.P. K.), Albert Einstein College of Medicine, Bronx, Mew York
In the KOP translocation, t(X;14)(q13; q32), virtually the entire long arm of t h e X has been translocated t o the end of the long arm of chromosome 14. Meiotic secondary nondisjunction in a female balanced carrier of the translocation has led t o a son with two der( 14) o r 14-X chromosomes. The normal X chromosome is late replicating in the mother. One of the two 14-X chromosomes is late replicating in the son, with heavy terminal labeling of all b u t t h e centromeric end of the chromosome. This suggests that genetic inactivation has spread from the Xq segment of the translocation chromosome t o at least two thirds of the segment derived from chromosome 14, and that the remaining proximal segment of chromosome 14 is possibly still genetically active. These findings provide an explanation for the phenotype: Klinefelter syndrome plus a few mild malformations that are sometimes seen in this syndrome but are also seen in duplication of the proximal portion of chromosome 14. Although t h e proband has a duplication of virtually an entire chromosome 14, 14(pter + q32), the phenotypic effect of the autosomal duplication has been mostly nullified by the spread of inactivation. Key words: X-autosome translocation, Klinefelter syndrome, trisomy 14, X inactivation, spreading of X inactivation
INTRODUCTION
X-autosome translocations in man are associated with male and female infertility and in some cases with multiple malformations. More than 30 such translocations have been reported, most of them since the introduction of chromosome banding techniques [Leisti e t al, 1975; Hagemeijer et al, 19771. In addition to their clinical interest, human Received for publication November 21, 1977. Penelope W. Allderdice is now at Memorial University, St Johns, Newfoundland. Address reprint requests to Orlando J. Miller, MD, HSC-1424,701 W 168 St, New York, NY 10032.
0148-7299/78/0203-0233$01.70 0 1 9 7 8 Alan R. Liss, Inc
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X-autosome translocations have been used t o map genes along the X chromosome [McKusick and Ruddle, 19771 and to study X inactivation. In women with a balanced translocation involving an X and an autosome, the normal X chromosome is ordinarily inactivated. This has been shown by the late replication of the normal X revealed by autoradiography after growth in 3H-thymidine [Buckton et al, 19711 ,or by its banding pattern after growth in the presence of BrdU [Latt et al, 1976; Hagemeijer et al, 19771 . In persons with an unbalanced translocation the situation is more complex, but in general the abnormal X chromosome is inactivated [Buckton et al, 1971; Therman and Patau, 19741 . In a translocation chromosome that includes both autosome- and X chromosome-derived segments, it is possible to observe spread of Xinactivation to the autosomal portion [Crandall et al, 1974; Summitt et al, 1974; Leisti et al, 1975; Hagemeijer et al, 19771 . We report the details of terminal replication studies in a mother and son with an X;14 translocation. Some of this work was reported earlier in abstract form [Allderdice et al, 1971al. A detailed clinical report will appear elsewhere [Opitz and Pallister, 19771 . The KOP-I and KOP-2 cell lines, which are available through the Human Genetic Mutant Cell Repository, Camden, New Jersey, as GM 73 and 74 [Opitz, Pallister, and Ruddle, 1973a,b] ,were derived from the mother and son, respectively. The KOP-1 line was used in the assignment of the nucleoside phosphorylase locus t o chromosome 14 [Ricciuti and Ruddle, 1973a1, and the assignment of the glucose&-phosphate dehydrogenase, hypoxanthine-phosphoribosyltransferase,and phosphoglycerate kinase loci to the long arm of the X chromosome [Grzeschik et al, 1972; Ricciuti and Ruddle, 1973b; Grzeschik and Siniscalco, 19761.
MATERIALS AND METHODS
Leukocyte cultures were set up in two laboratories from blood samples taken from the normal mother and from her son with the Klinefelter syndrome. After about 68 hours of incubation, tritiated thymidine (spec act 1.9 C/mM) was added to give a final concentration of 0.5 pC/ml. Colcemid was added two hours before harvesting and cultures were harvested three and six hours after the initial addition of the tritiated thymidine. After application of Kodak AR-10 stripping film, some metaphase spreads were exposed in the dark for a relatively short time to facilitate grain counting. Other slides were exposed to film for a longer time, to produce denser grain clusters. The chromosomes of both mother and son were also examined after Q-banding with quinacrine dihydrochloride. Cell lines were established from skin biopsies of both individuals, and the chromosome complements of these were determined.
RESULTS
In both blood and skin cells the karyotype of the mother was 46,X,t(X;14)(Xpter Xq13::14q32 + 14qter;l4pter + 14q32::Xq13 Xqter) (Fig 1). The der(l4) chromosome will be referred to as 14-X and the der(X) chromosome as Xq-. The normal X chromosome was late replicating in all the informative cells from the mother (36 cells after six hours of H-thymidine exposure) (Fig 2 ) . In 18 cells from one culture on the mother, it was possible to distinguish the D-group chromosomes on the basis of distri-
-+
-+
X-Autosome Translocation
23 5
Fig 1. Q-banded karyotype of the mother: 46,X,t(X;14)(q13;q32). Arrows point t o the translocation chromosomes der(l4) or 14-X, and der(X) or Xq-.
bution of silver grains. In these cells the mean number of grains over the long arm of chromosome 14 was almost the same as the number over the proximal half of the 14-X chromosome (Table I). The karyotype of the son in blood and skin was 47,Y,t(X;14)(q13;q32)mat,+der (14),t(X;14)(q13;q32)mat (Fig 3). He had no normal X chromosome, but received the Xq- chromosome and two copies of the 14-X chromosome (Fig 3). Thus he had a duplication of almost an entire chromosome 14 (pter q32), and he had two copies of most of the long arm of the X chromosome (q13 -+ qter), in addition to a Y chromosome. One 14-X chromosome was late replicating in all 25 informative cells from this individual (Figs 4, 5); in 22 other cells no late replicating chromosome could be distinguished, usually because of generally heavy labeling. Autoradiographic silver grains were not restricted to the distal half (the X chromosome-derived portion) of the 14-X chromosome. Instead, they were found over about 80%of the length of the chromosome, with the proximal 20% unlabeled in most of the cells (Figs 4, 5). The mean number of silver grains overlying the proximal half (the 14-derived portion) of the late replicating 14-X chromosome in lightly labeled cells from the son was twice that found over the other 14-X chromosome (Table I). -+
DISCUSS10N
Translocations of the type found in this family are of particular interest because they can lead to several kinds of abnormalities. Adjacent-I meiotic segregation could lead
236
Allderdice et a1
Fig 2. Partial karyotypes of the mother, who is a balanced carrier of an X-14 translocation. The top row shows quinacrine banding, the second row Giemsa staining, and the next three rows terminal labeling. The mother’s normal X is late replicating.
to sibs with Turner, Klinefelter, triplo-X, or embryonic lethal phenotypes. Secondary nondisjunction at the second meiotic division may also occur. In this family the mother had one normal son and six spontaneous abortions, in addition to the son whose Klinefelter syndrome was the result of secondary nondisjunction [Pallister and Opitz, 19771 . The normal X chromosome was late replicating in at least 15 of 18 balanced carriers of an X-autosome translocation [Summitt et al, 1974; Leisti et al, 1975; Garcia et al, 1977; Hagemeijer et al, 19771 . This is true in the balanced translocation carrier female in the present family as well. However, the late replicating chromosome in the unbalanced complement of the son is one of the 14-X chromosomes. This 14-X chromosome shows late labeling over the distal half (derived from Xq), and over much of its proximal half (derived from 14), indicating spread of inactivation from the X-derived segment to the autosome-derived segment of the translocation chromosome. But the most proximal segment of all, comprising about 20% of the chromosome, is not late replicating. If the spread of inactivation does not involve this portion of the chromosome, this individual is functionally partially trisomic, with a duplication of the proximal portion of chromosome 14. Duplication of the proximal segment of chromosome 14 produces a fairly characteristic syndrome [Allerdice e t al, 1971b; Short et al, 1972; Fawcett et al, 19751 which is detailed in Table 11. Most of these features are absent in the proband, but a few are
X-Autosome Translocation
237
Fig 3. Q-banded karyotype of the son: 47,Y,t(X;14)(q 13; q32)mat,+der(l4),t(X;14)(q13; q32)mat.
Fig 4. Partial karyotypes of the son. One of the two 14-X translocation chromosomes is late replicating, with silver grains present over both X- and lrlderived portions.
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Fig 5. More heavliy labeled partial karyotypes of the son illustrating the spreading of late replication from the X chromosomederived distal half of the 14-X chromosome into the number 14derived portion. Note that the region adjacent to the centromere is not late replicating (arrows).
TABLE I. Grain Counts Over Chromosomes 14 and 14-Xin Cells With Distinctive D-Group Labeling Patterns Mean number of grains
Mother Son
No. of cells
14a
Proximal half of late replicating 14-X
Second 14-X
18 17
11.7 1.4
... 15.0
10.7 6.5
"Chromosome 14 or 15 with the largest number of grains.
present: brachycephaly, low hair line, micrognathia, epicanthal folds, camptodactyly, and psychomotor retardation. He also shows a number of other abnormalities not characteristically though occasionally associated with this syndrome : Brushfield spots, retention of some deciduous teeth, slight pes cavus, calcaneovalgus, metatarsus varus, relatively short metatarsals, genu valgum and recurvatum, a single flexion crease on the fifth finger, simian crease, and inguinal hernia [Pallister and Opitz, 19771 . In view of the small number of examples of duplication 14q, and the uncertainty about the effect of variation in size of the duplicated segment or the alleles it carries, one cannot rule out the possibility that some of the minor malformations seen in the proband are due to continued expression of genes in the proximal segment of chromosome 14, though this may be unlikely. It seems even less likely that the translocation was not reciprocal and that these malformations are due to monosomy of the tiny distal segment of chromosome 14 (q32 + qter). Deletion of this segment plus duplication of part of the short arm of chromosome 5 was associated with epilepsy and childhood schizophrenia in the family reported by DeCapoa et al [ 19671 . The spread of inactivation from an X-derived segment to an autosome-derived segment of a translocation chromosome has been demonstrated in several individuals. In
X-Autosome Translocation
239
TABLE 11. Comparison of Clinical Findings in the Proband With Those in Trisomy for the Proximal Part of Chromosome 14 Abnormality Brachycephaly Low hair line Micrognathia Epicanthal folds Camptodactyly Psychomotor retardation Microcephaly Hyper (or hypo) telorism Ptosis of eyelids Downward slanting palpebral fissures Small palpebral fissures Microphthalmia Strabismus Nose broad, tip prominent High arched or cleft palate Short neck Congenital heart disease Hypoplastic 12th rib Seizures or hypertonia Facial asymmetry Brushfield spots Retention of some deciduous teeth Pes cavus, calcaneovalgus Short metatarsals 2-5 Cenu valgum and recurvatum Single flexion crease, 5 th finger Simian crease Inguinal hernia
Partial trisomy 14
+ + + + +
+ + + + + + + +
-
-
Proband
+ + -+
+
+ + -
-
-
+ +
some cases involving unbalanced X-autosome translocations, the results were similar to ours, with suppression of the autosomal duplication phenotypes [Crandall et al, 1974; Leisti et al, 1975; Garcia et al, 19771 . In other cases the spread of inactivation resulted in deletion phenotypes [Thelen et al, 1971 ;Summitt et al, 19741 . However, spread of inactivation was not observed in every individual with an unbalanced X-autosome translocation. In some cases the phenotype resembled that of an autosomal trisomy [Mikkelsen and Dahl, 1973; Hagemeijer et al, 19771, and in another case it was close to normal, rather than the deletion phenotype which would have resulted from spread of inactivation [Jenkins et al, 19741. Whether spread of inactivation occurs in human X-autosome translocations may depend on the location of the translocation breakpoint relative to the position of the inactivation center(s) in the X [Cohen et al, 1972; Therman and Patau, 19741, as it appears to in the mouse [Eicher, 19701.
ACKNOWLEDGMENTS
This work was supported by grants from the National Institutes of Health (CA 12504 and GM 22966), and The National Foundation-March of Dimes.
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RE FE RENCES Allderdice PW, Miller OJ, Klinger HP, Pallister PD, Opitz JM (197 la). Demonstration of a spreading effect in an X-autosome translocation by combined autoradiographic and quinacrine-fluorescence studies. (Abstract) Excerpta Med Int Congr Ser 233:14-15. Allderdice PW, Miller OJ, Miller DA, Breg WR, Gendel E, Zelson C (197 lb). Familial translocation involving chromosomes 6, 14, and 2 0 identified by quinacrine fluorescence. Humengenetik 13 : 205 -209. Buckton KE, Jacobs PA, Rae LA, Newton MS, Sanger R (1972). An inherited X-autosome translocation inman. AnnHum Genet 35:171-178. Cohen MM, Lin CC, Sybert V, Orecchio EJ (1972). Two human X-autosorne translocations identified by autoradiography and fluorescence. Am J Hum Genet 24:583-597. Crandall BF, Carrel1 RE, Howard J, Schroeder WA, Muller H (1974). Trisomy 13 with a 13-X translocation. Am J Hum Genet 26:385-392. DeCapoa A, Warburton D, Breg WR, Miller DA, Miller OJ (1967). Translocation heterozygosis: a cause of five cases of the cri du chat syndrome and two cases with a duplication of chromosome number five in three families. Am J Hum Genet 19:586-603. Eicher EM (1970). X-autosome translocations in the mouse: total inactivation versus partial inactivation of the X chromosome. Adv Genet 15:175-259. Fawcett WA, McCord WK, Francke U (1975). Trisomy 14q-. In “New Chromosomal and Malformation Syndromes (1974 Birth Defects Conference). Miami: Symposia Specialists for The National Foundation-March of Dimes, BD:OAS XI(5):223-228. Garcia JE, Cummings DK, Wentz AC, Jones HW Jr, Rary JM (1977). A S/X chromosomal translocation in a patient with premature menopause. J Hered 68:75 -80. Grzeschik KH, Allderdice PW, Grzeschik A, Opitz JM, Miller OJ, Siniscalco M (1972). Cytological mapping of human X-linked genes by use of somatic cell hybrids involving an X-autosome translocation. Proc Natl Acad Sci USA 69:69-73. Grzeschik KH, Siniscalco M (1976). Identification of a de novo chromosome rearrangement in a manmouse hybrid clone and its bearing on the cytological map of the human X chromosome. Cytogenet Cell Genet 16:149-156. Hagemeijer A, Hoovers J , Smit EME, Bootsma D (1977). Replication pattern of the X chromosomes in three X/autosome translocations. Cytogenet Cell Genet 18:333-348. Jenkins MB, Davis E, Thelen TH, Boyd L (1974). A familial X-22 translocation with an extra X chromosome. Am J Hum Genet 26:736-745. Latt SA, Willard HF, Gerald PS (1976). BrdU-33258 Hoechst analysis of DNA replication in human lymphocytes with supernumerary or structurally abnormal X chromosomes. Chrornosoma 57: 135 -15 3. Leisti JT, Kaback MM, Rimoin DL (1975). Human X-autosome translocations: differential inactivation of the X chromosome in a kindred with an X-9 translocation. Am J Hum Genet 27:441453. McKusick VA, Ruddle FH (1977). The status of the gene map of the human chromosomes. Science 196 :3 60 -4 05. Mikkelsen M, Dahl G (1973). Unbalanced X/autosomal translocation with inactivation of the normal chromosome. Cytogenet Cell Genet 12 :35 7 -366. Opitz J, Pallister PD, Ruddle FH (1973a). An (X;14) translocation, balanced, 46 chromosomes. Repository identification No. GM-73, Cytogenet Cell Genet 12:289-290. Opitz J, Pallister PD, Ruddle FH (197 3b). An (X;14) translocation, unbalanced, 47 chromosomes. Repository identification No. GM-74. Cytogenet Cell Genet 12:291-292. Riccuiti FC, Ruddle FH (1973a). Assignment of nucleoside phosphorylase to D14 and localization of X-linked loci in man by somatic cell genetics. Nature New Biol241:180-181. Ricciuti FC, Ruddle FH (1973b). Assignment of three gene loci (PGK, HGPRT, G6PD) t o the long arm of the human X chromosome b y somatic cell genetics. Genetics 74:66 1-678. Short EM, Solitaire GB, Breg WR (1972). A case of partial 14 trisomy 47,XY, (14q-)+ and translocation t(9p+;14q-) in mother and brother. J Med Genet 9:367-373. Summitt RL, Martens PR, Wilroy RS Jr (1974). X-autosome translocation in normal mother and effectively 21-monosomic daughter. J Pediatr 84539-546. Thelen TH, Abrams DJ, Fisch RO (1971). Multiple abnormalities due to possible genetic inactivation in an X/autosome translocation. Am J Hum Genet 23:410-418. Therman E, Patau K (1974). Abnormal X chromosomes in man: origin, behavior and effects. Humangenetik 25:l-16.
Edited by John M. Opitz
Spreading of Inactivation in an (X;14) Translocation Penelope W. Allderdice, Orlando J. Miller, Dorothy A. Miller, and Harold P. Klinger Department of Human Genetics and Development [P. W.A., O.J.M., D.A.M.), and Department of Obstetrics and Gynecology (O.J.M.), College of Physicians and Surgeons, Columbia University, Mew York; and Department of Genetics (H.P. K.), Albert Einstein College of Medicine, Bronx, Mew York
In the KOP translocation, t(X;14)(q13; q32), virtually the entire long arm of t h e X has been translocated t o the end of the long arm of chromosome 14. Meiotic secondary nondisjunction in a female balanced carrier of the translocation has led t o a son with two der( 14) o r 14-X chromosomes. The normal X chromosome is late replicating in the mother. One of the two 14-X chromosomes is late replicating in the son, with heavy terminal labeling of all b u t t h e centromeric end of the chromosome. This suggests that genetic inactivation has spread from the Xq segment of the translocation chromosome t o at least two thirds of the segment derived from chromosome 14, and that the remaining proximal segment of chromosome 14 is possibly still genetically active. These findings provide an explanation for the phenotype: Klinefelter syndrome plus a few mild malformations that are sometimes seen in this syndrome but are also seen in duplication of the proximal portion of chromosome 14. Although t h e proband has a duplication of virtually an entire chromosome 14, 14(pter + q32), the phenotypic effect of the autosomal duplication has been mostly nullified by the spread of inactivation. Key words: X-autosome translocation, Klinefelter syndrome, trisomy 14, X inactivation, spreading of X inactivation
INTRODUCTION
X-autosome translocations in man are associated with male and female infertility and in some cases with multiple malformations. More than 30 such translocations have been reported, most of them since the introduction of chromosome banding techniques [Leisti e t al, 1975; Hagemeijer et al, 19771. In addition to their clinical interest, human Received for publication November 21, 1977. Penelope W. Allderdice is now at Memorial University, St Johns, Newfoundland. Address reprint requests to Orlando J. Miller, MD, HSC-1424,701 W 168 St, New York, NY 10032.
0148-7299/78/0203-0233$01.70 0 1 9 7 8 Alan R. Liss, Inc
234
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X-autosome translocations have been used t o map genes along the X chromosome [McKusick and Ruddle, 19771 and to study X inactivation. In women with a balanced translocation involving an X and an autosome, the normal X chromosome is ordinarily inactivated. This has been shown by the late replication of the normal X revealed by autoradiography after growth in 3H-thymidine [Buckton et al, 19711 ,or by its banding pattern after growth in the presence of BrdU [Latt et al, 1976; Hagemeijer et al, 19771 . In persons with an unbalanced translocation the situation is more complex, but in general the abnormal X chromosome is inactivated [Buckton et al, 1971; Therman and Patau, 19741 . In a translocation chromosome that includes both autosome- and X chromosome-derived segments, it is possible to observe spread of Xinactivation to the autosomal portion [Crandall et al, 1974; Summitt et al, 1974; Leisti et al, 1975; Hagemeijer et al, 19771 . We report the details of terminal replication studies in a mother and son with an X;14 translocation. Some of this work was reported earlier in abstract form [Allderdice et al, 1971al. A detailed clinical report will appear elsewhere [Opitz and Pallister, 19771 . The KOP-I and KOP-2 cell lines, which are available through the Human Genetic Mutant Cell Repository, Camden, New Jersey, as GM 73 and 74 [Opitz, Pallister, and Ruddle, 1973a,b] ,were derived from the mother and son, respectively. The KOP-1 line was used in the assignment of the nucleoside phosphorylase locus t o chromosome 14 [Ricciuti and Ruddle, 1973a1, and the assignment of the glucose&-phosphate dehydrogenase, hypoxanthine-phosphoribosyltransferase,and phosphoglycerate kinase loci to the long arm of the X chromosome [Grzeschik et al, 1972; Ricciuti and Ruddle, 1973b; Grzeschik and Siniscalco, 19761.
MATERIALS AND METHODS
Leukocyte cultures were set up in two laboratories from blood samples taken from the normal mother and from her son with the Klinefelter syndrome. After about 68 hours of incubation, tritiated thymidine (spec act 1.9 C/mM) was added to give a final concentration of 0.5 pC/ml. Colcemid was added two hours before harvesting and cultures were harvested three and six hours after the initial addition of the tritiated thymidine. After application of Kodak AR-10 stripping film, some metaphase spreads were exposed in the dark for a relatively short time to facilitate grain counting. Other slides were exposed to film for a longer time, to produce denser grain clusters. The chromosomes of both mother and son were also examined after Q-banding with quinacrine dihydrochloride. Cell lines were established from skin biopsies of both individuals, and the chromosome complements of these were determined.
RESULTS
In both blood and skin cells the karyotype of the mother was 46,X,t(X;14)(Xpter Xq13::14q32 + 14qter;l4pter + 14q32::Xq13 Xqter) (Fig 1). The der(l4) chromosome will be referred to as 14-X and the der(X) chromosome as Xq-. The normal X chromosome was late replicating in all the informative cells from the mother (36 cells after six hours of H-thymidine exposure) (Fig 2 ) . In 18 cells from one culture on the mother, it was possible to distinguish the D-group chromosomes on the basis of distri-
-+
-+
X-Autosome Translocation
23 5
Fig 1. Q-banded karyotype of the mother: 46,X,t(X;14)(q13;q32). Arrows point t o the translocation chromosomes der(l4) or 14-X, and der(X) or Xq-.
bution of silver grains. In these cells the mean number of grains over the long arm of chromosome 14 was almost the same as the number over the proximal half of the 14-X chromosome (Table I). The karyotype of the son in blood and skin was 47,Y,t(X;14)(q13;q32)mat,+der (14),t(X;14)(q13;q32)mat (Fig 3). He had no normal X chromosome, but received the Xq- chromosome and two copies of the 14-X chromosome (Fig 3). Thus he had a duplication of almost an entire chromosome 14 (pter q32), and he had two copies of most of the long arm of the X chromosome (q13 -+ qter), in addition to a Y chromosome. One 14-X chromosome was late replicating in all 25 informative cells from this individual (Figs 4, 5); in 22 other cells no late replicating chromosome could be distinguished, usually because of generally heavy labeling. Autoradiographic silver grains were not restricted to the distal half (the X chromosome-derived portion) of the 14-X chromosome. Instead, they were found over about 80%of the length of the chromosome, with the proximal 20% unlabeled in most of the cells (Figs 4, 5). The mean number of silver grains overlying the proximal half (the 14-derived portion) of the late replicating 14-X chromosome in lightly labeled cells from the son was twice that found over the other 14-X chromosome (Table I). -+
DISCUSS10N
Translocations of the type found in this family are of particular interest because they can lead to several kinds of abnormalities. Adjacent-I meiotic segregation could lead
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Allderdice et a1
Fig 2. Partial karyotypes of the mother, who is a balanced carrier of an X-14 translocation. The top row shows quinacrine banding, the second row Giemsa staining, and the next three rows terminal labeling. The mother’s normal X is late replicating.
to sibs with Turner, Klinefelter, triplo-X, or embryonic lethal phenotypes. Secondary nondisjunction at the second meiotic division may also occur. In this family the mother had one normal son and six spontaneous abortions, in addition to the son whose Klinefelter syndrome was the result of secondary nondisjunction [Pallister and Opitz, 19771 . The normal X chromosome was late replicating in at least 15 of 18 balanced carriers of an X-autosome translocation [Summitt et al, 1974; Leisti et al, 1975; Garcia et al, 1977; Hagemeijer et al, 19771 . This is true in the balanced translocation carrier female in the present family as well. However, the late replicating chromosome in the unbalanced complement of the son is one of the 14-X chromosomes. This 14-X chromosome shows late labeling over the distal half (derived from Xq), and over much of its proximal half (derived from 14), indicating spread of inactivation from the X-derived segment to the autosome-derived segment of the translocation chromosome. But the most proximal segment of all, comprising about 20% of the chromosome, is not late replicating. If the spread of inactivation does not involve this portion of the chromosome, this individual is functionally partially trisomic, with a duplication of the proximal portion of chromosome 14. Duplication of the proximal segment of chromosome 14 produces a fairly characteristic syndrome [Allerdice e t al, 1971b; Short et al, 1972; Fawcett et al, 19751 which is detailed in Table 11. Most of these features are absent in the proband, but a few are
X-Autosome Translocation
237
Fig 3. Q-banded karyotype of the son: 47,Y,t(X;14)(q 13; q32)mat,+der(l4),t(X;14)(q13; q32)mat.
Fig 4. Partial karyotypes of the son. One of the two 14-X translocation chromosomes is late replicating, with silver grains present over both X- and lrlderived portions.
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Fig 5. More heavliy labeled partial karyotypes of the son illustrating the spreading of late replication from the X chromosomederived distal half of the 14-X chromosome into the number 14derived portion. Note that the region adjacent to the centromere is not late replicating (arrows).
TABLE I. Grain Counts Over Chromosomes 14 and 14-Xin Cells With Distinctive D-Group Labeling Patterns Mean number of grains
Mother Son
No. of cells
14a
Proximal half of late replicating 14-X
Second 14-X
18 17
11.7 1.4
... 15.0
10.7 6.5
"Chromosome 14 or 15 with the largest number of grains.
present: brachycephaly, low hair line, micrognathia, epicanthal folds, camptodactyly, and psychomotor retardation. He also shows a number of other abnormalities not characteristically though occasionally associated with this syndrome : Brushfield spots, retention of some deciduous teeth, slight pes cavus, calcaneovalgus, metatarsus varus, relatively short metatarsals, genu valgum and recurvatum, a single flexion crease on the fifth finger, simian crease, and inguinal hernia [Pallister and Opitz, 19771 . In view of the small number of examples of duplication 14q, and the uncertainty about the effect of variation in size of the duplicated segment or the alleles it carries, one cannot rule out the possibility that some of the minor malformations seen in the proband are due to continued expression of genes in the proximal segment of chromosome 14, though this may be unlikely. It seems even less likely that the translocation was not reciprocal and that these malformations are due to monosomy of the tiny distal segment of chromosome 14 (q32 + qter). Deletion of this segment plus duplication of part of the short arm of chromosome 5 was associated with epilepsy and childhood schizophrenia in the family reported by DeCapoa et al [ 19671 . The spread of inactivation from an X-derived segment to an autosome-derived segment of a translocation chromosome has been demonstrated in several individuals. In
X-Autosome Translocation
239
TABLE 11. Comparison of Clinical Findings in the Proband With Those in Trisomy for the Proximal Part of Chromosome 14 Abnormality Brachycephaly Low hair line Micrognathia Epicanthal folds Camptodactyly Psychomotor retardation Microcephaly Hyper (or hypo) telorism Ptosis of eyelids Downward slanting palpebral fissures Small palpebral fissures Microphthalmia Strabismus Nose broad, tip prominent High arched or cleft palate Short neck Congenital heart disease Hypoplastic 12th rib Seizures or hypertonia Facial asymmetry Brushfield spots Retention of some deciduous teeth Pes cavus, calcaneovalgus Short metatarsals 2-5 Cenu valgum and recurvatum Single flexion crease, 5 th finger Simian crease Inguinal hernia
Partial trisomy 14
+ + + + +
+ + + + + + + +
-
-
Proband
+ + -+
+
+ + -
-
-
+ +
some cases involving unbalanced X-autosome translocations, the results were similar to ours, with suppression of the autosomal duplication phenotypes [Crandall et al, 1974; Leisti et al, 1975; Garcia et al, 19771 . In other cases the spread of inactivation resulted in deletion phenotypes [Thelen et al, 1971 ;Summitt et al, 19741 . However, spread of inactivation was not observed in every individual with an unbalanced X-autosome translocation. In some cases the phenotype resembled that of an autosomal trisomy [Mikkelsen and Dahl, 1973; Hagemeijer et al, 19771, and in another case it was close to normal, rather than the deletion phenotype which would have resulted from spread of inactivation [Jenkins et al, 19741. Whether spread of inactivation occurs in human X-autosome translocations may depend on the location of the translocation breakpoint relative to the position of the inactivation center(s) in the X [Cohen et al, 1972; Therman and Patau, 19741, as it appears to in the mouse [Eicher, 19701.
ACKNOWLEDGMENTS
This work was supported by grants from the National Institutes of Health (CA 12504 and GM 22966), and The National Foundation-March of Dimes.
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Edited by John M. Opitz
