Archs oral Bid. Vol. 36, No. 6, pp. 411-414, 1991 Printed in Great Britain. All rights reserved
TOOTH
CROWN J. T.
Copyright 0
SIZE IN 46, X, i (Xq) HUMAN
MAYHALL,’
L. ALVESALO~
and G. C.
ooo3-9969/91 $3.00 + 0.00 1991 Pergamon Press plc
FEMALES
TOWNSEND~
‘Faculty of Dentistry, University of Toronto, Toronto, Canada MSG lG6, 21nstitute of Dentistry, University of Oulu, Oulu, Finland and )Department of Dentistry, University of Adelaide, Adelaide, Australia (Accepted 30 January 1991)
Summary-Permanent tooth crown sizes of constitution (isochromosome for the long arm and compared with those of normal women, diameters of the 46, X, i (Xq) females were not
six Finnish females with a 46,X,i (Xq) chromosome of the X chromosome) were measured from dental casts first-degree female relatives and 45, X females. Crown only smaller than in the normal women but even smaller
than the 45, X females. These findings can be considered indirect evidence that X chromosome gt.le(s) for tooth crown growth are most probably located on the short arm. Key words: tooth crown, X chromosome
MATERIALS
INTRODUCTION
Studies of dental crown size in relatives and in individuals with various sex-chromosome complements have given good evidence that both the X and Y chromosomes exert growth effects within the dentition (Alvesalo, 1971, 1985). Furthermore, radiographic analyses of patients with sex-chromosome anomalies have revealed that the X chromosome mainly influences enamel deposition, with little or no effect on the growth of dentine, whereas the Y chromosome affects growth of both tissues (Alvesalo and Tammisalo, 1981; Alvesalo, Tammisalo and Hakola, 1985; Alvesalo, 1985; Alvesalo, Tammisalo and Therman, 1987; Alvesalo, Tammisalo and Townsend, 1988). Specifically, studies in females with a 45, X chromosome constitution (Filipsson, Lindsten and Almqvist, 1965; Kari, Alvesalo and Manninen, 1980; Townsend, Jensen and Alvesalo, 1984) have shown that the deciduous and permanent teeth are smaller than normal and that 45, X/46, XX females also have smaller teeth, but only in the mesiodistal diameter (Varrela, Townsend and Alvesalo, 1988). Measurements of the size of teeth in two males with deletions of part of the Y chromosome suggest that its growthpromoting region is located in the non-fluorescent area of the long arm (Alvesalo and de la Chapelle, 1981) and measurements of enamel in 46, X, i (Xq) females suggest that the location of gene(s) affecting amelogenesis within the X chromosome is in the short arm (Alvesalo, Tammisalo and de la Chapelle, 1981). Interestingly, the findings of Lau et al. (1989) and Lau, Slavkin and Snead (1990) suggest that the human amelogenin gene(s) are located on the distal portion of the short arm of the X chromosome. We now compare the tooth size of females with a 46, X, i (Xq) chromosome constitution with that of 45, X females and normal 46, XX females in order to obtain further information about growth-promoting genes on the X chromosome.
AND METHODS
Six Finnish women identified through karyotyping as having one normal X chromosome and one isochromosome with the long arm duplicated, i.e. 46, X, i (Xq), were examined, together with three of their first-degree female relatives, 89 Finnish women with 45, X chromosomal constitutions, and 168 women from the general population. The women with i (Xq) were phenotypically similar to those with a 45, X constitution, having short stature, a low hair-line and a short neck. The population controls were normal women from a Finnish rural community (Hailuoto); the female relatives served as controls for any familial factors that might influence tooth size. Maximum mesiodistal and labiolingual dimensions of permanent tooth crowns were measured from plaster casts of the maxillary and mandibular dentitions of each subject, as described by Alvesalo (197 1). Data for the teeth from the right-hand side are presented, although, if a tooth was missing, values for the antimere were included whenever possible. Replicability studies indicated that errors of measurement, expressed as the SD of a single determination, were small and averaged less than 0.1 mm. The F-test and the r-test were used to compare variances and mean values respectively between groups. RESULTS
Tables 1 and 2 give mesiodistal and labiolingual crown dimensions for 46, X, i (Xq) females, population controls and female relatives. All of the teeth were smaller in the 46, X, i (Xq) females compared with population controls, and most differences were statistically significant at p < 0.05. A similar trend was noted when affected women were compared with their normal relatives. The number of statistically significant differences was smaller but this is not unexpected, given the size of the samples. The
411
J.T.
412 Table
MAYHALL~~
al
tooth dimensions (mm) in Finnish 46, X, i (Xq) females, population control females, and female relatives
I. Mesiodistal
46, X, i (Xq) females
Normal females (population) _________ N Mean SD
Normal females (relatives)
Tooth
N
Mean
SD
N
Mean
Maxilla I1 I2 C PI P2 MI M2
6 5 6 5 5 5 3
7.6 6.2 1.4 6.5 6.0 8.9 8.8
0.2 0.3 0.3 0.3 0.5 0.4 0.3
162 8.7** 136 6.7 Ill 1.7 111 7.0* 91 6.8** 141 10.21; 63 9.1+
0.5 0.6 0.4 0.5 0.5 0.5 0.6
2 2 3 2 2
I
10.0
~
Mandible II 12 C PI P2 Ml M2
5
6 6 6 5 5 2
4.8 5.4 6.3 6.6 6.3 9.9 9.6
0.4 0.2 0.2 0.3 0.3 0.4 0.2
154 5.5** 168 6.0** 144 6.7+* 148 7.0 114 7.1** 112 11.0** 67 10.4
0.3 0.3 0.3 0.5 0.4 0.6 0.6
3 3 3 3 2
5.4 5.9* 6.7* 1.2* 7.2*
0.2 0.3 0.1 0.2 0.2
8.4** 6.6 7.5 7.1* 7.0
SD 0.2 0.6 0.2 0.1 0.4
‘p < 0.05; **p < 0.01.
average reduction in tooth size of 46, X, i (Xq) females compared to population controls was 9.2% for the mesiodistal dimensions and 7.6% for labiolingual dimensions. Comparisons of 46, X, i (Xq) with 45, X females are made in Table 3. Earlier studies have shown average reductions in mesiodistal and labiolingual crown dimensions of 45, X females compared with normal women of 5.6 and 3.1%, respectively. Our results show that women with the isochromosome have even smaller teeth than the 45, X females, with one exception, the mesiodistal diameter of the mandibular second molar. Thus, a trend in tooth size has been noted between the groups, being, from largest to smallest: normal women; 45, X; 46, X, i (Xq).
DISCUSSION
Studies of dental crown size in individuals with X chromosome aneuploidies have demonstrated a ‘dosage effect’, with tooth size increasing regularly as the number of X chromosomes increases (Townsend et al., 1988). Similar results have also been noted for other body features, including finger-ridge counts, birth weight, stature and palate shape (Barlow, 1973; Gorlin, Redman and Shapiro, 1965). Radiographic analyses have further demonstrated that extra X chromosomes lead primarily to increases in enamel thickness of tooth crowns, although the effect of each additional X chromosome relatively diminishes (Alvesalo et al., 1987).
Table 2. Labiolingual tooth dimensions (mm) in Finnish 46, X, i (Xq) females, population control females and female relatives Normal females 46, X, i (Xq) females
(population) _
Tooth
N
Mean
SD
N
Maxilla II I2 C PI P2 Ml M2
5 3 6 5 5 6 3
6.6 5.9 7.8 8.7 9.0 10.6 10.1
0.4 0.2 0.5 0.5 0.4 0.3 0.1
Mandible I1 I2 C Pl P2 Ml M2
5
4 6 6 6 4 2
5.5 5.7 7.0 7.5 7.9 9.5 8.8
0.3 0.4 0.6 0.8 0.6 0.4 0.1
Mean
SD
N
Mean
SD
91 70 94 121 106 147 70
7.3** 6.4 8.2 9.2” 9.3 11.3** 11.1**
0.5 0.6 0.5 0.5 0.5 0.6 0.7
2 2 3 3 3 2 2
7.1 6.5 8.2 9.3 9.2 11.1 11.1**
0.6 0.6 0.5 0.4 0.7 0.1 0.1
85 88 108 144 122 127 64
6.0** 6.4** 7.51 7.8 8.4; 10.7** 10.3**
0.4 0.4 0.5 0.5 0.5 0.5 0.6
I I
6.1 6.5 7.7 7.7 8.5 10.7 10.2
0.4 0.1 0.3
‘p < 0.05; **p < 0.01. 46, X. i (Xq) females
Normal females (relatives)
versus each control
group.
3 3 3
1 I
46, X, i (Xq) Tooth size
413
Table 3. Tooth sizes of 46, X, i (Xq) females and 45, X females Labiolingual dimensions (mm)
Mesiodistal dimensions (mm)
_
46, X, i o(q)
46, X, i o(q)
45, x
Tooth
N
Mean
SD
N
Maxilla 11 12 C Pl P2 Ml M2
6 5 6 5 5 5 3
1.6 6.2 7.4 6.5 6.0 8.9 8.8
0.2 0.3 0.3 0.3 0.5 0.4 0.3
87 81 84 19 14 70 42
Mandible 11 I2 C Pl P2 Ml M2
5 6 6 6 5 5 2
4.8 5.4 6.3 6.6 6.3 9.9 9.6
0.4 0.2 0.2 0.3 0.3 0.4 0.2
86 87 89 88 78 62 35
Mean
45, x
SD
N
Mean
SD
N
Mean
SD
8.1” 6.5 7.6 6.7 6.3 9.4** 9.3
0.5 0.5 0.4 0.4 0.4 0.4 0.5
5 3 6 5 5 6 3
6.6 5.9 7.8 8.7 9.0 10.6
0.4 0.2 0.5 0.5 0.4 0.3
75 61 83 81 83 80
6.9 6.3 8.1 9.0 9.2 10.9
0.5 0.5 0.5 0.5 0.5 0.5
IO.1
0.1
50
10.8** 0.7
5.1* 5.6 6.5 6.9 6.7* 10.0 9.4
0.3 0.4 0.4 0.4 0.4 0.6 0.5
5 4 6 6 6 4 2
5.5 5.7 7.0 1.5 7.9 9.5 8.8
0.3 0.4 0.6 0.8 0.6 0.4 0.1
7s 79 87 84 82 61 42
5.8 6.0 7.3 7.8 8.2 9.9 9.6.
0.4 0.5 0.5 0.5 0.5 0.5 0.5
*p < 0.05; **p < 0.01. 46, X, i (Xq) females versus 45, X females. Data for 45, X females from Varrela et al. (1988). It was originally thought that only one X chromosome was active within each human cell, making it difficult to explain in genetic terms the phenotypic abnormalities observed in individuals with extra or missing X chromosomes. However, it is now apparent that part(s) of the supposedly ‘inactive’ X chromosome remain active throughout life, even though the genes in these active regions have less effect than the same genes on the active X chromosome (Lyon, 1983). An active region has now been localized to the tip of the short arm, Xp (Therman, 1983). In our study, women with an isochromosome for the long arm of the X chromosome had smaller teeth than normal, providing indirect evidence that X chromosome gene(s) for tooth crown growth (and perhaps for other somatic quantitative features) are most probably located on the short arm. Further confirmation that gene(s) promoting growth of other physical features apart from tooth size may be located on the short arm of the X chromosome is provided by Goldman et al. (1982), who examined people with partial deletions of the X chromosome and found that short-arm deletions appeared to have a greater effect on stature than deletions of the long arm. Several others, including Jacobs et al. (1961), Ferguson-Smith (1965) and Ballabio et al. (1989), have also suggested that genes controlling physical features, e.g. stature, are likely to be on the short arm of the X chromosome. Whether the gene(s) for tooth growth and statural growth are the same cannot be distinguished in this type of study. However, it is possible that there are pleiotropic effects operating. It appears that in individuals with sex-chromosome mosaicism, selection occurs during development to the advantage of the normal cell population (Neilson, 1976). For example, normalization of growth by 46, XX cells is likely to account for the range of Turner stigmata observed in 45, X/46, XX mosaics (Sarkar and Marimathu, 1983). In a similar fashion,
the normal and abnormal chromosomes in women with an i (Xq) chromosome are likely to be initially alternately inactivated, although the genetically better-balanced cell line seems to eventually take over (Therman et al., 1980; Therman, 1983). The reduction in tooth size in 46, X, i (Xq) compared with 45, X females is, therefore, probably at least in part due to a retarding effect exerted during development by cells where the normal X chromosome was inactive and in which there was no functioning Xp. The radiographic assessments have shown a definite reduction of enamel thickness of maxillary anterior teeth in 45, X females, obvious reduction of enamel in 46, X, i (Xq) females, and suggest also less thick dentine in 46, X, i (Xq) than in normal women (Alvesalo and Tammisalo, 1981: Alvesalo et al., 1981). Acknowledgement-This Academy of Finland Foundation.
study was supported by the and the University of Turku
REFERENCES
Alvesalo L. (1971) The influence of sex-chromosome genes on tooth size in man. Proc. Finn. dent. Sot. 67, 3-54. Alvesalo L. (1985) Dental growth in 47, XYY males and in conditions with other sex-chromosome anomalies. In The Y Chromosome, Parr B: Clinical Aspects of Y Chromosome Abnormalities (Ed. Sandberg A. A.), pp. 277-300. Alan R. Liss, New York. Alvesalo L. and de la Chapelle A. (1981) Tooth sizes in two males with deletions of the long arm of the Y-chromosome. Ann. hum. Genet. 45, 49-54. Alvesalo L. and Tammisalo E. (1981) Enamel thickness in 45, X females’ permanent teeth. Am. J. hum. Gener. 33, 464469. Alvesalo L., Tammisalo E. and de la Chapelle A. (1981) Mapping of the gene(s) influencing amelogenesis in man. J. dent. Res. 60, 403 (abstract). Alvesalo L., Tammisalo E. and Hakola P. (1985) Enamel thickness in 47, XYY males’ permanent teeth. Ann. hum. Biol. 12, 421427.
414
J. T. MAYHALLet al.
Alvesalo L., Tammisalo E. and Therman E. (1987) 47, XXX females, sex chromosomes, and tooth crown structure. Hum Genet. 77, 345-348. Alvesalo L.. Tammisalo E. and Townsend C. G. (1988) Enamel thickness in 47, XXY males’ (Kleinfelter syn: drome) permanent teeth. J. dent.Res. 67, 116 (abstract). Ballabio A., Bardoni B., Carrozzo R., Andria G., Bick D., Campbell L., Hamel B., Ferguson-Smith M. A., Gimelli G., Fraccaro M., Maraschio P., Zuffardi O., Guioli S. and Camerino G. (1989) Continuous gene syndrome due to deletions in the short arm of the human X chromosome. Proc. natn. Acad. Sci. U.S.A. 96, lO,OOl-10,005. Barlow P. (1973) The influence of inactive chromosomes on human development. Anomalous sex chromosome complements and the phenotype. Humangenetik. 17, 105-136.
Ferguson-Smith M. A. (1965) Karyotype-phenotype correlations in gonadal dysgenesis and their bearing on the pathogenesis of malformations. J. med. Genet. 2, 1422185. Filipsson R., Lindsten J. and Almqvist S. (1965) Time of eruption of the permanent teeth, cephalometric and tooth measurement and sulphation factor activity in 45 patients with Turner’s syndrome with different types of X chromosome aberrations. Acta Endocr. 48, 91-113. Goldman B., Polani P. E., Daker M. G. and Angel1 R. R. (1982) Clinical and cytogenetic aspects of X chromosome deletions. Clin. Genet. 21, 3652.. Gorlin R. J.. Redman R. S. and Shaniro B. L. (1965) Effect of X-chromosome aneuploidy of; jaw growth. j. dent. Res. 44, 269-282. Jacobs P. A., Harnden D. G., Buckton K. E., Court Brown W. M., King M. J., McBride J. A., MacGregor T. N. and MacLean N. (1961) Cytogenetic studies in primary amenorrhoea. Lancet 1, 1183-1189. Kari M., Alvesalo L. and Manninen K. (1980) Sizes of deciduous teeth in 45, X females. J. dent. Res. 59, 1382-1385.
Lau E. C., Mohandas T., Shapiro L. J., Slavkin H. C. and Snead M. L. (1989) Human and mouse amelogenin gene loci are on the sex chromosomes. Genomics 4, 162-168. Lau E. C.. Slavkin H. C. and Snead M. L. (1990) Analysis of human enamel genes: insights into genetic disorders of enamel. Cleft Palate J. 27, 121-130. Lvon M. F. (1983) The X chromosomes and their levels of activation. In Cytogenetics of the Mammalian X Chromosome, Part A: Basic Mechanisms of X Chromosome Behaviour (Ed. Sandberg A. A.), pp. 187-204. Alan R. Liss,
New York. Neilson J. (1976)Cell selection in uiuo in normal/aneuploid chromosome abnormalities. Hum. Genet. 32, 2033206. Sarkar R. and Marimuthu K. M. (1983) Association between the degree of mosaicism and the severity of syndrome in Turner mosaics and Klinefelter mosaics. C/in. Genet. 24, 42@428. Therman E. (1983) Mechanisms through which abnormal X-chromosome constitutions affect the phenotype. In Cytogenetics of the Mammalian X Chromosome, Part B: Clinical Aspects of X Chromosome Abnormalities (Ed.
Sandberg A. A.), pp. 1599173. Alan R. Liss, New York. Therman E., Denniston C.. Sarto G. and Ulber M. (1980) X chromosome constitution and the human female phenotype. Hum. Genet. 54, 133-143. Townsend G. C., Alvesalo L., Jensen B. L. and Kari M. (1988j Patterns of tooth size in chromosome aneuploides. In Teeth Revisited: Proc. VIIth Int. Symp. Dental Morphology (Eds Russell D. E., Santoro J-P. and Sigogneaukus&l D.), Vol. 53, pp. 25-45. Memoires du Museum National D’Histoire Naturelle. Sciences de Terre. Paris. Townsend G. C., Jensen B. L.. and Alvesalo L. (1984) Reduced tooth size in 45, X (Turner syndrome) females. Am. J. phys. Anthrop. 65, 367-371.
Varrela J., Townsend G. C. and Alvesalo L. (1988) Tooth crown size in human females with 45, X/46, XX chromosomes. Archs oral Biol. 33, 291-294.
TOOTH
CROWN J. T.
Copyright 0
SIZE IN 46, X, i (Xq) HUMAN
MAYHALL,’
L. ALVESALO~
and G. C.
ooo3-9969/91 $3.00 + 0.00 1991 Pergamon Press plc
FEMALES
TOWNSEND~
‘Faculty of Dentistry, University of Toronto, Toronto, Canada MSG lG6, 21nstitute of Dentistry, University of Oulu, Oulu, Finland and )Department of Dentistry, University of Adelaide, Adelaide, Australia (Accepted 30 January 1991)
Summary-Permanent tooth crown sizes of constitution (isochromosome for the long arm and compared with those of normal women, diameters of the 46, X, i (Xq) females were not
six Finnish females with a 46,X,i (Xq) chromosome of the X chromosome) were measured from dental casts first-degree female relatives and 45, X females. Crown only smaller than in the normal women but even smaller
than the 45, X females. These findings can be considered indirect evidence that X chromosome gt.le(s) for tooth crown growth are most probably located on the short arm. Key words: tooth crown, X chromosome
MATERIALS
INTRODUCTION
Studies of dental crown size in relatives and in individuals with various sex-chromosome complements have given good evidence that both the X and Y chromosomes exert growth effects within the dentition (Alvesalo, 1971, 1985). Furthermore, radiographic analyses of patients with sex-chromosome anomalies have revealed that the X chromosome mainly influences enamel deposition, with little or no effect on the growth of dentine, whereas the Y chromosome affects growth of both tissues (Alvesalo and Tammisalo, 1981; Alvesalo, Tammisalo and Hakola, 1985; Alvesalo, 1985; Alvesalo, Tammisalo and Therman, 1987; Alvesalo, Tammisalo and Townsend, 1988). Specifically, studies in females with a 45, X chromosome constitution (Filipsson, Lindsten and Almqvist, 1965; Kari, Alvesalo and Manninen, 1980; Townsend, Jensen and Alvesalo, 1984) have shown that the deciduous and permanent teeth are smaller than normal and that 45, X/46, XX females also have smaller teeth, but only in the mesiodistal diameter (Varrela, Townsend and Alvesalo, 1988). Measurements of the size of teeth in two males with deletions of part of the Y chromosome suggest that its growthpromoting region is located in the non-fluorescent area of the long arm (Alvesalo and de la Chapelle, 1981) and measurements of enamel in 46, X, i (Xq) females suggest that the location of gene(s) affecting amelogenesis within the X chromosome is in the short arm (Alvesalo, Tammisalo and de la Chapelle, 1981). Interestingly, the findings of Lau et al. (1989) and Lau, Slavkin and Snead (1990) suggest that the human amelogenin gene(s) are located on the distal portion of the short arm of the X chromosome. We now compare the tooth size of females with a 46, X, i (Xq) chromosome constitution with that of 45, X females and normal 46, XX females in order to obtain further information about growth-promoting genes on the X chromosome.
AND METHODS
Six Finnish women identified through karyotyping as having one normal X chromosome and one isochromosome with the long arm duplicated, i.e. 46, X, i (Xq), were examined, together with three of their first-degree female relatives, 89 Finnish women with 45, X chromosomal constitutions, and 168 women from the general population. The women with i (Xq) were phenotypically similar to those with a 45, X constitution, having short stature, a low hair-line and a short neck. The population controls were normal women from a Finnish rural community (Hailuoto); the female relatives served as controls for any familial factors that might influence tooth size. Maximum mesiodistal and labiolingual dimensions of permanent tooth crowns were measured from plaster casts of the maxillary and mandibular dentitions of each subject, as described by Alvesalo (197 1). Data for the teeth from the right-hand side are presented, although, if a tooth was missing, values for the antimere were included whenever possible. Replicability studies indicated that errors of measurement, expressed as the SD of a single determination, were small and averaged less than 0.1 mm. The F-test and the r-test were used to compare variances and mean values respectively between groups. RESULTS
Tables 1 and 2 give mesiodistal and labiolingual crown dimensions for 46, X, i (Xq) females, population controls and female relatives. All of the teeth were smaller in the 46, X, i (Xq) females compared with population controls, and most differences were statistically significant at p < 0.05. A similar trend was noted when affected women were compared with their normal relatives. The number of statistically significant differences was smaller but this is not unexpected, given the size of the samples. The
411
J.T.
412 Table
MAYHALL~~
al
tooth dimensions (mm) in Finnish 46, X, i (Xq) females, population control females, and female relatives
I. Mesiodistal
46, X, i (Xq) females
Normal females (population) _________ N Mean SD
Normal females (relatives)
Tooth
N
Mean
SD
N
Mean
Maxilla I1 I2 C PI P2 MI M2
6 5 6 5 5 5 3
7.6 6.2 1.4 6.5 6.0 8.9 8.8
0.2 0.3 0.3 0.3 0.5 0.4 0.3
162 8.7** 136 6.7 Ill 1.7 111 7.0* 91 6.8** 141 10.21; 63 9.1+
0.5 0.6 0.4 0.5 0.5 0.5 0.6
2 2 3 2 2
I
10.0
~
Mandible II 12 C PI P2 Ml M2
5
6 6 6 5 5 2
4.8 5.4 6.3 6.6 6.3 9.9 9.6
0.4 0.2 0.2 0.3 0.3 0.4 0.2
154 5.5** 168 6.0** 144 6.7+* 148 7.0 114 7.1** 112 11.0** 67 10.4
0.3 0.3 0.3 0.5 0.4 0.6 0.6
3 3 3 3 2
5.4 5.9* 6.7* 1.2* 7.2*
0.2 0.3 0.1 0.2 0.2
8.4** 6.6 7.5 7.1* 7.0
SD 0.2 0.6 0.2 0.1 0.4
‘p < 0.05; **p < 0.01.
average reduction in tooth size of 46, X, i (Xq) females compared to population controls was 9.2% for the mesiodistal dimensions and 7.6% for labiolingual dimensions. Comparisons of 46, X, i (Xq) with 45, X females are made in Table 3. Earlier studies have shown average reductions in mesiodistal and labiolingual crown dimensions of 45, X females compared with normal women of 5.6 and 3.1%, respectively. Our results show that women with the isochromosome have even smaller teeth than the 45, X females, with one exception, the mesiodistal diameter of the mandibular second molar. Thus, a trend in tooth size has been noted between the groups, being, from largest to smallest: normal women; 45, X; 46, X, i (Xq).
DISCUSSION
Studies of dental crown size in individuals with X chromosome aneuploidies have demonstrated a ‘dosage effect’, with tooth size increasing regularly as the number of X chromosomes increases (Townsend et al., 1988). Similar results have also been noted for other body features, including finger-ridge counts, birth weight, stature and palate shape (Barlow, 1973; Gorlin, Redman and Shapiro, 1965). Radiographic analyses have further demonstrated that extra X chromosomes lead primarily to increases in enamel thickness of tooth crowns, although the effect of each additional X chromosome relatively diminishes (Alvesalo et al., 1987).
Table 2. Labiolingual tooth dimensions (mm) in Finnish 46, X, i (Xq) females, population control females and female relatives Normal females 46, X, i (Xq) females
(population) _
Tooth
N
Mean
SD
N
Maxilla II I2 C PI P2 Ml M2
5 3 6 5 5 6 3
6.6 5.9 7.8 8.7 9.0 10.6 10.1
0.4 0.2 0.5 0.5 0.4 0.3 0.1
Mandible I1 I2 C Pl P2 Ml M2
5
4 6 6 6 4 2
5.5 5.7 7.0 7.5 7.9 9.5 8.8
0.3 0.4 0.6 0.8 0.6 0.4 0.1
Mean
SD
N
Mean
SD
91 70 94 121 106 147 70
7.3** 6.4 8.2 9.2” 9.3 11.3** 11.1**
0.5 0.6 0.5 0.5 0.5 0.6 0.7
2 2 3 3 3 2 2
7.1 6.5 8.2 9.3 9.2 11.1 11.1**
0.6 0.6 0.5 0.4 0.7 0.1 0.1
85 88 108 144 122 127 64
6.0** 6.4** 7.51 7.8 8.4; 10.7** 10.3**
0.4 0.4 0.5 0.5 0.5 0.5 0.6
I I
6.1 6.5 7.7 7.7 8.5 10.7 10.2
0.4 0.1 0.3
‘p < 0.05; **p < 0.01. 46, X. i (Xq) females
Normal females (relatives)
versus each control
group.
3 3 3
1 I
46, X, i (Xq) Tooth size
413
Table 3. Tooth sizes of 46, X, i (Xq) females and 45, X females Labiolingual dimensions (mm)
Mesiodistal dimensions (mm)
_
46, X, i o(q)
46, X, i o(q)
45, x
Tooth
N
Mean
SD
N
Maxilla 11 12 C Pl P2 Ml M2
6 5 6 5 5 5 3
1.6 6.2 7.4 6.5 6.0 8.9 8.8
0.2 0.3 0.3 0.3 0.5 0.4 0.3
87 81 84 19 14 70 42
Mandible 11 I2 C Pl P2 Ml M2
5 6 6 6 5 5 2
4.8 5.4 6.3 6.6 6.3 9.9 9.6
0.4 0.2 0.2 0.3 0.3 0.4 0.2
86 87 89 88 78 62 35
Mean
45, x
SD
N
Mean
SD
N
Mean
SD
8.1” 6.5 7.6 6.7 6.3 9.4** 9.3
0.5 0.5 0.4 0.4 0.4 0.4 0.5
5 3 6 5 5 6 3
6.6 5.9 7.8 8.7 9.0 10.6
0.4 0.2 0.5 0.5 0.4 0.3
75 61 83 81 83 80
6.9 6.3 8.1 9.0 9.2 10.9
0.5 0.5 0.5 0.5 0.5 0.5
IO.1
0.1
50
10.8** 0.7
5.1* 5.6 6.5 6.9 6.7* 10.0 9.4
0.3 0.4 0.4 0.4 0.4 0.6 0.5
5 4 6 6 6 4 2
5.5 5.7 7.0 1.5 7.9 9.5 8.8
0.3 0.4 0.6 0.8 0.6 0.4 0.1
7s 79 87 84 82 61 42
5.8 6.0 7.3 7.8 8.2 9.9 9.6.
0.4 0.5 0.5 0.5 0.5 0.5 0.5
*p < 0.05; **p < 0.01. 46, X, i (Xq) females versus 45, X females. Data for 45, X females from Varrela et al. (1988). It was originally thought that only one X chromosome was active within each human cell, making it difficult to explain in genetic terms the phenotypic abnormalities observed in individuals with extra or missing X chromosomes. However, it is now apparent that part(s) of the supposedly ‘inactive’ X chromosome remain active throughout life, even though the genes in these active regions have less effect than the same genes on the active X chromosome (Lyon, 1983). An active region has now been localized to the tip of the short arm, Xp (Therman, 1983). In our study, women with an isochromosome for the long arm of the X chromosome had smaller teeth than normal, providing indirect evidence that X chromosome gene(s) for tooth crown growth (and perhaps for other somatic quantitative features) are most probably located on the short arm. Further confirmation that gene(s) promoting growth of other physical features apart from tooth size may be located on the short arm of the X chromosome is provided by Goldman et al. (1982), who examined people with partial deletions of the X chromosome and found that short-arm deletions appeared to have a greater effect on stature than deletions of the long arm. Several others, including Jacobs et al. (1961), Ferguson-Smith (1965) and Ballabio et al. (1989), have also suggested that genes controlling physical features, e.g. stature, are likely to be on the short arm of the X chromosome. Whether the gene(s) for tooth growth and statural growth are the same cannot be distinguished in this type of study. However, it is possible that there are pleiotropic effects operating. It appears that in individuals with sex-chromosome mosaicism, selection occurs during development to the advantage of the normal cell population (Neilson, 1976). For example, normalization of growth by 46, XX cells is likely to account for the range of Turner stigmata observed in 45, X/46, XX mosaics (Sarkar and Marimathu, 1983). In a similar fashion,
the normal and abnormal chromosomes in women with an i (Xq) chromosome are likely to be initially alternately inactivated, although the genetically better-balanced cell line seems to eventually take over (Therman et al., 1980; Therman, 1983). The reduction in tooth size in 46, X, i (Xq) compared with 45, X females is, therefore, probably at least in part due to a retarding effect exerted during development by cells where the normal X chromosome was inactive and in which there was no functioning Xp. The radiographic assessments have shown a definite reduction of enamel thickness of maxillary anterior teeth in 45, X females, obvious reduction of enamel in 46, X, i (Xq) females, and suggest also less thick dentine in 46, X, i (Xq) than in normal women (Alvesalo and Tammisalo, 1981: Alvesalo et al., 1981). Acknowledgement-This Academy of Finland Foundation.
study was supported by the and the University of Turku
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