H um . H ercd. 2.5. 172 176 (1975)
Phosphoglucomutase Phenotypes and Prenatal Selection Studies of Spontaneous and Induced Abortions'
G. Beckman and L. Beckman Department of Medical Genetics, University of Umca, Sweden
Key Words. Phosphoglucomutase phenotype ■Spontaneous abortion Abstract. The PGM, and PG M:> phenotypes were examined in extracts of chorionic tissue from 97 spontaneous and 266 induced abortions. Contamination by maternal tissue or blood cells was shown to be insignificant. A positive association was found between the PGMj and PGM.' genes. No significant differences in phenotype distributions were found between the population of spontaneously aborted fetuses and the normal fetal or adult populations. Hence it was concluded that there is no evidence so far for prenatal selection operating in the PGM, and PGM:1 polymorphisms.
In a previous investigation [Beckman et al.. 1972] we have studied the placental alkaline phosphatase phenotypes in chorionic tissue from spon taneous and induced abortions. A statistically significant overrepresentalion of phenotypes having the F 1 variant was found. In this paper we report the results of a study of phosphoglucomutase ( PGM : PGM | and PGM.,) phenotypes in the same series of abortions. The human PGM isozymes, which can be detected by electrophoresis, are con trolled by three distinct autosomal loci: PGM,. PGM2and PGM3 [Spencer et a i. 1964; H opkinson and H arris. 1965. 1966. 1968], The PGM, and PGM., loci are polymorphic but at the PGM., locus only rare variant alleles have been found. The PGM, isozymes are readily detectable in most tissues and cells including red cells while the PGM., isozymes are usually not de tectable in red cells. Placental tissue, however, has been found to have readily detectable PGM., isozymes.
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1 This investigation was supported by the Swedish Medical Research Council (project No. 05X-2725) and the J.C. Kempe Foundation.
Hi ckmav Bickman
17.?
Material and Methods The placental tissue, and in very early abortions the corresponding chorionic material, was prepared and homogenized according to the procedure described in a previous publi cation | Bickman el at., 1972] except that butanol extraction was not applied. The series of induced and spontaneous abortions examined were essentially the same as in the pre vious study. The present series includes some additional samples. Electrophoresis and staining were done according to S pencer et at. [1964]. The per sons who classified the electrophoretic patterns did not know whether the samples were derived from spontaneous or induced abortions.
The PGM, and PGM., isozymes were readily detectable in a high propor tion of the cell extracts. Out of 274 individual samples from induced abor tions detectable patterns in both systems were found in 266 samples. Among spontaneous abortions 97 out of 105 samples examined had detectable patterns. Thus there was no significant difference between induced and spontaneous abortions with respect to the detectability of PGM phenotypes. Table I shows the PGM, phenotypes in spontaneously aborted fetuses, apparently normal fetuses (induced abortions) and in the adult population of Vasterbotlen county, where the university hospital of Umeii is located. The determinations of the PGM, phenotypes in the adult populations were done on lyzates of red cells. The phenotype distributions in the three dilferent population samples showed a close agreement with the expected ones, assuming a Hardy-Weinberg equilibrium. The frequency of the PGMj gene was very similar in the three population samples. In table II the distributions of PGM., phenotypes among aborted fetuses have been compared with those in a series of English placentae, which represents the phenotype distribution in the birth population. The PGM., gene frequencies in aborted fetuses and in the birth population were very similar and varied between 74 and 78%. Lamm [1971] found a PGM$ fre quency of 0.745 among adult Danes. In the induced abortions there was a highly significant deviation between observed and expected numbers, assum ing a Hardy-Weinberg equilibrium. There was en excess of heterozygotes and a deficit of homozygotes. Table III shows the relationship between PGM, and PGM., phenotypes. Spontaneous and induced abortions were added together, since there was
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
Results
174
Beckman/ Bi ckman
Table I. PGM, phenotypes in chorionic tissue from aborted fetuses and in the adult population 1
2
2-1
Xi (1 d.f.)
PGM] gene
Number examined
Spontaneous abortions obs. 55 55.7 exp.
37 35.6
5 5.7
0.15
0.757
97
huhteetl abortions obs. 147 exp. 149.6
105 99.8
14 16.6
0.72
0.750
266
Allah population ( V'iisterbotten) obs. 1.172 699 1,170.9 701.1 exp.
106 104.9
0.02
0.770
1,977
obs. = Observed numbers; exp. = expected numbers assuming a Hardy-Weinberg equilibrium.
Table II. PGM;I phenotypes in chorionic tissue from aborted fetuses and in the English birth population (Hopkinson and Harris, 1968] 1 Spontaneous abortions obs. 59 exp. 58.7
2-1
(i d.f.)
PGMJ gene
2
Number examined
33 33.5
5 4.8
0.02
0.778
97
113 91.3
2 12.9
15.09
0.780
266
English birth population obs. 315 238 exp. 322.7 222.1
30 38.2
3.07
0.744
583
Inilnced abortions obs. 151 exp. 161.8
obs. - Observed numbers; exp. = expected numbers assuming a Hardy-Weinberg equilibrium.
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
no difference between these two groups. There was a tendency towards an association between the PGM] and PGM] genes. When the infrequent phe notypes (PGM,2 and PGM.,2) were pooled together with the heterozygotes and the data were tested as a 2 2 contingency table was found to be 4.51
175
Phosphoglucom utase Phenotypes and Prenatal Selection
Table III. Distributions of PGM, and PGM;, phenotypes in chorionic tissue front 363 aborted fetuses (spontaneous and induced abortions) PGM, phenotype PGM,,phenotype I 1 2 1 2 Total
127 (116.9) 74 (82.1) 9 (11.0) 210(210.0)
Total 2-1
2
72 (81.2) 64 (57.1) 10 (7.6) 146 (145.9)
3 (3.9) 4 (2.7) 0 (0.4) 7 (7.0)
202 (202.0) 142 (141.9) 19 (19.0) 363 (362.9)
Numbers in parantheses are those expected in absence of an association between the PGM, and PGMlt phenotypes.
(p
0.05). In the previous studies by H opkinson and H arris [l%8] and Lamm [1971] no significant associations were found between PGM, and
PGM., systems. The gestation length varied between 5 and 22 weeks. There was no cor relation between PGM phenotypes and gestation length. In about one half of the tissue samples it was possible to detect placental alkaline phosphatase phenotypes [cf. B bckman et a i, 1972]. There was no significant difference in the distributions of PGM phenotypes between the samples with detectable placental alkaline phosphatase patterns and those without detectable pat terns.
The PGM, and PGM., phenotypes were readily distinguishable in a very high proportion of the tissue specimens, irrespective of gestation length in contrast to placental alkaline phosphatase, where only about 50% of the samples had detectable patterns and where the detectability was clearly dependent on the week of gestation. A question of importance is, of course, to what extent contamination of maternal tissue or lyzed blood cells may occur. Such contamination is very unlikely for the following reasons: presence ol maternal tissue is unlikely since the chorionic material was collected manually with tweezers and other kinds of tissue were removed. Maternal red blood cells may occur, but can only interfere with the PGM, system. A mixture of maternal and fetal cells or cell products will lead to an overrepresentation of heterozygotes in both systems since I x 2 -l, 2-1 x I. 2*2-1 and 2-1 *2 mother-child combina
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
Discussion
17(.
Hickman Hickman
tions may all be read as heierozygotes. In sucli heterozygotes the relative strengths of the isozyme bands are expected to deviate from the normal. Heterozygotes where the PGM] and PGM' components are stronger arc expected to predominante. In this study no such unusual heterozygotes were found. Furthermore no consistent excess of heierozygotes was found. An excess of heterozygotes was found only for the PGM., system and only in the induced abortions. In the PGM, system, where contamination of mater nal blood might interfere, no distortions of the Hardy-Weinberg distribu tions were noted. Thus we may conclude that the PGM types recorded are with a high degree of certainty representing the fetus. In the previous studies by H opkinson and H arris [1968] and Lamm [1971] no significant associations were found between the PGM, and PGM., systems and the two loci arc not closely linked [Lamm. 1971], The (weak) association found in this study may be due to chance. In the PGM., system there was a marked deviation from the Hardy-Weinberg equilibrium among induced abortions, for which we have no explanation. Also in the material of English placentae examined by H opkinson and H arris [1968] there was a tendency towards an excess of heierozygotes. Comparing the gene fre quencies in both systems we can conclude that there is no difference between the fetal and adult populations. Since the phenotype distributions in the series of spontaneously aborted fetuses showed no statistically significant deviations we may conclude that there is no evidence so far for prenatal selection in the PGM, and PGM3 polymorphisms.
References Beckman, G .; Beckman. L.. and M agnusson, S. S.: Placental alkaline phosphatase
phenotypes and pre-natal selection. Hunt. Hered. 22: 473 (1972). Hopkinson , D. A. and H arris, H.: Evidence for a second 'structural' locus determining
human phosphoglucomulase. Nature, Lond. 208: 410 (1965). Hopkinson, D. A. and H arris, II.: Rare phosphoglueomutasc phenotypes. Ann. hum.
Genet. JO: 167 (1966). Hopkinson , D. A. and H arris, H.: A third phosphoglucomulase locus in man. Ann. hum.
Genet. 31: 359 (1968). Lamm. L. U . : Genetic studies of phosphoglucomulase (PG M) in man with special reference
to PGM:l; thesis Aarhus (1971). S pencer, N.: Hopkinson , D. A., and H arris, H.: Phosphoglucomulase polymorphism
in man. Nature, Lond. 204 : 742 (1964).
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
Dr. G . Beckman, Department of Medical Genetics, University of Umca, Unwa (Sweden)
Phosphoglucomutase Phenotypes and Prenatal Selection Studies of Spontaneous and Induced Abortions'
G. Beckman and L. Beckman Department of Medical Genetics, University of Umca, Sweden
Key Words. Phosphoglucomutase phenotype ■Spontaneous abortion Abstract. The PGM, and PG M:> phenotypes were examined in extracts of chorionic tissue from 97 spontaneous and 266 induced abortions. Contamination by maternal tissue or blood cells was shown to be insignificant. A positive association was found between the PGMj and PGM.' genes. No significant differences in phenotype distributions were found between the population of spontaneously aborted fetuses and the normal fetal or adult populations. Hence it was concluded that there is no evidence so far for prenatal selection operating in the PGM, and PGM:1 polymorphisms.
In a previous investigation [Beckman et al.. 1972] we have studied the placental alkaline phosphatase phenotypes in chorionic tissue from spon taneous and induced abortions. A statistically significant overrepresentalion of phenotypes having the F 1 variant was found. In this paper we report the results of a study of phosphoglucomutase ( PGM : PGM | and PGM.,) phenotypes in the same series of abortions. The human PGM isozymes, which can be detected by electrophoresis, are con trolled by three distinct autosomal loci: PGM,. PGM2and PGM3 [Spencer et a i. 1964; H opkinson and H arris. 1965. 1966. 1968], The PGM, and PGM., loci are polymorphic but at the PGM., locus only rare variant alleles have been found. The PGM, isozymes are readily detectable in most tissues and cells including red cells while the PGM., isozymes are usually not de tectable in red cells. Placental tissue, however, has been found to have readily detectable PGM., isozymes.
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
1 This investigation was supported by the Swedish Medical Research Council (project No. 05X-2725) and the J.C. Kempe Foundation.
Hi ckmav Bickman
17.?
Material and Methods The placental tissue, and in very early abortions the corresponding chorionic material, was prepared and homogenized according to the procedure described in a previous publi cation | Bickman el at., 1972] except that butanol extraction was not applied. The series of induced and spontaneous abortions examined were essentially the same as in the pre vious study. The present series includes some additional samples. Electrophoresis and staining were done according to S pencer et at. [1964]. The per sons who classified the electrophoretic patterns did not know whether the samples were derived from spontaneous or induced abortions.
The PGM, and PGM., isozymes were readily detectable in a high propor tion of the cell extracts. Out of 274 individual samples from induced abor tions detectable patterns in both systems were found in 266 samples. Among spontaneous abortions 97 out of 105 samples examined had detectable patterns. Thus there was no significant difference between induced and spontaneous abortions with respect to the detectability of PGM phenotypes. Table I shows the PGM, phenotypes in spontaneously aborted fetuses, apparently normal fetuses (induced abortions) and in the adult population of Vasterbotlen county, where the university hospital of Umeii is located. The determinations of the PGM, phenotypes in the adult populations were done on lyzates of red cells. The phenotype distributions in the three dilferent population samples showed a close agreement with the expected ones, assuming a Hardy-Weinberg equilibrium. The frequency of the PGMj gene was very similar in the three population samples. In table II the distributions of PGM., phenotypes among aborted fetuses have been compared with those in a series of English placentae, which represents the phenotype distribution in the birth population. The PGM., gene frequencies in aborted fetuses and in the birth population were very similar and varied between 74 and 78%. Lamm [1971] found a PGM$ fre quency of 0.745 among adult Danes. In the induced abortions there was a highly significant deviation between observed and expected numbers, assum ing a Hardy-Weinberg equilibrium. There was en excess of heterozygotes and a deficit of homozygotes. Table III shows the relationship between PGM, and PGM., phenotypes. Spontaneous and induced abortions were added together, since there was
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
Results
174
Beckman/ Bi ckman
Table I. PGM, phenotypes in chorionic tissue from aborted fetuses and in the adult population 1
2
2-1
Xi (1 d.f.)
PGM] gene
Number examined
Spontaneous abortions obs. 55 55.7 exp.
37 35.6
5 5.7
0.15
0.757
97
huhteetl abortions obs. 147 exp. 149.6
105 99.8
14 16.6
0.72
0.750
266
Allah population ( V'iisterbotten) obs. 1.172 699 1,170.9 701.1 exp.
106 104.9
0.02
0.770
1,977
obs. = Observed numbers; exp. = expected numbers assuming a Hardy-Weinberg equilibrium.
Table II. PGM;I phenotypes in chorionic tissue from aborted fetuses and in the English birth population (Hopkinson and Harris, 1968] 1 Spontaneous abortions obs. 59 exp. 58.7
2-1
(i d.f.)
PGMJ gene
2
Number examined
33 33.5
5 4.8
0.02
0.778
97
113 91.3
2 12.9
15.09
0.780
266
English birth population obs. 315 238 exp. 322.7 222.1
30 38.2
3.07
0.744
583
Inilnced abortions obs. 151 exp. 161.8
obs. - Observed numbers; exp. = expected numbers assuming a Hardy-Weinberg equilibrium.
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
no difference between these two groups. There was a tendency towards an association between the PGM] and PGM] genes. When the infrequent phe notypes (PGM,2 and PGM.,2) were pooled together with the heterozygotes and the data were tested as a 2 2 contingency table was found to be 4.51
175
Phosphoglucom utase Phenotypes and Prenatal Selection
Table III. Distributions of PGM, and PGM;, phenotypes in chorionic tissue front 363 aborted fetuses (spontaneous and induced abortions) PGM, phenotype PGM,,phenotype I 1 2 1 2 Total
127 (116.9) 74 (82.1) 9 (11.0) 210(210.0)
Total 2-1
2
72 (81.2) 64 (57.1) 10 (7.6) 146 (145.9)
3 (3.9) 4 (2.7) 0 (0.4) 7 (7.0)
202 (202.0) 142 (141.9) 19 (19.0) 363 (362.9)
Numbers in parantheses are those expected in absence of an association between the PGM, and PGMlt phenotypes.
(p
0.05). In the previous studies by H opkinson and H arris [l%8] and Lamm [1971] no significant associations were found between PGM, and
PGM., systems. The gestation length varied between 5 and 22 weeks. There was no cor relation between PGM phenotypes and gestation length. In about one half of the tissue samples it was possible to detect placental alkaline phosphatase phenotypes [cf. B bckman et a i, 1972]. There was no significant difference in the distributions of PGM phenotypes between the samples with detectable placental alkaline phosphatase patterns and those without detectable pat terns.
The PGM, and PGM., phenotypes were readily distinguishable in a very high proportion of the tissue specimens, irrespective of gestation length in contrast to placental alkaline phosphatase, where only about 50% of the samples had detectable patterns and where the detectability was clearly dependent on the week of gestation. A question of importance is, of course, to what extent contamination of maternal tissue or lyzed blood cells may occur. Such contamination is very unlikely for the following reasons: presence ol maternal tissue is unlikely since the chorionic material was collected manually with tweezers and other kinds of tissue were removed. Maternal red blood cells may occur, but can only interfere with the PGM, system. A mixture of maternal and fetal cells or cell products will lead to an overrepresentation of heterozygotes in both systems since I x 2 -l, 2-1 x I. 2*2-1 and 2-1 *2 mother-child combina
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
Discussion
17(.
Hickman Hickman
tions may all be read as heierozygotes. In sucli heterozygotes the relative strengths of the isozyme bands are expected to deviate from the normal. Heterozygotes where the PGM] and PGM' components are stronger arc expected to predominante. In this study no such unusual heterozygotes were found. Furthermore no consistent excess of heierozygotes was found. An excess of heterozygotes was found only for the PGM., system and only in the induced abortions. In the PGM, system, where contamination of mater nal blood might interfere, no distortions of the Hardy-Weinberg distribu tions were noted. Thus we may conclude that the PGM types recorded are with a high degree of certainty representing the fetus. In the previous studies by H opkinson and H arris [1968] and Lamm [1971] no significant associations were found between the PGM, and PGM., systems and the two loci arc not closely linked [Lamm. 1971], The (weak) association found in this study may be due to chance. In the PGM., system there was a marked deviation from the Hardy-Weinberg equilibrium among induced abortions, for which we have no explanation. Also in the material of English placentae examined by H opkinson and H arris [1968] there was a tendency towards an excess of heierozygotes. Comparing the gene fre quencies in both systems we can conclude that there is no difference between the fetal and adult populations. Since the phenotype distributions in the series of spontaneously aborted fetuses showed no statistically significant deviations we may conclude that there is no evidence so far for prenatal selection in the PGM, and PGM3 polymorphisms.
References Beckman, G .; Beckman. L.. and M agnusson, S. S.: Placental alkaline phosphatase
phenotypes and pre-natal selection. Hunt. Hered. 22: 473 (1972). Hopkinson , D. A. and H arris, H.: Evidence for a second 'structural' locus determining
human phosphoglucomulase. Nature, Lond. 208: 410 (1965). Hopkinson, D. A. and H arris, II.: Rare phosphoglueomutasc phenotypes. Ann. hum.
Genet. JO: 167 (1966). Hopkinson , D. A. and H arris, H.: A third phosphoglucomulase locus in man. Ann. hum.
Genet. 31: 359 (1968). Lamm. L. U . : Genetic studies of phosphoglucomulase (PG M) in man with special reference
to PGM:l; thesis Aarhus (1971). S pencer, N.: Hopkinson , D. A., and H arris, H.: Phosphoglucomulase polymorphism
in man. Nature, Lond. 204 : 742 (1964).
Downloaded by: Nagoya University 133.6.82.173 - 1/10/2019 10:22:08 PM
Dr. G . Beckman, Department of Medical Genetics, University of Umca, Unwa (Sweden)
