Am J Hum Genet 28:253-256, 1976
A Third Type of Serum Cholinesterase Deficiency in Eskimos EDWARD M. SCOTT1 AND RITA C. WRIGHT
Two types of deficiency of serum cholinesterase due to silent genes have been reported in Eskimos from western Alaska [1]. In a population of about 5,000, 39 persons completely lack the enzyme (E1S or 0 type deficiency) and 24 have 2%o10%o of the normal activity (E1T or T type deficiency). The two types of deficiency are probably allelic [2]. In E1S serum, no cholinesterase activity whatever can be shown by hydrolysis of benzoylcholine [3 ] or after electrophoresis. The E1T type of deficiency has been reported only in Eskimos [2, 4, 5]. The amount of activity demonstrable with benzoylcholine has varied from 4 to 20 U; only three persons in 24 have had more than 8 U. After electrophoresis, the enzyme is found as a weak band located midway to the band of the usual enzyme [6]. This type of deficiency is due to the EjSE1T or ETE1T genotypes, which are not phenotypically distinguishable. Seven persons with the genotype EjsElT [2] had an average of 6 U of cholinesterase activity. A third type of deficiency, distinguishable from the E1T type by electrophoresis, is described here. METHODS
Cholinesterase activity was determined by the rate of hydrolysis of benzoylcholine and is expressed here as micromoles of acetylcholine hydrolyzed per hour/ml serum at 370 C [7]. Electrophoresis was in starch gel at pH 5.3, and a-naphthyl acetate or butyrylthiocholine were substrates for the staining reaction [6]. RESULTS AND DISCUSSION
The new type of deficiency was found in an Eskimo boy whose family is shown in figure 1. When serum from this child was first tested, it was thought to have a normal enzyme of low activity [6]. The new variant is distinguished, however, by an electrophoretic mobility slightly greater than that of the usual E1U enzyme and definitely faster than that of the E1T enzyme [6]. When sera from the boy's mother and other relatives were tested, several of them were also found to have a rapidly migrating component E1R (fig. 2); the existence of a hereditary variant became evident. The boy appeared to inherit the new variant gene from his mother and a Received July 19, 1975; revised November 24, 1975. 1 Both authors: Alaska Activities, Center for Disease Control, 225 Eagle Street, Anchorage, Alaska 99501. © 1976 by the American Society of Human Genetics. All rights reserved.
253
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SCOTT AND WRIGHT
t[^l 1
2
3
4
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182
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_
+
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_
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FIG. 1.-Family with new type of cholinesterase deficiency. J = homozygote for usual enzyme; O, O = heterozygote for deficiency; * = homozygote for deficiency. Age in years is above the symbols; units of cholinesterase activity, below. + or - indicates presence or absence of a fast cholinesterase component after electrophoresis.
second deficient gene from his father. His sister (II-1) also inherited the new gene, while his brother (II-2) had the paternal deficient gene. Three samples of serum collected from the boy over a 6 year period had 16-23 U of activity. Part of this activity could be due to the presence of the E1T enzyme which would be masked
FIG. 2.-Serum cholinesterase after electrophoresis. 0 is the origin. Sample numbers are taken from figure 1.
SERUM CHOLINESTERASE DEFICIENCY
255
in the deficient child as well as in his relatives; thus his father's genotype could be either E1UElT or EluEls, and he could be E1RE T or E1REls. Families with E1S and E1T deficiency also live in the village where the boy resides. Using az-naphthyl acetate for color development after electrophoresis, the new variant gave an unusually strong reaction. Hydrolysis of a-naphthyl acetate by serum of the proband was 2.5 times as rapid as expected from the rate of benzoylcholine hydrolysis when compared to the normal enzyme. The variant is not a nonspecific esterase, since color development with butyrylthiocholine [6] gave a band at the same location as with az-naphthyl acetate, and inhibition by dibucaine and fluoride was within the range found for the usual enzyme. The E1U-R phenotype in this family also showed enhanced activity with at-naphthyl acetate but, as expected, the increase was small (10 ± 4%). The variant enzyme and cholinesterase deficiency segregate together in the mother's sister and the children of her second marriage (fig. 1). The probability is one in 32 that the results in these five children could arise by chance alone, and thus the variant and deficiency are probably allelic. The small difference in mobility between the variant and the usual enzyme was evident only by comparing mobility of adjacent samples. While demonstrable and reproducible in this family, the difference did not appear to be great enough to make screening for the variant practical. In this population the maximum likelihood estimates of the gene frequencies of the three forms of deficiency are E18, .096; E1T, .030; and the new variant E1R, .002 [2]. Although Eskimos lacking the usual enzyme react abnormally to succinylcholine administration, they have no other known disability, lead normal lives, and have no obvious advantage. While heterogeneity of cholinesterase deficiency might be expected [8], a reason for the occurrence of three variants in a small population of Eskimos is not evident. SUMMARY
A new type of serum cholinesterase deficiency with less than 10% of the normal activity was found in an Alaskan Eskimo. The new type of deficiency appeared to be allelic with two types previously described in this population. REFERENCES 1. GUTSCHE BB, SCOTT EM, WRIGHT RC: Hereditary deficiency of pseudocholinesterase in Eskimos. Nature 215:322-323, 1967 2. SCOTT EM: Inheritance of two types of deficiency of human serum cholinesterase. Ann Hum Genet 37:139-143, 1973 3. HODGKIN WE, GIBLETT ER, LEVINE H, BAUER W, MOTULSKY AG: Complete pseudocholinesterase deficiency: genetic and immunologic characterization. J Clin Invest 44: 486-493, 1965 4. RuBINSTEIN HM, DIETz AA, HODGES LK, LUBRANO T, CZEBOTAR V: Silent cholinesterase gene: variations in the properties of serum enzyme in apparent homozygotes. J Clin Invest 49:479-486, 1970 5. SCOTT EM: Properties of the trace enzyme in human serum cholinesterase deficiency. Biochem Biophys Res Commun 38:902-906, 1970
256
SCOTT AND WRIGHT
6. Scor-r EM, WEAVER DD: Electrophoresis in starch gel of human serum cholinesterase. Biockem Med 4:349-352, 1970 7. KALOW W, LINDSAY HA: A comparison of optical and manometric methods for the assay of human serum cholinesterase. Can J Biochem Physiol 33:568-574, 1955 8. ALTLAND K, GOEDDE HW: Heterogeneity in the silent gene phenotype of pseudocholinesterase of human serum. Biochem Genet 4:321-338, 1970
Birth Defects Institute Symposium The New York State Health Department is sponsoring the Seventh Birth Defects Institute Symposium on "Genetic Mechanisms of Sexual Development" to be held November 8-9, 1976 in Albany, New York. For further information contact Dr. H. Lawrence Vallet, Symposium, Room 572, Empire State Plaza Tower Building, Albany, New York 12237.
National Foundation-March of Dimes Research Proposals The National Foundation-March of Dimes will entertain a limited number of research proposals for the support of basic and clinical research in birth defects. The National Foundation defines a birth defect as an abnormality of structure, function, or metabolism, whether genetically determined or a result of environmental interference during embryonic or fetal life. Requests dealing with the structure and function of chromosomes, their subunites, genes, supporting structures, and repressor substances are encouraged. For details contact Vice President for Research, The National Foundation-March of Dimes, 1275 Mamaroneck Avenue, White Plains, New York 10605.
A Third Type of Serum Cholinesterase Deficiency in Eskimos EDWARD M. SCOTT1 AND RITA C. WRIGHT
Two types of deficiency of serum cholinesterase due to silent genes have been reported in Eskimos from western Alaska [1]. In a population of about 5,000, 39 persons completely lack the enzyme (E1S or 0 type deficiency) and 24 have 2%o10%o of the normal activity (E1T or T type deficiency). The two types of deficiency are probably allelic [2]. In E1S serum, no cholinesterase activity whatever can be shown by hydrolysis of benzoylcholine [3 ] or after electrophoresis. The E1T type of deficiency has been reported only in Eskimos [2, 4, 5]. The amount of activity demonstrable with benzoylcholine has varied from 4 to 20 U; only three persons in 24 have had more than 8 U. After electrophoresis, the enzyme is found as a weak band located midway to the band of the usual enzyme [6]. This type of deficiency is due to the EjSE1T or ETE1T genotypes, which are not phenotypically distinguishable. Seven persons with the genotype EjsElT [2] had an average of 6 U of cholinesterase activity. A third type of deficiency, distinguishable from the E1T type by electrophoresis, is described here. METHODS
Cholinesterase activity was determined by the rate of hydrolysis of benzoylcholine and is expressed here as micromoles of acetylcholine hydrolyzed per hour/ml serum at 370 C [7]. Electrophoresis was in starch gel at pH 5.3, and a-naphthyl acetate or butyrylthiocholine were substrates for the staining reaction [6]. RESULTS AND DISCUSSION
The new type of deficiency was found in an Eskimo boy whose family is shown in figure 1. When serum from this child was first tested, it was thought to have a normal enzyme of low activity [6]. The new variant is distinguished, however, by an electrophoretic mobility slightly greater than that of the usual E1U enzyme and definitely faster than that of the E1T enzyme [6]. When sera from the boy's mother and other relatives were tested, several of them were also found to have a rapidly migrating component E1R (fig. 2); the existence of a hereditary variant became evident. The boy appeared to inherit the new variant gene from his mother and a Received July 19, 1975; revised November 24, 1975. 1 Both authors: Alaska Activities, Center for Disease Control, 225 Eagle Street, Anchorage, Alaska 99501. © 1976 by the American Society of Human Genetics. All rights reserved.
253
254
II
SCOTT AND WRIGHT
t[^l 1
2
3
4
133
198
23
182
295
167
201
+
203
_
+
+
_
+
+
+
8
6
FIG. 1.-Family with new type of cholinesterase deficiency. J = homozygote for usual enzyme; O, O = heterozygote for deficiency; * = homozygote for deficiency. Age in years is above the symbols; units of cholinesterase activity, below. + or - indicates presence or absence of a fast cholinesterase component after electrophoresis.
second deficient gene from his father. His sister (II-1) also inherited the new gene, while his brother (II-2) had the paternal deficient gene. Three samples of serum collected from the boy over a 6 year period had 16-23 U of activity. Part of this activity could be due to the presence of the E1T enzyme which would be masked
FIG. 2.-Serum cholinesterase after electrophoresis. 0 is the origin. Sample numbers are taken from figure 1.
SERUM CHOLINESTERASE DEFICIENCY
255
in the deficient child as well as in his relatives; thus his father's genotype could be either E1UElT or EluEls, and he could be E1RE T or E1REls. Families with E1S and E1T deficiency also live in the village where the boy resides. Using az-naphthyl acetate for color development after electrophoresis, the new variant gave an unusually strong reaction. Hydrolysis of a-naphthyl acetate by serum of the proband was 2.5 times as rapid as expected from the rate of benzoylcholine hydrolysis when compared to the normal enzyme. The variant is not a nonspecific esterase, since color development with butyrylthiocholine [6] gave a band at the same location as with az-naphthyl acetate, and inhibition by dibucaine and fluoride was within the range found for the usual enzyme. The E1U-R phenotype in this family also showed enhanced activity with at-naphthyl acetate but, as expected, the increase was small (10 ± 4%). The variant enzyme and cholinesterase deficiency segregate together in the mother's sister and the children of her second marriage (fig. 1). The probability is one in 32 that the results in these five children could arise by chance alone, and thus the variant and deficiency are probably allelic. The small difference in mobility between the variant and the usual enzyme was evident only by comparing mobility of adjacent samples. While demonstrable and reproducible in this family, the difference did not appear to be great enough to make screening for the variant practical. In this population the maximum likelihood estimates of the gene frequencies of the three forms of deficiency are E18, .096; E1T, .030; and the new variant E1R, .002 [2]. Although Eskimos lacking the usual enzyme react abnormally to succinylcholine administration, they have no other known disability, lead normal lives, and have no obvious advantage. While heterogeneity of cholinesterase deficiency might be expected [8], a reason for the occurrence of three variants in a small population of Eskimos is not evident. SUMMARY
A new type of serum cholinesterase deficiency with less than 10% of the normal activity was found in an Alaskan Eskimo. The new type of deficiency appeared to be allelic with two types previously described in this population. REFERENCES 1. GUTSCHE BB, SCOTT EM, WRIGHT RC: Hereditary deficiency of pseudocholinesterase in Eskimos. Nature 215:322-323, 1967 2. SCOTT EM: Inheritance of two types of deficiency of human serum cholinesterase. Ann Hum Genet 37:139-143, 1973 3. HODGKIN WE, GIBLETT ER, LEVINE H, BAUER W, MOTULSKY AG: Complete pseudocholinesterase deficiency: genetic and immunologic characterization. J Clin Invest 44: 486-493, 1965 4. RuBINSTEIN HM, DIETz AA, HODGES LK, LUBRANO T, CZEBOTAR V: Silent cholinesterase gene: variations in the properties of serum enzyme in apparent homozygotes. J Clin Invest 49:479-486, 1970 5. SCOTT EM: Properties of the trace enzyme in human serum cholinesterase deficiency. Biochem Biophys Res Commun 38:902-906, 1970
256
SCOTT AND WRIGHT
6. Scor-r EM, WEAVER DD: Electrophoresis in starch gel of human serum cholinesterase. Biockem Med 4:349-352, 1970 7. KALOW W, LINDSAY HA: A comparison of optical and manometric methods for the assay of human serum cholinesterase. Can J Biochem Physiol 33:568-574, 1955 8. ALTLAND K, GOEDDE HW: Heterogeneity in the silent gene phenotype of pseudocholinesterase of human serum. Biochem Genet 4:321-338, 1970
Birth Defects Institute Symposium The New York State Health Department is sponsoring the Seventh Birth Defects Institute Symposium on "Genetic Mechanisms of Sexual Development" to be held November 8-9, 1976 in Albany, New York. For further information contact Dr. H. Lawrence Vallet, Symposium, Room 572, Empire State Plaza Tower Building, Albany, New York 12237.
National Foundation-March of Dimes Research Proposals The National Foundation-March of Dimes will entertain a limited number of research proposals for the support of basic and clinical research in birth defects. The National Foundation defines a birth defect as an abnormality of structure, function, or metabolism, whether genetically determined or a result of environmental interference during embryonic or fetal life. Requests dealing with the structure and function of chromosomes, their subunites, genes, supporting structures, and repressor substances are encouraged. For details contact Vice President for Research, The National Foundation-March of Dimes, 1275 Mamaroneck Avenue, White Plains, New York 10605.
