1288 HETEROZYGOTE DISADVANTAGE IN CYSTIC FIBROSIS
SIR,-I have found
that cystic fibrosis (C.F.), which is very in South West Africa, occurs almost exclusively in white Afrikaners,’ probably as a result of inbreeding,2 the drift from the Northern Cape Colony,3 and religious and geographical separation.’ However, I have not found c.F. in the descendants of the Angola Boers, a small proportion (6-7%) of the White population who belong to a small branch of the Dutch Reformed Church. The absence of c.F. may stem from their limited numbers (7000) but I suggest that it may have at least partially a genetic basis. Homozygotes with c.F. are subject to salt-losing crises4 which can be fatal in hot weather and heterozygotes often have an increased concentration of sodium and chlorine ions in their sweat.5 Today’s Angola Boers are descended from those who migrated from Western Transvaal across the Kalahair Desert in the Dorsland (literally "thirstland") treks of 1875-19056 (see map), during which many died of thirst. I suggest that heterozygotes for c.F., because of their impaired electrolyte regulation, died more readily during these treks, thus reducing the frequency of the deleterious c.F. gene among their descendants. I know of several children with c.F. in South Africa whose great-grandparents were Boers born in Western Transvaal who did not make the trek.s The influence of environmental temperature and drought may explain why c.F. occurs among Blacks in temperate zones of the United States9 but not in Africa, and is less frequent in the hot southern regions of Europe than in the colder, more northern areas.lO c.F. occurs less in Ashkenazi Jews in Israel than in European Caucasians but is even rarer among Sephardic Jews." Did the heterozygotes die in the wilderness during common
1. 2. 3.
Super, M. S. Afr. med. J. 1975, 49, 818. Super, M. Unpublished. Goldblatt, I. in History of South West Africa from the Beginning of the Nineteenth Century; p. 170. Cape Town, 1971. 4. Kessler, W. R., Andersen, D. H. Pediatrics, 1951, 8, 648. 5. Schwachman, A. in Guide to Diagnosis and Management of Cystic Fibrosis; p. 33. Atlanta, 1974. 6. Vedder, H. in South West Africa in Early Times; p. 420. London, 1966. 7. Trümpelman, G. P. J. in Die Boer in Suidwes Africa. Archives Year Book for South African History II; Cape Town, 1948. 8. Super, M. S. Afr. med. J. (in the press). 9. Kulczycki, L. L., Schaut, V. Am. J. Dis. Child. 1974, 127, 64. 10. 11.
Di Sant’Agnese, P. A., Davies, P. B. N. Engl. J. Med. 1976, 295, 481. Levin, S. in Genetics of Migrant and Isolated Populations (edited by
E.
Goldschmidt);p. 294. Baltimore, 1963.
Main
routes
pewman).
of the Dorsland treks of 1874 and 1875
(after
the flight from Egypt? The Sephardim returned to Israel from far hotter countries than did the Ashkenazim. Negative selection of this type may have operated only in hot, arid environments and the possibility that other environments offered advantages to C.F. heterozygotes cannot be excluded. Nevertheless data from clinically controlled heatexposure experiments with parents of c.F. children would be of considerable interest in testing this hypothesis. P.O. Box 2619,
Windhoek, South West Africa
M. SUPE
HIGH BREAST-MILK SODIUM IN CYSTIC FIBROSIS
SIR,-Increased sodium concentration in sweat is a characteristic of cystic fibrosis. However, we have read nothing on the sodium content of breast milk in this condition. A patient with sweat-test-proven cystic fibrosis with mild pulmonary disease had her first baby by normal delivery at term. The baby weighed 2.75 kg and had no neonatal problems and a normal sweat sodium. Samples of breast milk were obtained on the sixth and seventh days post partum when the mother was not breast feeding. Sodium concentration was measured by atomic-absorption spectrophotometry after deproteinisation of the milk with trichloroacetic acid (Miss Lesley Cooper). The two sodium concentrations were 132 and 280 mmol/1, respectively, concentrations much higher than in any other milk sample tested at this hospital in a large survey and higher than any we have seen in the literature. Milk of such high sodium content would be unsafe for a baby, and we suggest that, if mothers with cystic fibrosis wish to breast feed, the sodium of their milk should be measured first. The breast, like so many other exocrine glands, seems to be affected by the secretory abnormalities of cystic fibrosis. Department of Pædiatrics, Queen Charlotte’s Maternity Hospital, London W6 0XG
ANDREW WHITELAW
ANDREW BUTTERFIELD
LOW GLUCOSE CONCENTRATIONS IN AMNIOTIC FL UIDS FROM ANENCEPHALIC PREGNANCIES
SIR,-We have examined amniotic-fluid samples for sugars and free organic acids by gas-chromatography/mass-spectrometry. An interfering glucose peak, present in all normal amniotic fluids, was absent from several samples from anen-
Triim-
Amniotic-fluid glucose concentrations.
SIR,-I have found
that cystic fibrosis (C.F.), which is very in South West Africa, occurs almost exclusively in white Afrikaners,’ probably as a result of inbreeding,2 the drift from the Northern Cape Colony,3 and religious and geographical separation.’ However, I have not found c.F. in the descendants of the Angola Boers, a small proportion (6-7%) of the White population who belong to a small branch of the Dutch Reformed Church. The absence of c.F. may stem from their limited numbers (7000) but I suggest that it may have at least partially a genetic basis. Homozygotes with c.F. are subject to salt-losing crises4 which can be fatal in hot weather and heterozygotes often have an increased concentration of sodium and chlorine ions in their sweat.5 Today’s Angola Boers are descended from those who migrated from Western Transvaal across the Kalahair Desert in the Dorsland (literally "thirstland") treks of 1875-19056 (see map), during which many died of thirst. I suggest that heterozygotes for c.F., because of their impaired electrolyte regulation, died more readily during these treks, thus reducing the frequency of the deleterious c.F. gene among their descendants. I know of several children with c.F. in South Africa whose great-grandparents were Boers born in Western Transvaal who did not make the trek.s The influence of environmental temperature and drought may explain why c.F. occurs among Blacks in temperate zones of the United States9 but not in Africa, and is less frequent in the hot southern regions of Europe than in the colder, more northern areas.lO c.F. occurs less in Ashkenazi Jews in Israel than in European Caucasians but is even rarer among Sephardic Jews." Did the heterozygotes die in the wilderness during common
1. 2. 3.
Super, M. S. Afr. med. J. 1975, 49, 818. Super, M. Unpublished. Goldblatt, I. in History of South West Africa from the Beginning of the Nineteenth Century; p. 170. Cape Town, 1971. 4. Kessler, W. R., Andersen, D. H. Pediatrics, 1951, 8, 648. 5. Schwachman, A. in Guide to Diagnosis and Management of Cystic Fibrosis; p. 33. Atlanta, 1974. 6. Vedder, H. in South West Africa in Early Times; p. 420. London, 1966. 7. Trümpelman, G. P. J. in Die Boer in Suidwes Africa. Archives Year Book for South African History II; Cape Town, 1948. 8. Super, M. S. Afr. med. J. (in the press). 9. Kulczycki, L. L., Schaut, V. Am. J. Dis. Child. 1974, 127, 64. 10. 11.
Di Sant’Agnese, P. A., Davies, P. B. N. Engl. J. Med. 1976, 295, 481. Levin, S. in Genetics of Migrant and Isolated Populations (edited by
E.
Goldschmidt);p. 294. Baltimore, 1963.
Main
routes
pewman).
of the Dorsland treks of 1874 and 1875
(after
the flight from Egypt? The Sephardim returned to Israel from far hotter countries than did the Ashkenazim. Negative selection of this type may have operated only in hot, arid environments and the possibility that other environments offered advantages to C.F. heterozygotes cannot be excluded. Nevertheless data from clinically controlled heatexposure experiments with parents of c.F. children would be of considerable interest in testing this hypothesis. P.O. Box 2619,
Windhoek, South West Africa
M. SUPE
HIGH BREAST-MILK SODIUM IN CYSTIC FIBROSIS
SIR,-Increased sodium concentration in sweat is a characteristic of cystic fibrosis. However, we have read nothing on the sodium content of breast milk in this condition. A patient with sweat-test-proven cystic fibrosis with mild pulmonary disease had her first baby by normal delivery at term. The baby weighed 2.75 kg and had no neonatal problems and a normal sweat sodium. Samples of breast milk were obtained on the sixth and seventh days post partum when the mother was not breast feeding. Sodium concentration was measured by atomic-absorption spectrophotometry after deproteinisation of the milk with trichloroacetic acid (Miss Lesley Cooper). The two sodium concentrations were 132 and 280 mmol/1, respectively, concentrations much higher than in any other milk sample tested at this hospital in a large survey and higher than any we have seen in the literature. Milk of such high sodium content would be unsafe for a baby, and we suggest that, if mothers with cystic fibrosis wish to breast feed, the sodium of their milk should be measured first. The breast, like so many other exocrine glands, seems to be affected by the secretory abnormalities of cystic fibrosis. Department of Pædiatrics, Queen Charlotte’s Maternity Hospital, London W6 0XG
ANDREW WHITELAW
ANDREW BUTTERFIELD
LOW GLUCOSE CONCENTRATIONS IN AMNIOTIC FL UIDS FROM ANENCEPHALIC PREGNANCIES
SIR,-We have examined amniotic-fluid samples for sugars and free organic acids by gas-chromatography/mass-spectrometry. An interfering glucose peak, present in all normal amniotic fluids, was absent from several samples from anen-
Triim-
Amniotic-fluid glucose concentrations.
