1139 PRENATAL DIAGNOSIS OF HYPOPHOSPHATASIA
TABLE I-A.P. ACTIVITIES IN TISSUES OBTAINED POST MORTEM FROM INFANTS WITH HYPOPHOSPHATASIA
SIR,-Hypophosphatasia,’ a rare inherited disease in which ossification may be severely impaired, shows genetic heterogeneity, and patients with some residual activity of alkaline phosphatase (A.P.) are less severely affected, roughly in proportion to the amount of enzyme activity remaining.22 We have attempted prenatal diagnosis in pregnancies at risk for hypophosphatasia, both by ultrasound3.4 and by measurement
of
A.P.
activities in amniotic fluid and cultured amnio-
tic-fluid cells.3-6 Our experiences may help to define the variant forms of hypophosphatasia for which prenatal
diagnosis might
be valuable. We have investigated A.P. activity and phosphorylethanolamine concentration of amniotic fluid and A.P. activity in cultured amniotic-fluid cells. Cell-free amniotic fluid from different pregnancies exhibited a wide range of A.P. activities, and activity did not correlate with the clinical picture,4,6 this is to be expected because amniotic-fluid A.P. is of the intestinal and/or placental type under genetic control distinct from that of the bone/liver/kidney locust Thus amniotic-fluid A.P. will be detectable even in pregnancies where the fetus is severely affected by hypophosphatasia, and this will prevent the accumulation in amniotic fluid of any phosphorylethanolamine which might be excreted by the fetus.8 Thus amniotic fluid cannot be reliably used in the prenatal diagnosis of hypophosphatasia. A.P. activities in cultured amniotic-fluid cells have, on the other hand, proved more useful, especially when used in conjunction with ultrasound and radiological examination. In the congenital lethal form of hypophosphatasia the fetus is severely affected in uter03,4 and may. survive for only a short time after birth. A.P. activities determined post mortem in bone, liver, and kidney from two of these infants were absent or much lower than normal (table I). Other tissues, such as skin and small intestine, containing, A.P. isoenzymes under separate genetic control also had low activities but these tissues
grossly deficient. activity varies widely in normal cultured amniotic-fluid cells,5,8 possibly for reasons connected with the conditions of culture or the cell types growing.9 Cultured amniotic-fluid cells from fetuses subsequently found to have the severe variant of hypophosphatasia had, in three cases out of four, A.P. activities low enough to distinguish them from normal. On the other were not
A.P.
was at risk for one of the milder forms of and was diagnosed radiologically after birth hypophosphatasia as being so affected was normal by ultrasonography and had high cultured amniotic-fluid cell A.P. activity (table n). If fetuses with the milder forms of hypophosphatasia cannot be distinguished at prenatal diagnosis as a distinct group they should be treated as normal and the pregnancy should be allowed to proceed to term. Where amniotic-fluid cell culture is ambiguous, ultrasound and radiography may give some indication of defective ossification in utero in fetuses with moderately severe variants of hypophosphatasia, but not necessarily in time for the pregnancy to be terminated. Unambiguous prenatal diagnosis of hypophosphatasia early enough to give the parents of an affected fetus the choice of termination of pregnancy is at present possible only for the congenital lethal (i.e., the. most severe) variants of the disease. As we learn more about other variants and about the factors
hand,
a
fetus that
*Boehringer C system "optimised". As wet weight. infants who died from causes not involving skeletal defects. italic type. ..
=
not
No. in
tested.
TABLE II-PRENATAL DIAGNOSIS OF HYPOPHOSPHATASIA AND
OUTCOME
*Unpublished Toronto cases (D.I.H. and N.L.R.). t2 cell clones out of 23 from five normal amniotic fluids.9 that govern the activity of A.P. in amniotic-fluid cells in culture, so we may be able to extend prenatal diagnosis. In the meantime we would stress the importance of accurately diagnosing hypophosphatasia after birth and of determining its severity, particularly by measuring A.P. activity in tissues so that the feasibility of prenatal diagnosis in subsequent pregnancies may be correctly assessed. Prenatal Biochemistry Unit, Bernhard Baron Memorial Research
Laboratories, Queen Charlotte’s Maternity Hospital, London W6 0XG
Department of Medical Genetics, University ofToronto,
KARL BLAU
Toronto, Canada
DAVID I. HOAR
Department of Pædiatric Biochemistry, Royal Hospital for Sick Children, Edinburgh
J. M. RATTENBURY
,
1. Rathbun, J. C. Am. J. Dis. Child. 1948, 75, 822. 2. Fraser, D. Am. J. Med. 1957, 22, 730. 3. Benzie, R., Doran, T. A., Escoffery, W., Gardner, H. A., Hoar, D. I., Hunter, A., Malone, R., Miskin, M., Rudd, N. L. Birth Defects orig. Art.
Ser. 1976, 12, 271. 4. Rudd, N. L.,
Miskin, M., Hoar, D. I., Benzie, R., Doran, T. A. New Engl.
J. Med. 1976, 295, 146.
5. Rattenbury, J. M., Blau, K., Sandler, M., Pryse-Davies, J., Clark, Pooley, S. S. F. Lancet, 1975, i, 306. 6. Blau, K., Rattenbury, J. M., Pryse-Davies, J., Clark, P. J., Sandler,
P. J., M. J.
Inher. metab. Dis. (in the press). 7. Hahnemann, N., Sørensen, S. A. Acta obstet. gynœc. scand. 1975, 53, 15. 8. Goldfischer, S., Johnson, A. B., Morecki, R. Lab. Invest. 1976, 35, 55. 9. Hoar, D. I., Rudd, N. Lancet, 1975, i, 1194.
Genetics
Department, Hospital for Sick Children, Toronto
NOREEN L. RUDD
PHENYLALANINE HAS NO EFFECT ON DIHYDROPTERIDINE REDUCTASE ACTIVITY IN PHENYLKETONURIA FIBROBLASTS
SIR,-In phenylketonuria (P.K.U.) there is a defect in phenylalanine metabolism. The enzyme system that catalyses the hydroxylation of phenylalanine to tryosine is complex, with two enzymes (phenylalanine hydroxylase and dihydropteridine reductase) and two cofactors (tetrahydrobiopterin and reduced pyridine nucleotide).’ The lack of any of these components will lead to a non-functional hydroxylating system. Addition of 95% pure phenylalanine hydroxylase from rat liver to a P.K.U. 1.
Kaufman, S. Biochem. Med. 1976, 15, 42.
TABLE I-A.P. ACTIVITIES IN TISSUES OBTAINED POST MORTEM FROM INFANTS WITH HYPOPHOSPHATASIA
SIR,-Hypophosphatasia,’ a rare inherited disease in which ossification may be severely impaired, shows genetic heterogeneity, and patients with some residual activity of alkaline phosphatase (A.P.) are less severely affected, roughly in proportion to the amount of enzyme activity remaining.22 We have attempted prenatal diagnosis in pregnancies at risk for hypophosphatasia, both by ultrasound3.4 and by measurement
of
A.P.
activities in amniotic fluid and cultured amnio-
tic-fluid cells.3-6 Our experiences may help to define the variant forms of hypophosphatasia for which prenatal
diagnosis might
be valuable. We have investigated A.P. activity and phosphorylethanolamine concentration of amniotic fluid and A.P. activity in cultured amniotic-fluid cells. Cell-free amniotic fluid from different pregnancies exhibited a wide range of A.P. activities, and activity did not correlate with the clinical picture,4,6 this is to be expected because amniotic-fluid A.P. is of the intestinal and/or placental type under genetic control distinct from that of the bone/liver/kidney locust Thus amniotic-fluid A.P. will be detectable even in pregnancies where the fetus is severely affected by hypophosphatasia, and this will prevent the accumulation in amniotic fluid of any phosphorylethanolamine which might be excreted by the fetus.8 Thus amniotic fluid cannot be reliably used in the prenatal diagnosis of hypophosphatasia. A.P. activities in cultured amniotic-fluid cells have, on the other hand, proved more useful, especially when used in conjunction with ultrasound and radiological examination. In the congenital lethal form of hypophosphatasia the fetus is severely affected in uter03,4 and may. survive for only a short time after birth. A.P. activities determined post mortem in bone, liver, and kidney from two of these infants were absent or much lower than normal (table I). Other tissues, such as skin and small intestine, containing, A.P. isoenzymes under separate genetic control also had low activities but these tissues
grossly deficient. activity varies widely in normal cultured amniotic-fluid cells,5,8 possibly for reasons connected with the conditions of culture or the cell types growing.9 Cultured amniotic-fluid cells from fetuses subsequently found to have the severe variant of hypophosphatasia had, in three cases out of four, A.P. activities low enough to distinguish them from normal. On the other were not
A.P.
was at risk for one of the milder forms of and was diagnosed radiologically after birth hypophosphatasia as being so affected was normal by ultrasonography and had high cultured amniotic-fluid cell A.P. activity (table n). If fetuses with the milder forms of hypophosphatasia cannot be distinguished at prenatal diagnosis as a distinct group they should be treated as normal and the pregnancy should be allowed to proceed to term. Where amniotic-fluid cell culture is ambiguous, ultrasound and radiography may give some indication of defective ossification in utero in fetuses with moderately severe variants of hypophosphatasia, but not necessarily in time for the pregnancy to be terminated. Unambiguous prenatal diagnosis of hypophosphatasia early enough to give the parents of an affected fetus the choice of termination of pregnancy is at present possible only for the congenital lethal (i.e., the. most severe) variants of the disease. As we learn more about other variants and about the factors
hand,
a
fetus that
*Boehringer C system "optimised". As wet weight. infants who died from causes not involving skeletal defects. italic type. ..
=
not
No. in
tested.
TABLE II-PRENATAL DIAGNOSIS OF HYPOPHOSPHATASIA AND
OUTCOME
*Unpublished Toronto cases (D.I.H. and N.L.R.). t2 cell clones out of 23 from five normal amniotic fluids.9 that govern the activity of A.P. in amniotic-fluid cells in culture, so we may be able to extend prenatal diagnosis. In the meantime we would stress the importance of accurately diagnosing hypophosphatasia after birth and of determining its severity, particularly by measuring A.P. activity in tissues so that the feasibility of prenatal diagnosis in subsequent pregnancies may be correctly assessed. Prenatal Biochemistry Unit, Bernhard Baron Memorial Research
Laboratories, Queen Charlotte’s Maternity Hospital, London W6 0XG
Department of Medical Genetics, University ofToronto,
KARL BLAU
Toronto, Canada
DAVID I. HOAR
Department of Pædiatric Biochemistry, Royal Hospital for Sick Children, Edinburgh
J. M. RATTENBURY
,
1. Rathbun, J. C. Am. J. Dis. Child. 1948, 75, 822. 2. Fraser, D. Am. J. Med. 1957, 22, 730. 3. Benzie, R., Doran, T. A., Escoffery, W., Gardner, H. A., Hoar, D. I., Hunter, A., Malone, R., Miskin, M., Rudd, N. L. Birth Defects orig. Art.
Ser. 1976, 12, 271. 4. Rudd, N. L.,
Miskin, M., Hoar, D. I., Benzie, R., Doran, T. A. New Engl.
J. Med. 1976, 295, 146.
5. Rattenbury, J. M., Blau, K., Sandler, M., Pryse-Davies, J., Clark, Pooley, S. S. F. Lancet, 1975, i, 306. 6. Blau, K., Rattenbury, J. M., Pryse-Davies, J., Clark, P. J., Sandler,
P. J., M. J.
Inher. metab. Dis. (in the press). 7. Hahnemann, N., Sørensen, S. A. Acta obstet. gynœc. scand. 1975, 53, 15. 8. Goldfischer, S., Johnson, A. B., Morecki, R. Lab. Invest. 1976, 35, 55. 9. Hoar, D. I., Rudd, N. Lancet, 1975, i, 1194.
Genetics
Department, Hospital for Sick Children, Toronto
NOREEN L. RUDD
PHENYLALANINE HAS NO EFFECT ON DIHYDROPTERIDINE REDUCTASE ACTIVITY IN PHENYLKETONURIA FIBROBLASTS
SIR,-In phenylketonuria (P.K.U.) there is a defect in phenylalanine metabolism. The enzyme system that catalyses the hydroxylation of phenylalanine to tryosine is complex, with two enzymes (phenylalanine hydroxylase and dihydropteridine reductase) and two cofactors (tetrahydrobiopterin and reduced pyridine nucleotide).’ The lack of any of these components will lead to a non-functional hydroxylating system. Addition of 95% pure phenylalanine hydroxylase from rat liver to a P.K.U. 1.
Kaufman, S. Biochem. Med. 1976, 15, 42.
