Pyruvate kinase: diagnostic value in neuromuscular disease

Clinical investigation in Duchenne dystrophy: V. Use of creatine kinase and pyruvate kinase in carrier detection

We have determined the value of creatine and pyruvate kinase (CK and PK) in carrier detection by evaluating 811 females in 73 families participating in the Collaborative Investigation of Duchenne Dystrophy. Thirty-nine obligate carriers, 244 normal controls (paternal females), as well as 76 possible carriers and 351 carrier suspects had three CK and PK specimens analyzed at a central laboratory. The CK and PK values varied with age in normals: both fell with age early in life, and CK rose after the fifth decade. Discriminant analysis indicated that the combination of mean CK and PK corrected for age yielded the best data for calculation of carrier probability. Using the best model, only 45% of obligate carriers could be identified at a false-positive rate of 2.5%. Daughters of obligate carriers have a disproportionate decline in CK and PK with age as compared to noncarrier females, suggesting that the rate of carrier detection will be higher in the first two decades. Our low rate of carrier detection, as compared to other studies, may reflect both the age of our obligate carrier population and the use of a control group that is more representative of the carrier population.

Plasma pyruvate kinase and creatine kinase activity in Becker muscular dystrophy

Plasma creatine kinase (CK) and pyruvate kinase (PK) were measured in 31 obligate carriers of Becker muscular dystrophy (BMD), 36 BMD patients and appropriate controls. Mean plasma CK was 108 U/l in obligate carriers and 62 U/l in 43 age- and sex-matched controls (P less than 0.001 carriers vs controls). Control CK reference range was 31-125 U/l (mean +/- 2 SD of log transformed values). Mean plasma PK was 40 U/l in obligate carriers and 34 U/l in 56 controls (P less than 0.02 carriers vs controls). Control PK reference range was 18-61 U/l. Values of CK above the reference range upper limit were found in 13 of 31 BMD obligate carriers but only 2 showed elevated PK values. The sensitivity of CK in determining BMD carrier status, although only 42%, was markedly better than PK at 6.5%. Mean plasma CK in BMD patients was 2366 U/l, a 19-fold increase over the control value of 127 U/l (P less than 0.001 patients vs controls). Control CK reference range was 40-316 U/l. In contrast, mean plasma PK in BMD patients was 353 U/l, only 7-fold higher than the mean control value of 57 U/l (P less than 0.001 patients vs controls). Control PK reference range was 22-126 U/l. Clearly, the estimation of plasma PK as a means of determining BMD carrier status is markedly inferior to CK. Previous reports of increased sensitivity of PK compared with CK may have been due to artefactually elevated PK levels produced during sample preparation.

The enzymology of skeletal muscle disorders

In myopathic disorders, abnormal serum enzyme activities are seen primarily in diseases of skeletal muscle where the condition involves the muscle fibers themselves. In denervation myopathies, serum enzyme activities are usually normal. The most dramatic increases of serum enzymes, particularly creatine kinase, are found in the dystrophic diseases, particularly Duchenne dystrophy. A review is given here of the many causes of abnormal serum enzyme activities where the source of enzymes is believed to be skeletal muscle. These include the dystrophies, various types of trauma, exercise, drug- and poison-induced causes including alcohol, malignant hyperthermia, inflammatory diseases, and miscellaneous causes. Tissue and serum activities are summarized for the commonly performed serum enzymes, i.e., CK, LD, AST, and aldolase. An extensive tabular and current description of the various types of dystrophies is given along with serum CK and pyruvate kinase activities.

Detection of carriers of X-linked gene for Duchenne muscular dystrophy by levels of creatine kinase and pyruvate kinase

Creatine kinase (CK) is the enzyme most often utilized for the detection of carriers of the gene for X-linked muscular dystrophies. In 1974, pyruvate kinase (PK) levels were also found to be increased in these carriers. The objective of the present study, carried out on 77 women related to patients with Duchenne muscular dystrophy (DMD), was to compare the efficiency of the two enzymes in the detection process. Of the 11 obligate heterozygotes for the DMD gene in the group, 8 exhibited elevated mean CK levels, 6 had elevated mean PK levels, and 9 had elevated mean levels of at least one of the enzymes. Among the mothers of isolated patients, 2/13 had elevated mean CK levels, 3/13 had elevated mean PK levels, and 5/13 had elevated mean levels of at least one of these enzymes. Thus, the study confirms data obtained by other investigators indicating that the use of PK can increase the detection rate of carriers of the gene for X-linked muscular dystrophies.

Serum pyruvate kinase in different neuromuscular diseases and in carriers of muscular dystrophy

Serum pyruvate kinase and creatine kinase activities were measured in a group of patients with various neuromuscular diseases and in carriers of muscular dystrophy. Elevated values of PK were usually but not invariably associated with elevated levels of CK. THe data showed that PK activity was elevated in all patients with DMD, high values generally correlating inversely with age or disease duration. In definite carriers, the level of PK was raised simultaneously with CK, while in potential carriers, classified by their relationship with MD patients in mothers, sisters and other relatives, the PK levels were elevated in 23%, 44% and 10% respectively, indicating especially for sisters, an increased genetic probability of being a definite carrier. In this way, we have confirmed that the serum PK assay is more sensitive in younger subjects and that combined CK and PK measurement will be of value in detecting a higher proportion of potential carriers.

Creatine-kinase (CK) and pyruvate-kinase (PK) activities in cord blood of normal newborn infants: application to Duchenne muscular dystrophy screening programs

Creatine-kinase (CK) and pyruvate-kinase (PK) were determined in cord blood samples from 125 normal newborn infants in order 1) to investigate the correlation between CK and PK, 2) to evaluate a possible influence of the mode of delivery (cesarean section versus vaginal delivery) and birth weight on enzyme activity, 3) to establish normal values for both sexes. In the present investigation, the enzyme activities of cord blood were significantly higher than in the normal adult, and no correlation was observed between enzyme activity and mode of delivery or birthweight. Although there was an apparent and significant correlation (r = 0.5) between CK and PK levels in cord blood samples, in no case did we find both high CK and PK values, something that would suggest preclinical DMD or a false-positive result. These results have led us to suggest determination of serum PK activity in male newborn screening programs. This would allow an early discrimination between false-positives and clinical cases already in the neonatal period. Furthermore, the concomitant use of PK and CK in boys not walking by 18 months could be a useful test for diagnosing preclinical DMD boys.

Improved detection of Duchenne muscular dystrophy heterozygotes using discriminant analysis of creatine kinase levels

We have assessed the sensitivity and specificity of tests to detect carriers of Duchenne muscular dystrophy by use of three serum enzymes (creatine kinase, pyruvate kinase, and aldolase) and discriminant analysis in 21 obligate heterozygotes and 28 normal controls. We found no significant age effects on enzyme levels. Each enzyme level considered separately was significantly higher in heterozygotes. Use of logs improved discrimination, and log CK was sufficient by itself as a discriminant (that is, addition of other enzymes did not significantly improve discrimination). We present procedures to generate posteriori probabilities for genetic counselling that incorporate prior probabilities and enzyme levels. Our results show both improved sensitivity (90%) and specificity (86%).

Pyruvate-kinase (PK) and creatine-kinase (CK) in normal pregnancy and its implication in genetic counseling of Duchenne muscular dystrophy (DMD)

The activities of pyruvate-kinase (PK) and creatine-kinase (CK) were measured in 50 normal pregnant women in both serum and amniotic fluid. Serum PK activity was found to be significantly higher in pregnant than in nonpregnant women, while serum CK did not differ significantly between the two population samples. In amniotic fluid, very little or no PK or CK activity was found. However, the mean PK activity in amniotic fluid obtained from women carrying male fetuses was significantly higher than in those carrying female fetuses. At the present time, it is concluded that if a woman at risk for having a son with Duchenne dystrophy is seeking genetic counseling when already pregnant her serum PK or CK should be compared with that of normal female pregnant controls. It is also suggested that determination of pyruvate-kinase in fetal blood might be used in addition to CK for prenatal diagnosis of Duchenne muscular dystrophy.

Duchenne muscular dystrophy carrier detection using logistic discrimination: serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase in combination

In the absence of an unambiguous test for identifying Duchenne muscular dystrophy (DMD) heterozygotes, methods are needed for combination of the results of individually equivocal tests as effectively and rationally as possible. Tw used logistic discrimination to assess the effectiveness of measurements of serum creatine kinase, hemopexin, pyruvate kinase, and lactate dehydrogenase alone and in various combinations in identifying DMD carriers. We analyzed 127 serum samples from 63 normal female controls (20-40 years old) and 67 from 38 obligate DMD carriers. The best two tests to use in combination were creatine kinase and hemopexin, and these two, with lactate dehydrogenase, were the best three. t the 95% level (with 5% of controls misclassified), 54% of the carriers were identified by CK alone, whereas 88% were identified by means of the four tests. Although a small proportion of known carriers still cannot be identified, application of the four tests to a group of 45 possible carrier mothers of isolated cases of DMD resolves the population into fairly discrete "normal" and "abnormal" subgroups. Thus, if bias of selection can be eliminated, application of logistic discrimination may permit a direct estimate of the proportion of mothers of affected boys who are homozygous normal.

The use of concomitant serum pyruvate-kinase (PK) and creatine-phosphokinase (CPK) for carrier detection in Duchenne's muscular dystrophy through discriminant analysis

Serum pyruvate-kinase (PK) and creatine-phosphokinase (CPK) determinations have been carried out in a sample of 30 obligate carriers for the DMD gene and 50 normal adult control females. In all the subjects under study blood samples have been collected 3 times on 3 independent occasions and the means of these 3 determinations were considered for both CPK and PK activities in the statistical analysis. Discriminant analysis has shown that in the group of 30 obligate carriers the estimated proportions of misclassification using either serum CPK, PK or both enzymes were fourn to be: 10/30 (33.3%) for CPK alone, 6/30 (20%) for PK alone and 5/30 (16.6%) for both enzymes. It is concluded that although a small proportion of carriers still remain undetected the concomitant use of PK and CPK determinations enhances the capability of detecting carriers for the Duchenne gene mainly when compared with CPK alone.

The importance of serum pyruvate kinase in neuromuscular diseases and carrier states

Serum pyruvate kinase activity was measured in several myopathic and denervating illnesses as well as in 86 potential carriers of Duchenne dystrophy. These data showed that in potential Duchenne carriers, the serum pyruvate kinase assay is more sensitive in younger patients, especially those under 20 years of age.

Serum creatine kinase and pyruvate kinase in Duchenne muscular dystrophy carrier detection

The incidence of elevated serum creatine kinase (CK) and pyruvate kinase (PK) activities was compared in 20 definite carriers of Duchenne muscular dystrophy (DMD), 47 possible carriers, and 42 female controls. When adult age was not regarded as a variable, 70% of the definite carriers had elevated PK, 55% had elevated CK, and 75% had elevated PK or elevated CK or both, 38% of the possible carriers had elevated PK, 19% had elevated CK, and 40% had elevated PK or elevated CK or both. The detection efficiency of the CK test was influenced by the age of the subjects: the upper normal limit of serum CK in the adult controls was at the minimum between 21 and 35 years of age, and CK activity in some carriers declined from elevated to normal levels with increasing age. With these considerations, 70% of definite carriers had elevated CK and 80% had elevated PK and/or CK; 34% of the possible carriers had elevated CK and 43% had elevated PK and/or CK. On the basis of the PK and CK measurements, only 16 of 24 possible carrier mothers were likely to be DMD carriers, implying that the other 8 were non-carrier mothers of new mutant sons.