Variability in the clinical manifestations of galactosemia

Management of severe hyperbilirubinemia in the cholestatic neonate: a review and an approach

A review of the literature demonstrates that severe total hyperbilirubinemia (total serum bilirubin ≥ 20 mg/dL [340 µmol/L]) in some cholestatic term (≥37 weeks) and late-preterm (≥34^0/7-36^6/7 weeks) gestation neonates poses a risk for bilirubin-induced brain damage. When the direct bilirubin fraction is <50% of the total serum bilirubin this risk is associated with the total serum bilirubin alone and treatment decisions should be based on the total serum bilirubin. On the other hand, there are limited data on the risk of bilirubin-induced brain damage in the neonate with severe total hyperbilirubinemia and a direct bilirubin fraction that is equal to or exceeds 50% of the total serum bilirubin. When this rare combination occurs, efforts to keep the indirect bilirubin fraction from reaching severe levels might, nevertheless, be prudent.

Galactose-1-phosphate uridyltransferase deficiency: A literature review of the putative mechanisms of short and long-term complications and allelic variants

Galactosemia type 1 is an autosomal recessive disorder of galactose metabolism, determined by a deficiency in the enzyme galactose-1-phosphate uridyltransferase (GALT). GALT deficiency is classified as severe or variant depending on biochemical phenotype, genotype and potential to develop acute and long-term complications. Neonatal symptoms usually resolve after galactose-restricted diet; however, some patients, despite the diet, can develop long-term complications, in particular when the GALT enzyme activity results absent or severely decreased. The mechanisms of acute and long-term complications are still discussed and several hypotheses are presented in the literature like enzymatic inhibition, osmotic stress, endoplasmic reticulum stress, oxidative stress, defects of glycosylation or epigenetic modification. This review summarizes the current knowledge of galactosemia, in particular the putative mechanisms of neonatal and long-term complications and the molecular genetics of GALT deficiency.

Ultra fast and sensitive liquid chromatography tandem mass spectrometry based assay for galactose-1-phosphate uridylyltransferase and galactokinase deficiencies

The diagnosis of transferase and galactokinase deficiency galactosemia usually involves the measurement of erythrocyte galactose-1-phosphate uridylyltransferase (GALT) and galactokinase (GALK) enzyme activity, respectively. The current gold standard assays for these enzymes are radioactive assays, which are laborious and/or incapable of measuring low enzyme activities. To further our knowledge of genotype-phenotype relationships, we had developed an assay for GALT activity alone using LC-MS/MS. In this study we generated a robust and sensitive LC-MS/MS based GALT and GALK assay using a novel normal phase chromatographic condition. We improved upon our earlier assay by drastically reducing the instrument run time and eliminating the use of an ion pairing reagent. Stable isotope labeled substrates were utilized in the GALT and GALK assays. The enzymatic products ([(13)C(6)]-uridine diphosphate galactose in GALT assay and [(13)C(6)]-galactose-1-phosphate in GALK assay) were quantified in a 3 min LC-MS/MS run. The assays were sensitive enough to allow for the quantification of enzyme activities as low as 0.2% and 0.3% of normal control values in the GALT and GALK assays, respectively. Thirty-three samples from non-galactosemic patients were assayed to have erythrocyte GALT activity of 23.4±4.2 and GALK activity of 1.8±0.47 (mean±SD) μmol⋅(g Hgb)(-1) h(-1). Erythrocyte GALT activities in a cohort of 16 patients with classic or severe galactosemia were measured: 4 patients had GALT activity less than 1% of normal control values and the remaining 12 had no detectable GALT activity. No GALK activity was detected in a GALK deficient sample we analyzed. Lastly, we tested the feasibility of adapting this LC-MS/MS based GALT/GALK assay as a newborn screening (NBS) test.

Quantification of galactose-1-phosphate uridyltransferase enzyme activity by liquid chromatography-tandem mass spectrometry

BACKGROUND

The diagnosis of galactosemia usually involves the measurement of galactose-1-phosphate uridyltransferase (GALT) activity. Traditional radioactive and fluorescent GALT assays are nonspecific, laborious, and/or lack sufficient analytical sensitivity. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based assay for GALT enzyme activity measurement.

METHOD

Our assay used stable isotope-labeled alpha- galactose-1-phosphate ([(13)C(6)]-Gal-1-P) as an enzyme substrate. Sample cleanup and separation were achieved by reversed-phase ion-pair chromatography, and the enzymatic product, isotope-labeled uridine diphosphate galactose ([(13)C(6)]-UDPGal), was detected by MS/MS at mass transition (571 > 323) and quantified by use of [(13)C(6)]-Glu-1-P (265 > 79) as an internal standard.

RESULTS

The method yielded a mean (SD) GALT enzyme activity of 23.8 (3.8) mumol x (g Hgb)(-1) x h(-1) in erythrocyte extracts from 71 controls. The limit of quantification was 0.04 micromol x (g Hgb)(-1) x h(-1) (0.2% of normal control value). Intraassay imprecision was determined at 4 different levels (100%, 25%, 5%, and 0.2% of the normal control values), and the CVs were calculated to be 2.1%, 2.5%, 4.6%, and 9.7%, respectively (n = 3). Interassay imprecision CVs were 4.5%, 6.7%, 8.2%, and 13.2% (n = 5), respectively. The assay recoveries at the 4 levels were higher than 90%. The apparent K(m) of the 2 substrates, Gal-1-P and UDPGlc, were determined to be 0.38 mmol/L and 0.071 mmol/L, respectively. The assay in erythrocytes of 33 patients with classical galactosemia revealed no detectable activity.

CONCLUSIONS

This LC-MS/MS-based assay for GALT enzyme activity will be useful for the diagnosis and study of biochemically heterogeneous patients with galactosemia, especially those with uncommon genotypes and detectable but low residual activities.

Longitudinal assessment of intellectual achievement in patients with classical galactosemia

OBJECTIVE

To conduct a longitudinal assessment of long-term cognitive outcome in patients with classical galactosemia.

METHODS

Inclusion criteria were (1) previous assessment of IQ dating back >10 years with tests being comparable with the recent German tests HAWIK-III and HAWIE-R, (2) absence of illnesses other than galactosemia, (3) absence of foreign language problems, (4) enzymatic-metabolic proof of classical galactosemia, (5) compliance with dietary therapy, and (6) written informed consent. Twenty-three patients who fulfilled these criteria were found. They underwent the first IQ test at a mean age of 11 +/- 5 years and the second 13.6 to 15.5 years later at a mean age of 26 +/- 5 years. Results were corrected for the obsolescence of test norms (Flynn effect).

RESULTS

Mean total IQ scores on the first and second tests were 78 +/- 14 and 73 +/- 15, respectively, and not significantly different. IQ scores in the average range were observed for 7 patients on the first test and for 5 patients on the second test. For 17 patients, the intraindividual IQ scores remained essentially unchanged. Five patients showed a decrease and 1 an increase of the IQ score over time. No consistent pattern of change was found with respect to performance or verbal IQ subscores or in achievements in the individual subtest.

CONCLUSIONS

The results confirm the presence of reduced cognitive ability in classical galactosemia and present evidence for an absence of substantial galactosemia-induced aggravation of this impairment with increasing age, at least in patients from 4 to 40 years of age. It remains to be clarified whether a reduction of cognitive function in galactosemia may be initiated by an in utero toxicity of endogenously formed galactose and which role such a process may play in the development of intellectual deficiencies that are later maintained throughout life.

Frequencies of the Los Angeles and Duarte galactose-1-phosphate uridyltransferase variant alleles in the Hungarian population

A klasszikus galactosaemia autoszomális recesszív módon öröklődő anyagcsere-betegség, amelynek hátterében a galaktóz-1-foszfát-uridil-transzferáz (GALT) enzim defektusa áll. Hazánkban a betegséget az újszülöttkori tömegszűrés keretében, 1976 óta szűrik. A p.N314D mutáció asszociál a GALT enzim Los Angeles és a Duarte variánsaival, attól függően, hogy a mutáció mely polimorfizmusokkal öröklődik együtt cis helyzetben. Célkitűzés: Munkánk célja volt a magyar egészséges populációban a p.N314D mutáció, valamint a Los Angeles és Duarte variánsok gyakoriságát meghatározni. Módszerek: A 100 donor személyből izolált genomiális DNS-mintát polimeráz láncreakció során amplifikáltuk, majd restrikciós endonukleázzal emésztettük. Eredmények: A p.N314D mutáció, a Los Angeles variáns és a Duarte variáns allélgyakorisága az általunk vizsgált populációban 11,5%, 2,5%, illetve 9% volt. Következtetés: A magyar populációban a Los Angeles és Duarte varánsok allélgyakorisága jól korrelál más kaukázusi populációkban detektált gyakoriságokkal.

Growth in treated classical galactosemia patients

Decreased height and weight in treated children with classical galactosemia have been reported. However, growth has not been extensively studied. Patients might be at risk for an abnormal growth because of either disease-related intrinsic factors or diet-related factors. The objective was to gain insight in growth in treated children and adolescents with classical galactosemia. The studied population was a previously reported group of 40 classical galactosemia children. Prenatal growth was evaluated using length, weight and head circumference (HC) data from welfare centers or parents. Postnatal growth was evaluated using three height and weight measurements at baseline, 1 and 2 years to calculate growth velocities. Height Z-score was also corrected for target height Z-score (height Z-score divided by target height Z-score). Linear regression analysis was performed between growth velocities, IGF-I, IGFBP-3, dietary intake and galactose-1-phosphate-uridyltransferase activity. We found normal length (median 50.5 cm), weight (median 3,255 grams) and HC (median 33.9 cm) at birth. Mean height growth velocity was 0.87+/-1.2 for boys and -0.89+/-2.1 for girls, and mean weight growth velocity was 0.91+/-1.6 for boys and -0.74+/-1.3 for girls. Mean height corrected for target height was -1.5+/-0.9 in girls and -0.6+/-0.7 in boys. Height growth velocity was correlated with IGF-I (Pearson correlation= 0.499), IGFBP-3 (Pearson correlation 0.4) and height Z-scores corrected for target height Z-scores (Pearson correlation=0.550). Five children grew beyond the age of 18 years. In conclusion, prenatal growth was normal but postnatal growth was affected. Predicted final height is less than target height in most patients; however, target height might be reached for the children who grow beyond the age of 18. Decreased IGF-I and IGFBP-3 and or suboptimal hormonal replacement in girls might play a role.

Optimality of the birth population reduces learning and behaviour disorders and sudden infant death after the first month

The weight distribution pattern of all births can be divided into a "skewing to the left" to lower weights and high neonatal mortality, a "skewing to the right" to higher weights (>3500g) and minimum neonatal and postneonatal mortality, and a "symmetrical distribution" with mortality in between. This study was initiated with the hypothesis that a deficit in newborns of more than 3500 g would adversely affect postneonatal death. Higher and rising postneonatal mortality solely attributable to sudden infant death of unknown cause (sudden infant death syndrome; SIDS) was observed in the Nordic countries with a lower proportion of heavy newborns. Minor environmental intervention almost eliminated excess mortality from this cause, supporting raised susceptibility with a depressed birthweight in postneonatal SIDS. This contrasts with classical neonatal low birthweight SIDS, which is stable despite numerous attempts at reduction, supporting a multi-factorial aetiology: low maternal age, low education, low socioeconomic status, maternal smoking, infection, etc. The postneonatal SIDS epidemic associated with a deficit in heavy newborns is thought to be a result of changing behaviour in pregnancy: moderate iatrogenic dietary restriction and young women favouring a low-calorie, low-fat diet, especially in the third trimester when the foetus is most vulnerable, which delays myelination and somatic growth and renders the infant susceptible to minor morbidity and irregularity. The timing of death and neuropathological findings suggestive of repeated hypoxic episodes in more than 80% of cases of SIDS prior to death support this theory. The similar weight distribution patterns in SIDS and all births in Denmark, the UK and the USA suggest a substantial proportion of the neonates in these countries could be growth-retarded and at risk of hypoxic episodes in infancy. A few cases, particularly males (sex-ratio = 1.7), suffer SIDS, the majority survive. Many, mostly males, present minor CNS signs and learning and behaviour problems. The male predominance accords with males more than 500 g higher optimal birthweight than females and susceptibility to a depressed weight at birth. In order to prevent postneonatal dying, SIDS and reduce learning/behaviour disorders it is necessary to raise the proportion of heavy newborns by promoting foetal growth rate equal to the maternal intrinsic rate by eating to one's appetite a balanced diet, favouring a diet high in marine fat, especially in third trimester, in order to ensure maturation of the CNS and prolong gestation, thereby increasing birthweight. Although the increased survival of some very low birthweight neonates confounds the issue, a division between SIDS in neonatal and postneonatal death is recommended in order to assess the proportion of "avoidable infant death" as opposed to persistent classical neonatal SIDS.

Vitreous hemorrhage as an ophthalmic complication of galactosemia

A major complication of galactosemia is cataracts. This is usually considered to be the sole ophthalmic feature of this disorder. However, we have encountered vitreous hemorrhage, a very rare ophthalmic finding, in five neonates with galactosemia and have found four probable additional cases in the literature. All of these infants had severe neonatal manifestations of galactosemia and were discovered to have vitreous hemorrhage by ophthalmologic examination initiated by the observation of clouding of the eye or on a routine basis. The infants lost most or all vision from the affected eye. Retinal abnormalities were present in the involved eyes of the five neonates of whom we have direct knowledge. Thus we believe that retinal hemorrhage is the most likely source of the vitreous hemorrhage and that the coagulopathy associated with neonatal disease in galactosemia leads to vitreous hemorrhage. Prompt recognition and therapy for the coagulopathy would likely prevent vitreous hemorrhage in galactosemia.

Radiochemical assay of minute quantities of galactose-1-phosphate uridyltransferase activity in erythrocytes and leukocytes of galactosemia patients

A sensitive radioisotopic method has been developed which can detect galactose-1-phosphate uridyltransferase (GALT) activity as low as 0.1% of normal control values in both erythrocytes and leukocytes. This assay utilizes carbon-14 labeled galactose-1-phosphate with high specific activity and requires removal of endogenous galactose-1-phosphate (Gal-1-P) and uridine diphosphate glucose (UDPGlc) through dialysis. Optimal exogenous UDPGlc concentration has been determined with a fixed concentration of Gal-1-P in the incubation. The rate of product, uridine diphosphate galactose (UDPGal), formation is monitored at three different times. Among 423 patients with galactosemia studied by this method, 363 patients exhibited no detectable GALT activity in their erythrocytes and 60 patients were found to have detectable erythrocyte GALT activity ranging from 0.02 to 5.0 units normal values: > 20 units). The former group of patients was designated as classic galactosemia (GG) and the latter group as galactosemia variant (GV). Leucocytes from ten patients belonging to the GG group also showed complete absence of GALT activity while leukocytes from two patients belonging to the GV group showed GALT activity at levels comparable with those found in their erythrocytes. Because there is extensive biochemical heterogeneity among galactosemia patients, we recommend that an assay with increase sensitivity be carried out on blood samples from galactosemia patients so that clinical, biochemical and molecular correlations made by different groups of investigators can be compared.

Galactosemia unsolved

Classic galactosemia is an enigmatic disorder that presents the challenge of unraveling the basis of the long-term complications of mental disability, speech defects, ovarian failure and neurologic syndromes which occur despite a galactose-restricted diet. A complete understanding of the pathobiochemistry and molecular genetics, and evaluation of the present theories for the poor long-term outcome, continuous intoxication, critical metabolite depletion and in utero damage is needed in order to design new therapeutic strategies. Answering this urgent question of how to treat galactosemic patients mandates enhanced clinical and basic research efforts.

In utero galactose intoxication in animals

To assess in utero effects of galactose, diets containing large amounts of the sugar have been fed to pregnant rats with examination of the fetuses and newborns. Galactose levels in fetal blood parallel those of the dam and amniotic fluid contains high concentrations of galactose and galactitol. In the offspring and in the fetuses cataracts, and a decrease in brain weight, protein content and DNA are observed. There is an elevated content of galactitol and decrease in myo-inositol in the brain of galactose-intoxicated newborns. Brain synaptosomes of young rats whose mothers were fed galactose show a reduced response in vitro to acetylcholine as evidenced by a decrease in incorporation of myo-inositol into phosphatidylinositol and an inappropriate change in phosphatidylinositol content. The data indicate that there can be significant effects in the offspring of pregnant rats fed a high galactose diet. The findings support the concept that in utero toxicity may occur in the human galactosemic fetus.

Effects of galactosemia in utero

There is direct evidence that in galactosemia, due to galactose-1-phosphate uridyltransferase deficiency, galactose, galactose-1-phosphate and galactitol accumulate in the fetus by week 20 of gestation. The metabolic abnormality may develop earlier than this, however, since the key enzymes in galactose metabolism have been shown to be present in normal fetal liver from the 10th week of gestation. There has been a single report of increased galactitol in amniotic fluid obtained at 10 weeks gestation, the outcome being a baby affected with galactosemia. Cataract formation in the fetus is rare and the only direct evidence that galactosemia may have harmful effects in utero. However, it has been concluded that the liver pathology seen in some patients who died in the neonatal period originated prenatally, and some studies have found that galactosemia is associated with reduced birth weight. Reports of two patients with histologically normal ovaries very soon after birth have been cited as evidence against gonadal dysfunction arising during fetal life, but it should be noted that this is not a constant feature in female galactosemics. Other observations, particularly those made from animal models, would suggest that ovarian dysfunction is most likely to have been caused in utero.

Biochemical and molecular studies of 132 patients with galactosemia

We evaluated 132 galactosemia patients for the Q188R (glutamine-188 to arginine) mutation in the human galactose-1-phosphate uridyltransferase (GALT) gene and for GALT activity in their hemolysates by a sensitive radioisotopic method. In those without any detectable GALT activity (GG), the Q188R mutation constituted 67% of the alleles. In patients with detectable GALT activity (GV), only 16% of the alleles were accounted for by Q188R. In all patients who were homozygous for the Q188R mutation, no erythrocyte GALT activity could be demonstrated. There was an extensive variation in the amount of detectable GALT activity ranging from 0.1% to 5% of the normal values among the GV patients. There was a difference in the frequency of Q188R mutation in the GALT alleles among patients belonging to different racial and ethnic groups. In Caucasian and Hispanic patients, the frequency was not far different (64% and 58%, respectively). On the other hand, only 12% of the GALT alleles with Q188R were found in African-American patients.

Hypoglycemia: a pathophysiologic approach

An exploration of the factors that sustain glucose levels in the normal fasting subject reveals that the single major component is conservation of glucose rather than gluconeogenesis. Conservation is achieved by recycling of glucose carbon as lactate, pyruvate and alanine, and a profound decrease in the oxidation of glucose by the brain brought about by the provision and use of ketones. What glucose continues to be oxidized is for the most part formed from glycerol. Gluconeogenesis from protein plays little part in the process. Fasting hypoglycemia results from disorders affecting either one of the two critical sustaining factors--the recycling process or the availability and use of ketones. Individual hypoglycemic entities are examined against this background.

Galactokinase activity in patients with idiopathic cataracts

Ninety-four consecutive patients admitted for elective cataract surgery were prospectively examined for erythrocyte galactokinase activity. The presumed etiology for the cataract was established by history and physical examination in 51 patients (21 were diabetic). The cataract was classified as idiopathic in 43 patients. Galactokinase activity was significantly lower in idiopathic vs. presumed (nondiabetic) etiology patients 50 years of age or younger (P less than 0.05) and in idiopathic cataract patients 50 years of age or younger vs. those older than 51 years of age (P = 0.0033). Three of the idiopathic cataract patients (6.9%) had galactokinase levels less than two standard deviations below the mean galactokinase level for age-matched patients with suspected (nondiabetic) etiology. Compared with the expected distribution for the heterozygote in the general population (0.2%), this was highly significant (P = 0.0001). Diminished galactokinase activity may increase the risk of developing presenile cataracts requiring surgery by the fourth decade.

Perinatal galactose metabolism

Galactose is a major nutrient in normal newborn infants and serves as a substrate for energy production and fuel storage and a regulator of carbohydrate assimilation. Inborn errors of galactose metabolism have contributed to our understanding of the potential toxicity of this carbohydrate. In addition to the classic acute manifestations of neonatal galactosemia, long-term follow-up of surviving patients have revealed unusual neurodevelopmental and reproductive problems. Many investigators have suggested that the newborn infant can utilize galactose better than adults and that neonatal galactose assimilation exceeds that of glucose. Galactose may be an excellent substitute for glucose among hyperinsulinemic infants of diabetic mothers or premature infants with glucose intolerance. However, until further investigations are performed to define the role of galactose in newborn nutrition and to determine its potential toxicity, galactose should not be used as the primary carbohydrate in sick newborn infants.

Direct and maternal aspects of the risk of cataract with partial disorders of galactose metabolism

Partial deficiencies of the enzymes of galactose metabolism can be associated with cataract, both directly and through maternal effects during pregnancy on enzymatically normal children. However, the associations are modest, variable and not obviously expressing cause and effect. We have recorded ophthalmological and biochemical observations including oral galactose tolerance on families with established enzyme deficiencies and/or cataracts, including possible effects during pregnancy. With the partial disorders a simple relationship between the extent of biochemical abnormality and the risk of cataract is not apparent and the association may be substantially coincidental. Cataract is common, and the attractive possibility that expression is significantly due to heterozygous or lesser deficiency of the enzymes of galactose metabolism, amenable to early dietary control of children or mothers at risk, is on present evidence not well supported.

Prenatal diagnosis of galactosemia and properties of galactose-1-phosphate uridyltransferase in erythrocytes of galactosemic variants as well as in human fetal and adult organs

The kinetic characteristics and isoelectrofocusing patterns of uridyltransferase and the concentrations of galactose-1-phosphate in hemolysates were investigated in a family with compound variants of Duarte and classical galactosemia. There were no significant differences in Km values between the genotypes. However, the isoelectrofocusing study with thin-layer polyacrylamide gels (PAGIF) as well as with agarose gels (AGIF) showed a distinctive difference. The enzyme from the Duarte variant resolved into at least two more activity bands at pH between 5.2 and 5.4. The accumulation of galactose-1-phosphate was observed only in homozygotes for classical galactosemia. Compound heterozygotes (G-D) without any clinical manifestations did not show an accumulation of galactose-1-phosphate. The isoelectrofocusing study of the enzyme in human tissues revealed their activity resolving into multiple bands, 6-8 bands at pH 5.50-6.00 and 1-3 bands at pH 4.9-5.2. No significant differences were found in the patterns between fetal and adult liver except that the intensity of the anodic bands (pH 4.9-5.2) was weaker in fetal tissues. Prenatal diagnosis of classical galactosemia was performed in nine families by measuring the enzyme activity in cultivated amniotic fluid cells. Absence of the enzyme activity in amniotic fluid cells was found in two cases, and in four cases the heterozygosity was diagnosed by a relative low enzyme activity, 30-50% of the activity in control cells cultured in parallel.

Galactosaemia with cataract and persistent hyaloid artery. A clinicopathological case report

A boy with galactosaemia and bilateral cataract developed large intraocular haemorrhages in the left eye which was enucleated. Histologically a persistent hyaloid artery was demonstrated. This combination with galactosaemia seems not to have been described in the literature before. The haemorrhages are most likely secondary to the persistent hyaloid artery system. In addition, some foci of extramedullary haemopoiesis were demonstrated in the retina.

Galactosaemia: case for neonatal screening illustrated by recent Australian experience

The varied presentation and clinical features of classical galactosaemia are illustrated by the case histories of seven babies born in Western Australia since January, 1962, and of two babies born in South Australia in whom diagnosis was made as a result of adding galactosaemia to the Guthrie screening programme in October, 1974. All were shown to have a severe deficiency of galactose-1-phosphate uridyl transferase in their red blood cells. We compare our findings with those in 10 galactosaemic babies born in Victoria over a similar period, and show that in both groups these were two main modes of onset: acute and insidious. Jaundice and Escherichia coli infection were prominent in the 13 babies with an acute onset of galactosaemia, while poor weight gain, intermittent vomiting and cataracts were features of the five babies with an insidious onset. An enlarged liver was usually found in both groups. We discuss the various approaches to neonatal screening of galactosaemia in the light of experience in Massachusetts and South Australia. The use of cord blood can be expected to lead to diagnosis before babies with acute onset become ill, while the use of blood collected at five days for the Guthrie test avoids the collection of another routine sample for a relatively rare disorder. The result of red cell transferase assays of parents and siblings of our patients are discussed in relation to their implication for genetic counselling. The relevance of antenatal diagnosis to the prevention of possible intrauterine damage to an affected fetus is pointed out.

An unusual form of galactosemia: studies on erythrocytes and hair roots

An unusual form of galactosemia is described in a 7-month-old boy, characterized by a late onset of the clinical symptoms. A high apparent residual activity of erythrocyte galactose-1-phosphate uridyl transferase (GT) was measured with the spectrophotometric UDP-Glucose consumption test(+/-25% of normal). The residual activity in erythrocyte lysates, determined when the patient was 7, 16 and 22 months old, significantly decreased upon storage and after preincubation with NAD-ase. The radiochemical measurement of GT activity demonstrated a severe deficiency: only a level of +/-1% of normal activity was observed, and no effects of storage or NAD-ase could be demonstrated. GT and galactokinase (GK) activities were measured radiochemically in lysates from hair roots obtained from the human scalp, and it was found that the GT/GK activity ratio is a useful index for the detection of heterozygotes. Erythrocyte and hair root lysates from the heterozygous parents of the patient displayed GT/GK ratios which were intermediate between mutant and normal. Because they offer a simple and fast way to obtain biopsy material, hair roots might become of increasing importance for carrier detection studies.

Biochemical studies of a human low-activity galactose-1-phosphate uridyl transferase variant

A low activity galactose-1-phosphate uridyl transferase (transferase) variant in a newborn infant has been demonstrated by biochemical studies in erythrocytes and cultured skin fibroblasts. The newborn infant was a galactosaemic suspect identified in a neonatal metabolic screening programme. On breast feeding, he did well without clinical symptoms of galactosaemia during the first 15 days of life. However, substantial amounts of erythrocyte galactose-1-phosphate and urinary galactitol corresponding to the levels in untreated galactosaemic patients, along with mild amino aciduria, were found. The transferase activity, as measured by a sensitive micro kinetic radioisotopic method, was about 7--10% of the normal. On starch gel electrophoresis, the enzyme from the haemolysate had similar mobility as the normal in Tris--glycine buffer, pH 8.8 and phosphate buffer, pH 7.0, but had a slower mobility than that of the normal in the histidine buffer, pH 7.8. The mobility difference was much clearer in a semipurified enzyme preparation. The transferase enzyme in the haemolysate appeared to be more heat labile.

Diagnosis of classical galactosaemia

We report a child with classical galactosaemia whose diagnosis was missed until 12 weeks of age. The limitations of urine screening tests are discussed and the wider use of a qualitative enzyme assay for screening is recommended. Reference ranges for a quantitative enzyme assay using 14galacoste-1-phosphate as substrate are presented.

The Chicago variant of clinical galactosemia

A new variant of clinical galactosemia with two hitherto unidentified alleles on the transferase locus in one family is described. This new clinical variant of transferase has 25% of normal control activity in blood and in skin fibroblasts, and the patient accumulates galactose-1-phosphate in blood on an unrestricted galactose diet. Using starch gel electrophoresis on the hemolysate of the family members, a fast-moving transferase with mobility in between those of the normal control and of the Duarte variant is identified. This new allele is designated as GALTC1 (fast-moving Chicago variant). In addition, a second new allele was documented in this family by studying the instability of the transferase enzyme in hemolysates of family members at 50 degrees C for various time intervals. This new allele is designated as GALTC2 (heat-labile Chicago variant). On the basis of these studies, the transferase genotype of this patient is thought to be a double heterozygote compound, GALTC1/GALTG.

Heterozygote advantage for the phenylketonuria allele

Mean weight at birth of unaffected (normal homozygous and PKU heterozygous) offspring of parents heterozygous for the phenylketonuria (PKU) allele averages significantly above that of Norwegian neonates, with no significant difference in mean age of mothers or in mean parity. It approaches the optimal birthweight--that which confers the minimum overall mortality in the pre-, peri-, and postnatal periods. This near-optimal birthweight together with the possibly higher effective fertility observed in PKU heterozygous couples (at least in those who married before 1940), has apparently more than outweighed the disadvantages of the allele in PKU homozygous offspring as shown, for example, in an excessive number of pre- and perinatal deaths among the total offspring of PKU heterozygotes, to say nothing of the PKU survivors who, often, used to die young. The two effects--fertility and viability--apparently both contribute in the same direction, to give a biological fitness in excess of 1 for the heterozygote. This heterozygote advantage presumably explains the presence of the allele at frequencies above those to be expected from the simple replacement of a homozygously-lethal allele by mutation alone.

Experience of routine live-birth screening for galactosaemia in a British hospital, with emphasis on heterozygote detection

Results are reported of a screening programme for galactosaemia covering a period of 2½ years and 6415 births. The gene frequency for galactosaemia estimated from the data of the screening programme was 0·002. This conflicted with the known live-birth incidence of at least 1: 50,000 during this same period. 2 of the 4 galactosaemic infants concerned died under circumstances that were preventable had they been screened at birth. The need to screen all sick infants for galactosaemia is emphasized, as is the requirement for reliable information on its incidence in Great Britain. The screening test employed (Beutler and Baluda, 1966a) seemed appropriate for this purpose. It was simple to perform and apparently accurate in galactosaemic infants. Its accuracy in detecting heterozygotes is uncertain. This test should be available in all hospitals receiving sick neonates.