Neil R.M. Buist

Neonatal screening for alpha1-antitrypsin deficiency

The Oregon State Public Health Laboratory screened 107,038 newborn infants between 1971 and 1974 to determine the frequency and clinical characteristics of alpha 1 -antitrypsin deficiency. The screening program was based upon an assay of the total trypsin inhibitory activity in dried blood specimens collected on filter paper from infants during the first week of life and again from 75% of the same infants at four to six weeks of age. Twenty-one homozygous-deficient (PiZ) infants were identified, an incidence of one in 5,000. Of the 18 infants studied and followed, only one had neonatal hepatitis; five had hepatomegaly or biochemical abnormalities or both, indicating hepatic damage. Presently, the children range from three to six years of age; all are asymptomatic. Four of them have mild hepatomegaly and biochemical evidence of liver damage. As a result of family studies, four homozygous-deficient (PiZ) siblings were identified. One child had evidence of mild hepatic dysfunction, but the other three were clinically and biochemically normal. Nine of the 21 PiZ infants detected were missed on the initial sample, but identified on the four to six week sample. If a screening method based upon TIA is to be utilized, these results indicate that a repeat screening specimen should be obtained at four to six weeks of age. Newborn screening for alpha 1 -antitrypsin deficiency is not warranted at this time in view of the low frequency of significant pulmonary or hepatic involvement in childhood and the absence of specific therapy for this condition.

Further studies on a patient with iminodipeptiduria: A probable case of prolidase deficiency

Abstract Some studies have been performed upon a urine sample obtained from a patient previously reported by Goodman et al. to exhibit massive iminodipeptiduria. 31,000 μmole (3.34 g) of dipeptide proline and 1900 μmole (250 mg) of dipeptide hydroxyproline were excreted in 24 hr. In addition to the six dipeptides originally reported, we have isolated and quantitated Pro-Pro (2180), Ala-Pro (1360), Tyr-Pro (1040), Phe-Pro (1880), and Lys-Pro (140). Twenty-four-hr values in micromoles are given in parentheses. Enzymatic data suggest the existence also of Asp-Pro (1610), Glu-Pro (70), Thr-Pro (1680), Ser-Pro (1630), His-Pro (390), Arg-Pro (100), and Tyr-Pro (170). No hydroxyproline-containing dipeptides have been isolated, but chromatographic evidence suggests the presence of Ser-Hyp, Glu-Hyp, Gly-Hyp, Ala-Hyp, Pro-Hyp, (or Hyp-Pro). All the abnormal peptides were hydrolyzed by a preparation of prolidase in vitro. The data suggest that a generalized defect of imino-carboxyterminal dipeptide catabolism was present, and they are consistent with the possibility that the patient possessed a defect of tissue prolidase activity. From the data, it can be calculated that 2.0–2.5 g of collagen was being degraded per day.

The separation of peptides from amino acids by ligand-exchange chromatography

Abstract A rapid ligand-exchange chromatographic method for the separation of α-amino acids from peptides is presented. All α-amino acids, apart from aspartic acid and glutamic acid, are totally excluded from the peptide fraction. Most simple peptides are eluted quantitatively in this fraction, with the exception of some oligopeptides containing carboxy-terminal basic amino acids which are retained on the column. 83% of a tryptic hydrolysate of globin eluted into the peptide fraction. In simple systems, the method can be used to separate peptides from amino acids and to quantitate the peptides at the same time.

Analysis of dentine pathogenesis in vitamin D--resistant rickets.

Abstract Vitamin D—resistant rickets, a disease that is inherited as a sex-linked dominant trait, is accompanied by characteristic dentine defects. Since children with this disorder are often found to have mothers with the same disorder, it is conceivable that the metabolism of an affected mother may affect the child in utero.

Citrullinemia: Investigation and treatment over afour-year period

A child with a severe form of citrullinemia has been studied over four years. The biochemical findings included increasedblood levels of citrulline, alanine, glutamine, homocitrulline, and carnosine, and increased urinary content of citrulline, glutamine, orotic acid, uracil, homocitrulline, and N-acetylcitrulline. Urea synthesis was compromised. The beneficial effect of dietary restriction of protein is illustrated by the rate of head growth and by the subsequent development of the child. Heterozygotes may be detected by assay of fasting plasma citrulline levels. Enzyme studies on cultured skin fibroblasts indicated a marked lack of argininosuccinate synthetase activity in the patient and approximately half-normal activity in three heterozygotes.

Sterol balance in abetalipoproteinemia: Studies in a patient with homozygous familial hypobetalipoproteinemia

A new case of homozygous familial hypobetalipoproteinemia is reported in a 16-yr-old girl. Apoprotein B was absent from plasma and the patient had acanthocytes and steatorrhea, but minimal neurologic dysfunction. Total body cholesterol synthesis was assessed intermittently over a 30-mo period by sterol balance techniques. The rate of synthesis of cholesterol was higher (15.0 +/- 2.9 mg/kg/day) in the patient (8.3 +/- 0.4 mg/kg/day than in 3 control children, p less than 0.005). Bile acid synthesis was similar (4.6 +/- 1.8 versus 4.0 +/- 1.7 mg/kg/day) in the patient and controls, but total body sterol synthesis was significantly higher (19.6 +/- 3.0 versus 12.2 +/- 2.0, p less than 0.005). The absorption of orally administered [1,2,(3)H] cholesterol in the patient was low and less than 0.5% of the label appeared in the total plasma volume at all times up to 48 hr. Estimates of the extent that malabsorption of biliary cholesterol contributes to the enhanced excretion of neutral sterols in this case indicate that all of the increase can be explained on this basis. Thus, although the mechanisms for the increased sterol synthesis in this case may relate to the absence of chylomicrons and low density lipoproteins in plasma, the magnitude of the increase can be fully explained on the basis of a compensatory mechanism to maintain cholesterol homeostasis in the face of enhanced fecal losses.

Excretion of α-N-acetylcitrulline in citrullinaemia

Abstract α-N-Acetylcitrulline has been identified in the urines of two unrelated patients with citrullinaemia. Identification was made on the basis of similarity to the synthetic compound prepared in this laboratory. Excretion of α-N-acetylcitrulline during normal protein intake was 75–120 mg/24 h compared to citrulline excretion of 360–770 mg/24 h in the 10-week-old patient, and in the 30-year-old patient it was 610 mg/24 h compared to citrulline excretion of 2200 mg/24 h.

The source of aromatic ketoacids in tyrosinaemia and phenylketonuria.

Abstract The studies reported here support the observation that elevated excretion of p -hydroxyphenylpyruvic acid could occur in the presence of deficient hepatic tyrosine aminotransferase activity. The ketoacid need not have come either from the liver or from the kidney. It appears possible that the urinary ketoacid, both in tyrosine aminotransferase deficiency and in phenylketonuria, originates not in the liver but in other tissues which possess transaminase but which lack hydroxylase activity. What emerges from these studies is the view that the consequence of a single enzyme deficiency in one tissue may be modified by the distribution of isozymes or related enzymes in that tissue as well as in other tissues.

Gyrate atrophy of the choroid and retina - Approaches to therapy

Gyrate atrophy of the choroid and retina is caused by deficient activity of ornithine ketoacid aminotransferase, a pyridoxal phosphate dependent enzyme. Besides the typical eye findings, abnormalities have been found on muscle biopsy, electro-encephalography, electromyography and electrocardiography, establishing this as a generalized disorder. Ornithine is markedly elevated in plasma and other body fluids. Plasma lysine, glutamate, glutamine and creatine are reduced. The possible contributions of these biochemical disturbances to the pathogenesis of gyrate atrophy are discussed. The disease is one of the few examples of an inherited chorioretinal dystrophy whose underlying biochemical defect is known. It therefore offers a unique opportunity to develop and test rational approaches to therapy. These include lowering of the abnormally high ornithine by dietary restriction of its precursor arginine, facilitation of ornithine excretion by administation of α-aminoisobutyric acid, replacement of deficient products such as lysine or creatine, or increasing residual enzyme activity by high levels of cofactor (vitamin B6). The results of several studies employing such approaches to therapy are presented as well as preliminary indications of possible benefit in a few patients.

A guide to screening newborn infants for inborn errors of metabolism

Summary In principle, screening of all newborn and older infants and children for inborn errors of metabolism makes good sense; and for some diseases there is a considerable financial and social inducement to do so. New techniques must be evaluated in pilot studies in order to establish the frequency of a disease and its clinical variation. Most of the biochemical diseases considered here are rare, whereas some conditions such as hypoglycemia, cretinism, and urinary tract infections are common in comparison and can be equally serious. We should strive for methods aimed at solving common medical problems in addition to having tests for rare and esoteric disorders. No metabolic screening program should be started without adequate facilities for clinical evaluation and follow-up and until the capacity to evaluate its results and to interpret them intelligently has been established. The optimum program for screening for biochemical disorders has not yet been defined; it would certainly vary in different geographic areas. Using the methods which are currently available, a possible schedule is given in Table VI. This schedule would not detect most of the diseases which cause symptoms shortly after birth (such as maple syrup urine disease and other diseases associated with ketoacidosis or with hyperammonemia). This program would need to be supplemented by amino acid chromatography of samples from those babies who become ill in the first month of life with a disorder which is not otherwise readily identified. This schedule would have the advantage of involving physicians more in the results of the screening program.