Selective screening for neonatal galactosemia: an alternative approach

No universal consensus exists for population-based neonatal screening for galactosemia. In our institution, selective screening for classical galactosemia is carried out on infants under 2 wk of age and those with symptoms suggestive of this disorder. Eighteen cases were diagnosed from 25,099 tests done; 17 were symptomatic at the time of diagnosis.

CONCLUSION

We suggest that improved clinical vigilance and selective screening would identify most infants with severe galactosemia as early as a population-based program.

"Hypotyrosinemia" in phenylketonuria

It has been postulated that the significant incidence of learning disabilities in well-treated patients with phenylketonuria (PKU) may be due, in part, to reduced production of neurotransmitters as a result of deficient tyrosine transport across the neuronal cell membrane. Hypotyrosinemia has been reported in treated and untreated PKU but virtually no data are available. We decided to examine this in our patient population and to compare it with the published norms, patient data from our hospital clinical biochemical laboratory database, and a group of normal children and adolescents in a private pediatric practice. We found that the mean nonfasting plasma tyrosine in 99 classical PKU patients was 41.1 micromol/L, in 26 mild (atypical) PKU patients 53.3 micromol/L, and in 35 non-PKU mild hyperphenylalaninemia patients 66.6 micromol/L. This compared to nonfasting plasma tyrosine levels in 102 non-PKU subjects of 64.0 micromol/L in our hospital biochemistry database, 69.1 micromol/L in 58 volunteers in the private office practice, and 64-78.8 micromol/L in infants, children, and adolescents in the literature review. Our data support the previously undocumented statements in the literature that plasma tyrosine levels are low in PKU.

Ethylmalonic and methylsuccinic aciduria in ethylmalonic encephalopathy arise from abnormal isoleucine metabolism

Ethylmalonic encephalopathy (EE), an organic aciduria of unknown etiology characterized by developmental delay, hypotonia, and vascular instability associated with lactic acidemia and urinary excretion of ethylmalonic acid (EMA) and methylsuccinic acid (MSA), has been described in 11 patients. To test the possibility that the underlying biochemical defect involves isoleucine catabolism, we determined the response to oral L-isoleucine (IIe) load (150 mg/kg) in a 5-year-old girl with EE and in three healthy, age- and sex-matched controls. Following IIe load in the patient, there was accumulation of 2-methylbutyrylglycine (2-MBG) and a delayed and lower peak urinary excretion of tiglylglycine (TGL), suggesting a partial defect in 2-methyl-branched chain acylcoenzyme A dehydrogenase (2M-BCAD). In vitro measurements 2M-BCAD activity in cultured skin fibroblasts from patients with EE have been reported to be normal. Our results show that isoleucine is a source for the elevated EMA and MSA in patients with EE, and suggest a functional, possibly secondary, deficiency of activity of 2M-BCAD in vivo.

Barth syndrome: clinical observations and genetic linkage studies

Barth syndrome is an X-linked recessive condition characterized by skeletal myopathy, cardiomyopathy, proportionate short stature, and recurrent neutropenia, but with normal cognitive function. Some, but not all patients, exhibit carnitine deficiency and/or the presence of 3-methylglutaconic and ethylhydracylic acids in urine. Recently the mutation causing Barth syndrome was localised to the Xq28 region by linkage analysis. We report 6 cases of Barth syndrome from 4 families and highlight the fact that neuromuscular and cardiovascular symptoms and the severity of infections tend to improve with age, while short stature persists. Also previously unreported was myopathic facies and nasal quality to speech in our cases. The urinary organic acid abnormalities and plasma carnitine deficiency were inconsistent findings. We propose that they may be epiphenomena rather than indicators of the primary metabolic defect, and that the primary defect or defects in this disorder may lie in the mitochondrial electron transport chain.