Biochemical and EEG studies in phenylketonuric children during phenylalanine tolerance testc

Phenylketonuria: a review of current and future treatments

Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism caused by a deficiency in the hepatic enzyme phenylalanine hydroxylase (PAH). If left untreated, the main clinical feature is intellectual disability. Treatment, which includes a low Phe diet supplemented with amino acid formulas, commences soon after diagnosis within the first weeks of life. Although dietary treatment has been successful in preventing intellectual disability in early treated PKU patients, there are major issues with dietary compliance due to palatability of the diet. Other potential issues associated with dietary therapy include nutritional deficiencies especially vitamin D and B12. Suboptimal outcomes in cognitive and executive functioning have been reported in patients who adhere poorly to dietary therapy. There have been continuous attempts at improving the quality of medical foods including their palatability. Advances in dietary therapy such as the use of large neutral amino acids (LNAA) and glycomacropeptides (GMP; found within the whey fraction of bovine milk) have been explored. Gene therapy and enzyme replacement or substitution therapy have yielded more promising data in the recent years. In this review the current and possible future treatments for PKU are discussed.

Newborn screening 50 years later: access issues faced by adults with PKU

Fifty years after the implementation of universal newborn screening programs for phenylketonuria, the first disease identified through newborn screening and considered a success story of newborn screening, a cohort of adults with phenylketonuria treated from birth provides valuable information about effects of long-term treatment for inborn errors of metabolism in general, and phenylketonuria specifically. For phenylketonuria, newborn screening allows early implementation of the phenylalanine-restricted diet, eliminating the severe neurocognitive and neuromotor impairment associated with untreated phenylketonuria. However, executive function impairments and psychiatric problems are frequently reported even for those treated early and continuously with the phenylalanine-restricted diet alone. Moreover, a large percentage of adults with phenylketonuria are reported as lost to follow-up by metabolic clinics. While a group of experts identified by the National Institutes of Health convenes to update treatment guidelines for phenylketonuria, we explore individual patient, social, and economic factors preventing >70% of adult phenylketonuria patients in the United States from accessing treatment. As more conditions are identified through newborn screening, factors affecting access to treatment grow in importance, and we must continue to be vigilant in assessing and addressing factors that affect patient treatment outcomes and not just celebrate amelioration of the most severe manifestations of disease.

EEG development in early treated PKU patients from birth to 6 years of age

In 126 early treated PKU patients (type I and type II) a close EEG follow up was performed from birth up to 6 years of age. A total of 1465 EEGs were performed before and after onset of dietary treatment and on 11 more subsequent occasions. The composition of the background activity was normal up to 6 years when only a small number of the children (19) showed no dominant alpha activity. The frequency of epileptiform activity of generalised as well as focal type was low in the first 2 years of life, but afterwards slightly enhanced in comparison to normal control groups. Other findings like generalised theta paroxysms or focal slow waves were rarely observed. Under a standardised protein load at 6 months (52 patients) and at 5 years of age (42 patients) a moderate generalised slowing of the background activity but no other abnormalities were noted.

Long-term development of intelligence (IQ) and EEG in 34 children with phenylketonuria treated early

In 34 children with phenylketonuria (PKU) treated early the prognostic value of the age on institution of the diet (within the first 3 months of life) and of the quality of dietary treatment was determined in two different ways: 1) following intelligence closely (IQ) and (2) evaluating the EEG development up to their 12th (n = 34) and 15th (n = 18) years of life as appropriate. In general, IQ scores were found to be normal from the 4th-15th years of life. In our group of patients there was no effect on the IQ of the timing of diet onset. Children with "strict" dietary control showed a significantly higher IQ than those with "loose" control. One hundred and fifty-four EEGs (10/20 system, awake with eyes closed) were recorded at intervals of 2 years and conventionally evaluated. The development of alpha-activity was found to be normal. Beta-activity was enhanced. Abnormal EEG findings like general slowing and generalized paroxysmal activity (GPA) with or without spikes were more frequent in children with PKU than in controls, with the exception of focal abnormalities. EEG abnormalities increased with advancing age independently of IQ development and showed no relation to either the age at the onset nor the quality of dietary treatment.

Pattern-reversal visual evoked potentials in phenylketonuric children

Pattern-reversal visual evoked potentials (PR-VEPs) and EEG were recorded in 14 phenylketonuric (PKU) children on a low-phenylalanine (phe) diet; the data obtained were correlated with metabolic parameters, namely, the actual phe plasma level, the mean phe plasma level in the last year, an the beginning of the diet. PR-VEPs seem to be more sensitive than EEG in detecting neurophysiological derangements in these subjects; in fact PR-VEPs were pathological in six patients while EEG detected three; no significant alterations were found in the neurophysiological tests among the children with good metabolic control, and only one child was abnormal among the six on an early dietetic regimen; in contrast, six of the nine subjects presenting with high mean phe plasma levels (greater than 10 mg/100 ml) and five of the eight whose diet started after the 2nd month of life showed pathological PR-VEPs.

Computer analysis of the EEG as an aid in the evaluation of dietetic treatment in phenylketonuria

The effect on the EEG of the reintroduction of phenylalanine in the diet of 6 patients with PKU on treatment was studied. Patients received daily loads of 100 or 150 mg L-phenylalanine/kg, equally divided over the meals, and computerized spectral EEG analysis was performed. The following EEG changes were seen: (1) occurrence of activity in the low frequency band (2--5 c/sec), (2) change of frequency of dominant rhythms; (3) change in the degree of synchrony between identical frequencies, occurring in different derivations. EEG changes increased quantitatively parallel to increasing blood phenylalanine and reversed after stopping the phenylalanine administration, suggesting that the EEG abnormalities are a measure for the degree of intoxication caused by phenylalanine or its metabolites. It is suggested that the EEG data may be useful deciding to terminate the diet in PKU.

Menkes' disease: neurophysiological aspects

The evolution of neurophysiological features including the electroencephalogram (EEG), electroretinogram (ERG), and visual evoked potentials (VEP) is reported in eight cases of Menkes' "kinky hair" disease. All EEGs were severely abnormal, with some characteristic features seen from 3-5 months of age, after the onset of clinical symptomatology. From the age of 5 months, the EEGs resembled hypsarrhythmic patterns. The ERG was not affected in any patient, but the VEP was either of low amplitude or completely absent in all but one of the six patients tested. All eight patients received copper injections without substantial effect on either the clinical course of the disease or the EEG features.

Neurological disturbance in a phenylketonic child after discontinuation of dietary treatment

Signs of moderately severe spastic diplegia appeared in 14-year-old late-treated phenylketonuric boy 13 months after dietary restrictions were lifted. The literature contains reports of untreated phenylketonuric patients developing demyelinating conditions in later childhood. The possible implications of relaxing the diet in early- and late-treated cases of phenylketonuria are discussed.

Histidinaemia. Study of relation between clinical and biological findings in 7 subjects

Seven subjects with raised plasma histidine and low skin histidase levels (histidinaemia) are described: 4 were severely retarded, 2 showing in addition features of an early infantile psychosis (autism); 3 were of normal intelligence. There were no biochemical differences between the two groups. In view of these findings and a study of patients reported in the literature, attention is drawn to the difficulty in making a decision about treatment of a neonate detected by screening and shown to have the biochemical features of histidinaemia. The natural history of the condition is further examined, particularly the question of deterioration at time of seizures or infection.

Phenylketonuria: a review

The development of a practical screening procedure for phenylketonuria and the improvement in methods of chemical analysis have led to a realization that Folling's (1934) disease of phenylketonuria is not a single entity.

In this commentary, the current view on some aspects of phenylketonuria will be reviewed and the problems illustrated by experience gained in the Phenylketonuria Clinic at the Royal Alexandra Hospital for Children in Sydney, at present attended by fifty-six children. From April 1964, fifty-six infants and children were referred because of a positive screening test. Six were no longer abnormal at the time of retesting, forty-two had classical phenylketonuria and eight showed an atypical pattern. Subsequent family studies revealed five other classical phenylketonuric children, all of whom were retarded, and one other atypical phenylketonuric boy.

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