Problemy w realizacji diety ubogofenyloalaninowej u dzieci chorych na fenyloketonurię

Joanna Woźniak-Holecka1*, Piotr Romaniuk2, Tomasz Holecki3, Aleksandra Tomanek4

1Department of Health Promotion, School of Public Health in Bytom, Medical University of Silesia in Katowice, Poland

2Department of Health Policy, School of Health Sciences in Bytom, Medical University of Silesia in Katowice, Poland

3Department of Health Economics and Health Management, School of Public Health in Bytom,  Medical University of Silesia in Katowice, Poland

4Department of Health Promotion, School of Public Health in Bytom, Medical University of Silesia in Katowice, Poland

Abstract

Introduction: Phenylketonuria in Polish population occurs with frequency about 1: 7000 births (60 newborns per year). Untreated or improperly treated phenylketonuria is the cause of the most severe forms of intellectual disability. The only effective treatment is the use a strict elimination diet for a lifelong. The diet consists on restriction of supply of phenylalanine, and it must be selected individually for each patient in accordance with the daily mean tolerance of phenylalanine, resulting from residual enzyme activity.

The aim: To examine the problems in the implementation of the low-phenylalanine diet in parents of children with phenylketonuria.

Material and Methods: The method used in the diagnostic survey based on the author’s questionnaire. For most parents the low-phenylalanine diet was difficult to implement. The most common problems in the implementation of the diet were: high costs of low protein food and a small variety of allowed products, which is associated with the difficulty of preparing varied meals. The research covered 50 parents of children with phenylketonuria.

Results: Most parents do not follow strict dietary recommendations, childrens were snacking prohibited products and they are refused to eat the medicinal product. More than half of the respondents had an opportunity to benefit from the advice of a dietitian. The main source of expansion of knowledge about the diet were health workers and the Internet.

Conclusions: For most parents, the low-phenylalanine diet was difficult to implement.

Key words: phenylketonuria, elimination diet, low-phenylalanine diet

Public Health Forum 2019;V(XIII)1(48):49-55

INTRODUCTION

Phenylketonuria (PKU) is a rare congenital disorder of metabolism of a not fully recognized etiology. Its symptom is a progressive mental retardation resulting of the accumulation of phenylalanine (Phe). The disease is included in the group of monogenic, congenital genetic errors inheriting in an autosomal recessive way, and is the most common metabolic error in amino acid metabolism [1, 2]. The cause of the disease is total absence or partial deficit of phenylalanine hydroxylase PAH activity resulting in inhibition of phenylalanine conversion to tyrosine [3]. Phenylalanine hydroxylase activity is proportional to the concentration of phenylalanine in blood [4]. Phe’s pathomechanism of neurotoxic activity is unknown. It is currently being studied in three aspects: the influence of high concentrations of Phe on the transport of other amino acids through cell membranes and blood-brain barrier, myelin synthesis and myelosomal abnormalities, and decreased synthesis of neurotransmitters [5].

Phenylalanine, which is an exogenous amino acid, must be supplied with food, because the body is unable to synthesize it from other compounds. It participates in protein synthesis, is a substrate for the production of hormones, neurotransmitters and dyes. The concentration of phenylalanine depends on the diet. Phe’s main source in food is protein products: meat, poultry, fish, eggs, legumes, milk and milk products [5, 6].

Following the accumulation of phenylalanine in the blood (hyperphenylalaninemia) and other body tissues, in patients with phenylketonuria there is irreversible damage to the central nervous system, which is manifested by mental retardation and neurological disorders. However, if the disease is early diagnosed and the dietary treatment is introduced in the early days of the newborn’s life, it is possible to ensure the proper development of the baby [2, 7]. This is conducive to screening newborns and initiate treatment before irreversible central nervous system disorders appear. In Poland around 60 children affected by phenylketonuria are born every year. It is also estimated that every 46 healthy people carry the defective PAH gene [7] and about 2000 people born between 1950 and 1980 can be considered as undiagnosed [8].

Currently in Poland the screening is mandatory for all neonates regardless of having health insurance and is financed by the Ministry of Health as part of health prevention. The neonatal screening test is performed by taking a few drops of blood from the heel of each newborn who has reached the age of 72 hours and marking the phenylalanine concentration.

Screening based on Guthrie’s test has been done voluntarily since 1965 and then in became compulsory since 1986. In 2002 pilot studies for rare metabolic defects with the use of tandem mass spectrometry were also launched. At present, this technique is in the implementation stage in individual voivodships (Polish administrative regions) [9, 10].

Following the publication in 1953 of Horst Bickel’s research results, who first applied the limited supply of phenylalanine, it turned out that the main way to treat this disease is elimination diet [8]. Treatment includes a diet low in phenylalanine, normocarbon and normocaloric [2]. In patients with phenylketonuria adequate supply of energy is conducive for reduction and stabilization of the Phe concentration in the blood. The source of energy in the low phenylalanine diet are: Phe-free substitutes of proteins, fats, low-protein and high-carbohydrates without Phe, sweets with a low protein content and fruits [11]. Protein sources are mixtures of synthetic L-amino acids with increased tyrosine content. The free amino acids contained therein are absorbed faster than those that are part of the natural protein. The preparations being in use differ in the content of Phe, proteins, fats, carbohydrates, minerals, vitamins, trace elements, and their selection depends on age, weight and individual patient tolerance of phenylalanine. The diet is based on special medicinal preparations that cover 70-95% of the daily protein requirement; the remaining 5-30% cover dietetic foods described as PKU products and traditional low phenylalanine products [2]. The daily dose should be given at least three portions per day. The patient may receive daily an amount of phenylalanine, which will not increase the levels of this amino acid in the blood and is sufficient to maintain a positive nitrogen balance [11]. It should be however noted that the tolerance to phenylalanine is individual, changes with age and, therefore, every patient has to follow a strict individual diet [3]. It should be also emphasized that diet low in Phe as a treatment for phenylketonuria classic form is a restrictive elimination diet, where the exclusion of a large number of high-quality natural products, which are a source of protein and other nutrients (vitamins, macro- and microelements), may predispose the patient suffering phenylketonuria nutritional deficiencies [11].

Extension of the diet by introducing natural foods while maintaining normal Phe concentrations does not guarantee coverage of daily protein requirements. Parents and their children planning a diet have to know the content of phenylalanine in all products and select these, which will not cause to exceed the allowable amount of this amino acid in the diet [2]. With regard to the content of phenylalanine, food products can be divided into three groups: not allowed, allowed in limited quantities and allowed without limitation [12]. Products and foods that do not contain phenylalanine need not be restricted. In order to properly balance the diet, instead of many prohibited products, it is necessary to introduce substitutes with low protein content. Extension of the diet may cause adverse effects, such as irritability, nervousness, problems with concentration, skin changes. If such symptoms occur, patient should return to a strict low-phenylalanine diet.

The aim

The aim of this study is to synthesize the results of research on the problems of the low phenylalanine diet among parents of children with phenylketonuria, identification of nutritional errors, identification of dietary knowledge sources and availability of dietary advice in prevention and treatment.

MATERIAL AND METHODS

The study covered 50 parents of children with phenylketonuria in Poland. The criterion for inclusion was the diagnosis of the classic form of phenylketonuria and the age of the child from 1 to 15 years. As a survey technique we used a questionnaire, which contained closed and open questions. There were questions about the child’s illness, treatment control, information provided on visits, availability of nutritionists, sources of illness information. Further questions related to problems in the use of low phenylalanine diet, the level of parents’ knowledge and the way of feeding children. The final questions allowed the parents to self-assess their current diet and level of nutritional knowledge. The results obtained were analyzed statistically. We determined the correlation coefficients of rhoSperman and V Cramer, followed by statistical tests: Mann-Whitney U and Chi2.

RESULTS

There were 46 women (92%) and 4 men (8%) in the study of parents with phenylketonuria. The largest group was between 30 and 39 years old (20 respondents; 40%) and between 20 and 29 years old (18 respondents; 36%). Among the respondents, the biggest was the group having higher education (26 persons; 52%). The study involved 33 parents (66%) of boys and 17 parents (34%) of girls aged between 1 and 15 years. 19 children were between 1 and 5 years (38%), in the group 6 to 10 years there were 24 children (48%), and children between 11 and 15 years constituted 14% (7) of the group. In 47 children (94%) the diagnosis was made immediately after birth, while in three cases (6%) the disease was diagnosed later (in the second, ninth and eighteenth month of the child’s life). Only one child has a chronic coexisting illness (epilepsy), the other 49 children do not suffer from other chronic diseases.

The control of phenylketonuria requires systematic visits to the clinic of metabolic diseases. 43 respondents (86%) declared that their control visits were systematic at scheduled times; 6 respondents (12%) were under the care of the clinic, but visits were sporadic or planned when worrisome symptoms occur. Only one person declared that the child is not under the care of a metabolic disease clinic.

The information that was provided to parents on the first visit to the clinic concerned primarily dietary recommendations, a list of products allowed and prohibited in the diet of patients suffering from phenylketonuria and the consequences of non-compliance. While addressing the frequency of dietary recommendations, 40 respondents (80%) reported that they received this information regularly during control visits to the metabolic diseases clinic, while 10 respondents (20%) received this information only once, at the first visit.

As far as the source of knowledge about phenylketonuria is concerned, the most frequent are direct interviews with health care personnel (72%), internet (70%) and information sharing with parents of other children (68%).

Nearly half of respondents (48%) have no problem identifying eligible products, while 13 respondents (26%) indicated that the difficulty was unreadable labels. Another 11 respondents (22%) identified the lack of information on the content of phenylalanine in food products. Other reported problem are manufacturers’ incorrect declarations on protein content (4%).

The highly significant, moderately strong correlation between dietician availability and problems with correct product identification is worth noting. The problems are much more frequent among people who do not have access to a dietitian than those with access (Table 1).

At the same time there is no statistically significant relationship between treatment in metabolic diseases clinic and problems with product identification, although the results show that the problems with product identification appears more often among people who have had occasional or no control visits (71.4%) than those who attended systematically (Table 2).

The most common issues related to preparations of meals were the unsatisfactory variety of allowed products (90%), the low availability of protein products (58%), the weighting and calculation of phenylalanine content in foods and products (58%) and high food costs (46%). Only 3 respondents (6%) reported no problems with preparation of meals. The problems parents most commonly encountered in application of the diet were child’s refusal to eat the preparation (36%), hunger (16%) and abnormal eating habits, such as eating banned products (16%). Over a half of parents (68%) have no problems in preparing the preparation for the child and 14 respondents (28%) indicated that such difficulties occur, especially outside the home. In terms of child’s independence, understood as preparation of meal and preparation according to dietary recommendations, 35,5% of respondents and 48,4% of respondents did not have difficulty. In case of indicating allowed and prohibited products, 48,4% and 64,5% of parents accordingly indicated lack of problems. As many as 20 respondents (40%) rated diet as difficult, 8 (16%) as very difficult. Only 7 people (14%) have no problems in following the diet recommendations and assess the diet as easy and quite easy. Details are given in Table 3.

The correlation between assessment of the implementation of diet and features of treatment was also statistically insignificant, as presented in Table 4.

Over half of respondents (60%) declared that they strictly adhere to dietary recommendations, while 20 respondents (40%) admitted that dietary lapses were occurring. The unallowable foods most commonly appearing in the diet were meat and its preparations and sweets. We found a highly statistically significant, moderately strong correlation between the level of education of the respondents and the frequency of dietary lapses – the higher the level of education, the less frequent lapses were declared. Details are presented in table 5.

A half of respondents (25 persons) declared that their child eat 4 to 5 meals during the day, while 7 parents (14%) admitted that the child consumes 3 meals a day. Almost all parents (96%) supplement the child’s diet (48 respondents), mainly with multivitamins, fish oil and vitamin D3. More than a half of respondents (52%) also declared low liquids intake by the child, meaning up to four glasses a day. The remaining respondents (48%) indicated drinking five or more glasses of liquid a day. The most commonly consumed liquids include water, tea and fruit juices. All respondents correctly indicated the recommended duration of diet. The vast majority – 44 respondents (88%) were able to indicate the products allowed in the diet. Nearly half of respondents (42%) were able to indicate symptoms of phenylalanine excess. In terms of self-assessment of the level of knowledge about the application of diets in phenylketonuria, 28 respondents (56%) assessed their knowledge level as sufficient, 14 (28%) indicated low level while demonstrating a desire to deepen their knowledge. We observed a highly statistically significant, positive correlation between the level of education and the self-assessment of knowledge. The higher the level of education, the better the self-esteem of the respondents’ knowledge (Rho=-0,510, p=0,000). At the same time we found statistically significant correlation between access to dietician and self-assessment of knowledge. However, it can be stated that those who do not have access to dietitian assess their knowledge as higher than those who have such access (U Mann-Whitney’s test: Z=-2,001, V Cramer’s=0,288, p=0,045).

DISCUSSION

The elimination diet applied in phenylketonuria is of particular importance, as it aims to prevent irreversible damage to the central nervous system. In addition, due to the limited group of allowed natural products, diets in phenylketonuria brings a risk of nutritional deficiencies. For this reason, the preparations used in the diet are enriched in many essential nutrients, such as micro and macroelements and vitamins. Of importance is that a properly balanced diet including all the recommendations is a full-fledged diet and should not lead to shortages [8, 11]. Optimal diet is low-phenylalanine, low protein, normocaloric, while its most important principles are [7, 13]:

the basis of properly used diets are special preparations with low level of phenylalanine or phenylalanine-free, enriched in tyrosine, which account for 70% of the protein demand.

It is necessary to provide 40-60 mg/kg/dl of phenylalanine in the diet of newborn child to achieve their normal growth. The tolerance of the amino acid in most older children and adults is on average 200-400 mg/dl.

Breastfeeding is usually possible and is currently recommended. Retrospective studies have shown that children with PKU breastfed have a significantly higher intelligence quotient than controls [14, 15].

It is necessary to supplement other essential amino acids, vitamins (especially riboflavin, vitamin B12, folic acid), minerals (especially zinc, selenium and iron). The demand should be met using low-calorie special PKU foods, such as pasta bread, rice, sweets, low protein and gluten-free flour, which cover a total of 5-30% of the diet.

• The energy and variety of the diet should be ensured by consuming low-protein foods in the form of fruits, low-starch vegetables, allowed products are also lollipops, drops and honey.

• It is necessary to completely eliminate high protein foods: meat, milk and milk products, eggs, fish, nuts. Bakings, including bread, pasta, groats, potatoes, beans, peas, soybeans are also forbidden.

• The aspartame, which is often included in dietetic sweetened drinks, vitamins or medicines, should be eliminated from the diet.

In a study by Mikołuć et al. conducted on a group of 107 children with phenylketonuria, an attempt was made to evaluate the nutritional compliance with recommendations [16]. This study has shown that childrens’ diets were properly balanced in terms of protein content and phenylalanine, but did not meet the need for fats and energy. Similar results were obtained in our study. The problem of demand for energy was related to 1/3 of respondents. Only half of the children ate from 4 to 5 meals a day, in line with current recommendations. More than one third of children eat 6 or more meals, which may contribute to over nutrition, both in energy and in the supply of phenylalanine. Nearly one third of parents reported they had a problem with ensuring the low level of this amino acid in the diet. It is worrisome that some children eat 3 meals a day, which poses a risk of food shortage, and a greater likelihood of eating between meals, due to the feeling of hunger. Parents admitted that hunger accompanies children who use the elimination diet. They also pointed out the problem of eating of prohibited products between meals. The statistical analysis showed the correlation between the level of education of the respondents and the frequency of lapses in the diet. The higher the education of parents, the dietary deviations occurred less often or not at all.

Properly balanced diet is extremely important especially during the child’s growth period. Studies show a link between abnormal control of PKU diet during intensive growth and accretion of the bones mass [17]. Causes of disorders in bone metabolism in patients with phenylketonuria are seen in long-term use of a diet low in natural protein and other nutrients. Calcium contained in medicinal preparations is much less absorbable than from natural sources [18].

In recent years, the importance of n-3 fatty acids in the development of nervous system, psychosomatic system and prevention of metabolic and psychological diseases has been emphasized. In patients with phenylketonuria, DHA supplementation at 15 mg/kg/day led to a reduction in neurological problems [19]. In our study, the respondents indicated supplementation with mainly multivitamin preparations and vitamin D3, including supplementation with fish oil by part of parents.

Treatment of phenylketonuria is subject to continuous and periodic control in metabolic diseases clinics. Continuous monitoring is based on a systematic determination of phenylalanine levels. Periodic inspection includes evaluation of mental, somatic and selected biochemical indicators of blood [7]. Most respondents report regular visits, always at designated times. In a study by Mroczek et al. conducted in a group of 16 children with phenylketonuria between ages 7 and 18, the proportion of people reporting a control visit was 62.5% [20]. The analysis did not show a statistically significant correlation between treatment control and dietary assessment. Both those who visited on a regular basis and those who visited occasionally likewise assessed the difficulty of dieting. This situation may be due to the specificity of treatment with strict elimination diet.

The vast majority of parents received dietary recommendations on each visit in the clinic. At the first of these, parents most often received information on permitted and prohibited foods, general dietary recommendations and the consequences of non-compliance. Statistical analysis revealed the relationship between access to dietitian, treatment control and product identification. This problem was reported more often by parents, who had occasional visits and had no access to a specialist. Continuous nutrition education plays an important role in controlling the treatment.

Parents’ nutritional knowledge about the basic principles of nutrition was good. Most parents were able to identify permitted and prohibited products. More than a half of respondents considered the level of their nutritional knowledge as sufficient. Statistical analysis revealed a correlation between the level of education and self-assessment of knowledge. The higher the level of parental education, the better they assessed their nutrition knowledge. In the study by Mroczek et al. all respondents rated their nutritional knowledge as good and were able to identify prohibited products [20]. The Internet (44%) and books (48%) were the sources of knowledge about the disease for adult respondents. In our study parents most often received information from health care personnel, the internet and parents of other children suffering the illness. Some respondents indicated that they use books, guides, leaflets, booklets and receive information from the Phenyloketonuria Children’s Aid Association.

Studies indicate that dietary restrictions in phenylketonuria should be respected throughout the entire life [21, 22]. However, the vast majority of the respondents considered that the low phenylalanine diet was difficult to be achieved. Similar results were obtained in a study by Sternal and Grzywna, where 84.6% of parents had problems implementing diet [23].

In our study most respondents rated the assortment and availability of low-protein products as quite good. While the most common problem in the diet was the small variety of products allowed, which was associated with a small variety of meals. The same problem was reported by 74% of parents in Sternal and Grzywna [23]. For more than a half of the respondents, difficulty in implementing the diet was weighting of products and calculation of the phenylalanine content, which in the case of the above study was reported as difficult by one third of parents (32.5%). Differences in results may be due to the fact that parents of older children do not need to carefully calculate the content of phenylalanine in products and meals, provided that the concentration of phenylalanine in the blood is kept within normal limits.

All respondents rated the cost of low protein foods as too high. For nearly half of the respondents the high cost of buying low phenylalanine products hindered the diet. In a similar study by Sternal and Grzywna [23]. This problem is undoubtedly related to the material situation that most of the respondents identified as average or bad.

More than half of parents said that they did not strictly follow the diet recommendations. These results are worrying because of the possibility of irreversible changes within the central nervous system of children suffering PKU. Eating habits are evolving from an early age, so it is important to educate children and parents in this area, while only strict compliance to the diet guarantees full sustainable development and independent living of the child.

CONCLUSIONS

1. For most parents the low phenylalanine diet was difficult to implement and was therefore not strictly followed.

2. The most common problems in the diets indicated by parents were: high cost of low protein foods and low variety of allowed products.

3. The most common problems in the implementation of the low phenylalanine diet on the part of the child were: refusal to consume preparations and breaking the prohibitions on non allowed products.

4. The main source of knowledge about the proper diet were health care personnel, as well as information from the internet. More than half of the respondents used advice from a qualified dietitian.

5. Continuous co-operation of parents of children with phenylketonuria with a qualified dietitian significantly reduces the problems associated with the use of low-phenylalanine diet.

Reference:

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ORCID

Joanna Woźniak-Holecka – 0000-0002-4468-063X

Tomasz Holecki – 0000-0003-1798-4133

Piotr Romaniuk – 0000-0003-4575-1345

Conflict of interest:

Authors declare no conflict of interest.

Correspondence author

Joanna Woźniak-Holecka,

Department of Health Promotion,

School of Public Health in Bytom,

Medical University of Silesia in Katowice, 41-902 Bytom, Poland,

ul. Piekarska 18

tel./fax (+48) 32 397 65 37,

e-mail: jwozniak@sum.edu.pl

Received: 03.02.2019

Accepted: 03.10.2019

Table 1. Availability of dietitian and problems with identification of products allowed in the diet of patients with phenylketonuria

Problems with identifying products

Access to dietitian

Total

Yes

No/don’t know

N

%

N

%

N

%

No

22

59,5%

2

15,4%

24

48,0%

Yes

15

40,5%

11

84,6%

26

52,0%

Total

37

100%

13

100%

50

100%

Chi2=7,487, p=0,006, V Cramer’s=0,387, p=0,006

Table 2. Relationship between treatment and problems with identification of products allowed in the diet of patients with phenylketonuria

Problems with identifying products

Treatment

Total

Systematic visits at scheduled times

Visits sporadic or when worrisome symptoms occur

N

%

N

%

N

%

No

22

51,2%

2

28,6%

24

48,0%

Yes

21

48,8%

5

71,4%

26

52,0%

Total

43

100%

7

100%

50

100%

Chi2=1,231, p=0,267, V Cramer’s=0,157, p=0,267

Table 3. Availability of dietitian vs assessment of the implementation of low phenylalanine diet

Assessment of the implementation of diet

Access to dietitian

Total

Yes

No/don’t know

N

%

N

%

N

%

Very difficult

7

18,9%

1

7,7%

8

16,0%

Difficult

16

43,2%

4

30,8%

20

40,0%

Quite difficult

11

29,7%

4

30,8%

15

30,0%

Quite easy

2

5,4%

2

15,4%

4

8,0%

Easy

1

2,7%

2

15,4%

3

6,0%

Total

37

100%

13

100%

50

100%

U Mann-Whitney test: Z=-1,860, p=0,063, V Cramer’s=0,313, p=0,296

Table 4. Correlation between treatment and assessment of the diet implementation

Assessment of the implementation of diet

Treatment

Total

Systematic visits at schedulet time

Visits sporadic or when worrisome symptoms occur

N

%

N

%

N

%

Very difficult

7

16,3%

1

14,3%

8

16,0%

Difficult

15

34,9%

5

71,4%

20

40,0%

Quite difficult

14

32,6%

1

14,3%

15

30,0%

Quite easy

4

9,3%

0

,0%

4

8,0%

Easy

3

7,0%

0

,0%

3

6,0%

Total

43

100%

7

100%

50

100%

U Mann-Whitney’s test: Z=-1,338, p=0,181, V Cramer’s=0,277, p=0,429

Table 5. Correlation between education of parents and lapses in child’s diet.

Dietary lapses

Education

Total

Vocational

Secondary

Higher

N

%

N

%

N

%

N

%

Yes, few times a week

1

16,7%

1

5,6%

0

,0%

2

4,0%

Yes, few times a month

3

50,0%

3

16,7%

1

3,8%

7

14,0%

Yes, once a month

0

,0%

3

16,7%

2

7,7%

5

10,0%

Yes, less often than once a mont

2

33,3%

2

11,1%

2

7,7%

6

12,0%

No

0

,0%

9

50,0%

21

80,8%

30

60,0%

Total

6

100%

18

100%

26

100%

50

100%

Rho=0,535, p=0,000