Entrance

Tetrahydrobiopterin (BH4) metabolism disorders constitute 1-2% of the causes of hyperphenylalaninemia. There are six distinct diseases characterized by inadequate synthesis of monoamine neurotransmitters. BH4 metabolism disorders; guanosine triphosphate cyclohydrolase (GTPCH1) deficiency, 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, Dihydropterin reductase (DHPR) deficiency, pterin carbinolamine dehydratase deficiency (PCD) and sepiapterin reductase (SR) deficiency. DHPR deficiency is the most common BH4 metabolism disorder in our country. Due to defects in the QDPR gene, Dihydrobiopterin (BH2) accumulates, which inhibits aromatic amino acid hydroxylases, resulting in low dopamine and serotonin concentrations. Our study aimed to examine the phenotypic findings of cases diagnosed with DHPR deficiency and to evaluate the relationship of the findings with the age at diagnosis and the beginning of treatment.

Method

In our study, the clinical and demographic characteristics of 32 patients from 27 different families diagnosed with DHPR deficiency between 1986 and 2022 were retrospectively examined. The demographic characteristics, neurocognitive development and phenotypic findings of these patients at diagnosis and follow-up were evaluated retrospectively. From the files of the patients included in the study, their age and gender, complaints at the time of admission and physical examination findings, complete blood counts, biochemical parameters, BH4 loading test results, cerebrospinal fluid (CSF) examinations, cranial imaging and developmental screening tests were retrospectively examined. The patients' DHPR activity and blood biopterin and neopterin levels were analyzed from dried blood samples taken on Guthrie paper. BH4 loading test; In patients with initial blood phenylalanine (Phe) concentration >360 μmol/L, after ingestion of 20 mg/kg sapropterin orally or via nasogastric tube; It was done by measuring Phe levels at 0, 4, 8 and 24 hours. Cerebrospinal fluid (CSF) pterins and neurotransmitters, 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), and other monoamine neurotransmitter metabolites were analyzed to support diagnosis and monitor treatment. Patients were evaluated with the Denver screening test or the Wechsler intelligence scale for children-Revised (WISC-R).

Results

17 of the thirty-two patients were women. The average age at presentation of the patients was 5.01±8.45 months (1 day-10 years). 15 of the patients (46.88%) were referred when pathology was detected in newborn screening, and 5 patients (15.63%) were diagnosed through family screening. At the time of admission, 13 patients had retarded motor or mental development, and 6 patients had a history of epileptic seizures. The average age at presentation of patients with delayed mental development was 5.5 months. There was consanguinity between the parents of 27 patients (84.3%). Ten patients had a family history. The average phenylalanine level measured at the time of admission was 624.5±504.0 μmol/L (23-2448). In the BH4 challenge test, the average response at the 8th hour was 60.92%. In the dry blood examination performed in all patients, DHPR enzyme activity was detected below normal values. The average DHPR enzyme activity was determined to be 0.16 (<1.8) mU/mgHb. The average value of neopterin level measured in the dried blood samples of the patients was 4.39±3.63 (7-27) μmol/L, and the average value of biopterin was 5.96±9.77 (3-11) μmol/L. The diagnosis of 14 patients was supported by lumbar puncture before treatment. The average 5-hydroxyindoleacetic acid (5-HIAA) value of the patients who underwent CSF examination before treatment was 42.21±42.22 nmol/L (89-341), and the average homovalinic acid (HVA) value was 173.59±92.84 nmol/L. (231-840), the average HVA/5-HIAA ratio was 6.13±4.27 (1.3-4). The diagnosis of nine patients was confirmed by genetic diagnosis. 15 patients were diagnosed with newborn screening and 5 patients were diagnosed with family screening. The neurological development of 10 patients diagnosed in the neonatal period was normal. Epileptic seizures were observed in 21 patients during the follow-up period. The average age of onset of the first seizure was 33.90±36.97 months (10 days - 9.5 years). Among those who underwent cranial MRI, hyperintense lesions in the cerebral white matter were observed in 5 patients. In electroencephalography examination, the most common finding was sharp waves in the temporoparietal region. During the follow-up of the patients, sleep disorders were observed in 18 patients (56.25%), thermoregulation defects in 14 patients (43.75%), hypersalivation in 13 patients (40.62%), and ataxic gait in 10 patients (31.25%). Skin findings consistent with eczema were observed in the follow-up of ten patients (31.25%). In patients with eczema, the eosinophil percentage was less than 4% and no increase in the number of eosinophils was detected (less than 500/μl).

In our patients, the frequency of skin findings of eczematous character, which had not been previously described in DHPR deficiency, was noted. Patients were treated with a phenylalanine-restricted diet, 5-hydroxytryptophan (5-HTP), carbidopa/levadopa, and folinic acid. After the treatment, findings suggesting an improvement in the neurological condition, such as increased academic success and a decrease in epileptic seizures or movement disorders, were observed.

Argument

DHPR deficiency is an autosomal recessive BH4 metabolism disorder caused by defects in the QDPR gene.1 Since consanguineous marriages are common, DHPR deficiency, like PKU disease, is relatively common in our country. In our patient group, there was consanguinity between the parents in 27 families (84.3%). All ten patients had a family history of hyperphenylalaninemia.

BH4 metabolism disorders reflect dopamine deficiency as well as an imbalance of other neurotransmitters such as serotonin, norepinephrine or epinephrine in the CSF. The most common symptoms in the literature are neuromotor developmental delay, hypotonia, and hypertonia in the extremities.2 In our study, there were 13 patients (40.6%) with motor or mental developmental delay at the time of admission, and 8 patients (25%) without pathological findings. BH4 metabolism disorders should be considered in children with high phenylalanine levels detected during newborn screening or at later ages or with clinical suspicion (insufficient sucking, hypotonia, hypertonia in the extremities, difficulty in swallowing, autonomic dysfunction; myoclonic seizures, oculogyric crises are described).

With the disruption of neurotransmitter homeostasis, patients experience symptoms of autonomic dysregulation such as increased salivation, coldness in the extremities, and sleep disorder. In the literature, findings of more frequent autonomic dysregulation in GTPCH1 and SR, which are BH4 metabolism disorders, were directed to the detection of pathology in newborn screening, although only eight patients (25%) were admitted within the first 30 days after birth. One of the most important reasons for this is that patients are referred from other cities. The average academic achievement and Denver developmental test results of these 8 patients are higher than the average of the other patients. Our study supports that, as stated in the literature, recognition of the disease in the neonatal period and early initiation of treatment are decisive in prognosis.2

Phenylalanine and tyrosine levels were measured in patients with pathology detected in newborn screening or in patients with clinical suspicion. DHPR activity and biopterin and neopterin levels were studied with dried blood from patients with high phenylalanine levels and high phenylalanine/tyrosine ratios. In the dry blood examination performed in our entire patient group, DHPR enzyme activity was detected below normal values. In the diagnosis of DHPR deficiency, detecting low DHPR activity in dry blood examination is reliable in the diagnosis. In the dry blood examination of our cases, low neopterin levels and normal biopterin levels were detected in most patients. In the literature, low or normal biopterin levels and normal neopterin levels have been reported in most patients with DHPR deficiency, but there are also cases with high neopterin and/or biopterin levels. For this reason, biopterin and/or neopterin levels in dry blood or urine examination are not guiding in the diagnosis of the disease. DHPR deficiency, which is a subgroup of BH4 deficiencies, is also in the rare hereditary neurological disease group that causes catecholamine and serotonin deficiency. Secondary to the impaired function of aromatic amino acid hydroxylases, 5-HIAA and HVA levels in the CSF are typically significantly low.4 In our study group, 5-HIAA levels were found to be low in the CSF of all patients except one, while HVA levels were normal in five patients. While it was in the range, it was low in other patients. For treatment monitoring, patients' CSF metabolite tests were sent repeatedly and treatment doses were adjusted.

It is recommended that treatment be started as soon as possible in cases of BH4 metabolism disorders.3 Patients were started on a phenylalanine-restricted diet, and dried blood and phenylalanine levels were closely monitored. Since patients with DHPR deficiency are more sensitive to high phenylalanine levels than patients with hyperphenylalaninemia, the Phe concentration was targeted to be <240 μmol/L when adjusting their diets. Although there is little evidence against its use, sapropterin dihydrochloride was not preferred in all but two patients because it could cause accumulation of the BH2 metabolite.4 After the CSF examination of the patients, 0.5-1 mg/kg/g L-Dopa treatment was started. If the side effects observed with L-Dopa treatment, movement disorders (dyskinesia, tremor, chorea, myoclonus), sleep disorders, psychiatric symptoms (anxiety, nervousness, hyperactivity and mood disorders) and gastrointestinal symptoms are not observed, L-tryptophan treatment is started with 0.5-1 mg/kg. kg/g added. Target doses of treatments vary depending on age. L-Dopa treatment in newborns 1-3mg/kg/g, 5-OH tryptophan treatment 1-2 mg/kg/day, L-dopa treatment under 2 years of age 4-7 mg/kg/g, 5-OH tryptophan 3-5 mg/kg/day, for patients over 2 years of age, L-dopa was targeted at 8-15 mg/kg/g, and 5-OH tryptophan treatment was targeted at 6-9 mg/kg/day. Treatments were started at a low dose, patients were monitored for side effects, and the dose was increased by 1 mg/kg weekly until therapeutic doses were reached. Among BH4 metabolism disorders, low cerebral folate level is most frequently detected in DHPR deficiency. Folinic acid therapy 15mg/day was added to each patient's treatment.5

Conclusion

This disease, which is included in the group of rare diseases, is more common in countries where consanguineous marriage is common. The rate of DHPR deficiency in our patients is similar to the rate of DHPR in PKU patients around the world. However, DHPR deficiency, like PKU disease, is relatively common due to the increase in consanguineous marriages in our country. Our study supported that, as stated in the literature, recognition of the disease in the neonatal period and early initiation of treatment are decisive in prognosis. Prospective studies are needed in terms of the frequency and types of skin findings that have not been previously described in BH4 metabolism disorders.