Diagnosis and clinical features of organic acidemias: A hospital-based study in a single center in Damascus, Syria

Background: Organic acidemias (OA) are a group of heterogeneous metabolic inherited disorders characterized by the accumulation of organic acids in body fluids and tissues. These are rare disorders and infrequently reported worldwide. In Syria, there is a lack of information regarding these disorders. Objective: Our hospital-based study aimed to describe the pattern of clinical and demographic presenting features of organic acidemias among Syrian children and to shed light on the diagnostic experience of organic acidemias in the Children's Hospital of Damascus through a five year period. Material and methods: We conducted a retrospective cohort study by reviewing the medical records of OA patients in the Children's Hospital of Damascus between 2008 and 2012. All cases were investigated by metabolic work up, including the acylcarnitine profile performed by tandem mass spectrometry (MS/MS) and quantitative urine organic acid analysis performed by gas chromatography mass spectrometry (GC-MS). Results: A total of 70 OA confirmed cases were included in the study. There were 46 males and 31 females. Twenty-seven cases were diagnosed after the first year of life. Methylmalonic acidemia was the most frequent disorder (57.1%). There were relatively high rates of family history of unexplained death and OA confirmed cases (50%), consanguinity (74.2%) and mortality (21.4%). The most frequent symptoms were apnea or respiratory distress (65.7%) and vomiting (40%). Conclusion: The lack of specific confirmatory diagnostic tests being performed and the high mortality and consanguinity rates among OA patients suggests high incidence of OA in Syria. Further studies are needed to determine the actual incidence of OA and the cost-effectiveness of applying a governmental mandatory newborn screening program.


INTRODUCTION
Organic acid disorders or organic acidemias (OA) are a group of metabolic disorders resulting from enzymatic deficiencies in the catabolic pathway of branched-chain amino acids and lysine and disorders result in accumulation of lactic acid and dicarboxylic acids, which leads to the accumulation of organic acids in the body fluids and tissues. 1,2,3 The accumulation of these toxic substances or their metabolites and lack of products of the defective pathway lead to the pathophysiology of these disorders. 4 The majority of these disorders have autosomal recessive inheritance pattern. 1,5 The affected neonate is usually normal at birth and within the first days of life. 1,6 The first clinical findings result from the toxic encephalopathy which usually arise as an acute attack within a few weeks of life with symptoms such as poor feeding, vomiting, hypotonia and lethargy. 1,6,7 In a milder form of the enzymatic deficiency, the onset of acute episodic symptoms is delayed and usually occurs within late infancy or even later, with symptom free intervals between attacks. Furthermore, these disorders can present as a chronic progressive form or even an asymptomatic form. 7 Patient prognosis can be much better with early diagnosis and treatment. 3,8 Organic acidemias are considered the most frequent metabolic disorders among critically ill children and one of the most frequent inborn errors of metabolism among high-risk populations. 3,9,10 Organic acidemias are rare disorders individually and infrequently reported worldwide. 11 The prevalence in British Columbia, Canada (1:27082), Italy (1:21422), and in the West Midlands, United Kingdom (1:7962), is closer to reality in comparison with Saudi Arabia (1:740), due to the high consanguinity rate among Arab populations. 12 -15 In Syria, it is believed that a considerable number of OA cases are undiagnosed or misdiagnosed due to the lack of expert knowledge and trained specialists, the high cost of diagnostic tests and lack of public awareness about these disorders. The absence of mandatory newborn screening programs and the lack of scientific or statistical information on OA disorders among the Syrian population explains the unavailability of information or data on the incidence of OA and its prevalence in Syria. The present retrospective cohort study aimed to collect clinical and demographic data on OA cases in Syrian patients and to report the diagnostic experience of OA in one medical establishment.

MATERIAL AND METHODS
A retrospective study was conducted in the Children's Hospital of Damascus, the largest specialized medical institution in Syria. Following approval of the study by the institutional ethics committee, the medical records of children diagnosed at the metabolic unit in the hospital with OA between 2008 and 2012 were reviewed. One hundred and thirty-four patients were referred to the metabolic unit in the Children's Hospital of Damascus with suspected OA during the mentioned study period. The suspicion was based on clinical presentation such as unexplained neurological or digestive symptoms and/or positive family history of OA cases or unexplained deaths, in addition to abnormal non-specific biochemical investigations which included: serum glucose, electrolytes, serum ketone bodies, arterial blood gases, ammonia and lactate. The confirmation was carried out by advanced diagnostic biochemical metabolic work up, including the acylcarnitine profile in dry blood spots performed by tandem mass spectrometry (MS/MS) and quantitative urine organic acid analysis performed by gas chromatography mass spectrometry (GC-MS), in collaboration with private laboratories in Damascus and abroad. The present study collected demographic and clinical data on confirmed OA cases including gender and age, consanguinity between parents, family history for unexplained death or the presence of OA confirmed cases in siblings or relatives and symptoms/clinical features. The number of mortality episodes was also recorded.

RESULTS
Out of 134 suspected OA patients, 70 patients (52.2%) underwent advanced diagnostic biochemical metabolic investigations and were diagnosed with one of the organic acids disorders, 54 cases (77.1%) were confirmed by urine organic acid analysis, and 16 cases (22.9%) were confirmed by acylcarnitine profile tandem mass spectrometry. No advanced biochemical metabolic investigations were performed in the remaining 64 patients (47.6%) Table 3. Results of acylcarnitine profile using MS/MS among organic acidemias confirmed cases.  to differentiate between organic acidemias and other causes of clinical manifestations as non-specific laboratory results indicated a possible metabolic disorder. Among these cases, seven were considered and treated as organic acidemias patients according to their clinical manifestation and known family history of confirmed OA cases in siblings and/or relatives, without performing any specific confirmatory tests. Males formed 60% (n ¼ 42) of the 70 cases, while females formed 40% (n ¼ 28). The mean age at diagnosis was 12.9 months (range 14 days -8 years).  Table 3 and Table 4 respectively. According to the present study, the most presented symptoms were apnea or respiratory distress (tachypnea) (65.7%), persistent or recurrent vomiting (40%) and dehydration (38.6%). The most frequent basic biochemical abnormalities were acidosis (58.6%), ketosis (47.1%) and hyperammonemia (44.3%). The presenting signs and symptoms and basic biochemical abnormalities are listed in Table 5 and Table 6 respectively.

DISCUSSION
Our study represents the first published data on the pattern, diagnosis, clinical and demographic characteristics of organic acidemias in a sample of Syrian OA patients. During the five-year period, 70 patients were diagnosed with organic acidemias at one medical establishment in Syria. Table 7 shows the number of cases of organic acidemias that were reported in our study and are similar to the number of cases reported from studies conducted in other countries. Methylmalonic acidemia is reported as the most frequent disorder in many Arab countries such as Tunisia and Lebanon, which is consistent with our findings. 16,17 We observed a delay in diagnosis similar to that reported in Brazil and Egypt, which might be attributed to the lack of newborn screening programs in Syria. 10,18 However, the delay of diagnosis in the neonatal form, which is the most frequent form of OA, can lead to the death of the affected neonate before establishing the diagnosis. This can explain the relatively limited number of cases diagnosed at the first month of life and suggests that almost 39 percent of cases in our study have late onset presentation. This however requires further study to determine the accurate age of onset. It is known that consanguinity between parents can increase the chance of offspring being affected by autosomal recessive disorders in general, including organic acidemias. These chances can be maximized especially in the case of positive family history of such diseases. 18 High rates of parental consanguinity and positive family history among OA patients were reported in our study and in Egypt. 19 The relatively high mortality rate among OA patients that was reported in our study could be attributed to several factors including the lack of public awareness about OA, the paucity of information on these disorders, their non-specific symptoms which are shared with other more common diseases such as infectious diseases, and the shortage of experienced physicians in the domain of metabolic disorders in general. These factors lead to the exclusion of OA from the differential diagnosis which results in delayed diagnosis, treatment and consequent death. Symptoms such as apnea or respiratory distress, persistent or recurrent vomiting and dehydration are more likely to appear in acute decompensation episodes that present in OA patients, and require hospitalization and immediate medical management.
The association of such unexplained symptoms with acidosis and/or ketosis and hyperammonemia, which were the most frequent biochemical abnormalities, leads to a high suspicion of organic acidemias. The estimation of the diagnosis was the major difficulty in dealing with these disorders due to the lack of confirmatory tests for financial reasons, in addition to the absence of mass or selective newborn screening program. In some cases, the patients died before the required tests were performed.

CONCLUSION
This study suggests that the clinical orientation is still the key factor in the diagnosis of these diseases in light of the lack of advanced specific laboratory tests and absence of newborn screening programs. Despite the importance of these results, it is difficult to generalize the findings to the entire society. Therefore, further studies are highly recommended in order to estimate the actual incidence of organic acid disorders and to assess the possibility, interest and cost-effectiveness of applying a selective newborn screening program of the most prevalent organic acid disorders within Syria.  11 4 years 30 PA Tunisia 16 23 years 158 MMA Lebanon 17 12 years 83 MMA Libya 20 12 years 10 MMA-PA Jordan 21 5 years 51 PA Thailand 22 5 years 5 MMA-IVA MMA: Methylmalonic acidemia; PA: Propionic acidemia; IVA: Isovaleric acidemia.