Error Of Amino Acid Metabolism Research Articles

Oxidative Stress in Homocystinuria Due to Cystathionine ß-Synthase Deficiency: Findings in Patients and in Animal Models.

Homocystinuria is an inborn error of amino acid metabolism caused by deficiency of cystathionine ß-synthase (CBS) activity, biochemically characterized by homocysteine (Hcy) and methionine (Met) accumulation in biological fluids and high urinary excretion of homocystine. Clinical manifestations include thinning and lengthening of long bones, osteoporosis, dislocation of the ocular lens, thromboembolism, and mental retardation. Although the pathophysiology of this disease is poorly known, the present review summarizes the available experimental findings obtained from patients and animal models indicating that oxidative stress may contribute to the pathogenesis of homocystinuria. In this scenario, several studies have shown that enzymatic and non-enzymatic antioxidant defenses are decreased in individuals affected by this disease. Furthermore, markers of lipid, protein, and DNA oxidative damage have been reported to be increased in blood, brain, liver, and skeletal muscle in animal models studied and in homocystinuric patients, probably as a result of increased free radical generation. On the other hand, in vitro and in vivo studies have shown that Hcy induces reactive species formation in brain, so that this major accumulating metabolite may underlie the oxidative damage observed in the animal model and human condition. Taken together, it may be presumed that the disruption of redox homeostasis may contribute to the tissue damage found in homocystinuria. Therefore, it is proposed that the use of appropriate antioxidants may represent a novel adjuvant therapy for patients affected by this disease.

SCREENING OF EGYPTIAN PATEINTS SUFFERING FROM INBORN AMINO ACID METABOLIC DISORDERS

Diagnosis of aminoacidopathies constitutes a challenge in a developing country with high positive consanguinity rate and no newborn screening programs. The number of diagnosed inborn errors of amino acid metabolism is growing constantly due to the availability of recent analytical technique as tandem mass spectrometry (LC/MS/MS). This study highlights the importance of clinical awareness among physicians in patients presenting with unexplained neurological signs and alarming features that are commonly associated with metabolic diseases. Our scope is an assessment of overall prevalence rate of amino acid inborn errors metabolism in Genetics Research Unit, Pediatric Hospital, Ain shams University. Results indicate that 851 patients with phenylketonuria (PKU), 109 patients with maple syrup urine disease (MSUD), 15 patients with nonketotic hyperglycinemia (NKH), 14 patients with tyrosinemia, 4 patients with homocystinuria, 4 patients with citruillinimia and 3 patients with arginimia. It is clear that high consanguinity rate among families in different types of diseases that 1st cousin consanguinity is the highest rate among patients.

Dietary intervention in the management of phenylketonuria: current perspectives.

Phenylketonuria (PKU) is a well-described inborn error of amino acid metabolism that has been treated for >60 years. Enzyme deficiency causes accumulation of phenylalanine (Phe) and if left untreated will lead to profound and irreversible intellectual disability in most children. Traditionally, it has been managed with a low-Phe diet supplemented with a Phe-free protein substitute although newer treatment options mainly in combination with diet are available for some subgroups of patients with PKU, for example, sapropterin, large neutral amino acids, and glycomacropeptide. The diet consists of three parts: 1) severe restriction of dietary Phe; 2) replacement of non-Phe l-amino acids with a protein substitute commonly supplemented with essential fatty acids and other micronutrients; and 3) low-protein foods from fruits, some vegetables, sugars, fats and oil, and special low-protein foods (SLPF). The prescription of diet is challenging for health professionals. The high-carbohydrate diet supplied by a limited range of foods may program food preferences and contribute to obesity in later life. Abnormal tasting and satiety-promoting protein substitutes are administered to coincide with peak appetite times to ensure their consumption, but this practice may impede appetite for other important foods. Intermittent dosing of micronutrients when combined with l-amino acid supplements may lead to their poor bioavailability. Much work is required on the ideal nutritional profiling for special SLPF and Phe-free l-amino acid supplements. Although non-diet treatments are being studied, it is important to continue to fully understand all the consequences of diet therapy as it is likely to remain the foundation of therapy for many years.

A Quantitative Method for the Measurement of Dried Blood Spot Amino Acids Using Ultra-Performance Liquid Chromatography.

Measurement of amino acids in dried blood spots has been extensively used for the detection of newborns with various inborn errors of amino acid metabolism including phenylketonuria (PKU) and maple syrup urine disease (MSUD). Whereas blood spot amino acid measurement has been invaluable for initial diagnosis, the relative insensitivity of blood spot measurement has found limited use in lifelong monitoring of patients with these disorders. The work described here outlines the evaluation of blood spot amino acid analysis using ultra-performance liquid chromatography (UPLC©) for use in follow-up testing. Dried blood spot amino acids were derivatized with a proprietary AccQTag® reagent and separated using UPLC. Plasma amino acids from dried bloods spots were obtained from 318 patient samples and compared to corresponding plasma samples measured using the same UPLC method. Dried blood spot amino acid concentrations were highly correlated but negatively biased vs plasma concentrations. Interassay imprecision studies using UPLC demonstrated a %CV for phenylalanine of 4.81%-16.07%, tyrosine 5.62%-20.16%, valine 4.23%-15.46%, leucine 8.3%-15.3%, and isoleucine 4.25%-16.80%. Intraassay imprecision studies using UPLC demonstrated a %CV for phenylalanine of 0.42%-3.4%, tyrosine 1.6%-7.85%, valine 0.14%-1.84%, leucine 0.28%-2.01%, and isoleucine 0.6%-2.65%. Blood spot amino acid concentrations were stable for at least 3 days at temperatures up to 65 °C. This UPLC-based method can reliably measure clinically significant amino acids in dried blood spots.

Molecular epidemiology, genotype-phenotype correlation and BH4 responsiveness in Spanish patients with phenylketonuria.

Phenylketonuria (PKU), the most common inborn error of amino acid metabolism, is caused by mutations in the phenylalanine-4-hydroxylase (PAH) gene. This study aimed to assess the genotype-phenotype correlation in the PKU Spanish population and the usefulness in establishing genotype-based predictions of BH4 responsiveness in our population. It involved the molecular characterization of 411 Spanish PKU patients: mild hyperphenylalaninemia non-treated (mild HPA-NT) (34%), mild HPA (8.8%), mild-moderate (20.7%) and classic (36.5%) PKU. BH4 responsiveness was evaluated using a 6R-BH4 loading test. We assessed genotype-phenotype associations and genotype-BH4 responsiveness in our population according to literature and classification of the mutations. The mutational spectrum analysis showed 116 distinct mutations, most missense (70.7%) and located in the catalytic domain (62.9%). The most prevalent mutations were c.1066-11G>A (9.7%), p.Val388Met (6.6%) and p.Arg261Gln (6.3%). Three novel mutations (c.61-13del9, p.Ile283Val and p.Gly148Val) were reported. Although good genotype-phenotype correlation was observed, there was no exact correlation for some genotypes. Among the patients monitored for the 6R-BH4 loading test: 102 were responders (87, carried either one or two BH4-responsive alleles) and 194 non-responders (50, had two non-responsive mutations). More discrepancies were observed in non-responders. Our data reveal a great genetic heterogeneity in our population. Genotype is quite a good predictor of phenotype and BH4 responsiveness, which is relevant for patient management, treatment and follow-up.

First structure of full-length mammalian phenylalanine hydroxylase reveals the architecture of an autoinhibited tetramer

Improved understanding of the relationship among structure, dynamics, and function for the enzyme phenylalanine hydroxylase (PAH) can lead to needed new therapies for phenylketonuria, the most common inborn error of amino acid metabolism. PAH is a multidomain homo-multimeric protein whose conformation and multimerization properties respond to allosteric activation by the substrate phenylalanine (Phe); the allosteric regulation is necessary to maintain Phe below neurotoxic levels. A recently introduced model for allosteric regulation of PAH involves major domain motions and architecturally distinct PAH tetramers [Jaffe EK, Stith L, Lawrence SH, Andrake M, Dunbrack RL, Jr (2013) Arch Biochem Biophys 530(2):73-82]. Herein, we present, to our knowledge, the first X-ray crystal structure for a full-length mammalian (rat) PAH in an autoinhibited conformation. Chromatographic isolation of a monodisperse tetrameric PAH, in the absence of Phe, facilitated determination of the 2.9 Å crystal structure. The structure of full-length PAH supersedes a composite homology model that had been used extensively to rationalize phenylketonuria genotype-phenotype relationships. Small-angle X-ray scattering (SAXS) confirms that this tetramer, which dominates in the absence of Phe, is different from a Phe-stabilized allosterically activated PAH tetramer. The lack of structural detail for activated PAH remains a barrier to complete understanding of phenylketonuria genotype-phenotype relationships. Nevertheless, the use of SAXS and X-ray crystallography together to inspect PAH structure provides, to our knowledge, the first complete view of the enzyme in a tetrameric form that was not possible with prior partial crystal structures, and facilitates interpretation of a wealth of biochemical and structural data that was hitherto impossible to evaluate.

Determination of Phenylalanine and Tyrosine by High Performance Liquid Chromatography-Tandem Mass Spectrometry.

Hyperphenylalaninemia/phenylketonuria (PKU) is one of the most common inborn errors of amino acid metabolism affecting about 1:15,000 infants in the United States. PKU is an autosomal recessive disorder that if untreated results in mental retardation. The most common cause of PKU is deficiency of the enzyme phenylalanine hydroxylase that converts phenylalanine to tyrosine. Tyrosine deficiency results in impaired synthesis of catecholamines and thyroxine. Less commonly, it can result from defects in the synthesis or regeneration of tetrahydrobiopterin (BH4), an essential cofactor for the enzyme phenylalanine hydroxylase. Increased phenylalanine and decreased tyrosine in blood are used in the diagnosis and follow-up of patients with PKU. LC/MS/MS method is described for the quantification of phenylalanine and tyrosine.

Difficult epidural in a patient with undiagnosed alkaptonuria.

Sir, Endogenous ochronosis or alkaptonuria is an extremely rare autosomal recessive inborn error of amino acid metabolism which was described by Garrod in 1901.[1] It occurs due to the absence of the enzyme homogentisate 1,2-dioxygenase that converts homogentisic acid to maleylacetoacetic acid in the process of tyrosine metabolism.[2] We wish to highlight difficulties faced in securing neuraxial anaesthesia in an undiagnosed case of alkaptonuria and the significance of identifying mucocutaneous markers of ochronosis which can be missed in dark-skinned Asian patients. A 69-year-old male, who presented with pain in both the knee and hip joints and no significant comorbidity, was posted for total replacement of the right hip joint, with a provisional diagnosis of osteoarthritis. General physical examination showed bilateral pigmented keratinised lesions on the palmar aspects and outer edges of his fingers [Figure 1a]. His vital parameters were stable and systemic examination was unremarkable. Airway examination revealed a mild restriction of neck extension and Malampatti class 3. The lumbar interspinous spaces were not distinctly felt. The electrocardiogram showed an incomplete right bundle branch block and the echocardiogram showed a degenerated sclerotic aortic valve, trivial regurgitations in the mitral and tricuspid valves and a normal left ventricular ejection fraction. Combined spinal–epidural anaesthesia was planned. Figure 1 (a) Greyish-blue, pitted, scaly and non-itchy lesions on the palms. (b) Greyish scleral pigmentation Lumbar epidural needle insertion was attempted long the midline but failed as bone was encountered with repeated attempts. The patient was then positioned on the right lateral side with the affected joint dependent and subarachnoid block through a paramedian approach was successful. The epidural space was reached after multiple attempts by the paramedian approach near L2-3 and an 18 gauge epidural catheter was successfully threaded into space. Intra-operatively, the surgeon alerted us regarding the dark colour of the cartilage around the hip joint. Ochronosis was then implicated to be the cause of arthritis and the difficulty in securing neuraxial anaesthesia. Close evaluation of the eyes revealed pigmented lesions bilaterally [Figure 1b] and the ears were found to be hard and thickened. The lumbar spine radiograph obtained subsequently showed calcification of the intervertebral discs [Figure 2a]. The urine was tested which turned dark after a few hours on exposure to air and further on alkalinisation [Figure 2b]. Histopathological evaluation of the femoral head confirmed the diagnosis [Figure 2c]. The patient later recollected that his unwashed underwear showed ash-coloured stains. Figure 2 (a) Intervertebral disc calcification (yellow arrows). (b) Change in the urine colour on alkalinisation and exposure to air. (c) Microscopic pigment deposition in the cartilage and in the synovium Since the disease often presents in the later decades of life with symptoms closely resembling other arthropathies, the diagnosis is often missed. Anaesthesiologists encounter these patients when they are posted for replacements of the hip or knee joints and for spine surgeries. They can present with ochronotic spondyloarthropathy with decreased range of movements of the spine and hips, facet joint degeneration, spinal canal stenosis and pseudo ankylosis of the cervical joints, reduced intervertebral disc spaces and dense disc calcification that can result in difficult neuraxial anaesthesia as well as intubation.[3,4] Bilaterally symmetrical scleral pigmented lesions, as seen in our patient, should rouse suspicion of an underlying systemic cause.[5] Greyish-blue, pitted, non-itchy, scaly lesions on the edges and palmar aspects of the hands, greyish discolouration of the ear pinna and stiff and hard helical cartilage were noted in our patient can easily be missed.[6] Calcifications in the coronaries, cardiac valves and aortic root, urinary pigment calculi and nephrotoxicity may be significant enough to alter anaesthetic management.[2] Although surgical implications are minimal, surgeons should involve the anaesthesiologist, physician and cardiologist early in the pre-operative period to establish a well-planned management approach. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Metabolic Diet App Suite for inborn errors of amino acid metabolism.

An increasing number of rare inborn errors of metabolism (IEMs) are amenable to targeted metabolic nutrition therapy. Daily adherence is important to attain metabolic control and prevent organ damage. This is challenging however, given the lack of information of disorder specific nutrient content of foods, the limited availability and cost of specialty products as well as difficulties in reliable calculation and tracking of dietary intake and targets. To develop apps for all inborn errors of amino acid metabolism for which the mainstay of treatment is a medical diet, and obtain patient and family feedback throughout the process to incorporate this into subsequent versions. The Metabolic Diet App Suite was created with input from health care professionals as a free, user-friendly, online tool for both mobile devices and desktop computers (http://www.metabolicdietapp.org) for 15 different IEMs. General information is provided for each IEM with links to useful online resources. Nutrient information is based on the MetabolicPro™, a North American food database compiled by the Genetic Metabolic Dietitians International (GMDI) Technology committee. After user registration, a personalized dashboard and management plan including specific nutrient goals are created. Each Diet App has a user-friendly interface and the functions include: nutrient intake counts, adding your own foods and homemade recipes and, managing a daily food diary. Patient and family feedback was overall positive and specific suggestions were used to further improve the App Suite. The Metabolic Diet App Suite aids individuals affected by IEMs to track and plan their meals. Future research should evaluate its impact on patient adherence, metabolic control, quality of life and health-related outcomes. The Suite will be updated and expanded to Apps for other categories of IEMs. Finally, this Suite is a support tool only, and does not replace medical/metabolic nutrition professional advice.

Molecular analysis of maple syrup urine disease in Jordanian families

Maple syrup urine disease (MSUD) is an autosomal-recessive inborn error of amino acid metabolism characterized by the accumulation of three branched-chain amino acids (BCAAs) in patients' cells due to reduced activity of the branched-chain α-ketoacid dehydrogenase complex (BCKD). In this study, we aimed to sequence the coding exons of the BCKDHA, BCKDHB, and DBT genes in five Jordanian families with MSUD and one family from Iraq with MSUD. BCAA levels were measured in probands initially presenting with developmental delay and encephalopathy. All of the coding exons and flanking intronic sequences of the BCKDHA, BCKDHB, and DBT genes were amplified and subjected to direct DNA sequencing. Four different mutations in the BCKDHA gene were identified, including a novel frame-shift mutation, c.908_909delTG, in family 4. Two novel missense mutations at residues Met263 and Gly353 in the DBT gene were also found to be cosegregated with the MSUD phenotype in families 5 and 6, respectively. Structural analyses suggested that these two mutations may affect the assembly of the intermediate E2 trimer. No BCKDHB gene mutations were found in Jordanian patients. The mutation profiles described in this study provide a basis for the early detection of MSUD disease. To our knowledge, this is the first molecular study of MSUD in Jordan and Middle Eastern Arabic countries.

Secondary NAD+ deficiency in the inherited defect of glutamine synthetase.

Glutamine synthetase (GS) deficiency is an ultra-rare inborn error of amino acid metabolism that has been described in only three patients so far. The disease is characterized by neonatal onset of severe encephalopathy, low levels of glutamine in blood and cerebrospinal fluid, chronic moderate hyperammonemia, and an overall poor prognosis in the absence of an effective treatment. Recently, enteral glutamine supplementation was shown to be a safe and effective therapy for this disease but there are no data available on the long-term effects of this intervention. The amino acid glutamine, severely lacking in this disorder, is central to many metabolic pathways in the human organism and is involved in the synthesis of nicotinamide adenine dinucleotide (NAD(+)) starting from tryptophan or niacin as nicotinate, but not nicotinamide. Using fibroblasts, leukocytes, and immortalized peripheral blood stem cells (PBSC) from a patient carrying a GLUL gene point mutation associated with impaired GS activity, we tested whether glutamine deficiency in this patient results in NAD(+) depletion and whether it can be rescued by supplementation with glutamine, nicotinamide or nicotinate. The present study shows that congenital GS deficiency is associated with NAD(+) depletion in fibroblasts, leukocytes and PBSC, which may contribute to the severe clinical phenotype of the disease. Furthermore, it shows that NAD(+) depletion can be rescued by nicotinamide supplementation in fibroblasts and leukocytes, which may open up potential therapeutic options for the treatment of this disorder.

Quality of Life (QoL) assessment in a cohort of patients with phenylketonuria.

BackgroundPhenylketonuria (PKU) is a chronic inborn error of amino acid metabolism that requires lifelong follow-up and intervention, which may represent strains on Quality of Life (QoL). This observational study evaluated QoL in a cohort of PKU patients, using updated and detailed instruments.Methods22 patients with mild PKU respondent to BH4 and 21 patients with classical PKU treated with diet were recruited in this study. Adult patients completed WHOQOL questionnaire-100 (WHOQOL-100) and pediatric patients the Pediatric QoL inventory (PedsQLTM). Psychiatric and mood disorders were also evaluated using TAD or BDI and STAI-Y inventories. A multivariable linear regression model was fitted to investigate the predictors of QoL, including age, sex, treatment type, length of current treatment, educational level and employment status (only for adults) as covariates. Results were presented as regression coefficients with 95% confidence interval.ResultsGlobal QoL scores were within normal range both in patients with mild and classical disease but global QoL scores were significantly higher in patients with mild PKU under BH4 treatment as compared to those affected by classical disease who were under diet regimen. Furthermore, QoL significantly increased in long treated PKU patients. Among adult patients, QoL scores were significantly lower in males, in patients with lower education and in those employed or unemployed as compared to students (baseline).ConclusionsBoth diet and medical treatment based upon BH4 seem to be associated with higher QoL in the long run. However, patients with mild PKU can rely on BH4 to achieve a higher Phe tolerance and a better compliance to therapy due to diet relaxation/avoidance. Some specific categories of patients with a lower QoL should be investigated more in depth, engaging with those at risk of lower treatment compliance. The questionnaires employed in the present study seemed to be able to effectively detect criticalities in QoL assessment and represent an advance from previous inventories employed in the past.

Application of Biotechnologycal Methods for Removal of Phenylalanıne from Different Protein Sources

Inborn errors of amino acid metabolism include inherited biochemical disorders in which a specific enzyme defect interferes with the normal metabolism of protein. In these disorders as a result of diminished or absent enzyme activity, certain compounds accumulate in the body to toxic levels. Metabolic disturbances can lead to severe cognitive impairment and even death. Phenylketonuria, is the most common amino acid disorder. Dietary restriction prevent the accumulation of a substrate to toxic levels to a certain extend but application of biotechnological methods could provided more promising tools. The main topics discussed are: removal of phenylalanine by activated carbon, by tailored enzymatic hydrolyses of cheese whey, by modified corn cobs as adsorbents and by using enzymatic membrane reactor.

Proline-induced changes in acetylcholinesterase activity and gene expression in zebrafish brain: Reversal by antipsychotic drugs

Hyperprolinemia is an inherited disorder of proline metabolism and hyperprolinemic patients can present neurological manifestations, such as seizures, cognitive dysfunctions, and schizoaffective disorders. However, the mechanisms related to these symptoms are still unclear. In the present study, we evaluated the in vivo and in vitro effects of proline on acetylcholinesterase (AChE) activity and gene expression in the zebrafish brain. For the in vivo studies, animals were exposed at two proline concentrations (1.5 and 3.0mM) during 1h or 7days (short- or long-term treatments, respectively). For the in vitro assays, different proline concentrations (ranging from 3.0 to 1000μM) were tested. Long-term proline exposures significantly increased AChE activity for both treated groups when compared to the control (34% and 39%). Moreover, the proline-induced increase on AChE activity was completely reverted by acute administration of antipsychotic drugs (haloperidol and sulpiride), as well as the changes induced in ache expression. When assessed in vitro, proline did not promote significant changes in AChE activity. Altogether, these data indicate that the enzyme responsible for the control of acetylcholine levels might be altered after proline exposure in the adult zebrafish. These findings contribute for better understanding of the pathophysiology of hyperprolinemia and might reinforce the use of the zebrafish as a complementary vertebrate model for studying inborn errors of amino acid metabolism.

Citrullinemia and Hyperglycinemia Presenting with Seizures - Case Report of a 4 Day Old Baby

Inborn errors of amino acid metabolism (IEM) are of concern in India, the spectrum being wide, varied and poorly diagnosed. Since aggregate incidence of inborn errors of metabolism is relatively high, in countries such as India, a high degree of suspicion is essential to correctly diagnose an inborn error of amino acid metabolism. We report a case of citrullinemia, glycinemia with hyperammonaemia and seizures in a 4-dayold previously asymptomatic baby, with a brief review of the literature. DOI: http://dx.doi.org/10.3126/ajms.v3i1.4801 Asian Journal of Medical Sciences 3(2012) 17-20

Cystathionine Β-Synthase Deficiency, Turner Syndrome and İmmune Hydrops Fetalis in a Newborn: A Rare Coincidence

Cystathionine β-synthase (CBS) deficiency is a rare inborn error of amino acid metabolism affecting energy supply at the cellular level. Neonatal screening allows early presymptomatic diagnosis and better outcome, by preventing the complications like thrombotic disease. Here we present a female newborn baby with immune hydrops fetalis and mosaic Turner syndrome who has incidentally been early diagnosed with CBS deficiency upon detection of increased methionine on serum amino acid chromatography. The patient was unresponsive to pridoxine treatment which was compatible with p.S349N mutation detected on both alleles of cystathionine β-synthase gene. We would like to stress the point that CBS deficiency can be diagnosed by screening even in the setting of exchange transfusions and amino acid paper chromotography is a cheap and valuable metabolic screening tool in experienced hands. Since routine newborn screening for many metabolic diseases is currently not practiced in Turkey, all newborns born to families in which previous siblings had died due to unknown cause should be evaluated by amino acid paper chromotography and by other conventional metabolic tests when necessary.

Early diagnosis of co-existent ß-thalassemia and alkaptonuria

Since the aggregate incidence of inborn errors of metabolism is relatively high, a high degree of suspicion is essential to correctly diagnose an inborn error of amino acid metabolism. We report a case of alkaptonuria an autosomal recessive disorder that occurs due to deficiency of homogentisic acid oxidasein a β-thalassemia infant presenting with reddish discoloration of nappies and clothes, breath holding spells, and microcytic hypochromic anemia. Born to consanguineous cousins, to our knowledge, the combination of β-thalassemia and alkaptonuria, which we have described in this baby, has not been reported earlier.

Neuroradiological findings in maple syrup urine disease

Maple syrup urine disease is a rare inborn error of amino acid metabolism involving catabolic pathway of the branched-chain amino acids. This disease, if left untreated, may cause damage to the brain and may even cause death. These patients typically present with distinctive maple syrup odour of sweat and urine. Patients typically present with skin and urine smelling like maple syrup. Here we describe a case with relevant magnetic resonance imaging findings and confirmatory biochemical findings.

Unusual Case of Phenylketonuria With Atypical Brain Magnetic Resonance Imaging Findings

Phenylketonuria is a treatable inborn error of amino acid metabolism caused by deficiency of the enzyme phenylalanine hydroxylase, responsible for converting phenylalanine to tyrosine. We report a 10-month-old boy with psychomotor regression and infantile spasms. He was diagnosed with classic phenylketonuria and West syndrome. Treatment was initiated with phenylalanine-restricted diet and vigabatrin. After 5 months of treatment, he persists with developmental delay, severe hypotonia, swallowing disorder, and drug-resistant epilepsy. Brain magnetic resonance imaging showed the typical abnormalities in supratentorial white matter and exceptional infratentorial and basal ganglia compromise. Severity of white matter abnormalities and neurologic symptoms correlates with blood levels of phenylalanine. Infratentorial changes occur in severe cases. Other mechanisms could take part in cases like this with atypical neuroimaging abnormalities of the basal ganglia.

Signes néonatals des maladies héréditaires du métabolisme

Inborn metabolic diseases (IMDs) that can start in the neonatal period include various defects in numerous metabolic pathways. Such diseases are due to the genetic deficiency of an enzyme or a transporter. From a physiopathological point of view, the metabolic disorders can be divided into 3 diagnostically useful groups of diseases. The first group is due to the accumulation of endogenous toxic metabolites and includes inborn errors of amino acid metabolism, organic acidemias, urea cycle disorders, and sugar intolerances. The second one includes IMDs of intermediary metabolism causing a disturbance in energy production or utilization resulting from a defect in the liver, the muscles, the myocardium, or the brain (fatty acid oxidation defects, congenital lactic acidosis, etc.). The third group includes diseases that disturb the synthesis or the catabolism of complex molecules (lysosomal or peroxisomal disorders, etc.). IMDs are individually rare, but collectively numerous. Therefore, it is difficult to acquire extensive experience in the management of these diseases. However, the neonate has a limited repertoire of responses to severe illness and, at first, presents with nonspecific symptoms that could be easily attributed to infection or some other common cause. An IMD must be suspected in all situations of neonatal distress for which there is no apparent reason and that does not respond to symptomatic therapy. The priority is given to IMDs that are amenable to treatment, and emergency management has to be scheduled as soon as the diagnosis is suspected, even if the precise diagnosis is still unknown. In fact, emergency treatment must be undertaken in parallel with metabolic investigations, to prevent any delay in the management of the disease. The neonatologist must be able to recognize the neonatal distresses that suggest the possibility of an IMD. In such situations, an adequate diagnostic approach can be based on the proper use of only a few screening tests, which will also be useful to schedule adequate emergency treatment.