The introduction of MS/MS and GC/MS allowed the detection of IEMs that supposed to be rare conditions; however, together they are not that rare. These technologies have considerably enhanced the diagnostic value for such disorders, and hence early management can be assumed before permanent clinical squeal takes place .
In such scenario, extended metabolic screening by MS/MS showed particular findings in 288 patients out of 4080; so, the second alternate test, such as urine organic acid analysis, was furthermore necessary as a confirmatory follow-up diagnostic test. Furthermore, this study revealed that IEMs were diagnosed in 320/2080 (7.8%) of the cases by the application of two metabolome analyses (MS/MS δ GC/MS).
In Egypt, a lack of awareness of such inherited diseases by the physicians particularly in the rural community leads to delayed diagnosis or misdiagnosis and recurrent metabolic crises with irreversible damage or death of the affected neonates before starting the diagnosis . This agreed with the findings of the present study as there was a delayed diagnosis of the patients (presenting age was around the end of the first year of life), which may be the cause of those severe and irreversible clinical complications. These results were consistent with reports by other studies [6, 19].
Furthermore, many older children exhibited poor response to particular therapies when started, while younger patients belonging to the same families displayed a considerably improved response. This indicates the absolute necessity for early recognition and intervention for promising results in such disorders .
Variable ratios of IEMs were found in diverse studies according to the type of selection of patients. In a study done by Shawky and his colleagues, IEMs were diagnosed in 20/50 (40%) infants and children who were supposed to have IEMs . In another study done by Selim and his colleagues, IEMs were confirmed in 6% (203/3380) of children suspected to have IEMs . Also, high incidence of IEMs (32.5%) was reported in the study of Shawky and his colleagues  compared to other studies that was due to the selection criteria of neonates with suspected IEMs, not all that admitted to the Neonatal Intensive Care Unit (NICU).
In the current study, out of 320 patients with IEMs, 184 patients (57.5%) had consanguineous parents. This was in line with other studies by El-Mesellamy et al. and Selim et al. [6, 22] in addition, there were a history of previous siblings’ death and similar cases in the family (up to 3 children in some cases) in 96/320 (30 %) and 88/320 (27.5%) patients respectively (Table 2). This might not be clarified only by the high consanguinity in Egypt that extends up to 35.3% , but also by the fact that most diagnosed IEMs are autosomal recessive which rise in occurrence by consanguineous coupling because relatives more often share abnormal genes innate from a shared ancestor . Hence, a history of parent consanguinity and/or sibling deaths would increase the suspicion of IEMs . This reflected the important influence of consanguinity in this specific health problem in Egypt due to lack of early detection, and absence of genetic follow-up and counseling when having a confirmed case .
In the current study, the most common IEMs were organic acidemias detected in 62.5%, aminoacidopathies in 25%, fatty acid oxidation disorders in 7.5%, and lactic acidemia in 4%. Methylmalonic acidemia (MMA) and maple syrup urine disease (MSUD) were the most frequently diagnosed types in the current study, while Phenylketonuria (PKU) and MMA, were the most commonly diagnosed disorders in a study done by Karam and his colleagues  similar to that reported from other Mediterranean countries like Tunisia . Furthermore, Selim and her colleagues  demonstrated that aminoacidopathies were in 127/203 (62.6%), mainly PKU in 100/203 (49.3%), followed by organic acidemias in 69/203 (34%).
The variation in the commonest types of IEMs in the current study is due to variation in performed investigations, the inconsistent diagnostic strategies (ammonia and lactate were measured in our study), and age variation of the patients.
In the current study, the shared presenting symptoms of the cases were sepsis-like symptoms (poor feeding, reduced activity, and poor crying) which were in agreement with the study of Shawky et al.  who recommended to take in mind inborn errors of metabolism at the same time as common developed disorders, for example, sepsis. The further common presenting symptom among the detected cases was convulsions. This came in agreement with the study of Shawky et al.  who reported that the major symptoms in neonates with the risk of metabolic disorders were convulsions and lethargy.
In the current study, there was a high frequency of hyperammonemia in 168 patients (52.5%) among the diagnosed cases of IEMs; 136 had organic acidemias, 16 had Maple syrup urine disease (MSUD) and 16 had orotic aciduria (data not shown), this was in line with the study of Shawky et al. . They were mainly presented with lethargy, poor feeding, suckling, crying, convulsions, persistent vomiting, and acidosis. This means that blood ammonia has to be measured for each neonate/infant presented by these symptoms, or supposed to have IEMs .
Methylmalonic acidemia (MMA) was detected in 48/320 (15%), by elevations of propionylcarnitine (C3) and the ratio of acetyl carnitine: propionylcarnitine (C3:C2) in dried blood spot samples. Diagnosis was confirmed by the elevated peaks of urinary methylmalonic acid, methylcitric acid, moderate elevation of 3-hydroxy propionic acid, and propionyl glycine detected by GC/MS. The diagnosis was according to the findings of El-Mesellamy et al. and Shennar et al. [22, 27]. It results from either deficiency of the methylmalonyl CoA mutase enzyme or the synthesis of its cofactor Vit B12 .
Glutaric acidemia (GA) was detected in 40/320 (12.5%): by elevation of glutarylcarnitine (C5DC) in dried blood spot samples. The diagnosis was confirmed by the detection of elevated peaks of urinary glutaric and 3-OH glutaric acids by GC/MS, which are the diagnostic metabolites according to the findings of the researchers [22, 27, 28].
Glutaric acidemia type 1 (GA-1) is caused by the defect in functional glutaryl-CoA dehydrogenase (GCDH) activity, an important enzyme in the catabolism of l-tryptophan, l-lysine, and l-hydroxylysine, leads to the accumulation of glutaric acid, 3-hydroxyglutaric acid (3-OH-GA), and occasionally glutaconic acid in the different body fluids .
Propionic acidemia (PA) was detected in 32/320 (10%) by elevations of C3 and the ratio of C3:C2 in dried blood spot samples. Diagnosis was confirmed by the highly elevated peaks of urinary 3-hydroxypropionic acid, propionylglycine, methylcitric acid, and the absence of methylmalonic acid by GC/MS (Fig. S3). The diagnosis was according to the findings of other studies [22, 27].
Isovaleric acidemia (IVA) was detected in 40/320 (12.5%) by elevations of isovalerylcarnitine (C5) in dried blood spot samples. It was confirmed by elevated peaks of urinary isovalerylglycine (mono and di-derivatives) and 3-hydroxyisovaleric acid by GC/MS as it was reported by other studies [27, 29]. It is caused by a defect in the function of the Apo enzyme of the mitochondrial enzyme isovaleryl-CoA dehydrogenase .
Methylcrotonyl glycinuria (MCG) was detected in twelve males and four female patients 16/320 (5%) by elevation of hydroxy isovalerylcarnitine (C5-OH) in dried blood spot samples. Diagnosis was confirmed by the detection of 3 hydroxyisovaleric acid, methylcrotonyl glycine, and methyl citric acid by GC/MS. These results were in line with other studies [6, 30]. It is caused by deficiency of 3-methyl crotonyl CoA carboxylase (3-MCC) enzyme; one of the four biotin-containing carboxylases known in human beings; hence, leucine catabolism is blocked .
Orotic acid was detected in 24/320 (7.5%). Low citrulline and high arginine levels were identified in four patients, associated with the detection of elevated peak of urinary orotic acid on GC/MS analysis that implies primary orotic acidemia/aciduria which is a disorder of pyrimidine metabolism or urea cycle disorder; however, genetic testing is the method of the first choice to confirm the diagnosis  that was consistent with the findings of El-Mesellamy and his colleagues . Likewise, family pedigree construction revealed a similar case (she was a female carrier) as it is x-linked disease that implies ornithine transcarboxylase OTC deficiency . The other cases were diagnosed by elevated peak of urinary orotic acid. These findings were in line with El-Mesellamy and his colleagues  who depended on the detection of orotic acid in urine for diagnosis of urea cycle defects.
MSUD was detected in 32/320 (10%); by elevated the ratio of Leucine/Isoleucine (Leu/Ile) and valine in dried blood spot samples and by confirmed by the detection of elevated peaks of alloisoleucine, 2-oxoisocaproate, and 2-hydroxyisovalerate in urine by GC/MS. In a study done by Fateen and his colleagues , MSUD, caused by a deficiency in the branched chain a-ketoacid dehydrogenase complex, was diagnosed in 12 cases [(12/1041 (1.2%)] which represent 4% out of 302 patients supposed to be aminoacidopathy; however, they were diagnosed by performing thin layer chromatographic separation of amino acids in plasma and urine that showed abnormal quantities of branched chain amino acids (valine, leucine, and isoleucine).
Phenylketonuria (PKU) was detected in 24/320 (7.5%) by quantitative elevation of phenylalanine level and the ratio of phenylalanine to tyrosine in dried blood spot samples according to the findings of the study of Fateen and his colleagues . It is caused by mutations in the phenylalanine hydroxylase (PAH) gene causing the accumulation of excessive quantities of phenylalanine which are harmful to brain development .
Around 1/3 of diagnosed cases with aminoacidopathies were identified as MSUD or PKU which is reasonably a great number, this was in line with the study done by Fateen and his colleagues .
Non-ketotic hyperglycinemia (NKH); was detected in eight male cases 8/320 (2.5%) by elevated glycine level in dried blood spot samples. It is a hereditary disorder characterized by unusual great levels of glycine produced by a defective glycine cleavage system, causing too much glycine concentrations in both blood and brain . In a study done by Fateen and his colleagues , only 3 patients (3/1041 0.3%) gave a band of glycine in thin layer chromatography (TLC) separation of free amino acids in urine and blood and this signifies 1% out of 302 cases diagnosed with aminoacidopathy.
Homocytinuria (HCU) was detected in 16/320 (5%) by increased level of blood methionine concentrations in filter paper. Quantitative analysis of plasma homocysteine was done for conformation of the diagnosis. It is a genetic deficiency of cystathionine β-synthase (CBS). This enzyme is involved in the transsulfuration of homocysteine to form cystathionine using pyridoxal-phosphate as a cofactor . In another study by Selim and her colleagues , Homocytinuria was detected in 4/203 (2%).
Fatty acid oxidation disorders (FAODs) are inborn errors of metabolism due to disruption of either mitochondrial β-oxidation or the fatty acid transport using the carnitine transport pathway. The presentation of a FAOD will depend upon the specific disorder, but common elements may be seen, and ultimately require a similar treatment. Furthermore, they are an important group to consider in hypoketotic hypoglycaemia conditions due to decreased ability to use stored fat as a source of energy during fasting periods .
In this study, fatty acid oxidation defects were detected only in 24 cases (7.5%); that was similar to other reports in some Arab populations like Lebanon (4%)  while Bahrain  have considerably higher prevalence rates for fatty acid oxidation defects (20%). The diagnosis was established according to Fingerhut et al.  by increased Hexanoylcarnitine (C6)-Decanoylcarnitine (C10) and low level of Hexadecanoylcarnitine (C16) and Linoleoylcarnitine (C18:1) and high free carnitines in eight cases and elevated dicarboxylic acids in urine such as adipic, suberic, dehydrosuberic, sebacic, dehydrosebacic, and modest amounts of 3-OH dicarboxylics-hexanoyl glycine in the other cases.
Lactic acid (di- and tri-TMS derivatives) were detected in (16/320, 5%) associated by elevated peaks of urinary 4-hydroxyphenyllactic acid by GC/MS. Lactic acidemia is a physiological condition that can occur due to a number of causes . It is also may be due to enzyme defect in krebs cycle leading to respiratory chain deficiencies such as pyruvate dehydrogenase (PDH), pyruvate carboxylase (PC), and electron transport chain (ETC) deficiencies as well as 4-hydroxyphenyllactic acid that is actually a tyrosine metabolite and may be elevated secondary to disorders of tyrosine catabolism, liver disease, or lactic acidemia so more enzyme studies and molecular genetic studies may be required . Interestingly, determining the acid-base status is important in the assessment of a patient with a potential inherited metabolic defect, because high anion gap metabolic acidosis is usually caused by the accumulation of organic acids including lactic acid, ketone bodies, or unusual acids and their derivatives. In contrast, diarrhea and renal tubular acidosis are the main causes of metabolic acidosis with a normal anion gap .
The only limitations to metabolome coverage result from the available volume of sample, restrictions of metabolite extraction, and the sensitivity and specificity of the analytical techniques in addition to the pretreatment of urine samples analyzed via GC-MS by urease to eliminate the significant amount of urea, as it might affect the chemical derivatization, causing overloading of column, peak alterations, and co-elution of metabolites peaks .