Abstract
This review article highlighted the need for clinicians to be alert to the possibility of an inherited metabolic disease (IMD) being the cause of a neonatal illness and provided a systematic approach to clinical diagnosis when IMD is suspected. Inherited metabolic disease (IMD) must be considered in the differential diagnosis of an ill neonate with nonspecific unexplained features, such as poor feeding, lethargy, failure to gain weight/weight loss, coma, apnoea, hyperventilation, seizures and hypotonia. Investigation for IMD should begin with simple urine and blood screening tests. For example, the urine examination includes checking for unusual odours, urinalysis (for ketones, amino acids, and organic acids), and reducing substance in urine, ferric chloride test and dinitrophenylhydrazine test. This is followed by simple blood tests e.g., full blood count, glucose, ammonia, amino acids, urea and electrolytes ( Na, K, Cl, P, Ca) levels, creatinine levels, liver function tests, serum lactate/pyruvate ratio and blood gases. In neonates, ketonuria with acidosis is a very important laboratory finding pointing to IMD. Although the prognosis for patients with IMD presenting in the neonatal period is often poor, every effort must be made to establish the diagnosis for parental counselling and in case prenatal diagnosis is possible in future pregnancies. In conclusion, when presented with an ill full-term neonate with nonspecific, unexplained/peculiar features pursue the usual bacterial septicaemia work-up, but in addition, consider IMD and evaluate, timely, for metabolic disease. This approach is very useful since the commonest mistake in the management of a neonate with IMD is a delay in diagnosis or a misdiagnosis, resulting in a delay in starting treatment with catastrophic consequences. Key words: inherited metabolic diseases; inborn errors of metabolism; clinical diagnosis; neonatal screening. DOI: http://dx.doi.org/10.3126/jnps.v32i1.4882 J. Nepal Paediatr. Soc. Vol.32(1) 2012 57-64
Highlights
Inherited metabolic disease (IMD) refers to a disorder in which single gene defects cause clinically significant blocks in metabolic pathways[1]
IMD results from mutations in DNA that code for a specific protein, which may act as an enzyme, receptor, transport vehicle, membrane pump or structural element[2,3]
Most IMDs are inherited as autosomal recessive trait and neonates with parental consanguinity are at increased risk[4]
Summary
Inherited metabolic disease (IMD) refers to a disorder in which single gene defects cause clinically significant blocks in metabolic pathways[1]. With the ever-increasing rate at which new ones and variations of old ones are being recognized, IMD is an area of paediatrics that is assuming an increasing role in both private practice and tertiary hospitals referral[14,15] The most common error in the management of neonates with IMD is a delay in diagnosis, resulting in a delay in commencement of appropriate treatment and, sometimes, a rapidly progressive neurologic deterioration, coma and death[9,16] In this regard, there is a need for the paediatrician to develop a system for identifying the patient who might have an IMD and, at least, for determining the general category to which the suspected IMD belongs. Inherited metabolic diseases (IMD) are revealed either as a result of the mass screening of neonates or by investigation of ill neonates presenting with a constellation of clinical features. Failure of usual therapies to alleviated the symptoms e.g., in hypoglycaemia
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