Inherited Metabolic Disease in the Neonatal Period: Approach to Clinical Diagnosis
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.
J. Nepal Paediatr. Soc. Vol.32(1) 2012 57-64
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