Mental retardation refers to significantly sub average general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period. Inborn errors of metabolism (IEMs) are a set of relatively uncommon complicated medical conditions involving abnormalities in the complex biochemical and metabolic pathways of the human body system. Most of the IEM are single gene defects, inherited in an autosomal recessive manner, with a 25% recurrence risk. Fortunately, treatment is possible for many IEM. Emergency treatment of metabolic disorders consists of symptomatic treatment, which is applied regardless of the underlying disorder, and specific treatment is possible by our understanding of the biochemical bases of the underlying disorder. This study included a study group which consisted of 186 cases of unexplained mentally retarded children and a control group which consisted of 35 children of matched age, sex and socio-economic status. All cases were subjected to the following: detailed history taking, family pedigree, thorough clinical examination, anthropometric measurements, routine investigations, urine metabolic screening tests (ferric chloride test and toluidine blue spot test) and urinary paper chromatography, EEG , IQ and psychiatric assessment. in patients (about 17.5%) were admitted to incubator& in control cases (about 8.5 %) cases were admitted to incubator, test of significance found to be significance. There was no significant difference between patients and control regarding their psychiatric disorders . There was significant difference between patients and control regarding their height, weight, BMI and head circumference. Delayed teething and delayed sphincter control were not significant between both groups. Toluidine blue test don`t show significant difference between both groups. High positivity of Urine metabolic screening tests and urinary paper chromatography in these patients beside the clinical presentation, consanguinity and family history of MR suggest a significant probability of the presence of a metabolic disease, which will need further specific investigations to confirm the diagnosis and determine the possible treatable cases.
Key Words: metabolic assessment, mental retardation
Introduction
Mental retardation is defined by American Association of Mental retardation (AAMR)(1) as it is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18 years.
Mental retardation (MR) is a common problem in Pediatrics with a reported frequency of about 2-3%(2).
The severity of mental retardation has been based on the IQ score, (I.Q score of below 70) the various groups as per the WHO classification are –Mild (IQ 55-69); Moderate (IQ 40-54); Severe (IQ 25-39) and Profound (IQ below 25)(3)
Mental Retardation is a condition with varying etiology. It may have genetic or non-genetic (environmental) origin(3)
Genetic causes of MR are broadly classified by Kumta(4) into:
1. Single gene disorders including all the inborn errors of metabolism.
2. Chromosomal disorders.
3. Multifactorial in origin.
Mental Retardation can be due to static or progressive encephalopathy. Progressive encephalopathy is where the child loses already acquired milestones and regresses from the higher level of CNS functioning to a lower level. It is due to neurodegenerative disorders which are very often metabolic in origin(4).
Inborn errors of metabolism (IEM) are a heterogeneous group of disorders caused by single gene defect which may manifest immediately after birth or within few days or weeks after birth(5).
Most of the IEM result from defects in any of the key enzymes of various metabolic pathways, leading to accumulation of compounds which follow an alternative pathway of metabolism, resulting in the production of toxic metabolites and deficiency of biologically important compounds(6).
Individually, IEM present variable incidences, but as a whole, they present a cumulative frequency of 1:500 newborns(7) among children with mental retardation it was reported that 5.75% of them were due to inherited metabolic disorders(8).
Most IEM are inherited as autosomal recessive traits. Hence a history of parental consanguinity and/or sibling deaths should increase the suspicion of IEM. IEM causing clinical manifestations in the neonatal period are usually severe and often lethal(9).
Early diagnosis of IEM is very important since the condition is rapidly progressive and results into irreversible damage in early childhood. It also helps in initiating the treatment in the earlier stages of development as it will be more effective and will improve the outcome at a later stage. The most important aspect of early diagnosis is that, genetic counseling(9).
Early diagnosis of the condition by various laboratory tests and initiation of prompt therapy is very much essential in order to prevent lethal complications which are irreversible. Various simple preliminary laboratory tests can aid in diagnosis of IEM which can be further confirmed by advanced diagnostic techniques(8).
The aim of this study is to detect inborn error of metabolism by simple method such as urine metabolic screening tests or paper chromatography that will improve outcome and quality of life through appropriate intervention and treatment.