There are no guidelines available for diagnostic studies in patients with mental retardation (MR) established in an evidence-based manner. Here we report such study, based on information from original studies on the results with respect to detected significant anomalies (yield) of six major diagnostic investigations, and evaluate whether the yield differs depending on setting, MR severity, and gender. Results for cytogenetic studies showed the mean yield of chromosome aberrations in classical cytogenetics to be 9.5% (variation: 5.4% in school populations to 13.3% in institute populations; 4.1% in borderline-mild MR to 13.3% in moderate-profound MR; more frequent structural anomalies in females). The median yield of subtelomeric studies was 4.4% (also showing female predominance). For fragile X screening, yields were 5.4% (cytogenetic studies) and 2.0% (molecular studies) (higher yield in moderate-profound MR; checklist use useful). In metabolic investigations, the mean yield of all studies was 1.0% (results depending on neonatal screening programmes; in individual populations higher yield for specific metabolic disorders). Studies on neurological examination all showed a high yield (mean 42.9%; irrespective of setting, degree of MR, and gender). The yield of neuroimaging studies for abnormalities was 30.0% (higher yield if performed on an indicated basis) and the yield for finding a diagnosis based on neuroradiological studies only was 1.3% (no data available on value of negative findings). A very high yield was found for dysmorphologic examination (variation 39-81%). The data from this review allow conclusions for most types of diagnostic investigations in MR patients. Recommendations for further studies are provided.

/pdf/diagnostic-investigations-in-individuals-with-mental-29or1tdp9a.pdf

Diagnostic investigations in individuals with mental retardation: a systematic literature review of their usefulness

Techniques of Autoradiography.Andrew W. Rogers

Chromosomal abnormalities are frequent events. Globally, at least 7.6 million children are born annually with severe genetic or congenital malformations. Precise prevalence data are difficult to collect, especially in India, owing to great diversity of conditions and also because many cases remain undiagnosed. Genetic and congenital abnormality is the second most common cause of infant and childhood mortality and occurs with a prevalence of 25- 60 per 1000 births. The higher prevalence of genetic diseases in a particular community may, however, be due to some social or cultural factors.

Chromosomal Abnormalities: Genetic Disease Burden in India

Chromosome 22q11.2 microdeletion syndrome is due to microdeletion of 22q11.2 region of chromosome 22. It is a common microdeletion syndrome however mosaic cases are very rare and reported only few previous occasions. In this report we describe two unrelated male children with clinical features consistent with 22q11.2 microdeletion syndrome characterized by cardiac defect, facial dysmorphism and developmental deficiency. One of the cases also had trigonocephaly. Interphase & metaphase FISH with 22q11.2 probe demonstrated mosaicism for hemizygous deletion of 22q11.2 region. Mosaicism is also observed in buccal cells as well as urine cells. Parents were without any deletion. These two cases represent rare cases of mosaic 22q11.2 microdeletion syndrome.

/pdf/mosaic-22q11-2-microdeletion-syndrome-diagnosis-and-clinical-343fkecfu1.pdf

Mosaic 22q11.2 microdeletion syndrome: diagnosis and clinical manifestations of two cases

The cytogenetic data of a large scale study in an institutionalized population of 1991 moderately and severely mentally retarded patients are presented. In 21.3% of these patients a chromosomal aberration was diagnosed (14.9% Down syndrome patients and 3.5% "other chromosomal anomalies"). A fragile X screening was performed in 354 males, and was found to be positive in 57 (16.1% positive). Different chromosomal variants were present in another 6% of this population. Detailed results are presented on the different groups of chromosomal aberrations.

Cytogenetic Findings in Moderate and Severe Mental Retardation A Study of an Institutionalized Population of 1991 Patients

Chromosomal abnormalities are an important cause of mental retardation. We studied the frequency of karyotype abnormalities in 74 mentally retarded patients selected from 306 patients referred to our clinic. Giemsa-banding was done on all cases. Additional studies in abnormal cases included autoradiography and X and Y chromatin. Karyotype analyses and blood group (Xg and Duffy) studies were carried out in family members in some cases.

Cytogenetic studies in a selected group of mentally retarded children.

A 2-year-old male child with mosaicism for monosomy of chromosome 22 is described. He had moderate psychomotor retardation, generalised hypotonia, large ears, epicanthus, synophrys, and cutaneous syndactyly between all the fingers.

https://jmg.bmj.com/content/jmedgenet/18/1/71.full.pdf

Monosomy 22 with mosaicism

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Cytogenetic studies in a selected group of mentally retarded children.

Monosomy 22 with mosaicism