Abstract
We report a case of an interstitial chromosome 20q11.21 microdeletion in a 7-year-old male child presenting with mild intellectual disability and facial dysmorphisms. Array comparative genomic hybridization (CGH) has shown that the deletion resulted in the loss of 68 genes, among which 5 genes (COX4I2, MYLK2, ASXL1, DNMT3B, and SNTA1) are disease causing. The size of the deletion was estimated to span 2.6 Mb. Only three cases of deletions encompassing this chromosomal region have been reported. The phenotype of the index patient was found to resemble the mildest cases of Bohring-Opitz syndrome that is caused by ASXL1 mutations. An in silico evaluation of the deleted genomic region has shown that benign genomic variations have never been observed to affect the ASXL1 gene, in contrast to the other disease-causing genes. As a result, it was suggested that ASXL1 loss is likely to be the main cause of the phenotypic manifestations. The present case report indicates that a loss of the disease-causing gene can produce a milder phenotype of a single gene condition.
Highlights
The application of array comparative genomic hybridization (CGH) in clinical cytogenetics has significantly increased the diagnostic yield [1, 2]
Array CGH molecular cytogenetic analysis has become almost indispensable in children suffering from intellectual disability and related neurobehavioral problems [1,2,3]
Performing a similar study in the Russian cohort of children with intellectual disability and congenital malformations, we have identified an interstitial 20q11.21 microdeletion in a 7-year-old male child presenting with mild intellectual disability and facial dysmorphisms
Summary
The application of array comparative genomic hybridization (CGH) in clinical cytogenetics has significantly increased the diagnostic yield [1, 2]. Studying genome variations in neurobehavioral diseases using array CGH has promoted the identification of new causative submicroscopic chromosome imbalances in the clinical population [2, 3]. Array CGH molecular cytogenetic analysis has become almost indispensable in children suffering from intellectual disability and related neurobehavioral problems [1,2,3]. According to the available literature, only three cases of chromosome 20 deletions encompassing the same chromosomal region (excluding somatic chromosome rearrangements associated with malignant pathology) have been reported and only two cases of interstitial deletions involving 20q11.21 were previously characterized by array CGH [5,6,7]
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