Abstract
Concurrent cryptic microdeletion and microduplication syndromes have recently started to reveal themselves with the advent of microarray technology. Analysis has shown that low-copy repeats (LCRs) have allowed chromosome regions throughout the genome to become hotspots for nonallelic homologous recombination to take place. Here, we report a case of a 7.5-year-old girl who manifests microcephaly, developmental delay, and mild dysmorphic features. Microarray analysis identified a microduplication in chromosome 17q21.31, which encompasses the CRHR1, MAPT, and KANSL1 genes, as well as a microdeletion in chromosome 7q31.33 that is localised within the GRM8 gene. To our knowledge this is one of only a few cases of 17q21.31 microduplication. The clinical phenotype of patients with this microduplication is milder than of those carrying the reciprocal microdeletions, and suggests that the lower incidence of the former compared to the latter may be due to underascertainment.
Highlights
Since the advent of microarray technology considerable progress has been made in identifying small scale chromosome imbalances
The MAPT gene located on chromosome 17q21.31 is flanked by low-copy repeats (LCRs) and two extended haplotypes, designated H1 and H2, have been identified [9, 10]
601116), while the 17q21.31 microduplication contains a number of genes including CRHR1 (OMIM 122561), IMP5 (SPPL2C; OMIM 608284), MAPT (OMIM 157140), and STH (OMIM 607067) and a partial duplication of the KANSL1 gene; see Figure 1
Summary
Since the advent of microarray technology considerable progress has been made in identifying small scale chromosome imbalances. The existence of colocalized microdeletion and microduplication syndrome sites has come to the fore in the recent years and a significant number of new microduplication syndromes have emerged such as 17p11.2 [1] and 22q11.21 [2] These syndromes, like the corresponding microdeletion syndromes at these locations, appear to be driven by nonallelic homologous recombination (NAHR) involving low-copy repeats (LCRs or segmental duplications) [3,4,5,6,7,8]. The H2 haplotype is a 900 kb inversion polymorphism that has been reported as the likely ancestral state and which has a tendency to undergo recombination [11] leading to the 17q21.31 microdeletion syndrome This syndrome has been well characterised and appears to be caused by haploinsufficiency of at least one gene, KANSL, within the deleted region [12, 13]. Case Reports in Genetics delay, microcephaly, and mild dysmorphisms, which are milder than those identified in patients with the 17q21.31 microdeletion syndrome
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