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Background: The chromosome 1 7q2 1.31 microdeletion syndrome is a novel genomic disorder that has originally been identified using high resolution genome analyses in patients with unexplained mental retardation. Aim: We report the molecular and/or clinical character- isation of 22 individuals with the 17q21.31 microdeletion syndrome. Results: We estimate the prevalence of the syndrome to be 1 in 16 000 and show that it is highly underdiagnosed. Extensive clinical examination reveals that developmental delay, hypotonia, facial dysmorphisms including a long face, a tubular or pear-shaped nose and a bulbous nasal tip, and a friendly/amiable behaviour are the most characteristic features. Other clinically important features include epilepsy, heart defects and kidney/urologic anomalies. Using high resolution oligonucleotide arrays we narrow the 17q21.31 critical region to a 424 kb genomic segment (chr17: 41046729-41470954, hg17) encompassing at least six genes, among which is the gene encoding microtubule associated protein tau (MAPT). Mutation screening of MAPT in 122 individuals with a phenotype suggestive of 17q21.31 deletion carriers, but who do not carry the recurrent deletion, failed to identify any disease associated variants. In five deletion carriers we identify a <500 bp rearrangement hotspot at the proximal breakpoint contained within an L2 LINE motif and show that in every case examined the parent originating the deletion carries a common 900 kb 17q21.31 inversion polymorphism, indicating that this inversion is a necessary factor for deletion to occur (p<105). Conclusion: Our data establish the 17q21.31 micro- deletion syndrome as a clinically and molecularly well recognisable genomic disorder. [ABSTRACT FROM AUTHOR]

Background: Microdeletions at 17q21.31 have recently been shown to cause a novel syndrome. Here we identify the reciprocal 17q21.31 duplication syndrome in 4 patients. Method: Patients with the 17q21.31 duplication were identified by screening a large cohort of patients (n = 13 070) with mental retardation and congenital malformation by comparative genomic hybridisation microarray. Parental origin was investigated in 3 patients by quantitative polymerase chain reaction and microsatellite genotyping. Results: In three cases it was possible to show that duplication arose de novo. Intellectual skills range from normal to mild mental retardation. Patients are characterised by poor social interaction, with relationship difficulties, reminiscent of autistic spectrum disorders. Other features are rather variable with no striking common phenotypic features. Parental origin was investigated for 3 patients. In all cases duplication was of maternal origin either through interchromosomal (2 cases) or interchromatid (1 case) rearrangement. The 3 mothers are all carriers of the inverted H2 haplotype, emphasising the role of local genomic architecture alteration as a predisposing factor for this duplication. Conclusion: Autistic features observed in our patients suggest that genes in the duplicated interval should be considered as candidates for disorders in the autistic spectrum. Other phenotypic observations are rather variable or aspecific. This adds 17q21.31 duplications to a growing group of recently identified genomic disorders with variable penetrance and expressivity. [ABSTRACT FROM AUTHOR]