Interstitial deletion of 18q: comparative genomic hybridization array analysis of 46, XX,del(18)(q21.2.q21.33)

Interstitial deletion of chromosome 18q is rare, making it difficult to assign phenotypes to particular cytogenetic deletions.

We present an 18-year-old female with an interstitial deletion of chromosome 18q21.2-q21.33. The clinical features included severe psychomotor retardation with mild growth retardation, hypotonia, midfacial hypoplasia, carp-shaped mouth, hypertelorism, strabismus, narrow upward slant palpebral fissures, short philtrum, everted lower lip, malformed ears, flat nasal bridge, and epicanthic folds. Brain abnormalities, such as agenesis of the corpus callosum, and abnormalities of the hands and feet were absent. Initially, the deletion was recognized as 18q21.1-q21.31 by conventional chromosomal analysis, and microarray-based comparative genomic hybridization revealed a 9.6-Mb deletion at 18q21.2-q21.33. The deletion included the transcription factor 4 gene and the methyl-CpG binding domain protein 2 (MBD2) gene, but not the MBD1 gene.

The deletion of the transcription factor 4 gene suggested a possible contribution of the deletion to the patient's facial abnormalities, as observed in Pitt-Hopkins syndrome. Together with other reported cases with interstitial deletion of 18q, a possible contribution of haploinsufficiency in both MBD1 and MBD2 genes to a Rett syndrome-like phenotype was suggested, but further genetic studies on other cases are necessary to clarify the genotype-phenotype correlation.