RESUMEN
<p><b>OBJECTIVE</b>To analyze a child with developmental delay, severe mental retardation, speech delay and muscular hypotonia.</p><p><b>METHODS</b>The karotypes of the child and her parents were analyzed with G-banding analysis. Their genome DNA was also analyzed with array comparative genomic hybridization (array-CGH).</p><p><b>RESULTS</b>No karyotypic abnormality was detected at cytogenetic level. However, array-CGH has identified a de novo 4q21.21-q22.1 deletion in the child, which has a size of 12.1 Mb.</p><p><b>CONCLUSION</b>The de novo interstitial 4q21.21-q22.1 deletion probably underlies the main clinical manifestation in the child. Array-CGH is useful for diagnosing children with multiple congenital anomalies with unclear etiology.</p>