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These studies expand the range of mutations identified in this disease, and broaden the phenotypic range to include clinically affected women and the first North American case with severe rickets.

The etiology of Rett syndrome is unknown. Structural mitochondrial abnormalities have been described in muscle in patients with Rett syndrome. We report three children with Rett syndrome and normal muscle mitochondrial structure on light and electron microscopy. However, all had abnormalities in mitochondrial respiratory chain enzymes.

We report a 15-month-old female with developmental delay, hypotonia, and minor anomalies whose karyotype is 47,XX,+r. Due to its small size, the origin of the ring chromosome was indeterminate by standard G-banded karyotyping. Fluorescent in situ hybridization was performed, which indicated that the ring chromosome was derived from the pericentric region of chromosome 8.

While duplication and deletion of the short arm of chromosome 12 cause well-recognized syndromes, duplication of the long arm chromosome 12 is rarely observe. We are reporting a duplication of chromosome 12 distal to band q24.1 in a five-month-old child. His chromosome constitution is 46,XY,-4+der(4),t(4:12)(p16;q24.1)mat. The balanced translocation is also carried by his maternal grandmother and two of the mother's brothers. The malformation syndrome consisted of unusual facial appearance and anomalies of the musculoskeletal, cardiovascular, genitourinary, and central nervous systems. Four previously reported patients had similar break points on chromosome 12 with similar malformations; therefore, phenotype-karyotype correlation suggests a definitive malformation syndrome associated with duplication of chromosome region 12q24.1 leads to qter.

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