Diagnosis: Mosaic Trisomy 8 Syndrome

ISCN: 47,XY,+8/46,XY

Discussion:
This child is mosaic for trisomy 8. Trisomy 8 mosaicism is very rare with an estimated frequency of 1/50,000 liveborn children, and a male to female ratio of approximately 5:1. Greater than 100 cases have been reported in the literature. Some of the most common findings in patients with trisomy 8 mosaicism include mental retardation, skeletal and joint anomalies, urogenital malformations, congenital heart defects, deep palmar and plantar creases, agenesis of the corpus callosum, and characteristic facies (prominent forehead, thick lips, deep-set eyes, malformed and prominent ears, and micrognathia). There is great phenotypic variability that does not seem to correlate with the degree of mosaicism in the blood or skin. Moderate mental retardation is usually present, however, several patients with normal intelligence have been reported.

Trisomy 8 mosaicism is caused by mitotic nondisjunction. The number of cells with trisomy 8 has been reported to vary between 0-100% in both blood and skin. The percentage of trisomy 8 cells has been noted to decrease with increasing age in patients that have been followed over time. No correlation between the percentage of trisomic cells and the phenotype has been identified.

As trisomy 8 mosaicism results from mitotic nondisjunction, karyotyping of parents and/or other family members was not indicated. Genetic counseling was recommended.

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