Background: Tetrasomy 18p is a rare disorder. It is known to affect about 250 families worldwide. Tetrasomy 18p is also the most common type of isochromosome. Here we report a de novo tetrasomy 18p.
Methods: The copy number variation of the patient was detected by microarray. Whether the abnormal gene was inherited from the parents was detected by karyotype analysis. Then the source of the chromosome was located by fluorescence in situ hybridization. Finally, we used MLPA technology to validate the results of patient testing.
Results: Microarray detection found that patients with 18p11.32p11.21 had duplication, with a copy number of four, which was tetrasomy 18 syndrome. The karyotype results showed 48,XY,+2mar?. Chromosome 18 telomere probe FISH experimental results: 48,XY,+i(18)(p10),+mar.ish. MLPA results showed that the number of chromosome 18 short arm copies is increased. Karyotype analysis results of his mother were 47,XX,+mar. Microarray results showed normal. Karyotype results of his father were normal.
Conclusions: This case is de novo case, the patient’s marker chromosome may be inherited from his mother, which does not rule out the influence of his mother’s marker chromosome on his isochromosome 18.