Inheritance of a t(13;14)(q10;q10) Robertsonian translocation with a low level of trisomy 13 mosaicism

Low level of trisomy 13 mosaicism is a rare condition. In the present report, we describe a case of a 19-month-old boy with poor feeding, poor weight gain, mild dysmorphic features, mild muscular hypotonia, and speech delay.

Cytogenetic analysis on metaphases of lymphocytes revealed an 8% mosaic Robertsonian translocation trisomy 13 in the boy and a balanced Robertsonian translocation, 45,XX,der(13;14)(q10;q10), in his normal mother. Fluorescence in situ hybridization (FISH) on patient lymphocytes disclosed 4% of metaphases with a trisomy 13. The trisomy 13 mosaicism in metaphases could not be identified by interphase FISH. The percentage of three signals (4%) was within the standard deviation in diploid controls. Follow-up of the patient was performed at the age of 7 1/12 years, and in cells from buccal smear of the patient, trisomy 13 was detected in 11% of interphases analyzed that is a higher frequency. Uniparental disomy of chromosomes 13 and 14 were excluded in the boy, and therefore, his phenotypic abnormalities most likely were caused by the low level of trisomy 13 mosaicism.

The detailed report of this patient described the infrequent occurrence of a low mosaic Robertsonian translocation trisomy 13. We suggest to study cases of low trisomy mosaicism preferentially using metaphase analyses rather than interphase FISH. Our case is helpful in further defining the phenotype of these patients.