Two independent chromosomal rearrangements, a very small (550 kb) duplication of the 7q subtelomeric region and an atypical 17q11.2 (NF1) microdeletion, in a girl with neurofibromatosis
Abstract
Most patients with neurofibromatosis (NF1) are endowed with heterozygous mutations in the NF1 gene. Approximately 5% show an interstitial deletion of chromosome 17q11.2 (including NF1) and in most cases also a more severe phenotype.
Here we report on a 7-year-old girl with classical NF1 signs, and in addition mild overgrowth (97th percentile), relatively low OFC (10th-25th percentile), facial dysmorphy, hoarse voice, and developmental delay. FISH analysis revealed a 17q11.2 microdeletion as well as an unbalanced 7p;13q translocation leading to trisomy of the 7q36.3 subtelomeric region.
The patient's mother and grandmother who were phenotypically normal carried the same unbalanced translocation. The 17q11.2 microdeletion had arisen de novo.
Array comparative genomic hybridization (CGH) demonstrated gain of a 550-kb segment from 7qter and loss of 2.5 Mb from 17q11.2 (an atypical NF1 microdeletion). We conclude that the patient's phenotype is caused by the atypical NF1 deletion, whereas 7q36.3 trisomy represents a subtelomeric copy number variation without phenotypic consequences.
To our knowledge this is the first report that a duplication of the subtelomeric region of chromosome 7q containing functional genes (FAM62B, WDR60, and VIPR2) can be tolerated without phenotypic consequences. The 17q11.2 microdeletion (containing nine more genes than the common NF1 microdeletions) and the 7qter duplication were not accompanied by unexpected clinical features.
Most likely the 7qter trisomy and the 17q11.2 microdeletion coincide by chance in our patient.