Rare case of patient with DiGeorge syndrome and limbs anomalies: the benefit of SNP microarray analysis?
Abstract
DiGeorge syndrome (velocardiofacial syndrome, VCFS, 22q11DS) is caused by a microdeletion of approximately 40 genes from one copy of chromosome 22. Expression of the syndrome is a variable combination of more than 190 phenotypic characteristics, the most common are congenital heart disease, cleft palate and velopharyngeal insufficiency.
Limb anomalies of hands and feets are not a typical clinical symptoms of DiGeorge syndrome. The aim of the study was to evaluate the extent of genomic changes in a 4.5 years old child with classical phenotypic features of 22q11DS in combination with severe ectrodactyly of all four limbs in addition; using microarray based single nucleotide polymorphism techniques in order to explain the origin of limb anomaly defects.
FISH analysis, TP63 gene sequencing and whole genome SNP array analysis using HumanCytoSNP-12 DNA Analysis Beadchip (Illumina Inc.) were performed. FISH method revealed DiGeorge syndrome, TP63 gene sequencing did not detect any deleterious mutation, microarray SNP analysis established microdeletion of 22q11.2 region in standard defined range of 2,9 Mb.
The original possible hypothesis, that in a patient it could exist a much more genomic changes than only these related to 22q11.2 region, involving genes associated with limb development and formation and thus explaining devastating limbs damage in patient, unfortunately was not confirmed. Although limb defects do not belong to the typical pathogenic signs of DiGeorge syndrome, this diagnosis should be considered in all neonate with congenital heart defect, cleft palate and limb anomalies.
Even though variable phenotypical expressivity in DiGeorge syndrome is frequent, we can not exclude the possibility of coincidence of two independent genetic defects in our patient; DiGeorge syndrome due to 22q11.2 microdeletion and ectrodactyly which results of another gene/s mutation.