Background: Small supernumerary marker chromosomes (sSMC) occur in 0.075% of unselected prenatal and in 0.044% of consecutively studied postnatal cases. Individuals with sSMC present with varying phenotype, ranging from normal to extremely mild or severe depending on the chromosomal region involved, the euchromatic content present and degree of mosaicism. Except for chromosomes 15 and 22, the number of reported cases of sSMC is extremely small to provide us with a good genotype-phenotype correlation. Analphoid sSMC are even rarer. To our knowledge only eight cases of analphoid inversion-duplication 3q sSMC are reported so far.
Results: We describe here a one month old female child with several dysmorphic features and with a de novo analphoid supernumerary marker chromosome only in cultured skin fibroblast cells and not in lymphocytes. The marker was characterized as analphoid inversion-duplication 3q25.33-qter by oligo array comparative genomic hybridization (aCGH) and fluorescence in situ hybridization (FISH) studies. The final skin fibroblast karyotype was interpreted as 47,XX,+der(3).ish inv dup(3)(qter-q25.33::q25.33-qter)(subtel 3q+,subtel 3q+) de novo.
Conclusion: In addition to the eight reported cases of analphoid inversion-duplication 3q supernumerary marker in the literature, this is yet another case of 3q sSMC with a new breakpoint at 3q25.33 and with varying phenotype as described in the case report. Identification of more and more similar cases of analphoid inversion-duplication 3q marker will help in establishing a better genotype-phenotype correlation. The study further demonstrates that aCGH in conjunction with routine cytogenetics and FISH is very useful in precisely identifying and characterizing a marker chromosome, and more importantly help in providing with an accurate genetic diagnosis and better counseling to the family.