ABSTRACT
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.
ABSTRACT
OBJECTIVE: To describe incidence of Down syndrome in Dubai, United Arab Emirates (UAE). SUBJECTS AND METHODS: A total of 63,398 newborn babies in Dubai (24,250 UAE nationals and 39,148 non-UAE) during a 5-year period of 1999-2003 were routinely examined by experienced nurses, neonatologists, pediatricians and/or general practitioners for symptoms of Down syndrome. Those suspected with Down syndrome were referred to the cytogenetic laboratory for karyotyping. RESULTS: A total of 141 cases were confirmed cytogenetically as Down syndrome. Of these, 139 were trisomy 21 and of the remaining 2, 1 was a translocation and the other a mosaic. Theoverall incidence of Down syndrome in Dubai was 1/449 live births (2.2 per 1,000); 1/319 live births (3.13 per 1,000) among UAE nationals and 1/602 live births (1.66 per 1,000) among non-UAE nationals. The mean maternal age of UAE national mothers was 33.48 +/- 8.08, with 41.66% of the mothers being in the advanced maternal age group (>35 years). The higher incidence of Down syndrome among UAE nationals is comparable to incidences reported for other Arab populations in the Middle Eastern region. Advanced maternal age, with mothers bearing children until their 50s and higher parity, appear to be the major contributing factors for the increased incidence. CONCLUSION: The study indicates the need to provide efficient genetic counseling and to introduce an effective antenatal screening program and prenatal diagnostic services to reduce the psychological and genetic burden on the families and community.
