Usefulness of a buccal smear in the initial assessment of a baby with a disorder of sex development

Abstract

Introduction: A newborn with a disorder of sex development (DSD) has ambiguous genitalia and thus, it is difficult to identify the sex of such a baby at birth. Early identification is essential for psychological, social and medical reasons. Therefore a karyotype is mandatory but the result takes time whereas a buccal smear result for Barr bodies is available within a few hours. Objective: Assess the usefulness of a buccal smear as an initial investigation for genetic assessment of a baby with a DSD. Method: A buccal smear and karyotype were done on all babies with a DSD referred to a ward at the Lady Ridgeway Hospital, Sri Lanka over 3 years from November 2008. A smear was made from the buccal mucosa and 100 squamous cells were examined for the presence of Barr bodies. Control samples were taken from their mothers. Barr bodies will be present in ≥25 cells if the baby is 46, XX and there will be no Barr bodies in 46, XY. Results: Buccal smear result corresponded to the karyotype in 23 of 33 (70%) patients. The smears were inconclusive in 5 and were negative in 4 with 45, X/46, XY. The strength of agreement between a buccal smear and karyotype in assessing sex was 'moderate' (kappa 0.571, p=0.001). All buccal smear results were available in 24-48 hours and 73% of the karyotype results after 4 weeks. Conclusions: This is a useful initial investigation for genetic assessment prior to a karyotype in a baby with a DSD. Sex chromosome mosaicism cannot be identified by this method.