An audit of thyroid function tests in a cohort of South African children with Down Syndrome
Down syndrome (DS) (OMIM #190685), the most common viable chromosome abnormality, is associated with an increased risk of medical complications. The most frequent endocrine abnormalities observed in children with DS involve the thyroid gland, and the risk of thyroid dysfunction increases with age. Global studies have documented a wide spectrum of thyroid dysfunction in children with DS. Due to the paucity of data from sub-Saharan Africa regarding thyroid function in African children with DS, this study was conceived. The main aim of the study was to document the range of thyroid function in a cohort of 391 South African children with DS, seen at the Genetic Clinics from 2003 to 2008. Referral and treatment practices at two tertiary hospitals in Johannesburg were also documented. The majority (84%) of children had at least one thyroid function test (TFT) performed, and the most common form of thyroid dysfunction encountered was subclinical hypothyroidism (25.3%). Notably, up to one third of patients with abnormal TFT results were not referred to the Endocrine Clinics for evaluation, and were thus not receiving the necessary treatment. There were 13 neonates with congenital hypothyroidism; at least two of them were not referred, and thus not treated during the sensitive neonatal period. A significant difference was noted between the results from Chris Hani Baragwanath Hospital and those from the other two hospitals. The difficulties in interpretation of results obtained from different biochemical machines and different populations, as compared to those used to derive the reference ranges, were raised. Problems with regular follow-up of patients and annual thyroid surveillance were also highlighted. The clinical features of hypothyroidism may be difficult to distinguish from the phenotypic features of DS. Thus, regular biochemical screening, even in the absence of physical signs and symptoms, is warranted in this group of children to ensure that hypothyroidism is treated, and further, irreversible neurological and physical impairment prevented.
M.Med. (Medical Genetics)--University of the Witwatersrand, Faculty of Health Sciences, School of Pathology, 2012