Re: Prevalence of microcephaly in Europe: population based study
We thank Kennedy et al for giving us an opportunity to clarify the role of ethnicity in the diagnosis of microcephaly in EUROCAT data.
EUROCAT is a surveillance network, which uses routinely collected data on congenital anomaly diagnoses made by clinicians in the European population. The diagnostic definitions are as used by clinicians (according to their own training and references), but the EUROCAT Coding and Classification Committee produces a set of “Descriptions of EUROCAT subgroups” (http://www.eurocat-network.eu/aboutus/
datacollection/guidelinesforregistration/guide1_4.) which describes the diagnostic definitions in use by clinicians in Europe. The Description given under microcephaly is “A reduction in the size of the brain with a skull circumference less than three standard deviations below the mean for sex, age and ethnic origin. Definitions known to vary between clinicians and regions.” The replies to the questionnaire to the registries showed that the growth charts in use differ between countries. 1The differences between growth charts may be due to methodological reasons in their construction or differences in growth between populations. Evidence that clinicians are all using a single growth standard would of course lead EUROCAT to remove “ethnicity” from its description. The reference to the 1991 paper was not in relation to the role of ethnicity in the definition, but to the role of different thresholds of small head size in the definition to support use of a 3 SD (rather than 2SD) threshold. 2
References
1. Morris JK, Rankin J, Garne E, et al. Prevalence of microcephaly in Europe: population based study. BMJ 2016;354:i4721. doi: 10.1136/bmj.i4721
2. Dolk H. The predictive value of microcephaly during the first year of life for mental retardation at seven years. Dev Med Child Neurol 1991;33:974-83.
Competing interests:
No competing interests
10 October 2016
Joan K Morris
Professor of Medical Statistics
Judith Rankin,Ester Garne, Maria Loane,Marie-Claude Addor,Larraitz Arriola, Ingeborg Barisic, Jorieke E H Bergman, Melinda Csaky-Szunyogh, Carlos Dias,Elizabeth S Draper, Miriam Gatt, Babak Khoshnood, Kari Klungsoyr, Jennifer J Kurinczuk, Catherine Lynch, Robert McDonnell, Vera Nelen, Amanda J Neville, Mary T O’Mahony, Anna Pierini, Hanitra Randrianaivo, Anke Rissmann, David Tucker, Christine Verellen-Dumoulin, Hermien E K de Walle, Diana Wellesley, Awi Wiesel, Helen Dolk
Queen Mary University of London
Wolfson Insitute of Preventive Medicine, Charterhouse Square, EC1M 6BQ
Rapid Response:
Re: Prevalence of microcephaly in Europe: population based study
We thank Kennedy et al for giving us an opportunity to clarify the role of ethnicity in the diagnosis of microcephaly in EUROCAT data.
EUROCAT is a surveillance network, which uses routinely collected data on congenital anomaly diagnoses made by clinicians in the European population. The diagnostic definitions are as used by clinicians (according to their own training and references), but the EUROCAT Coding and Classification Committee produces a set of “Descriptions of EUROCAT subgroups” (http://www.eurocat-network.eu/aboutus/
datacollection/guidelinesforregistration/guide1_4.) which describes the diagnostic definitions in use by clinicians in Europe. The Description given under microcephaly is “A reduction in the size of the brain with a skull circumference less than three standard deviations below the mean for sex, age and ethnic origin. Definitions known to vary between clinicians and regions.” The replies to the questionnaire to the registries showed that the growth charts in use differ between countries. 1The differences between growth charts may be due to methodological reasons in their construction or differences in growth between populations. Evidence that clinicians are all using a single growth standard would of course lead EUROCAT to remove “ethnicity” from its description. The reference to the 1991 paper was not in relation to the role of ethnicity in the definition, but to the role of different thresholds of small head size in the definition to support use of a 3 SD (rather than 2SD) threshold. 2
References
1. Morris JK, Rankin J, Garne E, et al. Prevalence of microcephaly in Europe: population based study. BMJ 2016;354:i4721. doi: 10.1136/bmj.i4721
2. Dolk H. The predictive value of microcephaly during the first year of life for mental retardation at seven years. Dev Med Child Neurol 1991;33:974-83.
Competing interests: No competing interests