Evidence for a cluster of rare birth defects in the Ain department (France)

REMERA (REgistre des Malformations En Rhône-Alpes) is a registry of congenital malformations that covers 58,000 births annually in Central-East France. In 2010, the registry raised an alarm to the health authorities (Santé publique France, SpF) about three cases of a unilateral isolated transverse upper limb reduction defect (UITULRD) in a small subarea; the general prevalence of this defect is one case in 10,000 births. In the following years, more infants were born with the same malformation in the same territory of the Ain department. Public health authorities, supported by an expert committee, rejected the existence of a cluster, but we aim here at providing evidence for this cluster.

Geocoded data for all UITULRD cases (ICD-10 codes Q71.2 and Q71.3) were extracted from the REMERA database. We conducted a Kulldorff cluster analysis of these data, using the spatial SaTScanTM algorithm.

The analysis found a cluster of eight cases of UITULRD among the 8,204 births occurring between 2009 and 2014 within a circle of 16.24 km radius centered on a village of the Ain department, whereas 0.82 cases were expected under a uniform probability of such a birth throughout the registry territory. This represents an almost 10fold excess over the expected number of cases (p = .0057).

The arguments used to deny the cluster are disputed and we present the evidence supporting its reality. The controversy that has followed the alarm has compromised the search for the cause(s) of this excess of rare malformations.