SIR–Murray and Jackson’s genetics update1 fails to mention the three most important prerequisites of microcephaly. First, the head circumference needs to be measured. Second, it needs to be measured accurately. Third, it needs to be plotted accurately. Children’s heights and weights are often measured, but by comparison head circumferences are the poor relation. Head circumferences are notoriously badly measured and badly plotted. I frequently test students and trainees in my clinic by getting them to measure a child’s head circumferences. Most have never done it before; almost none have been taught how to do it. I see head circumference measurements recorded in the hospital records that would indicate that the infant’s head had shrunk if they were correct compared to previous measurements.
A colleague and I did an audit of children on the waiting list for brain magnetic resonance imaging (MRI).2 Half of them had not had their head circumference measured. Hopefully, we encourage trainees and students that the principles of making a diagnosis are ‘history and examination’. Yet an MRI costing, say £1000 (including anaesthetic and interpretation by a neuroradiologist), was requested before using a £1.50 tape measure.
The authors say that microcephaly is defined as ‘… a significant decrease in head circumference.’ Surely the head circumference does not decrease, rather it fails to grow at the normal rate and so falls away significantly from its original position on the centile chart.