• microcephaly
• MCPH6
• cerebral cortex
• autozygosity mapping

Microcephaly is the clinical finding of a head circumference measurement greater than three standard deviations (SD) below the population mean for age and sex. It is usually accompanied by mental retardation and there are many diagnoses with both environmental and genetic aetiologies.¹ Autosomal recessive primary microcephaly (MCPH) (MIM 251200) is a disorder in which affected subjects are born with a small head circumference, explained by a cerebral cortex of reduced size, and are mentally retarded. The brain is structurally normal and, apart from the intellectual impairment, there are no other significant neurological problems, dysmorphic features, or malformations.^2,3 In a study carried out in The Netherlands,⁴ the incidence of MCPH was approximately 1/250 000 but it is probably greater in populations with a high rate of consanguineous marriages. MCPH has been shown to be genetically heterogeneous with the identification of five loci: MCPH1 on 8p23,⁵ MCPH2 on 19q13,⁶ MCPH3 on 9q34,⁷ MCPH4 on 15q15-q21,⁸ and MCPH5 on 1q31.^9,10 MCPH1, 2, and 3 were mapped in northern Pakistani families, MCPH4 in a Moroccan family, and MCPH5 in northern Pakistani and Turkish families. Here we report the identification by autozygosity mapping¹¹ of a novel locus for primary microcephaly, MCPH6, in a north eastern Brazilian family.