SUMMARY A family in which a pericentric inversion of chromosome 22, inv(22)(pllql2), is segregating is described. Special reference is made to a unique recombinant subject with a 'pure' partial monosomy 22 syndrome of maternal origin. An attempt has been made to correlate the phenotypic abnormalities with monosomy for the segment 22ql2--qter.Pericentric inversions are two break events which are much less frequent than translocations (incidence 0-01%).' In addition to the relatively common pericentric inversion of chromosome 9,2 now considered to be a harmless polymorphism, pericentric inversions have been described for most human chromosomes. We are aware of only two other reports of pericentric inversion of chromosome 22. 4 We describe here a family in which a pericentric inversion of chromosome 22 is segregating, including what we believe to be the first case of 'pure'

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A premature male infant is described in whom the presence of coarse facies, diaphragmatic hernia, genital anomalies and Dandy‐Walker malformation suggested a diagnosis of Fryns' syndrome. Lymphocyte karyotype revealed a partial trisomy 22, and his mother carried an apparently balanced 11/22 translocation. Three infants have been described recently with features of Fryns' syndrome and various aneuploidies. It is suggested that amplified developmental instability of the midline developmental field may account for some of the phenotypic resemblances between these cases.