26 Deletion of Chromosome No. 18 (Long Arm). A New Syndrome

Four unrelated examples of partial deletion of the long arm of chromosome No. 18 have been briefly reported by us (Lancet ii: 641 [1966]). These patients have now been studied in detail. The typical features of this syndrome are mental retardation, short stature, impaired hearing with atretic or narrow ear canals, prominent antihelix, mild microcephaly, typical facies manifested by prominent forehead—perioral areas and deep set eyes, proximal implantation of the thumbs, increased number of whorl fingerprint patterns, hypotonia, vertical tali, fundoscopic anomalies and asymptomatic congenital heart anomalies. Relatives of three of the patients had normal chromosomes. The father and two siblings of the fourth patient had one metacentric No. 18, interpreted as a pericentric inversion. The deletion in this last patient probably arose by a crossover in the father between the metacentric and the normal No. 18 (‘aneusomy by recombination’). These four patients represent partial monosomy No. 18 but nonetheless the findings are not obviously the antithesis of the trisomy 18 syndrome. The retardation and morbidity associated with this chromosome disorder are less severe than those found with the usual autosomal trisomies. Since survival does not seem to be affected by this disorder, these patients will likely be found among older children. (SPR)