Because of the significant differences between the juve-nile and adult forms of open-angle glaucoma, especially with regard to inheritance, prevalence, severity, and age of onset, we read with interest the recent publication by Morissette et al.(1995), describing a pedigree with a phenotype that overlaps the distinctive features of juvenile-onset open-angle glaucoma (JOAG) and adult-onset primary open-angle glaucoma (usually abbreviated as POAG or COAG). These authors conclude that a gene mapped to humanchromosome lq21-q31 (GLC1A) can be responsible for both juvenile and adult forms of open-angle glaucoma. The implications of such a result could be extremely important, in light of the high prevalence of the adult form of the disease. However, while the data presented in this report suggest that variable expressivity of the GLC1A gene may lead to a broader range of onset for this form of juvenile glaucoma, these data do not identify the GLC1A gene as an important cause of POAG. To prevent misleading interpretations of this and similar studies, we wish to clarify the distinction between the juvenile and adult forms of open-angle glaucoma.

Glaucoma is a term used to describe a disease process that results in a loss of retinal ganglion cells, causing a characteristic degeneration of the optic nerve. Typically the deterioration of the optic nerve is associated with an elevation of intraocular pressure that is probably related to the pathogenesis of the disorder. The ocular structures comprising the fluid pathways that contribute to the variation in intraocular pressure are located in the" angle" created by the junction of the cornea with the iris. Clinical descriptions of the various types of glau-coma often refer to the appearance of the angle; in particular, glaucoma is frequently divided into the openangle and closed-angle subtypes. Closed-angle glaucoma is very rare and is usually caused by anatomical abnormalities. Open-angle glaucoma is much more common and is likely to result from a number of different, and as yet undefined, physiological and biochemical abnormalities. Although glaucoma eventually causes a complete loss of sight, the destructive process is usually very slowly progressive, and most patients are unaware of a loss of vision, or any other symptom, until quite late in the course of the disease. Of the many different types of glaucoma, the most common is POAG, which affects individuals in the later decades of life, with an onset usually after the age of 50 years (Armaly 1962, 1969). A rare form of glaucoma that has been recently well studied is the primary open-angle glaucoma of juvenileonset (JOAG). Unlike the adult-onset disease, the juvenile type almost always develops before the age of 40 years and is an unusually severe form of the disease, frequently causing substantial visual impairment in affected individuals (Wiggs et al. 1995). While the adult form of the disease is likely to be inherited as a complex trait, without an obvious segregation pattern, the juvenile form is inherited as an autosomal dominant Mendelian trait with high penetrance. One locus for JOAG has been mapped to human chromosome lq21-q31 (Sheffield et al. 1993; Richards et al. 1994; Wiggs et al. 1994). The clinical phenotype of the pedigrees shown to be linked to the lq21-q31 region is remarkably uniform (Johnson et al. 1994; Wiggs et al. 1995). In the recent publication by Morissette et al.(1995), a common haplotype derived from microsatellite markers located in the lq21-q31 region segregates with the disease phenotype in 40 individuals included in this study. Of these 40, 36 were documented to develop the disease before the age of 40 years and consequently …