To the Editor: In response to the admirable report entitled “Nutritional koilonychia in 32 Iraqi subjects” by professor Taher Q. Al-Dabbagh and Khalid G. Al-Abachi, that was published in your March-April 2005 25(2) issue, I wish to convey the following comment:In 1908 Osler described blue sclerae in iron deficient undernourished teen-age girls. In 1971, Agnoletto described the same sign being used in diagnosis of hookworm anemia. These observations were later confirmed and explained by Karla et al in a research report published in the November 29, 1986 issue of the Lancet. After confirming the relationship of blue sclerae to iron deficiency anemia, the authors biochemically rationalized the etiologic association between iron deficiency and blue sclerae by presenting the fact that iron, in addition to vitamin C, oxygen and ketoglutarate, is essential to the conversion of proline to hydroxylproline. The later constitute 14% of the structure of collagen and 2% of elastin. They moreover disclosed that fibroblasts in culture do not synthesize collagen in the presence of iron chelating agents. Thus, iron deficiency appears to impair collagen synthesis, which in turn leads to thinning of the sclera through which the choroids can be seen, making it look blue.Realizing the essential role of iron in collagen synthesis makes it very likely that its deficiency leads to defective synthesis of nails, hence, their thinning and later on hollowing (koilonychia), in the same way its deficiency does with the sclerae. These reasons substantiate the long held idea of iron deficiency as a cause for koilonychias. However, this does not deny the role of other nutritional factors such as sulphur-containing amino acid deficiency that was proposed by the above report, confirming the predating Jalili-Kassab concept (1959). Having no significant iron deficiency in the above report is likely due to the non-homogeneity (randomization of the studied sample or to the reduction in incidence of iron deficiency in the Iraqi community in comparison to animal protein deficiency. This can be attributed to better means of diagnosing and treating chronic blood loss states like duodenal ulcers, ulcerative colitis, gluten enteropathy and hookworm infection in addition to the fact that iron resources, such as the cheap green vegetables, are more readily available, and supplemental iron pills used to be dispensed freely to pregnant and nursing women in the primary care centers even during the embargo period.In conclusion the report oriented us to the presence of another cause of nutritional koilonychia in addition to the old well known one (iron deficiency), a cause that may work alone or in conjunction with the latter.