I read the recent article on this subject with interest(1). Since the twins mentioned in the case are dizygotic, any discordance between them in the occurrence of a genetic disorder is not surprising, as indeed that is what is expected in most such cases. Since these twins are dizygotic, the chances of both of them having Cornelia de Lange syndrome is the same as between any siblings, i.e., less than 1%. As such, their discordance is of only as much relevance as with the elder normal sibling. If indeed they were dizygotic and concordant for this disorder, it would have been of great interest, as that would have pointed to some environmental cause for this putative genetic disorder. And if they were monozygotic and discordant for any disease, it also would have been interesting, as that would also have pointed to some environmental cause for that disorder.

Alexander Mathew,
Department of Pediatrics,
St. Joseph’s Hospital,
Manjummel, Kochi 683 501, India.

1. Sheela SR. Cornelia de Lange syndrome: Discordance in twins. Indian Pediatr 1999; 36: 1267-1270.

Reply

In principle the basic point regarding the significance of concordance versus discordance in dizygotic twins is correct. Nevertheless after a detailed medline search which picked up reviews of 310 individuals(1) and 64 patients(2) with this syndrome, I could still come across only a single similar case in the world literature.

S.R. Sheela,
Snehanjali,
Seevali Nagar,
Kaithamukku,
Thiruvanthapuram 695 024,Kerala, India.