Correspondence

Correction

Correction and Withdrawal of Conclusion — A Child with Phenotypic Laron Dwarfism and Normal Somatomedin Levels

N Engl J Med 1990; 323:1485November 22, 1990

Article

To the Editor:

We previously reported on a child from Sardinia who had the phenotype of Laron-type dwarfism, but had a serum level of insulin-like growth factor I (IGF-I), or somatomedin C, that was within normal limits, as determined by assay of unextracted serum (Nichols radioimmunoassay) (Feb. 9, 1989, issue).1 In subsequent correspondence, Laron and Silbergeld2 expressed doubt, as they and others have done elsewhere,3 , 4 about the reliability of IGF-I measurements in unextracted serum, because of the interference of IGF-I—binding proteins in the assay. We have restudied this child, as well as another Sardinian child with a similar syndrome. IGF-I was measured by Nichols radioimmunoassay after acid extraction of serum and purification on octadecasilyl silica cartridges.5 The serum IGF-I levels were less than 10 ng per milliliter (1.3 nmol per liter) in both children — values clearly below the normal range. This contrasts with the previous values, ranging from 0.34 to 1.76 U per milliliter (roughly equivalent to 80 to 340 ng per milliliter [10 to 44 nmol per liter]). On the basis of this finding, we believe that the child previously reported on should be classified as a classic Laron-type dwarf. This case demonstrates the need to use acid extraction of serum before measurement of IGF-I (somatomedin C).

Carlo Pintor, M.D.
Sandro Loche, M.D.
University of Cagliari, 09100 Cagliari, Italy

Silvano G. Cella, M.D.
Eugenio E. Müller, M.D., Ph.D.
University of Milan, F-20129 Milan, Italy

Gerhard Baumann, M.D.
Northwestern University Medical School, Chicago, IL 60611

5 References

1. 1

   Pintor C, Loche S, Cella SG, Müller EE, Baumann G. A child with phenotypic Laron dwarfism and normal somatomedin levels . N Engl J Med 1989; 320:376–9.
   Full Text | Web of Science | Medline

2. 2

   Laron Z, Silbergeld A. A child with phenotypic Laron dwarfism and normal somatomedin levels . N Engl J Med 1989; 320:1698.
   Full Text | Web of Science | Medline

3. 3

   Silbergeld A, Jaber L, Lilos P, Laron Z. A comparison of IGF-I levels measured by two commercially available radioimmunoassays . Acta Endocrinol (Copenh) 1988; 119:333–8.
   Medline

4. 4

   Underwood LE, Murphy MG. Radioimmunoassay of the somatomedins/ insulin-like growth factors. In: Patrono C, Peskar BA, eds. Radioimmunoassay in basic and clinical pharmacology. Vol. 82 of Handbook of experimental pharmacology. Berlin, Germany: Springer-Verlag, 1987:561–74.
   

5. 5

   Davenport ML, Svoboda ME, Koerber KL, Van Wyk JJ, Clemmons DR, Underwood LE. Serum concentrations of insulin-like growth factor II are not changed by short-term fasting and refeeding . J Clin Endocrinol Metab 1988; 67:1231–6.
   CrossRef | Web of Science | Medline