Immunoreactive somatomedin (IRSM) levels in term pregnancy material sera (MS) and newborn cord sera (CS) were higher and lower, respectively, than those in normal adults. IRSM levels in MS and CS were not correlated, suggesting that SM dose not cross the placenta. The similar levels of IRSM in arterial and venous CS suggest that the placenta does not produce SM. IRSM levels in CS were higher than those in newborn sera and were correlated with day 1 newborn sera, suggesting that the placenta may regulate fetal serum IRSM levels. Serum IRSM levels in normal children gradually increased from birth to peak levels at puberty. The mean levels of serum IRSM reached peak levels 2 yr earlier in females. Males near pubertal age with constitutionally delayed growth had lower serum IRSM levels than age-matched controls. Diagnostic measurements of serum IRSM in children requires comparison with age- and sex-matched controls. Serum SM levels may only approximately reflect the local concentrations or activities of SM in various tissues.

Skin fibroblast cultures from six patients with Down's syndrome (Trisomy 21) were compared with four i n vitro age-matched normal fibroblast cultures. Growth rates were calculated from increases i n cell number and total protein during exponential growth, early in culture lifetime (less than 20 doublings). The Down's syndrome (D.S.) cultures had a n average population doubling time of 35.6 i 1.1 hours and average mass doubling time of 38.6 i 3.

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Five new patients are reported and the pathogenesis of the hypoglycaemia without ketogenesis is discussed. This report extends a recent review.