Marfan Syndrome Upper to Lower Segment Ratios

Establishing whether the upper segment to lower segment ratio is reduced requires two things. The first is what are normal upper segment to lower segment ratios, and the second is how much lower should be considered reduced. I was able to identify a few sources of normal curves. One is from Dr. Hall's Handbook of Normal Physical Measurements. This is also reproduced in the Harriett Lane handbook, although the most recent Harriett Lane handbook version looks a little strange because of the way the axes are done and gives no reference for the source of the data so it is only infered that it is from the data represented in Dr. Hall's handbook. The advantage of this graph is that it displays data for ages birth to sixteen years. It has a major disadvantage of only showing the mean values. The other source was the curves printed in Emory and Rimoin's Principles and Practice of Medical Genetics. The normal-curve lines on these plots were adapted from Dr. Victor McKusick's 1972 publication. These only show normal curves for about four years of age to 14 years of age. A significant advantage of these curves is that they show the two standard deviation below the mean lines.

The data read off these two plots was re-plotted on a single set of axes. This shows quite a difference between the mean normal population upper segment to lower segment ratios between the datasets. There is also known to be racial variation that is not accounted for and it should also be pointed out that, from this clnician's experience, obtaining precise upper and lower segment measurments can be difficult. Variation occurs because of technique, such as whether the patient is standing or laying down and because of the soft symphysis pubis reference point.

For the automated diagnostic criteria checklist the "reference" used is the reprinted plots of McKusick's 1972 data from Emory and Rimoin's Principles and Practices of Medical Genetics extrapolated horizontally for ages below 4 years and greater than 14 years. The threshold used to consider the ratio reduced is two standard deviations below the mean. This is smaller than 97.7% of the normal population.

From Hall JG, Froster-Iskenius UG, Allanson JE. Handbook of Normal Physical Measurements, Oxford: Oxford Univ. Press, pp 270-275. From Emory and Rimoin's Principles and Practice of Medical Genetics

Upper-to-lower segment ratio, both sexes, birth to 16 years. (From Harriet Lane Handbook (1975), by permission.)

Upper-to-lower segment rations in Marfan syndrome. The US/LS falls with increasing age through early puberty. Points show the means for caucasian Marfan patients grouped in one-year intervals. Bars show +1 SD. The solid red curve is the mean and the dashed red curve 2SD below the mean for unaffected caucasians. (Normal curves adapted from McKusick, 1972, by Emory and Rimoin, with permission)

From Harriet Lane, 15th edition.

Data from Emory and Rimoin's and Hall's plots merged onto one set of axes for comparison purposes.