Exercise: Primary pulmonary hypertension

The serotonin transporter (5-HTT) is associated with increased pulmonary artery smooth muscle cell growth and so may be associated with primary pulmonary hypertension (PPH). The gene which controls production of 5-HTT is found in two variants (alleles). The long (L) variant of the gene is associated with 5-HTT overexpression compared to the short (S) variant. People each have two copies of the gene and hence two alleles, and can be LL when both alleles are of the long type, SL when they have one long and one short, or SS when both copies are short. A group of patients with PPH were compared with a group of healthy controls (Eddahibi et al., 2001).

The following table was given:

Table 1. Genotypic distribution of serotonin transporter gene polymorphism in the promotor region in patients with PPH and in controls
Number of subjects Polymorphism in promoter region
n (%) n (%) n (%)
Normal controls 84 (100%) 16 (19%) 45 (54%) 23 (27%)
Patients with PPH 89 (100%) 7 (8%)   24 (27%) 58 (65%)
S, short variant of genotypic polymorphism, L, long variant of genotypic polymorphism

The authors commented that "The distributions of the 5-HTT genotypes in 89 patients with PPH and 84 controls were evaluated (Table 1). . . . We found the genotype characterized by two long alleles in 65% of the patients with PPH and only 27% of the controls (P < 0.001)."


1. What kinds of variables are genotype and PPH?

Check suggested answer.

2. What statistical method should be used to calculate this P value, and why?

Check suggested answer.


Eddahibi S, Humbert M, Fadel E, Raffestin B, Darmon M, Capron F, Simonneau G, Dartevelle P, Hamon M, Adnot S. (2001) Serotonin transporter overexpression is responsible for pulmonary artery smooth muscle hyperplasia in primary pulmonary hypertension Journal of Clinical Investigation 108, 1141-1150.

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Last updated: 7 November, 2006.

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