Introduction 2003 2005 2005 1996 2002 1995 2006 2005 2005 2006 2005 2005 2004 2004 2004 2005 2003 2005 2005 2003 1988 2003 2006 2006 2005 2003 2001 2005 2001 The aim of the present study was to investigate whether the subgroup of children with PDD having increased PLT 5-HT levels, is the same as the one exhibiting increased intestinal permeability as established by a SAT. Methods Patients n 1994 Sugar Absorption Test 1995 1986 1995 Serotonin Assays 2001 2001 2005 2 2 2 5 2001 9 2000 9 2004 2005 Exclusion of Celiac Disease 1993 Statistics W α Results Patients 1 Table 1 Characteristics of patients with pervasive developmental disorders in Curaçao tested for platelet serotonin and intestinal permeability Parameter Gender (male/female) 18 (75%) / 6 (25%) Age (years) 9.9 (±3.9) DSM-IV TR diagnoses     299.00 (autistic disorder) 8 (33%)     299.80 (PDD-NOS) 16 (67%) Ethnicity     Caucasian 8 (33%)     African–American 13 (54%)     Other 3 (13%) Comorbidity     Epilepsy 5 (22%)     Allergy 2 (9%)     Asthma 1 (4%)     Intestinal yeast infection 1 (4%) Medication for comorbidity 9 (38%) ω 9 (38%) / 2 (4%) a 2 (9%) a 13 (57%)     Nausea 0 (0%)     Vomiting 1 (4%)     Diarrhea 4 (17%)     Constipation 4 (17%)     Bloating and gaseousness 8 (35%) a n SD 2 Table 2 Indices of serotonin (5-HT) turnover and intestinal permeability in patients with pervasive developmental disorders in Curaçao Parameter  Reference values  <RV ≥RV 9 a 3.4 (2.0–7.1) b   6 (26%)  c   4 (17%) μ a 50.0 (±10.9) d  0 (0%) 0 (0%)  d }    d 3 (13%) 0 (0%)  d   μ e 8.4 (3.9–36.4) d }    d 1 (5%) 1 (5%)  d    d   e 305 (±92)     f 0.024 (±0.11)     f 1.32 (±0.59)     f 0.019 (±0.007) g  23 (100%) 0 (0%) a n b 2004 c 2000 d 2005 e n f n g 1995 SD RV; reference value; PLT, platelet; Tryp, tryptophan; 5-HIAA, 5-hydroxyindoleacetic acid; L/M, lactulose/mannitol Sugar Absorption Test Intestinal permeability, reflected by the L/M ratio [median (range) 0.017 mol/mol (0.008–0.035)], indicated that none of the patients had increased intestinal permeability (i.e. L/M ratio ≥ 0.090). Serotonin Assays 9 9 9 2000 9 2004 9 μ 9 Exclusion of Celiac Disease n n Statistics p r p p r p r Discussion 2004 9 1996 2002 2004 1990 2006 In conclusion, the finding of a subgroup of children with PDD exhibiting hyperserotonemia was replicated. None of the children exhibited increased intestinal permeability, while PLT 5-HT was unrelated to both intestinal permeability and GI symptoms. Additional studies are needed to elucidate the etiology of increased PLT 5-HT in PDD and to establish its relation with intestinal pathology, if any.