Skin fibroblasts from the majority of patients with the clinical diagnosis of Ehlers-Danlos syndrome type VI (EDS VI; kyphoscoliosis type), have significantly decreased lysyl hydroxylase (LH) activity due to mutations in the LH1 gene (classified as EDS VIA: OMIM no. 225400). A rare condition exists in which patients are clinically similar but have normal levels of LH activity (designated EDS VIB: OMIM no. 229200). To define the biochemical defect, we have examined cultured fibroblasts from four EDS VIB patients for changes in the levels of the mRNAs for LH1, LH2, and LH3, collagen cross-linking patterns, and the extent of lysine hydroxylation of type I collagen alpha chains. Although normal levels of LH1 mRNA were observed in all four patients, in two patients the levels of LH2 mRNA were decreased by >50%, and a similar decrease was observed in LH3 mRNA in the other two patients. A distinct pattern of collagen cross-links, indicative of decreased lysyl hydroxylation, could be identified in EDS VIA patients, but there was no clear correlation between collagen cross-link pattern and changes in the individual LH mRNAs in EDS VIB patients. Linkage to tenascin-X was excluded in these patients. This study suggests that the basis for this form of EDS VI is genetically heterogeneous, and that alternative pathways in addition to lysine hydroxylation of collagen may be affected.