Nail-Patella syndrome, or osteo-onychodysplasia, is an autosomal dominant disorder characterized by nail dysplasia, absent or hypoplastic patellae, iliac horns and nephropathy. Previous studies have demonstrated linkage of the Nail-Patella locus with polymorphic markers on human chromosome 9q34. Recently, point mutations in the LMX1B gene have been identified in Nail-Patella patients and in families with recurrence of Nail-Patella syndrome and open-angle glaucoma. We describe here the identification of additional point mutations in the LMX1B gene in a set of Italian patients affected with Nail-Patella syndrome: two deletions of 1 and 2 bp causing a frameshift in two sporadic patients and nonsense mutations in two familial and one sporadic cases have been identified. All the mutations affect the homeodomain of the LMX1B protein and could cause the Nail-Patella syndrome through a loss of function as well as a dominant negative effect. Haplotype analysis in the two familial cases carrying the same stop codon mutation suggests the presence of a founder effect. Finally, analysis of cDNA clones obtained from human fetal kidney has revealed the existence of two different transcripts of LMX1B gene likely due to an alternative splicing.