A correlation between consanguinity and homozygousity of the mutations could be established. The homozygous mutation in exon 1, p.Q12X (c.34C > T) is associated with severe phenotype of MPS IVA. Mutations to codon no. 254 of exon 8 are most probably associated with the classic severe phenotype of MPS IVA. No correlation between the enzyme activity and position of mutation could be established according the used techniques.