Mucopolysaccharidosis type II (Hunter syndrome, MPS II, OMIM 309900) is an X-linked lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase (IDS). We analyzed clinical and laboratory data from 44 Slavic patients with this disease. In total, 21 Czech, 7 Slovak, 9 Croatian and 7 Serbian patients (43 M/1 F) were included in the study (median age 11.0 years, range 1.2-43 years). Birth prevalence ranged from 1:69,223 (Serbia) to 1:192,626 (Czech Rep.). In the majority of patients (71%), the disease manifested in infancy. Cognitive functions were normal in 10 patients. Four, six and 24 patients had mild, moderate, and severe developmental delay, respectively, typically subsequent to developmental regression (59%). Residual enzyme activity showed no predictive value, and estimation of glycosaminoglycans (GAGs) had only limited importance for prognosis. Mutation analysis performed in 36 families led to the identification of 12 novel mutations, eight of which were small deletions/insertions. Large deletions/rearrangements and all but one small deletion/insertion led to a severe phenotype. This genotype-phenotype correlation was also identified in six cases with recurrent missense mutations. Based on patient genotype, the severity of the disease may be predicted with high probability in approximately half of MPS II patients.
X-ALD is a neurological disorder associated with inherited defects in the ABCD1 (ALD) gene located on Xq28 and with impaired peroxisomal very long-chain fatty acid beta-oxidation. We examined the ABCD1 gene in probands from 11 unrelated X-ALD Czech and Slovak families by the direct sequencing of cDNA or genomic PCR products. In 10 families there were 10 different mutations, eight of which were novel. The spectrum of mutations consists of six point mutations, three microdeletions (1bp, 2bp, 4 bp), and one large deletion (229bp). In the 11th family we detected two novel single-base pair substitutions in exon 1 (c.38 A>C and c.649 A>G), both causing amino acid exchanges (N13T and K217E). Expression studies revealed that only K217E is a deleterious mutation, because a plasmid encoding ALDP with K217E was ineffective in the restoration of defective beta-oxidation in X-ALD fibroblasts. The N13T amino acid exchange, on the other hand, did not affect ALDP function. Thus, N13T represents the first polymorphism causing an amino acid exchange in the ABCD1 gene. As this polymorphism was observed neither in 100 control alleles nor in 300 X-ALD patients who have been sequenced so far world-wide, it seems to be very rare or unique. Two additional novel polymorphisms were found by the sequencing of the ABCD1 gene from our patients: c.-59 C/T in the 5'untranslated region and c.2019 C/T (F673F) in exon 10. The frequencies of these two polymorphisms, were 11/150 and 2/150 control alleles, respectively.
In a female patient with signs of ornithine carbamoyltransferase deficiency (OTCD), the only variation found was a heterozygous single nucleotide substitution c.-366A>G. Determination of transcription start sites of human OTC 95, 119 and 169 bp upstream of the initiation codon located the variation upstream of the 5'-untranslated region. We predicted the human promoter and enhancer elements from homology with rat and mouse, performed function analysis of both regulatory regions and assessed the impact of the promoter variation in functional studies using dual luciferase reporter assay. Our data indicate that: (i) Full transcriptional activity of human OTC promoter depends on an upstream enhancer, as do the rodent promoters. (ii) The promoter variation c.-366A>G does not affect the function of the promoter alone but it disrupts the interaction of the promoter with the enhancer. (iii) The promoter-enhancer interaction contributes to tissue specific expression of OTC in the liver. We conclude that mutations in the regulatory regions of OTC can lead to OTCD and should be included in genetic testing.
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