• Sanfilippo A
• novel mutations

Sanfilippo A is a neurodegenerative disease characterised by progressive dementia, sleep disturbance, developmental delay, hyperactivity, and aggressive behaviour. Sanfilippo A is inherited as an autosomal recessive disease caused by a defect of the lysosomal enzyme sulphamidase (N–sulphoglucosamine sulphohydrolase, SGSH, EC 3.10.1.1). Failure of the degradative effect of sulphamidase is thought to cause lysosomal accumulation of heparan sulphate, leading to neuronal dysfunction. Developmental abnormality is often noticed at 2 or 3 years of age and severe neurological deterioration occurs in most patients by 6 to 10 years of age.¹ The average age at death is 13 years.² The comparatively mild somatic manifestations often cause a delay in the diagnosis.^1,2 The gene encoding Sanfilippo A has been cloned.³ We now report on a Japanese Sanfilippo A patient.

A 26 year old patient had no recognisable developmental abnormality until the age of 4 years, when he had mild language disability without motor dysfunction. Mild ventricular enlargement and brain atrophy were found at the age of 12 years. Despite his language disability, motor function was well retained even in high school. Hyperactivity and irritability appeared at the age of 17 years, and mental deterioration ensued. Simple conversation was retained until the age of 24 years. The diagnosis was made then with the demonstration of increased excretion of heparan sulphate in urine and decreased sulphamidase activity in cultured fibroblasts (not detected; control 3.2–7.2 nmol/h/mg). His older brother had a mild language disability and died as a result of an accident at the age of 19 years. There was no family history of consanguinity.

The patient was 164 cm in height, and weighed 50.4 kg. There was no recognisable pattern of malformation. His hair was stiff and coarse. No corneal opacities were found. Facial expression was poor, and affect was flattened. He had no meaningful expressive language. Visual pursuit was poor and frequently discontinued. Agitation could be induced by tactile or visual stimuli. Touching his limbs and trunk induced coordinated repetitive coarse movements such as holding up both arms and legs. There was no obvious weakness found, but ankle contractures render him wheelchair bound. Deep tendon reflexes were normal.

A magnetic resonance imaging examination of the brain revealed thinning of the corpus callosum, ventricular enlargement and widening of the sulci. Cribriform changes (small cystic lesions) were found in the frontal lobe.

Genomic DNA was extracted from peripheral blood leucocytes using the Capture Column kit (Gentra systems, MN). The sulphamidase gene consists of eight exons. The primer pairs used to amplify the exons by polymerase chain reaction (PCR) were described by Weber et al.⁴ Sequencing was done using an ABI 377 automated fluorescence sequencer (Perkin Elmer, Foster City, CA). Numbering of amino acids and nucleotides is according to Scott et al.³

To determine the possibility of mutations in the sulphamidase gene, PCR was done on the genomic DNA of the patient. We sequenced all the coding regions and the sequence obtained showed two heterozygous nucleotide substitutions: a C to T at the position 1052 (S347F) and an A to G transition at the position 1343 (D444G), and one homozygous polymorphism: a G to A transition at the position 1367 (R456H). The patient's mother had a single heterozygous nucleotide substitution: a C to T transition at the position 1052 (S347F), while his father had a heterozygous nucleotide substitution: an A to G transition at the position 1343 (D444G) (fig 1).

This is the first report of a genetically identified Japanese Sanfilippo A patient. The gene encoding sulphamidase spans about 11 kb, includes 8 exons, and is localised to chromosome 17q25.3.³ We found two novel mutations (S347F, TCC to TTC and D444G, GAC to GGC) in exon 8. The sulphamidase shares few commonly conserved sites toward the C terminus, and the conserved sites are relatively scarce in exon 7 and exon 8.⁴ The serine (S) residue at position 347 and the aspartic acid (D) residue at position 444 are located on sparsely distributed conserved sites among sulphatase families under the superimposition of the sequence of protein sulphatases. Polymorphisms were not reported at these two sites (1052 C to T, and 1343 A to G). These two mutational sites are conserved in the evolutional process and obey the rule of Mendelian inheritance. Therefore, these mutations were predicted to cause disease.

The clinical course of the patient in this report was relatively slow. In reporting 73 patients with Sanfilippo syndrome, van de Kamp et al found that Sanfilippo A had a more severe phenotype than Sanfilippo B and C.² The average age of death of Sanfilippo A was 13 years (range 6–25) and the age range of the living patients was 5–26 years.² Motor functions of the patient in this report were well retained and language abilities remained until the age of 24 years. Significant clinical heterogeneity has been known in Sanfilippo syndrome (include Sanfilippo A).² Mild somatic abnormalities and false negative results of urine tests in the Sanfilippo A patients often cause a delay in diagnosis.¹ Therefore, it is important to investigate the genetic background in patients with the milder form of Sanfilippo A syndrome. The residual function derived from the better allele may be critical for enzyme activity in an autosomal recessive disease. Large scale statistical analysis of Sanfilippo A patients has not been performed in Japan. Date and coworkers reported long term surviving Japanese siblings (32 and 34 year old brothers) with enzymatically diagnosed Sanfilippo A.⁵ Patients with the clinically milder course may predominate in Japan. Further study is needed for evaluating mutational predominance and its clinical relevance in Japanese Sanfilippo A patients.

Competing interests: none declared.

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Figure 1

(A) Pedigree of the patient. The arrow represents the proband. (B) Direct sequencing of polymerase chain reaction amplified products from exon 8 of sulphamidase gene. Bold letters indicate the mutation site. R indicates nucleotides A and G, Y indicates nucleotides C and T.