DNA was extracted from blood leukocytes and saliva samples by the Western Australian DNA Bank (www.wadb.org.au) and analysed for disease causing mutations in RS1. The six exons and flanking intronic regions of RS1 were amplified by PCR using published, exon flanking intronic primers (Sauer et al. 1997). Amplified DNA was purified and directly sequenced (Macrogen, Seoul). Sequences were compared (Sequencher 4.8) to human RS1 reference sequence (NM_000330.2).

Likely pathogenicity of novel variants was confirmed by DNA sequencing of family members and 135 X chromosomes from unrelated individuals with no known family history of retinal disease and deemed normal following electrophysiological, ophthalmological and psychophysical tests.

32.2.2 Electrophysiological Studies

The electrophysiological tests reported in this paper were perfomed to International Society for Clinical Electrophysiology of Vision (ISCEV) standards. Full-field and multifocal (mf) electroretinograms (ERGs) were recorded using HK-loop and Burian-Allen contact lens electrodes respectively on LKC UTAS 3000 and EDI VERISTM Science data acquisition systems. Results were analysed by comparison to aged-matched normal ranges.

32.3 Results

32.3.1 RS1 Mutations in Western Australian Families

An RS1 mutation was confirmed for each clinically diagnosed individual. In total, three distinct genetic variants from four families were identified, one being novel (Table 32.1). These include; (1) an exon one splice donor mutation (52+1G > T) found in two families, (2) an exon four missense genetic variant (289T > G), and (3) an exon five, frameshift mutation (416delA). Comparison of clinical data (ophthalmological, electrophysiological and psychophysical) did not indicate a correlation between patient genotype and the manifestation of clinical symptoms.

Table 32.1 XLRS mutations identified in the RS1 gene within the Western Australian population. To the best of our knowledge, the 289T > G genetic variant observed is novel

32.3.2 Compromised Full-Field and mfERG in an Obligate Carrier with 52+1G > T Mutation

Full-field and mfERG tracings from the affected male with a 52+1G > T mutation were typical for XLRS with reduced b-wave amplitudes and response densities respectively (Fig. 32.1a, b). A related obligate carrier, heterozygous for this mutation, similarly recorded a bilaterally abnormal rod ERG with delayed b-waves as well as mildly abnormal photopic responses; cone and flicker ERG tracings showed slightly reduced and delayed b-wave amplitdues respectively. mfERG trace arrays showed reduced response density in the paramacular region extending futher temporally for each eye (Fig. 32.1a, b).

32.3.3 Likely Pathogenicity of the Novel 289T > G Genetic Variant

32.3.3.1 Family Information

In this family, the proband was the only individual clinically diagnosed with XLRS (Fig. 32.2a; III:1). The proband reported however, that his younger male sibling had very recently began to suffer similar visual symptoms (age 17) but had not yet consulted an ophthalmologist. He also reported that maternal uncles (Thailand) suffered similar visual symptoms. None have seen a medical practitioner for diagnosis.

32.3.3.2 Patient Information

Upon presentation at age 18, fundus examination revealed the proband’s perifoveal retina was spokewheel in appearance accompanied by a peripheral retinal sheen, but no schisis. Electroretinographic findings were typical for an XLRS diagnosis; scotopic, photopic and flicker tracings revealed severely reduced b-wave amplitudes and slightly delayed a-waves. Pattern ERG was normal. Eight years later a mfERG trace array showed responses with normal mophology but delayed latencies as well as reduced densities throughout the central retina, being more severe in the macula.

32.3.3.3 Genetic Information

This 289T > G single base substitution found in exon four is likely to cause a W92G amino acid change in the discoidin domain of the translated product and to the best of our knowledge has not before been reported in the literature (Fig. 32.2b).

Fig. 32.1 (continued) (right). (a) mfERG first order kernel results; full-field trace arrays, response densities and latencies in rows 1–3 respectively. (b) Full-field ERG results; rod, maximal rod-cone, cone and flicker waveforms in rows 1–4 respectively. Amplitude (uV) is plotted on the Y axis and time (ms) on the X axis