Two previously unrecognized splicing mutations of GCH1 in Dopa-responsive dystonia: exon skipping and one base insertion

Abstract

We describe two previously unrecognized splice site mutations of GCH1 in Dopa responsive dystonia (DRD). Both mutations affect consensus splice acceptor (AG) sites. The first mutation is an A-->G transition at position -2 of intron 1 of GCH1. This mutation results in skipping of exon 2. Fusion of exons 1 and 3 causes a frame shift that generates a premature stop codon. The second mutation is an A-->G transition at position -2 of intron 2. The mutation generates a new splice acceptor site AG one base pair upstream of the wild-type splice site. This, together with a pyrimidine stretch upstream of the new splice site, renders this site functional and generates a transcript with the insertion of one base, i.e. the G of the wild-type splice site. This in turn causes a frame shift including the introduction of a premature stop codon. The two different mutations generate truncated GTP cyclohydrolase polypeptides.

High penetrance and pronounced variation in expressivity of GCH1 mutations in five families with dopa‐responsive dystonia

“…The splice site mutations have been described by our group previously. 16 The clinical findings in the five families investigated confirm the broad spectrum of symptoms observed in DRD.3 Whereas some patients are aMicted with generalized dystonia, others have either subtle signs or symptoms that can only be induced by a special writing test. As a result of the highly variable expressivity, misdiagnoses are common in DRD.…”

Aberrant 3′ splice sites in human disease genes: mutation pattern, nucleotide structure and comparison of computational tools that predict their utilization

“…The increase of purines in aberrant 3′ss was the highest in position −3 where As were 6× more frequent than in authentic 3′ss (Supplementary Figure 2A, χ 2 = 26.5, P < 0.000001). The number of aberrant 3′ss with G in position −3 was also higher (7 versus 2) in aberrant ( 65 , 66 , 69 – 73 ) than in corresponding authentic ( 70 , 74 ) 3′ss. Positive associations between −3C and upstream Cs in the PPT and between −3T and upstream Ts, which were described previously for authentic 3′ss ( 75 ), were observed also for aberrant 3′ss (Supplementary Table 2).…”

“…Interestingly, as many as 14/53 (26%) point mutations in position −1 (IVS-1G>A if the first exon nucleotide was G) ( 34 , 53 – 64 ), 3/48 (6%) substitutions in position −2 (IVS-2A>G) ( 65 , 66 ) and 2/9 (22%) point mutations in position −3 [IVS-3T>G ( 67 ) and IVS-3A >G( 68 )] created new 3′AG sites that were used in vivo ( Figure 1 ). The proportion of AG-creating mutations in position −1 was higher than in position −2 ( P = 0.01, Fisher's exact test), which may have contributed to the higher number of substitutions observed in position −1 than −2 ( Table 3 ).…”

New nonsense mutation in the GTP‐cyclohydrolase I gene in L‐DOPA responsive dystonia‐parkinsonism

“…Tetrahydrobiopterin functions as a coenzyme of tyrosine hydroxylase, the rate‐limiting enzyme in the biosynthesis of catecholamines. Several heterozygous mutations have been reported in Caucasian and Japanese DRD patients 1–18…”