OBJECTIVES: Till date, mutations in the genes PAX3 and MITF have been described 
in Waardenburg syndrome (WS), which is clinically characterised by congenital 
hearing loss and pigmentation anomalies. Our study intended to determine the 
frequency of mutations and deletions in these genes, to assess the clinical 
phenotype in detail and to identify rational priorities for molecular genetic 
diagnostics procedures.
DESIGN: Prospective analysis.
PATIENTS: 19 Caucasian patients with typical features of WS underwent stepwise 
investigation of PAX3 and MITF. When point mutations and small 
insertions/deletions were excluded by direct sequencing, copy number analysis by 
multiplex ligation-dependent probe amplification was performed to detect larger 
deletions and duplications. Clinical data and photographs were collected to 
facilitate genotype-phenotype analyses.
SETTING: All analyses were performed in a large German laboratory specialised in 
genetic diagnostics.
RESULTS: 15 novel and 4 previously published heterozygous mutations in PAX3 and 
MITF were identified. Of these, six were large deletions or duplications that 
were only detectable by copy number analysis. All patients with PAX3 mutations 
had typical phenotype of WS with dystopia canthorum (WS1), whereas patients with 
MITF gene mutations presented without dystopia canthorum (WS2). In addition, one 
patient with bilateral hearing loss and blue eyes with iris stroma dysplasia had 
a de novo missense mutation (p.Arg217Ile) in MITF. MITF 3-bp deletions at amino 
acid position 217 have previously been described in patients with Tietz syndrome 
(TS), a clinical entity with hearing loss and generalised hypopigmentation.
CONCLUSIONS: On the basis of these findings, we conclude that sequencing and 
copy number analysis of both PAX3 and MITF have to be recommended in the routine 
molecular diagnostic setting for patients, WS1 and WS2. Furthermore, our 
genotype-phenotype analyses indicate that WS2 and TS correspond to a clinical 
spectrum that is influenced by MITF mutation type and position.