Mutation analysis in the long isoform of USH2A
in American patients with Usher Syndrome type II
Denise Yan1,3, Xiaomei Ouyang1,3, D Michael Patterson1,3, Li Lin Du1, Samuel G Jacobson2and Xue-Zhong Liu1
Usher syndrome type II (USH2) is an autosomal recessive disorder characterized by moderate to severe hearing impairment
and progressive visual loss due to retinitis pigmentosa (RP). To identify novel mutations and determine the frequency of USH2A
mutations as a cause of USH2, we have carried out mutation screening of all 72 coding exons and exon–intron splice sites of
the USH2A gene. A total of 20 USH2 American probands of European descent were analyzed using single strand conformational
polymorphism (SSCP) and direct sequencing methods. Ten different USH2A mutations were identified in 55% of the probands,
five of which were novel mutations. The detected mutations include three missense, three frameshifts and four nonsense
mutations, with c.2299delG/p.E767fs mutation, accounting for 38.9% of the pathological alleles. Two cases were homozygotes,
two cases were compound heterozygotes and one case had complex allele with three variants. In seven probands, only one
USH2A mutation was detected and no pathological mutation was found in the remaining eight individuals. Altogether, our data
support the fact that c.2299delG/p.E767fs is indeed the most common USH2A mutation found in USH2 patients of European
Caucasian background. Thus, if screening for mutations in USH2A is considered, it is reasonable to screen for the c.2299delG
Journal of Human Genetics (2009) 54, 732–738; doi:10.1038/jhg.2009.107; published online 30 October 2009
Keywords: mutations; usherin; Usher syndrome; USH2; USH2A
Combined deafness and blindness is a feature of at least 40 recognized
human syndromes. Usher syndrome (USH) accounts for over 50% of
these and has an estimated incidence of 4.4:100000.1,2USH is the most
frequent cause of recessive retinitis pigmentosa (RP).3The disorder is
both clinically and genetically heterogeneous. Three clinical types have
been defined, USH1, USH2 and USH3 on the basis of the severity and
age during the onset of hearing impairment, vestibular dysfunction and
retinal phenotypes. USH1 is the most severe with congenital profound
hearing loss and vestibular dysfunction. USH2 is defined as moderate to
severe, early onset, bilateral and symmetric sensorineural hearing loss.
The symptomatic onset of RP is often in late adolescence and the
vestibular system is normal. USH3 is distinguished from USH2 by the
progressive nature of its hearing loss and variable impairment of vesti-
bular function. Although USH3A is relatively rare in most populations, it
may account for approximately 40% of USH cases in Finland4–6and in
Ashkenazi Jews.7–9Progressive pigmentary retinopathy is usually typical
for RP in all clinical types, but has been reported as occuring earlier in
USH1; however, because of the considerable overlap between the ages of
onset of visual disturbance in the USH subtypes, the onset of night
blindness cannot be regarded as a reliable diagnostic discriminator.10–15
Further subdivision of USH has been possible based on the genomic
loci and causative genes. To date, 11 loci have been mapped for USH
and genes for 10 of them have been cloned.16USH1 is genetically
heterogeneous. Five corresponding genes of the seven USH1 loci
(USH1B–USH1H) have been identified so far. Known USH1 mole-
cules are the molecular motor myosin VIIa (USH1B), the two cell–cell
adhesion proteins, cadherin 23 (USH1D) and protocadherin 15
(USH1F) and the scaffold proteins, harmonin (USH1C), which
contains post-synaptic density, disc-large, Zo-1 protein domains
(PDZ) domains and SANS (scaffold protein containing ankyrin
repeats and SAM domain, USH1G). There are three genetic loci
now reported for USH2 (USH2A, USH2C and USH2D). The affected
genes at these loci have been determined. The USH2 protein whirlin
(USH2D) is also a PDZ domain-containing scaffold protein, whereas
the remaining two USH2 proteins, usherin (USH2A) and GPR98
(G protein-coupled receptor 98 also known as VLGR1b or MASS1)
(USH2C), are large transmembrane proteins and have similar pen-
traxin (PTX) homology domains,17suggesting that they may share
an affinity for a common binding partner. Only one locus for
USH3 (USH3A) has been reported so far. USH3A transcripts encode
clarin-1, a membrane glycoprotein with four transmembrane domains
from the clarin family.
Molecular analysis of USH protein function revealed that all the
identified USH proteins are integrated into a protein network.18–24
PDZ domains are protein modules that mediate protein–protein
Received 4 June 2009; revised 24 September 2009; accepted 28 September 2009; published online 30 October 2009
1Department of Otolaryngology, University of Miami, Miami, FL, USA and2Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia, PA, USA
Correspondence: Dr X-Z Liu, Department of Otolaryngology (D-48), University of Miami, 1666 NW 12th Avenue, Miami, FL 33136, USA.
3These authors contributed equally to this work.
Journal of Human Genetics (2009) 54, 732–738
& 2009 The Japan Society of Human Genetics All rights reserved 1434-5161/09 $32.00
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Journal of Human Genetics