LETTER TO THE EDITOR
Mutations in MYH9 Exons 1, 16, 26, and 30 Are InfrequentlyFound in Japanese Patients with Nonsyndromic Deafness
Shinji Kunishima,1 Tatsuo Matsunaga,2 Yoshimi Ito,1 and Hidehiko Saito3
Mutations in MYH9 result in the autosomal dominant giant platelet disorders with leukocyte inclusion bodieswith varying degrees of Alport manifestations, including nephritis, deafness, and cataracts. A specific MYH9mutation in exon 16, R705H, causes nonsyndromic deafness DFNA17. We searched for mutations in MYH9exons 1, 16, 26, and 30 in a total of 157 Japanese patients with nonsyndromic deafness without known cause ofhearing loss, but no mutations were found. We conclude that mutations in MYH9 are infrequently found inpatients with nonsyndromic deafness and suggest that MYH9 mutations infrequently cause isolated sensori-neural hearing loss. Thus, MYH9 may not currently be a good candidate gene for efficient screening of geneticcauses in nonsyndromic deafness.
MYH9 encodes a nonmuscle myosin heavy chain IIA(NMMHC-IIA) and is expressed in many different tis-sues, including blood cells, kidney, and cochlea (Simons et al.,1991; Toothaker et al., 1991; DApolito et al., 2002). NMMHC-IIA is a component of the hexameric myosin molecule, whichbinds actin, has ATPase activity, and is required for motoractivity (Sellers, 2000). Mutations in MYH9 result in the au-tosomal dominant giant platelet disorders with leukocyteinclusion bodies with varying degrees of Alport manifesta-tions, including nephritis, deafness, and cataracts (Kelley et al.,2000; The May-Hegglin=Fechtner Syndrome Consortium,2000; Kunishima et al., 2001a). These disorders include May-Hegglin anomaly (OMIM 15100), Sebastian syndrome(OMIM 605249), Fechtner syndrome (OMIM 153640), andEpstein syndrome (OMIM 153650), and were recently re-classified as MYH9 disorders (Heath et al., 2001; Kunishimaet al., 2001b; Seri et al., 2003). In these disorders an MYH9mutation is always associated with giant platelets and leu-kocyte inclusion bodies from birth, but it does not predict thedevelopment of Alport manifestations (Pecci et al., 2008).
Mutations in MYH9 cause not only classical giant plateletdisorders but also autosomal dominant nonsyndromic deaf-ness, DFNA17 (OMIM 603622) (Lalwani et al., 1997, 1999,2000). The affected family members appear to exhibit senso-rineural hearing loss due to cochleosaccular degenerationwithout any hematological manifestations. The hearing lossbegins at the age of 10 years and involves only the high fre-quencies; by the third decade of life, affected family members
have moderate to severe deafness. Nonsyndromic deafnessaccounts for 70% of hereditary hearing loss in prelingualdeafness, and is a highly genetically heterogeneous group ofdisorder (Van Camp et al., 2009). It is not possible to distin-guish DFNA17 from other nonsyndromic deafness based onclinical features. So far the prevalence of DFNA17 has notbeen evaluated.
Materials and Methods
To investigate the prevalence of MYH9 mutations in non-syndromic deafness, the present study was carried out in atotal of 157 unrelated Japanese patients with nonsyndromicdeafness: 92 patients were sporadic cases and the other 65patients had autosomal dominant family history. Patientswere selected based on the following criteria: (i) patients withbilateral hearing loss without known cause or risk factors fordeafness except for family history; (ii) patients without path-ogenic mutations in the connexin 26 gene (GJB2), and withoutA1555G and A3243G mitochondrial DNA mutations (Okaet al., 1993; Matsunaga et al., 2004, 2006); (iii) patients withonset of hearing loss before age 40 (Pecci et al., 2008); (iv)patients without severe or profound hearing loss before age 6;(v) patients without inner, middle, or external ear anomaly;(vi) only one patient from each family (usually the index pa-tient). Because DFNA17 is associated with MYH9 R705Hmutation in exon 16 (Lalwani et al., 2000) and patients withmutations in exons 1, 16, 26, and 30 often develop high-frequency sensorineural hearing loss (Mhatre et al., 2003;Seri et al., 2003; Pecci et al., 2008), we performed mutational
1Department of Advanced Diagnosis, Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Japan.2Laboratory of Auditory Disorders, National Tokyo Medical Center, National Institute of Sensory Organs, Tokyo, Japan.3Nagoya Central Hospital, Nagoya, Japan.
GENETIC TESTING AND MOLECULAR BIOMARKERSVolume 13, Number 5, 2009 Mary Ann Liebert, Inc.Pp. 705707DOI: 10.1089=gtmb.2009.0044
analysis of these four exons according to previously describedmethods (Kunishima et al., 2001b). Oligonucleotide primersused for polymerase chain reaction are listed in Table 1. Theethics committees of Nagoya Medical Center and NationalTokyo Medical Center approved this study.
Results and Discussion
No mutations were found in MYH9 exons 1, 16, 26, and 30in 157 unrelated Japanese patients with nonsyndromic deaf-ness.
NMMHC-IIA consists of an N-terminal head domain and aC-terminal tail domain that undergo homodimerization toform a coiled-coil rod structure (Sellers, 2000). R705, the mu-tated residue in DFNA17, lies in the SH1 helix in myosin head,a critical segment for ATPase and motile activities (Lalwaniet al., 2000). So far, several mutations located in or near to theSH1 helix encoded by exons 1 and 16 such as S96L, R702C,and R702H have been described in MYH9 disorders (Heathet al., 2001; Kunishima et al., 2001b, 2005, 2007; Seri et al., 2003;Pecci et al., 2008). These mutations are frequently associatedwith sensorineural hearing loss. Based on these observations,we initially searched for mutations in these two exons in pa-tients with nonsyndromic deafness, but no mutations werefound. We extended our mutational analysis to include exons26 and 30, although the association of deafness is less than thatin exons 1 and 16, but no mutations were found.
Recent in vitro expression studies have shown that R702Ccauses a significant impairment in both ATPase and motileactivities, whereas R689H mutation in Dictyostelium myosinII (R689 is the homologous residue to human NMMHC-IIAR705) results in a significant impairment in motile activity butATPase activity is only slightly affected (Hu et al., 2002; Iwaiet al., 2006). Thus, the differences in ATPase activity mightresult in the different phenotypic consequences of the muta-tions; that is, patients with R702C mutation suffer fromhematological abnormalities and Alport manifestations,whereas patients with R705H mutation=DFNA17 do exhibithematological abnormalities. Further studies are necessary toexamine whether R705H mutation indeed develops isolatedhearing loss only.
We conclude that mutations in MYH9 exons 1, 16, 26, and30 are infrequently found in patients with nonsyndromicdeafness and suggest that MYH9 mutations infrequentlycause isolated sensorineural hearing loss. Thus, MYH9 maynot currently be a good candidate gene for efficient screeningof genetic causes in nonsyndromic deafness using conven-tional DNA sequencing. However, identification of DFNA17cases through future mutational screening of MYH9 in non-syndromic deafness will improve our understanding andclassification of nonsyndromic hereditary deafness.
This work was supported by grants from the Japan Societyfor the Promotion of Science; The Ministry of Health, Laborand Welfare (Grant for Child Health and Development19C-2); Charitable Trust Laboratory Medicine Foundation ofJapan; Mitsubishi Pharma Research Foundation; and NationalHospital Organization (network research grants for disordersof sensory organs and congenital thrombocytopenia).
No competing financial interests exist.
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