Usher Syndrome, Type I
A number sign (#) is used with this entry because Usher syndrome type IB (USH1B) is caused by homozygous or compound heterozygous mutation in the MYO7A gene (276903) on chromosome 11q13.
DescriptionUsher syndrome type I is an autosomal recessive condition characterized by profound congenital hearing impairment with unintelligible speech, early retinitis pigmentosa (usually evident within the first decade), and constant vestibular dysfunction. Type I is distinguished from type II (276901) on the basis of severity of hearing loss and the extent of vestibular involvement. Type I patients are profoundly deaf, whereas type II patients are 'hard of hearing.' Vestibular function is defective in type I patients, whereas type II patients have normal vestibular function (Moller et al., 1989). Patients with type III (USH3; 276902) have progressive hearing loss. Patients with type IV (USH4; 618144) have late onset of both retinitis pigmentosa and progressive, moderate to severe sensorineural hearing loss without vestibular involvement (Khateb et al., 2018).
Genetic Heterogeneity of Usher Syndrome Type I
USH type I is genetically heterogeneous. USH1C (276904), the 'Acadian variety,' is caused by mutation in harmonin (605242), on 11p15. USH1D (601067) is caused by mutation in the cadherin-23 (CDH23; 605516) on 10q21. USH1F (602083) is caused by mutation in the protocadherin-15 (PCDH15; 605514) on 10q22. USH1G (606943) is caused by mutation in the SANS gene (607696), on 17q25. USH1E (602097) maps to 21q21, and USH1H (612632) maps to 15q22-q23. USH1J (614869) is caused by mutation in the CIB2 gene (605564) on 15q24. USH1K (614990) maps to chromosome 10p11.21-q21.1.
A form of USH type I in which affected members carried heterozygous mutations in both CDH23 and PCDH15 has been reported (USH1D/F; see 601067), thus supporting a digenic model for some individuals with this phenotype.
Gerber et al. (2006) presented evidence that the form of USH1 previously called USH1A, or the 'French variety,' and mapped to chromosome 14 does not in fact exist; mutations in the MYO7A gene were found in most of these families, and in others the phenotype was found to map to other loci.
Ahmed et al. (2003) reviewed the molecular genetics of Usher syndrome and indicated that at least 12 loci had been identified as underlying the 3 different clinical subtypes.
Clinical FeaturesUsher syndrome, or more appropriately the Usher syndromes, are named for Charles Usher (1914), a British ophthalmologist who emphasized their hereditary nature. The earliest descriptions were given by Von Graefe (1858), Liebreich (1861), who observed the syndrome among Jews in Berlin, and Hammerschlag (1907). Lindenov (1945) wrote on deaf-mutism associated with retinitis pigmentosa and 'feeblemindedness.' Lang (1959) observed 5 affected children out of 10 from a first-cousin marriage. Hallgren (1959) found 177 affected persons in 102 families. In addition to the features noted in the title of his paper, cataract developed by age 40 in most. Mental deficiency and psychosis occurred in about one-quarter of cases. A large majority had a disturbance of gait attributed to a lesion of the labyrinth.
In Finland, Nuutila (1970) found 133 persons with retinitis pigmentosa and congenital sensory deafness, 4 with RP and progressive sensory deafness. Numerous studies suggest genetic heterogeneity of this phenotype. On the basis of 133 patients in Finland, Forsius et al. (1971) concluded that there are 2 distinct forms of the Usher syndrome: one characterized by congenital deafness and severe retinitis pigmentosa, and a second less frequent form in which the inner ear and retina are less severely affected.
Holland et al. (1972) found gyrate atrophy in a few heterozygotes. Davenport et al. (1978) found that about 90% of reported cases had profound congenital deafness with onset of RP before puberty, whereas the rest had moderate to severe hearing loss from birth and RP beginning after puberty. Ataxia, probably labyrinthine in origin, occurred in a great majority of the first type and in a few of the second. The possibility of an X-linked form was suggested by 2 pairs of affected brothers whose mothers were sisters.
Gorlin et al. (1979) summarized the classification of Davenport and Omenn (1977) as follows: type I--profound congenital deafness with onset of RP by age 10; type II--moderate to severe congenital deafness with onset of RP in late teens (276901); type III--RP first noted at puberty with progressive hearing loss; type IV--possible X-linked form. The fourth type was based on the observation of 4 affected brothers reported by Davenport et al. (1978). In fact, autosomal recessive inheritance was considered most likely; the heterozygous parents showed unilateral high-frequency hearing loss with normal retinal and vestibular function.
Jay (1982) found 16 Usher syndrome families out of 571 RP families in the experience of the Moorfields Eye Hospital in London. Other numbers were: autosomal dominant, 130 families; X-linked, 27; autosomal recessive, 5; male multiplex, 24; mixed multiplex, 76; simplex, 292 and adopted, 1. In 4 of 10 sibs, Karjalainen et al. (1983) described an unusual form of Usher syndrome. In 2, hearing loss developed in school age; in the other 2, it developed in the thirties. In 1, retinitis pigmentosa was diagnosed before hearing impairment was evident. In a study of 70 patients, Fishman et al. (1983) also suggested the existence of 2 distinct types of Usher syndrome. In their experience, the deafness is congenital and nonprogressive, whereas the retinitis pigmentosa is progressive. In their type I, onset of night blindness was earlier, visual field loss occurred earlier and in greater severity, hearing impairment was more severe, speech was more likely to be unintelligible, vestibular reflexes and clinically evident ataxia were more frequently found--all as contrasted with type II. Of the 70 patients, 46 were type II.
Boughman et al. (1983) reviewed information on 600 cases of deaf-blindness in the registry of the Helen Keller National Center for Deaf Blind Youths and Adults. Of these, 54% satisfied criteria for the diagnosis of Usher syndrome, although only 23.8% had been so diagnosed. From the Louisiana School for the Deaf, they ascertained 30 males and 18 females in 26 nuclear families, reflecting the recognized high frequency in the Louisiana Acadian population.
Grondahl and Mjoen (1986) found 18 cases of Usher syndrome among 89 probands selected for tapetoretinal degeneration. Among the relatives, another 10 cases of Usher syndrome were found. These fell into the 3 types as follows: type I, 14 cases; type II, 10 cases; type III (according to Davenport and Omenn (1977)), 4 cases. In 12 families the pattern of inheritance was autosomal recessive; the remaining 6 probands were solitary cases without parental consanguinity. There was a high intrafamilial correlation with respect to hearing function. Vestibular response was abolished in 3 patients with type I and was normal in 3 patients with type II and in 1 patient with type III.
In Norway, Grondahl (1987) found 28 patients from 18 families with Usher syndrome. Both retinitis pigmentosa and Usher syndrome were more prevalent in Lapps than in other Norwegians.
Davenport et al. (1988) recognized 2 main types and a third rare type. Type I not only has congenital profound deafness and early onset of RP, but also congenitally absent vestibular function. Their type II has hearing loss which is congenital and of high frequency type, with little deterioration and with later onset of RP and normal vestibular function. In type III both hearing and vision start out normal or near-normal and progressively deteriorate over several decades. Type I children, because of the vestibular defect, have delayed motor milestones and clumsiness. Type II children are usually 'mainstreamed' with no problems until teen age.
Smith et al. (1994) described criteria for the clinical diagnosis of Usher syndrome, adopted by the Usher Syndrome Consortium. They pointed out that there was evidence for at least 3 distinct USH1 loci (USH1A, USH1B, USH1C) and 2 distinct USH2 loci. They pointed to the need to exclude congenital infections, such as rubella, syphilis, and cytomegalovirus, and problems associated with gestation, delivery, or the perinatal period that also can cause profound hearing loss and retinal damage.
Photoreceptors, auditory hair cells, and vestibular hair cells develop from ciliated progenitors. Several lines of evidence suggest that a generalized abnormality of axoneme structure is present in patients with Usher syndrome. Hunter et al. (1986) found a high proportion of abnormal axonemes in retinal photoreceptor cells of a patient with Usher syndrome. Shinkawa and Nadol (1986) found a decrease in outer ciliary cells in the lower part of the cochlea in this syndrome. Structural and functional evidence for abnormal nasal cilia has been found in this disorder as in other patients with retinitis pigmentosa (Arden and Fox, 1979). Finally, sperm motility, velocity, and structure have been found abnormal in Usher syndrome, a feature probably related to the markedly decreased fertility of these patients (Hunter et al., 1986; Nuutila, 1970). Brueckner et al. (1989) found that the iv (inversus viscerum; see 603339) mutation in the mouse maps to a corresponding region; this mouse mutation may be homologous to Kartagener syndrome (244400). Lake and Sharma (1973) reported the association of Kartagener syndrome with retinitis pigmentosa and congenital deafness. Bonneau et al. (1993) reported the association of type I Usher syndrome with bronchiectasis, chronic sinusitis, and reduced nasal mucociliary clearance in 2 brothers and suggested that USH1 could be a primary ciliary disorder.
Schaefer et al. (1998) performed quantitative analysis of magnetic resonance imaging studies of 19 patients with Usher syndrome (8 with type I, 11 with type II). They found a significant decrease in intracranial volume and in size of the brain and cerebellum with a trend toward an increase in the size of the subarachnoid spaces. These data suggested that the disease process in Usher syndrome involves the entire brain and is not limited to the posterior fossa or auditory and visual systems.
Malm et al. (2011) evaluated visual function, comprising both the severity of the rod cone degeneration and the function in the macular region, in 12 patients genotyped as Usher syndrome 1B, 1D, 1F, 2A, 2C, or 3A, including 3 families with affected sibs, and confirmed phenotypic heterogeneity between sibs with the same genotype and between patients with different genotypes. In all patients examined with ERG, the 30 Hz flicker response revealed remaining cone function. In 3 of the patients with Usher type I, multifocal electroretinography (mfERG) demonstrated a specific pattern with a sharp distinction between the area of reduced function and the central area with remaining macular function and normal peak time. Optical coherence tomography (OCT) demonstrated loss of foveal depression with distortion of the foveal architecture in the macula of all patients. The foveal thickness ranged from 159 to 384 micrometers and was not correlated with retinal function.
InheritanceUsher syndrome is inherited in an autosomal recessive manner. In an extensive genetic study of 9 Usher syndrome genes in 172 patients with Usher syndrome due to various genetic defects, Le Quesne Stabej et al. (2012) found no evidence for digenic inheritance. Mutations in the MYO7A gene were the most common, accounting for 53.2% of families.
Population GeneticsThe frequency of Usher syndrome was estimated to be 3.0/100,000 in Scandinavia (Hallgren, 1959) and 4.4/100,000 in the United States (Boughman et al., 1983). Grondahl (1987) calculated the prevalence of Usher syndrome in Norway to be 3.6 in 100,000. In Colombia, Tamayo et al. (1991) found that about 70% of the Usher syndrome cases were type I, about 26% type II, and 4% type III.
Weil et al. (1995) stated that USH1B accounts for about 75% of type I Usher syndrome patients.
In 6 (42.86%) of 14 indigenous South African probands with USH, Roberts et al. (2015) identified a homozygous mutation (c.6377delC) in the MYO7A gene. All 6 shared a common haplotype.
MappingKimberling et al. (1992) mapped a form of Usher syndrome to 11q, probably distal to marker D11S527. Their study was based on 27 families from the United States, Sweden, Ireland, and South Africa. There were no families from either the Louisiana Acadian population or the Poitou-Charentes region of France.
Smith et al. (1992) investigated 11 British USH1 families and confirmed linkage to D11S527 at 11q. The locus for Best disease (153700) also maps to 11q3. In an extensive Samaritan kindred in Israel, Bonne-Tamir et al. (1994) demonstrated linkage of the Usher syndrome phenotype to markers on 11q. Complete linkage disequilibrium between D11S533 and the Usher gene suggested that these loci are either identical or adjacent.
Wagenaar et al. (1995) studied 17 obligate carriers from 9 families with autosomal recessive Usher syndrome type I. Linkage studies showed linkage to 11q13.5 in 6 families, while 3 families failed to show linkage to candidate regions. Eight obligate carriers had an abnormal pure-tone audiogram. Four carriers had significant sensorineural hearing loss which increased at higher frequencies. The other 13 carriers had sensorineural hearing loss of about 10 dB at 0.25 and 0.5 kHz, but less at higher frequencies. Electrooculography demonstrated a significantly lower mean light peak/dark trough ratio in carriers than in controls. The methods were, however, not sufficiently specific to identify carriers with confidence.
Molecular GeneticsWeil et al. (1995) demonstrated that mutation in the gene encoding myosin VIIA is responsible for Usher syndrome type IB. Two different premature stop codons, a 6-bp deletion, and 2 missense mutations were detected in 5 unrelated families (see, e.g., 276903.0001-276903.0005). In 1 of these families, the mutations were identified in both alleles. These mutations, which are located at the amino-terminal end of the motor domain of the protein, are likely to result in the absence of a functional protein.
Zina et al. (2001) reevaluated a large consanguineous family from Tunisia, originally reported by Guilford et al. (1994) to have autosomal recessive sensorineural deafness (600060) and in which Weil et al. (1997) identified homozygosity for a missense mutation in the MYO7A gene (276903.0010). Since the original reports, 5 patients had developed mild retinal degeneration in addition to the progressive deafness. Fundus examination of 1 patient showed spicule pigmentary changes consistent with retinal dystrophy. Another previously unaffected family member, homozygous for the mutation, had retinitis pigmentosa. Seven patients had abnormal vestibular function as assessed by caloric tests. Zina et al. (2001) concluded that some patients in this Tunisian family had features consistent with Usher syndrome type IB, and suggested that other factors must modulate the expression of the phenotype.
Adato et al. (1999) described a complex rearrangement of the MYO7A gene that might have a synergistic effect on the symptoms of another type of Usher syndrome, namely USH3 (276902), the rarest form of USH. Adato et al. (1997) reported a nonconsanguineous family of Jewish Yemenite origin with 2 affected and 6 healthy sibs, in which the 2 affected brothers had different USH phenotypes: one had a typical USH1 phenotype, whereas the other had a typical USH3 phenotype. Both affected brothers had onset of bilateral progressive pigmentary retinopathy during early adolescence. Adato et al. (1999) performed haplotype segregation and linkage analysis in this family that resulted in exclusion of all USH1 and USH2 loci and suggested linkage only to the USH3 locus on chromosome 3q21; both affected brothers were homozygous for alleles of 4 markers on 3q. Since one of the affected brothers had a USH1 phenotype, family members were screened for mutations in the MYO7A gene, and 2 novel, closely situated nucleotide changes were detected in exon 25 of the MYO7A gene on 1 maternal chromosome: a T-to-C transition and a guanine deletion 5 nucleotides upstream of this transition (276903.0014). The mutated MYO7A gene was carried by the brother with the more severe USH1 phenotype, but not by his affected brother with the USH3 phenotype. The mother and 2 unaffected sibs, who were all double heterozygotes for the mutated MYO7A and for a single USH3 haplotype, showed no evidence of any Usher symptoms or nonsyndromic deafness. This suggested a digenic inheritance pattern, with a possible synergistic interaction between MYO7A and the USH3 gene product, where presence of a single defective MYO7A allele seemed to increase the severity of deafness as a part of the clinical symptoms associated with USH3. Adato et al. (2002) restudied the Jewish Yemenite family originally reported by Adato et al. (1997) and identified homozygosity for a 23-bp deletion in the CLRN1 gene (606397.0007) in the affected brothers. The authors stated that this represented a departure from the monogenic model for Usher syndrome.
In a 4-year follow-up of their diagnostic service in France for patients with Usher syndrome type I, which included preliminary haplotyping before gene sequencing, Roux et al. (2011) stated that they had identified the pathogenic genotype in over 90% of patients. Of the mutations identified, 32% were novel.
HistoryUsher Syndrome Type IA
In an intriguing 'chronicle of a slow death,' Gerber et al. (2006) concluded that the presumed USH1A locus on 14q32 does not exist. The USH1A locus was described by Kaplan et al. (1992) and Larget-Piet et al. (1994) on the basis of linkage studies in 9 families originating from the Poitou-Charentes region, around the town of Bressuire in France. This form of Usher syndrome was also referred to as the French variety. No disease-associated alteration was found in any candidate gene candidate gene at the USH1A locus. Results of studies of a new multiplex family with Usher syndrome type 1 originating from the Bressuire region surprisingly showed exclusion of linkage to chromosome 14 but were compatible with linkage to the USH1B locus on 11q. Furthermore, Gerber et al. (2006) had an opportunity to study a healthy individual in 1 of the 8 original USH1A families who was unavailable for study in 1992; this individual turned out to be haploidentical to his affected sibs, which strongly challenged the existence of the USHA1 locus. These 2 unexpected data prompted a screening for mutations in the major USH1 gene myosin VIIA (MYO7A; 276903) in the Bressuire families. The results of this study 'signed the death warrant of the USH1A locus,' since mutations were identified in 6 of the 9 original families. Of these and the 1 additional family, 7 harbored mutations in the MYO7A gene, 1 was compatible with linkage to USH1D and USH1E loci, and 1 excluded all USH1 loci including the 14q32.1 region. No DNA was available for further linkage studies in the last family.
In the reevaluation, Kaplan and her colleagues (Gerber et al., 2006) suggested that they should not have made the hypothesis of a founder effect in the original study without evidence for linkage disequilibrium. Indeed most of the patients of Bressuire harbored different MYO7A mutations. A parallel was drawn to the case in the isolated Newfoundland population where a high incidence of Bardet-Biedl syndrome (209900) exists. The genetic study of 17 BBS kindreds hailing from this region showed that at least 4 loci might account for the disease (Woods et al., 1999).
Gerber et al. (1996) suggested the existence of a novel form of Usher syndrome type I from the fact that the 3 previously reported loci on chromosomes 14q32, 11q13, and 11p15 were excluded by linkage studies in 2 large multiplex families of Moroccan and Pakistani ancestry.