PROFOUND CHILDHOOD DEAFNESS

Approach and solutions to congenital hearing impairment in Cameroon: perspective of hearing professionals

OBJECTIVES

To bring out the diagnostic attitude of hearing professionals in Cameroon towards congenital hearing impairment (CHI), assess availability of tests, neonatal screening, and create a national map of availability of treatment opportunities.

METHODS

We conducted a cross-sectional online-based survey from June to December 2021, concerning ear-nose-throat (ENT) specialists, hearing care professionals, speech therapists and ENT nurses. A Google Forms online questionnaire was used to collect data, filled by eligible professionals involved in hearing care in Cameroon.

RESULTS

A total of 93 professionals working in 31 different health facilities participated. A cumulative percentage of 79.9% of ENTs were found in just two out of 10 regions. Specialists sought by ENTs for assessment of patients with CHI included neurologists/neuro-pediatricians (96.8%), pediatricians (47.6%), other ENTs (34.9%), and psychologists (3.2%). Investigations requested included auditory-evoked brainstem response (ABR; 87.3%), otoacoustic emissions recording (OAE; 71.4%), and tympanometry (66.7%). There were eight OAE and nine ABR machines in the country. Twenty-five (88.6%) out of 31 facilities with otolaryngologists did not carry out systematic neonatal screening. Reasons included unavailability of equipment (21; 84%), and administrative delays (14; 56%). Sixteen (51.6%) facilities had ENTs with additional training in otologic surgery and 11 (35.5%) were equipped to perform ear surgery. Three centers (9.7%) specialized in hearing aid provision and maintenance services. Three hospitals (9.7%) had performed cochlear implantation.

CONCLUSION

Our results show scarcity and overt unevenness in distribution of specialists, equipment and solutions to CHI in Cameroon. A serious negative health care consequence of this shortage is the unavailability of universal newborn hearing screening and implementation programs.

Etiologies of Childhood Hearing Impairment in Schools for the Deaf in Mali

Objectives: To identify the etiologies of hearing impairment (HI) in schools for students who are deaf and to use a systematic review to summarize reports on the etiologies and clinical and genetic features of HI in Mali. Methods: We included individuals with HI that started before the age of 15 years old. Patients were carefully evaluated under standard practices, and pure-tone audiometry was performed where possible. We then searched for articles published on HI in the Malian population from the databases' inception to March 30, 2020. Results: A total of 117 individuals from two schools for the deaf were included, and a male predominance (sex ratio 1.3; 65/52) was noted. HI was pre-lingual in 82.2% (n = 117), and the median age at diagnosis was 12 years old. The etiologies were environmental in 59.4% (70/117), with meningitis being the leading cause (40%, 20/70), followed by cases with genetic suspicion (29.3%, 21/117). In 11.3% (8/117) of patients, no etiology was identified. Among cases with genetic suspicion, three were syndromic, including two cases of Waardenburg syndrome, while 15 individuals had non-syndromic HI. An autosomal recessive inheritance pattern was observed in 83.3% of families (15/18), and consanguinity was reported in 55.5% (10/18) of putative genetic cases. Conclusion: This study concludes that environmental factors are the leading causes of HI in Mali. However, genetic causes should be investigated, particularly in the context of a population with a high consanguinity rate.

Hearing Impairment Overview in Africa: the Case of Cameroon

The incidence of hearing impairment (HI) is higher in low- and middle-income countries when compared to high-income countries. There is therefore a necessity to estimate the burden of this condition in developing world. The aim of our study was to use a systematic approach to provide summarized data on the prevalence, etiologies, clinical patterns and genetics of HI in Cameroon. We searched PubMed, Scopus, African Journals Online, AFROLIB and African Index Medicus to identify relevant studies on HI in Cameroon, published from inception to 31 October, 2019, with no language restrictions. Reference lists of included studies were also scrutinized, and data were summarized narratively. This study is registered with PROSPERO, number CRD42019142788. We screened 333 records, of which 17 studies were finally included in the review. The prevalence of HI in Cameroon ranges from 0.9% to 3.6% in population-based studies and increases with age. Environmental factors contribute to 52.6% to 62.2% of HI cases, with meningitis, impacted wax and age-related disorder being the most common ones. Hereditary HI comprises 0.8% to 14.8% of all cases. In 32.6% to 37% of HI cases, the origin remains unknown. Non-syndromic hearing impairment (NSHI) is the most frequent clinical entity and accounts for 86.1% to 92.5% of cases of HI of genetic origin. Waardenburg and Usher syndromes account for 50% to 57.14% and 8.9% to 42.9% of genetic syndromic cases, respectively. No pathogenic mutation was described in GJB6 gene, and the prevalence of pathogenic mutations in GJB2 gene ranged from 0% to 0.5%. The prevalence of pathogenic mutations in other known NSHI genes was <10% in Cameroonian probands. Environmental factors are the leading etiology of HI in Cameroon, and mutations in most important HI genes are infrequent in Cameroon. Whole genome sequencing therefore appears as the most effective way to identify variants associated with HI in Cameroon and sub-Saharan Africa in general.

Fokouo JV, Oluwole OG, Nguefack S, Chimusa ER, Wonkam A. Hearing Impairment Overview in Africa: the Case of Cameroon

The incidence of hearing impairment (HI) is higher in low- and middle-income countries when compared to high-income countries. There is therefore a necessity to estimate the burden of this condition in developing world. The aim of our study was to use a systematic approach to provide summarized data on the prevalence, etiologies, clinical patterns and genetics of HI in Cameroon. We searched PubMed, Scopus, African Journals Online, AFROLIB and African Index Medicus to identify relevant studies on HI in Cameroon, published from inception to 31 October, 2019, with no language restrictions. Reference lists of included studies were also scrutinized, and data were summarized narratively. This study is registered with PROSPERO, number CRD42019142788. We screened 333 records, of which 17 studies were finally included in the review. The prevalence of HI in Cameroon ranges from 0.9% to 3.6% in population-based studies and increases with age. Environmental factors contribute to 52.6% to 62.2% of HI cases, with meningitis, impacted wax and age-related disorder being the most common ones. Hereditary HI comprises 0.8% to 14.8% of all cases. In 32.6% to 37% of HI cases, the origin remains unknown. Non-syndromic hearing impairment (NSHI) is the most frequent clinical entity and accounts for 86.1% to 92.5% of cases of HI of genetic origin. Waardenburg and Usher syndromes account for 50% to 57.14% and 8.9% to 42.9% of genetic syndromic cases, respectively. No pathogenic mutation was described in GJB6 gene, and the prevalence of pathogenic mutations in GJB2 gene ranged from 0% to 0.5%. The prevalence of pathogenic mutations in other known NSHI genes was <10% in Cameroonian probands. Environmental factors are the leading etiology of HI in Cameroon, and mutations in most important HI genes are infrequent in Cameroon. Whole genome sequencing therefore appears as the most effective way to identify variants associated with HI in Cameroon and sub-Saharan Africa in general.

Common genes for non-syndromic deafness are uncommon in sub-Saharan Africa: a report from Nigeria

INTRODUCTION

Little is known about the molecular epidemiology of deafness in sub-Saharan Africa (SSA). Even in Nigeria, the most populous African nation, no genetic studies of deafness have been conducted. This pioneering work aims at investigating the frequencies of gene mutations relatively common in other parts of the world (i.e. those in GJB2, GJB6, and mitochondrial DNA) among subjects from Nigeria with hearing loss (HL) with no evidence of acquired pathology or syndromic findings. In addition, we review the literature on the genetics of deafness in SSA.

METHOD

We evaluated 81 unrelated deaf probands from the Yoruba tribe residing in Ibadan, a suburban city in Nigeria, for the aetiology of their deafness. Subjects underwent genetic testing if their history was negative for an environmental cause and physical examination did not find evidence of a syndrome. Both exons of GJB2 and mitochondrial DNA flanking the 1555A>G mutations were PCR-amplified followed by Sanger sequencing. GJB6 deletions were screened via quantitative PCR.

RESULT

We identified 44 probands who had nonsyndromic deafness with no environmental cause. The age at study time ranged between 8 months and 45 years (mean=24 years) and age at onset was congenital or prelingual (<age 2 years) in 37 (84%) probands and postlingual in 7 (16%) probands. Among these, 35 probands were the only affected members of their families (simplex cases), while there were at least two affected family members in nine cases (multiplex). Molecular analyses did not show a pathogenic variant in any one of the 44 probands studied.

CONCLUSION

GJB2, GJB6 and mitochondrial DNA 1555A>G mutations were not found among this initial cohort of the deaf in Nigeria. This makes imperative the search for other genes in the aetiology of HL in this population.

Genetic Counseling in Congenital Deafness

The risk of having a child affected by isolated congenital deafness (or deafmutism) is high, if the two parents are affected, if only one parent is affected, but belonging to an affected family, and if the couple has already an affected child.

Jervell and Lange-Nielsen syndrome in a father and daughter from a large highly inbred family: a 16-year follow-up of 59 living members

OBJECTIVE

To report the autosomal dominant inheritance of the Jervell and Lange-Nielsen syndrome in a highly inbred family, the initiation of Torsades de Pointes, and the natural history of the syndrome based on a 16-year follow-up of the kindred.

METHOD

A family tree was constructed that included 66 blood relatives from three successive generations. Electrocardiograms were obtained from 59 living members including the proband, four members from a nuclear family, and 54 from the extended family. Evoked response audiometry was recorded for the proband and the nuclear family. All 59 family members were followed up regularly for 16 years.

RESULTS

A total of 24 living members were affected--QTc: 480-680 ms. The proband had long QTc, bilateral high-tone sensorineural deafness, recurrent syncope, and Torsades de Pointes. The asymptomatic father had long QTc and unilateral high-tone sensorineural deafness that involved specifically the left ear. One asymptomatic sibling of the proband had long QTc and normal hearing. The mother and another sibling were asymptomatic; QTc and hearing were normal in both. A total of 21 affected members from the extended family had only long QTc, and all were asymptomatic. There were three congenitally deaf first cousins who had recurrent syncope and adrenergic-triggered sudden death. In all, seven of 10 parents had consanguineous marriage to a first cousin. Each affected offspring had at least one affected parent. The severely symptomatic proband who received only β-blocker therapy and the 23 affected members without antiadrenergic therapy, all remained asymptomatic throughout the 16-year follow-up period.

CONCLUSION

Jervell and Lange-Nielsen syndrome was inherited as autosomal dominant in this kindred. The majority of the affected members had a mild phenotype. The severity of auditory and cardiac phenotypes corresponded.

The petrous portion of the temporal bone as shown on sonography between 14 and 40 weeks' gestation

OBJECTIVES

The purpose of this study was to examine the feasibility of sonographically identifying, measuring, and constructing nomograms of the fetal petrous bone, the part of the temporal bone that houses the auditory apparatus.

METHODS

A total of 248 consecutive pregnant women between 14 and 40 weeks' gestation were included. During a routine scan using transvaginal or transabdominal sonography, the fetal head was assessed in transverse sections. First, the parotid gland or external ear was identified, followed by the petrous bone. This annular echogenic structure, located medially and superior to the parotid gland or external ear, was measured at its largest anteroposterior diameter. The petrous bone on at least one side was measured; if both sides were visualized easily, both petrous bones were measured.

RESULTS

In 247 fetuses, at least one petrous bone was measured. The petrous bone measurement correlated well with the gestational age (R = 0.908; P < .001), biparietal diameter (R = 0.983; P < .001), and femur length (R = 0.913; P < .001).

CONCLUSIONS

Depiction of the petrous bone is feasible at all gestational ages and correlates well with the gestational age, biparietal diameter, and femur length. The usefulness of the ability to depict this bone in prenatal diagnosis of congenital malformations of the inner ear should be tested in prospective studies.

Hearing loss: mechanisms revealed by genetics and cell biology

Hearing loss (HL), or deafness in its most severe form, affects an estimated 28 and 22.5 million Americans and Europeans, respectively. The numbers are higher in regions such as India and the Middle East, where consanguinity contributes to larger numbers of recessively inherited hearing impairment (HI). As a result of work-related difficulties, educational and developmental delays, and social stigmas and exclusion, the economic impact of HL is very high. At the other end of the spectrum, a rich deaf culture, particularly for individuals whose parents and even grandparents were deaf, is a social movement that believes that deafness is a difference in human experience rather than a disability. This review attempts to cover the remarkable progress made in the field of the genetics of HL over the past 20 years. Mutations in a significant number of genes have been discovered over the years that contribute to clinically heterogeneous forms of HL, enabling genetic counseling and prediction of progression of HL. Cell biological assays, protein localization in the inner ear, and detailed analysis of spontaneous and transgenic mouse models have provided an incredibly rich resource for elucidating mechanisms of hereditary hearing loss (HHL). This knowledge is providing answers for the families with HL, who contribute a great deal to the research being performed worldwide.

Challenges in management of childhood sensorineural hearing loss in sub-Saharan Africa, Nigeria

The evaluation of a hearing-impaired child attempts to determine the aetiology, the degree of hearing loss and intervention to aid speech and language. This remains a challenge to practising otolaryngologists, especially in the developing countries as 85-90% of causes of hearing losses were never discovered leading to delayed intervention and irreversible effects. In a review of children presenting at the otolaryngology outpatient in the University College Hospital, Ibadan, Nigeria, sensorineural hearing loss was found in 103, giving a hospital prevalence rate of 14%, we still perceived this figure to be unrepresentatively and low, probably due to poor access to medicare, poverty and other factors. Genetic factor accounted for 25%, followed by measles infections 13% and meningitis 8%. About 60% of them had educationally significant hearing loss at presentation. Access to hearing aid was poor as only 12.5% of the patients could afford it and the rest were managed by deaf training. We conclude by suggesting an audiologic programme which has the comprehensive function of neonatal and infant hearing screening, subsidized hearing aid services and hearing rehabilitation surgery.

Therapeutics of hearing loss: expectations vs reality

With the completion of the sequencing of the human genome, the field of medicine is undergoing a dramatic and fundamental change. The identification of our genes and the proteins they encode and the mechanisms of mutations that are pathogenic will allow us to devise revolutionary new ways to diagnose, treat and prevent the thousands of disorders that affect us. Certainly, disorders of the auditory system are no exception. Revealing the molecular mechanisms of hearing and understanding the role of each player in the intricate auditory network could enable us to employ gene- or cell-based therapy to cure or prevent hearing loss. To this end, much emphasis has been placed on the identification and characterization of genes involved in human deafness, as well as research on mouse models for deafness. Ultimately, the effect of genomics on medicine will be dramatic, providing us with the ability to cure sensory defects, a tangible goal that is now within our reach.

Stem cells as therapy for hearing loss

One of the greatest challenges in the treatment of inner-ear disorders is to find a cure for the hearing loss that is caused by the loss of cochlear hair cells or spiral ganglion neurons. The recent discovery of stem cells in the adult inner ear that are capable of differentiating into hair cells, as well as the finding that embryonic stem cells can be converted into hair cells, raise hope for the future development of stem-cell-based treatment regimens. Here, we propose different approaches for using stem cells to regenerate the damaged inner ear and we describe the potential obstacles that translational approaches must overcome for the development of stem-cell-based cell-replacement therapies for the damaged inner ear.

Clinical Genetic Study of 144 Patients With Nonsyndromic Hearing Loss

Hearing loss constitutes an important category of congenital defects that can be isolated or part of the phenotypic spectrum of several syndromes. A clinical genetic study was performed on a sample of 144 patients with nonsyndromic hearing loss, establishing the sex distribution, type, degree, symmetry, laterality, progression, etiology, and, when possible, inheritance pattern.

Histopathology and molecular genetics of hearing loss in the human

Hearing loss is among the most common disabilities of man. It has been estimated that over 70 million individuals in the world are hearing impaired with pure tone averages greater than 55 dB. A genetic etiology is thought to be responsible for over half of early onset hearing loss and at least one third of late onset hearing loss. In this review, examples of the histopathology of the inner ear in known genetic syndromes in the human will be presented in order to provide a structural basis for understanding molecular mechanisms of development and maintenance in the inner ear, and to serve the essential function of validating the applicability of animal genetic models of hearing loss to the human condition.

Theoretical and empirical aspects of gene-culture coevolution

Cultural transmission can be roughly defined as the transfer of information between individuals by social learning (see below). Genes used to be, and for most species still are, the only means available for the accurate transfer of information across generations. In species where cultural transmission has developed, notably the human, interactions can occur between the two inheritance systems. Gene-culture coevolution refers to the evolutionary phenomena that arise from these interactions. As we shall see, these interactions can take various forms.

DFNA25, a novel locus for dominant nonsyndromic hereditary hearing impairment, maps to 12q21-24

Using linkage analysis, we identified a novel dominant locus, DFNA25, for delayed-onset, progressive, high-frequency, nonsyndromic sensorineural hearing loss in a large, multigenerational United States family of Czech descent. On the basis of recombinations in affected individuals, we determined that DFNA25 is located in a 20-cM region of chromosome 12q21-24 between D12S327 (centromeric) and D12S84 (telomeric), with a maximum two-point LOD score of 6.82, at recombination fraction.041, for D12S1030. Candidate genes in this region include ATP2A2, ATP2B1, UBE3B, and VR-OAC. DFNA25 may be the human ortholog of bronx waltzer (bv).

Genetic hearing loss: a study of 228 Brazilian patients

We studied 228 patients, with suspected or confirmed genetic hearing loss, in order to determine the clinical and genetic diagnoses and etiology of each case. Deafness with no associated abnormalities was found in 146 patients (64%) belonging to 112 families. Syndromic deafness was diagnosed in 82 patients (36%) belonging to 76 families. The genetic etiology was as follows: autosomal recessive inheritance in 40.8% of syndromics and non-syndromics, autosomal dominant inheritance in 13.2% and X-linked recessive in 1.3%. In 44.7% of the cases, the etiology of the hearing loss could not be determined. Monogenic causes are the most possible etiology in the latter cases. Parental consanguinity was found in 22.4% of the cases, and deafness was bilateral, profound and neurosensorial in 47.4% of the patients. An early onset of hearing loss (< 2 years of age) occurred in 46.5% of the cases. These results are similar to previous literature reports.

A stepwise approach to the diagnosis and treatment of hereditary hearing loss

What To Do Do suspect a genetic cause in all cases of hearing loss. Do develop a working knowledge of common types of HHI that you may draw on to aid in diagnosis. Do think of HHI when the audiogram reveals a hearing loss with a "cookie bite" configuration. Do refer the infant to a geneticist in cases where you suspect a syndromic HHI, a nonsyndromic HHI, and in cases of "cryptogenic" hearing loss where an underlying HHI may be present. Often, the associated symptoms are subtle and best detected by a professional who deals with these issues on a daily basis. Do get the infant or family plugged into an audiologist or otolaryngologist and speech pathologist who will preferably work as a team to maximize aural rehabilitation and ensure serial follow-up. It is never too early to fit a child with hearing aids. Do refer to the HHIRR center at Boys Town. Do refer to the correct "deaf" organization or "blind-deaf" organization. Do think about working up other siblings or family members. Do keep in mind that some members of the "deaf society" may regard deafness as an alternative lifestyle and may not be amenable to their child's referral for additional workup and aural rehabilitation. What Not To Do Do not assume the child is deaf and nothing can be done. Do not wait until the child is older to refer to an otolaryngologist, speech therapist, and audiologist. Do not order a sonogram. Do not order a temporal bone CT scan on newborns. Do not forget about other siblings who may have a similar pathology. Do not forget that some forms of HHI can present beyond infancy. The pediatrician is the front line and can play a major role in the diagnosis, workup, and treatment of HHI. Armed with the proper degree of suspicion, careful elicitation of family history, meticulous physical examination, evaluation of the audiogram, and adequate fund of knowledge of common types of genetic deafness, the pediatrician can make a timely diagnosis and appropriate referrals. This avoids delay in detection of significant hearing impairment and the associated lack of essential skills in speech, language, and social interaction. No child is too young to have some type of hearing assessment. Early detection and intervention are best done with a multidisciplinary team approach with a neonatologist or pediatrician, audiologist, speech therapist, and otolaryngologist. In the future, blood tests using genetic probes may be available to screen for many types of HHI.

Linkage studies of non-syndromic recessive deafness (NSRD) in a family originating from the Mirpur region of Pakistan maps DFNB1 centromeric to D13S175

Autosomal recessive non-syndromal hearing impairment (NSRD) is genetically heterogeneous. Five loci have been identified to date which map to chromosomes 13 (DFNB1), 11 (DFNB2), 17 (DFNB3), 7 (DFNB4) and 14 (DFBN5). We report definite linkage of NSRD to the locus DFNB1 in a single family of 27 families studied of Pakistani origin. Haplotype analysis of markers in the pericentromeric region of chromosome 13q revealed a recombination event which maps DFNB1 proximal to the marker D13S175 and in the vicinity of D13S143.

Waardenburg syndrome type II: phenotypic findings and diagnostic criteria

The Waardenburg syndrome (WS) consists of at least two distinct autosomal dominant hereditary disorders. WS Type I has been mapped to the distal part of chromosome 2q and the gene identified as PAX3. Other gene(s) are responsible for WS Type II. Mapping WS Type II requires accurate diagnosis within affected families. To establish diagnostic criteria for WS Type II, 81 individuals from 21 families with Type II WS were personally studied, and compared with 60 personally studied patients from 8 families with Type I and 253 cases of WS (Type I or II) from the literature. Sensorineural hearing loss (77%) and heterochromia iridum (47%) were the two most important diagnostic indicators for WS Type II. Both were more common in Type II than in Type I. Other clinical manifestations, such as white forelock and skin patches, were more frequent in Type I. We estimate the frequency of phenotypic traits and propose diagnostic criteria for WS Type II. In practice, a diagnosis of WS Type II can be made with confidence given a family history of congenital hearing loss and pigmentary disorders, where individuals have been accurately measured for ocular distances to exclude dystopia canthorum.

Hearing impairment and pigmentary disturbance

Hearing impairment is a variable manifestation of several heritable conditions in which pigmentation of the skin or eyes is abnormal. Some of these disorders are well recognized although uncommon, while others are virtually private syndromes. Practical issues concerning the major conditions of this type are reviewed in this article on a basis of a survey of 4452 profoundly deaf children attending special schools in Southern Africa, together with investigations in affected families. The Waardenburg syndrome (WS), which is the most common deafness-depigmentation disorder, was present in 121 (2.7%) of the 4452 deaf scholars. Further studies in 7 multigeneration affected families confirmed phenotypic variability and indicated a need for internationally agreed diagnostic criteria. In 4 Cape Town families of mixed ancestry the WS-I gene was linked to the 2q37 locus, but in another large kindred no linkage could be demonstrated. Nonallelic heterogeneity is possible. There is uncertainty concerning possible interrelationship between WS and piebaldism. The phenotypic consistency of a South African family in which 7 persons in 3 generations had gross piebaldism in the absence of disturbance of hearing or involvement of the eyes and periorbital structures is suggestive that this disorder and WS are separate entities. Molecular investigations indicate that the gene for piebaldism in this kindred is not situated at the WS-I locus 2q37. Deafness and hyperpigmentation are present in neurofibromatosis type II (acoustic neuromata) and the multiple lentigines syndrome, while retinal pigmentation is a feature of the Usher syndrome. This latter entity is apparently much less common in Southern Africa than in other parts of the world.

Review of a high risk register for congenital or early-onset deafness

This paper is an attempt to assess the success of a high risk register for congenital or early onset of severe to profound hearing impairment. With some years experience, and a large number of publications, it is possible to evaluate (at least in part) the extent to which such a register actually does permit us to identify these infants. To that end, an extensive review is reported here and some recommendations are made.

Incidence, prevalence and etiology of hearing impairment in children in the county of Västerbotten, Sweden

During the period 1964-83, 63,463 children were born in the county of Västerbotten, Sweden. Of these children, 160 had a hearing impairment greater than or equal to 30 dB HL mean hearing loss for the frequencies 0.5, 1.0 and 2.0 kHz in the better-hearing ear. The mean annual incidence of hearing impairment was 2.5 per 1,000 and the prevalence was 2.6 per 1,000. Hereditary factors were present in 46% and no etiology could be established in 34% of the cases. The incidence of hearing impairment was greater than has been presented in studies from other areas in Europe.

On the genetics of prelingual deafness

In view of the many discordant findings in previous studies regarding the genetics of prelingual deafness, family data (133 nuclear families and 25 pedigrees) were gathered from India. Analysis of these data has revealed that the defect is primarily genetic, which is in agreement with earlier findings. Segregation analysis was performed to compare various autosomal diallelic one-locus and multilocus models. Our analysis revealed that the most parsimonious model for prelingual deafness is that it is controlled by recessive genes at a pair of unlinked diallelic autosomal loci. Individuals are affected if and only if they are recessive homozygous at both loci. The likelihood of the present data under this two-locus multiple recessive homozygosis model is at least 10(8) times higher than that of the one-locus models that were examined in previous studies. This model is also the best-fitting model among other plausible two-locus models.

The gene for X-linked progressive mixed deafness with perilymphatic gusher during stapes surgery (DFN3) is linked to PGK

A linkage analysis has been performed in a large Dutch kindred with progressive mixed deafness with perilymphatic gusher during stapes surgery (DFN3) using a panel of X-chromosomal RFLPs. Tight linkage (zmax = 3.07 at 0 = theta = 0.00) was demonstrated with the locus for phosphoglycerate kinase (PGK), which is located at Xq13. Tight linkage was excluded for DXS9 (probe RC8) and DXS41 (probe 99.6) on Xp and for blood clotting factor 9 (FIX) on distal Xq. Deafness is one of the predominant clinical features in males with deletions of the Xq21 band. Our results suggest that this association may be due to involvement of the DFN3 gene.

Usher's syndrome, temporal bone pathology

The histological findings in the right temporal bone of a 65-year-old deaf and blind man are presented. The subject suffered from the autosomal recessive Usher's syndrome, as did 2 of his 5 siblings. They are the offspring of a consanguineous marriage. This man died from an intra-abdominal hemorrhage. Within 3 h after death the temporal bones were donated for study and were processed for histopathological examination.

Isolated and syndromic cryptophthalmos

The association between cryptophthalmos and multiple congenital malformations has been well documented over the last century. Numerous authors have described cases as the cryptophthalmos syndrome, but recently reports of cases without cryptophthalmos have led several authors to use the eponymic designation Fraser syndrome. We have seen seven cases of cryptophthalmos syndrome, including three sib pairs. All presented with cryptophthalmos and bilateral renal agenesis in addition to other characteristic associated malformations. A literature review showed 124 cases in which 27 demonstrated isolated cryptophthalmos, while 97 showed a pattern of multiple congenital malformations. We selected four major and eight minor criteria which enabled us to classify 86 of those cases as having cryptophthalmos syndrome with 11 remaining unclassified. Cryptophthalmos demonstrates equal sex distribution, occurrence in sibs, consanguinity in families with more than one affected child, and lack of vertical transmission--strongly suggesting autosomal recessive inheritance. Isolated cryptophthalmos or cryptophthalmos sequence was sporadic in 16 cases and familial in 11. The familial cases occurred in three families and demonstrated vertical transmission. The pathogenesis of this syndrome is unknown. There are similarities to animal models of maternal vitamin A deprivation and defects in programmed cell death. Cryptophthalmos syndrome should be considered in the differential diagnosis of cases with multiple congenital malformations, especially when they are associated with renal agenesis, even in the absence of cryptophthalmos.

Childhood deafness in southern Africa. An aetiological survey of 3,064 deaf children

We have completed a survey of the causes of deafness in 3,064 children with defective hearing who attend special schools in Southern Africa. Specific genetic or multifactorial syndromes were diagnosed in 7 per cent, familial undifferentiated deafness was recognized in 11 per cent, while in 25 per cent the deafness was acquired.

Klippel-Feil syndrome with conductive deafness and histological findings of removed stapes

The Klippel-Feil syndrome is usually associated with sensorineural hearing impairment, but rarely is it associated with conductive or mixed deafness. A 22-year-old female presented with fusion of the cervical vertebrae, torticollis, scoliosis, pterygium colli, the Sprengel deformity with an omovertebral bone, concavity of the thorax and conductive hearing impairment of the right ear. Tympanotomy disclosed an atrophic long process of incus and a fixation of the stapes footplate, and stapedectomy was performed with immediate postoperative improvement of hearing. However, she developed a sudden hearing loss with dizziness soon after she had physical exercise on the 15th postoperative day, and revision surgery revealed a perilymph fistula of the oval window. Histological investigations of the removed stapes showed no specific osseous changes but hyperostosis of the posterior edge of the footplate. The literature is reviewed and the etiology of the conductive deafness and the perilymph fistula is discussed.

Mesodermal induction defect as a possible cause of ear malformations

Deafness due to inner ear anomalies is rarely associated with malformations of the auricles. We describe two brothers with profound congenital sensorineural deafness, abnormal vestibular function, normal ossicles, and delayed motor development. Since the external and inner ear originate from distinctly separate structures, the embryogenesis of this malformation association is less clear than in the more common association of external and middle anomalies, where the latter two structures are derived from the first and second branchial arches. The combination of auricular and inner ear anomalies, with sparing of the middle ear structures, can be explained on the assumption that mesodermal induction is responsible for normal differentiation of both the otocyst and of the branchial arch ectoderm. A recessive mutant gene may lead to a deficiency of a mesodermal inducer substance of a target tissue receptor site. A similar mechanism may be involved in other multiple malformation syndromes, whereby a mutant gene acting during a specific period of organogenesis causes disruption of the normal induction-competence relationship.

The genetic dynamics of disease

The notional principles of the genetics of disease are broadly discussed. Disease is an intrinsically vague term that represents the incongruity between the inner milieu of the organism and the environment. Its dynamics, then, cannot be reduced to naive statements about selection which may operate, and operate conflictingly, on several different levels or organization. Evolutionary selection results from the advantage of complexity, and the fundamental theorem of genetic dynamics - that mutational debts must eventually be paid in full-may be false or, at best approximate. The traditional models (mendelian, galtonian, and threshold) are set in a context that identifies certain features of disease that hitherto have been totally ignored. Neither invention nor traditional analysis has been adequate. Models should be made individually adequate for the study of diseases; the diseases should not be trimmed to fit the models.

Culture and deafness in a Maya Indian village

Over the years, the question of psychosocial adjustment among the deaf has attracted a great deal of attention. Pioneer work by Levine (1960, 1963); Rainer, Altshuler, and Kallmann (1963); Myklebust (1964); Rainer and Altshuler (1968); Grinker (1969); Mindel and Vernon (1971); and Schlesinger and Meadow (1972), to mention but a few, has aided our understanding of how the deaf adjust to the stress which their handicap imposes upon them. We know a great deal less, however, about the deaf in other societies. Altable (1947); Altshuler, Vollenweider, and Rainer (1971); Youniss (1974); and Sarfaty and Katz (1978) are among the handful of references which appear, and they all deal with urban populations. Kuschel (1973) considers a single deaf man on Rennell Island, in Polynesia, but his concern is primarily the sign language devised by this ingenious man. As far as I am aware, only Woodward (1978) and his associates have an ongoing program for the investigation of deafness in a nonurban society (Washabaugh, Woodward, and DeSantis, 1978). To neglect the way in which other societies handle these problems is to deprive ourselves of a rich source of comparative data. It is also to avoid a strenuous challenge, for the methodology that is appropriate for use in literate, urban societies may have little applicability in a tribal or peasant group. The purpose of this paper, therefore, is to present preliminary data on a group of profoundly, congenitally deaf Maya Indians of southeastern Mexico, with the aim of suggesting hypotheses which may be investigated by future research. The fieldwork upon which the report is based, however, was not part of a purposeful attempt to study the deaf of the village in question; rather, the village was selected as part of the Maya Film Project, directed by Hubert Smith, and at the time the project took to the field the fieldworkers had no idea that the village eventually chosen would contain a high number of deaf inhabitants.

Neurochemistry of the auditory system

Two areas of auditory biochemistry are reviewed: the identification and characterization of neurotransmitters in the auditory system and the biochemical approach to the study of genetic hearing disorders. Studies to identify neurotransmitters at major auditory synapses are outlined. Evidence supporting glutamate or aspartate as the neurotransmitter for the auditory nerve is presented. The application of biochemistry to the study of genetic hearing disorders is discussed.

Identification of impaired hearing in early childhood

Although the incidence of congenital deafness is high, routine neonatal screening for this problem is not practised, and early identification of congenital or early acquired deafness is relatively rare. Delaying therapy until a child is 3 or more years old severely limits speech development, language acquisition and learning. The commonest causes of delay in diagnosis are the refusal of physicians to listen to the parents' observations, their failure to screen children for hearing and speech problems, and their reluctance to arrange prompt referral for audiologic assessment. Diagnostic delay occurs even though half the children who have impaired hearing are known to be at increased risk. A plea is made for the setting up of a register of infants known to be at risk for impaired hearing. First-contact physicians should be alert to the possibility of hearing problems, particularly in children at high risk. Screening methods for use by nonspecialist practitioners are outlined.

Reliability of Békésy threshold tracing in identification of carriers of genes for an X-linked disease with deafness

Seven identified carriers and 20 potential carriers of Norris's disease have been examined by pure tone octave audiometry and Békésy audiometry. The investigation supports earlier results of Békésy threshold tracings performed in heterozygote carriers of genes for recessive hearing impairment. The sensitivity of the method is poor. The specificity of the Békésy threshold tracing is high, meaning that an absent dip cannot exclude the possibility of a subject being a carrier, whereas a present dip can be regarded as an indication of carrier. When comparing conventional octave audiometry and Békésy threshold tracing, the latter method is found to be more subtle in finding carriers of genes for recessive deafness. Therefore, Békésy threshold tracing may be of help in the genetic counselling of potential carriers of genes for recessive deafness.

Cervical vertebral fusion (Klippel-Feil) syndrome with consanguineous parents

We describe a female infant with the cervical vertebral fusion (Klippel-Feil) syndrome whom we recognized at birth because of her short neck, restriction of cervical movement, and low posterior hairline. X-ray examination showed anomalies of C1, and between C2-3 and C3-4; thus, we classified her as type II, with variable cervical fusion. At 24 months she was small and manifested hearing deficiency. The mother and father were consanguineous with five common ancestors four generations ago, which resulted in a coefficient of inbreeding equivalent to a second cousin relationship. The parents and grandparents were phenotypically normal, and the parents were radiologically normal. This form of the syndrome has previously been said to be autosomal dominant. Our conclusion of determination by a single autosomal recessive gene is evidence of genetic heterogeneity.

Hypoactive labyrinths and motor development

This study examines the relation of hypoac tive labyrinths to the achievement of motor milestones such as sitting and walking. Two children with genetic sensorineural hearing losses with vestibular dysfunction who walked very late did not show any evidence to suggest a diffuse neurologic cause for this delay at follow-up examinations. A review of electronys tagmographic (ENG) vestibular tests of 353 children under age ten years discovered 17 children who had been tested twice or more. There was disagreement between the two tests in four (24%), suggesting less than adequate relia bility of ENG test results in infants and chil dren. Forty-nine children had hypoactive labyrinths. The records of 22 of these were suitable for surveying the relation of the vestibu lar dysfunction to age at walking. Ten of the 22 children walked at 18 months or later, indicating that some, but not all children with vestibular dysfunction will be late walkers. Some of the children who walked at a normal age were described as having "weak necks" or "floppy heads," and some sat late. Accordingly, counsel ing of parents of deaf children who walk late should be delayed until vestibular testing has been carried out to avoid false diagnoses of associated brain damage or mental retardation. It is urged that all deaf children undergo vestibular testing, and that those with abnormal tests be retested to make certain of the results. Procedures to test vestibular function in infants and children need to be standardized, as shown by personal observations and a survey of the pertinent literature.