Myopia and models and mechanisms of refractive error control

Myopia represents a failure of the normal process of emmetropization, which is essentially endogenous to the eye. Emmetropization involves defocus detection at the level of the amacrine and bipolar cells of the outer retina, diffusion of a signal or signals across the retinal pigment epithelium and choroid, and alteration of the scleral matrix, likely through modulation of proteoglycan synthesis. Elucidating and effectively bolstering the deficient steps in this regulatory pathway would mark a significant advance given myopia's tremendous impact. Clinical experience, longitudinal studies, epidemiological data and numerous animal experiments have enhanced our understanding of myopia. Interpretation of the epidemiological data is often complicated by the difficulties of distinguishing environmental from genetic influences, especially those pertaining to slow developmental changes. Likewise, it is important that the animal models be interpreted with an appreciation that the human eye varies structurally and developmentally from that of other species. Studies of the chick eye have formed the basis for several hypotheses of myopic development, but the chick does not possess a fovea or retinal blood supply. It is unclear whether these differences alter the pathways of emmetropization. Even closely related primate species can exhibit different responses to form deprivation conditions, suggesting differing mechanisms of eye growth control. Monocular occlusion of the rhesus macaque, for instance, results in myopia when the ciliary muscle is paralyzed or the optic nerve cut, but does not in the stumptailed macaque, suggesting a role of excessive accommodation in the development of myopia in the stumptail but not the rhesus [36]. Given such variability in the models a persisting element of continued myopia research must be an evaluation of the relevance of any given model to the human condition. In this regard, the study of changing patterns of gene expression within and among species during emmetropization and myopic progression may offer a productive avenue for future research.

A novel approach to search for identity by descent in small samples of patients and controls from the same mendelian breeding unit: a pilot study on myopia

Autosomal dominant high myopia, a genetic disorder already mapped to region 18p11.31, is common in Carloforte (Sardinia, Italy), an isolated village of 8,000 inhabitants descending from a founder group of 300 in the early 1700s. Fifteen myopic propositi and 36 normal controls were selected for not having ancestors in common at least up to the grandparental generation, although still descendants of the original founders. All subjects were genotyped for 14 markers located on autosome 18 at a resolution of about 10 cM. Allelic distributions were found to be similar at all tested loci in propositi and controls, except for the candidate marker D18S63 known to segregate in close linkage association with high myopia. In particular, the frequency of allele 85 among the propositi was almost double that of the controls (Fisher's exact test, p = 0.037). The association is more striking when the frequency of the genotype 85/85 in the two groups is compared (Fisher's exact test, p = 0.005). This conclusion was further evaluated through a bootstrap analysis by computing the overall probability of the observed data under the null hypothesis (i.e. no difference between the two groups in frequency distributions for the chromosome 18 markers). Again, marker D18S63 was found to have a sample probability lower than 0.004, which is significant at the 0.05 level after correcting for simultaneous testing of multiple loci. The study demonstrates the efficiency of our novel strategy to detect identity by descent (IBD) in small numbers of patients and controls when they are both part of well-defined Mendelian breeding units (MBUs). The iterative application of our strategy in separate MBUs is expected to become the method of choice to evaluate the ever-growing number of reported associations between candidate genes and multifactorial traits and diseases.

Mirror image myopic anisometropia in two pairs of monozygotic twins

Two sets of monozygotic twins with mirror image myopic anisometropia are reported. The first set were two boys aged 1 year 8 months. There was a right eye myopic anisometropia in one twin, and a left eye myopic anisometropia in the other. The differences in refractive power between both eyes were 11.6 and 7.6 dpt, respectively (spherical equivalent). The second set were two 6-year-old boys. The right eye had myopic anisometropia in one twin, while the left eye was affected in the other. The differences in refractive power between both eyes were 6.5 and 3.7 dpt, respectively (spherical equivalent). Exotropia was recognized in 3 cases. Previously only two sets of monozygotic twins with mirror image myopic anisometropia have been reported. Monozygotic twins with mirror image myopic anisometropia are extremely rare.

Familial pathologic myopia, corneal dystrophy, and deafness: a new syndrome

BACKGROUND

Numerous syndromes with myopia and hearing loss have been described up to now. We present a family with pathologic myopia, corneal dystrophy, and deafness distinct from these syndromes.

CASES

Ten patients in the same Turkish family were evaluated by ophthalmologic, audiologic, physical, radiologic, genetic, serologic, and biochemical examinations.

OBSERVATIONS

Ophthalmic examination indicated that all the cases had myopia, 7 of them had pathologic myopia, 1 had intermediate, and 2 had mild. Four of the patients with pathologic myopia had corneal dystrophy that was bilaterally manifest as white opacities in the posterior stroma near Descemet's membrane in an axial distribution; 1 of these 4 patients also had a tilted disc. Otolaryngologic examination revealed conductive hearing loss in 3 cases, mixed hearing loss in 2, and sensorineural hearing loss in 1. The results of karyotypic analyses of all cases were normal. The pedigree analysis showed the disease was inherited through successive generations as an autosomal dominant trait. The results of biochemical, serologic, and radiologic investigations were normal. The same pathophysiologic process in all cases seemed to account for the myopia, the corneal dystrophy and the deafness.

CONCLUSIONS

To our knowledge, this type of case has not been reported in the literature. Therefore, we named this syndrome "familial pathologic myopia, corneal dystrophy and deafness."

Pineal control of the dopamine D2-receptor gene and dopamine release in the retina of the chicken and their possible relation to growth rhythms of the eye

Retinal dopamine (DA) and the DA D2-receptor have been implicated in the development of "deprivation myopia", induced by frosted eye occluders. We have studied the changes in D2-mediated dopaminergic transmission in the retina, their possible relations to eye growth rhythms and myopia, and their control by the pineal gland. (1) We found that the sensitivity of eye growth to retinal image degradation varied over the day. Intermittent periods of normal vision inhibited deprivation myopia more if they occurred in the evening than in the morning. (2) Diurnal growth rhythms in both eyes interacted even though it was previously shown that both deprivation myopia and the accompanying changes in retinal DA release can be monocularly induced. (3) The D2-receptor mRNA concentration in the retina showed no systemic diurnal changes and was not affected by deprivation myopia, but was increased after 2 days in darkness. Since DA release varies over the day, the gain of dopaminergic transmission may also vary, which could explain the observation described in (1) above. (4) Depletion of retinal DA by intravitreal application of reserpine, which lowers DA content severely, had little effect on D2-receptor mRNA concentration. (5) Selective illumination of the pineal gland reduced the D2-receptor mRNA content in the retina to a similar level to full illumination, indicating that the pineal gland controls the D2-receptor mRNA content in the retina. The pineal also controlled DA release in the retina. These results show that the pineal has a surprisingly large influence on both the retinal DA receptor gene transcription and DA release. It can probably control the gain of dopaminergic transmission in the retina and deprivation myopia and mediate the interactions of the growth rhythms in both eyes.

Familial clustering and myopia progression in Singapore school children

BACKGROUND

Familial factors may be related to the progression of myopia in children. A cohort study was conducted to determine the relationship between familial factors and myopia progression in children.

METHODS

From a larger clinical trial (n = 311), 153 Singapore children aged 6--12 years were recruited to participate in a cohort study of the risk factors for myopia progression. An in-person interview was conducted whereby information on the history of myopia in first-degree relatives was obtained. Other information collected included housing type, parental education and income. Cycloplegic refractive error as measured by subjective refraction and autorefraction were ascertained every six months. The average length of follow-up was 28 months.

RESULTS

The adjusted mean rate of progression of myopia was -0.60 (95% confidence interval -0.66, -0.55) diopters per year. The average rate of progression of myopia for children with a parental history of myopia was -0.63 (95% confidence interval -0.69, -0.56) diopters per year compared to -0.42 (95% confidence interval -0.57, -0.27) diopters per year for children whose parents were not myopic. The different measures of family history of myopia were related to rate of change in refractive error and refractive error in the final visit. There was no association between close work and myopia progression.

CONCLUSIONS

A positive family history is related to the progression of myopia and final refractive error in Singapore children, thus supporting evidence that hereditary factors may play an important role in myopia progression.

Academic achievement, close up work parameters, and myopia in Singapore military conscripts

AIM

To determine the relation of refractive error to environmental factors, including close up work, in Singapore military conscripts.

METHODS

A cross sectional study was conducted on 429 Singapore military conscripts. Non-cycloplegic refraction and A-scan biometry were performed in both eyes. A detailed questionnaire was administered by in-person interview to obtain information about current and past near work activity, extra tuition lessons, educational experiences, and family demographics.

RESULTS

Myopia associated with the conscript having been educated in the (gifted, special, or express) educational streams (adjusted odds ratio (OR) = 3.8, 95% confidence interval CI 2.0-7.3), and having completed pre-university education (OR=4.1, 95% CI 1.9-8.8). The reported close up work activity at age 7 years did correlate with age of onset of myopia (p<0.001). In parallel, supplemental tuition lessons in primary school has (OR=2.6, 95% CI 1.4-4.9) associated with conscript myopia. Parental myopia was positively associated with myopia (p<0.001), but this relation disappeared when adjusted for environmental factors. Current (p=0.83) and past close up work activity at age 7 years (p=0.13) did not correlate with myopia.

CONCLUSION

Educational level and educational stream positively related to myopia. A relation was observed with reported close up work activity in early childhood and with tuition classes during elementary school, but not with current close up work activity. These results underscore the strong influence of environment in myopia pathogenesis but a role for close up work activity remains indeterminate.

Further refinement of the MYP2 locus for autosomal dominant high myopia by linkage disequilibrium analysis

INTRODUCTION

High myopia (>-6.00 diopters) is a complex common disorder that predisposes individuals to retinal detachment, glaucoma, macular degeneration, and premature cataracts. A recent linkage analysis of seven families with autosomal dominant high myopia has identified one locus (MYP2) for high myopia on chromosome 18p11.31 (Young et al.: Am J Hum Genet 1998;63:109-119). Haplotype analysis revealed an initial interval of 7.6 centimorgans (cM).

METHODS

Transmission disequilibrium tests (TDT) with both the Statistical Analysis for Genetic Epidemiology (SAGE) 3.1 TDTEX and GENEHUNTER 2 (GH2) programs were performed using chromosome 18p marker alleles for this interval.

RESULTS

Using SAGE analysis, the following p values were obtained for markers in marker order in this region: D18S1146 (p = 0.227), D18S481 (p = 0.001), D18S63 (p = 0.062), D18S1138 (p = 0.0004), D18S52 (p = 1.79 x 10(-6)), and D18S62 (p = 0.141). GH2 TDT analysis revealed the following p values for the best allele for the markers: D18S1146 (p = 0.083), D18S481 (p = 0.108), D18S63 (p = 0.034), D18S1138 (p = 0.011), D18S52 (p = 0.007), and D18S62 (p = 0.479).

CONCLUSION

These data suggest that the gene for 18p11.31-linked high myopia is most proximal to marker D18S52, with a likely interval of 0.8 cM between markers D18S63 and D18S52. Due to the contraction of the interval size by TDT, these results provide a basis for focused positional cloning and candidate gene analysis at the MYP2 locus.

Clinical features of hereditary progressive arthro-ophthalmopathy (Stickler syndrome): a survey

PURPOSE

To define variations in the clinical manifestations of Stickler syndrome.

METHODS

A questionnaire was sent to 612 persons.

RESULTS

Of the 316 usable replies, 95% of persons had eye problems (retinal detachment occurred in 60% of patients, myopia in 90%, and blindness in 4%); 84% had problems with facial structures such as a flat face, small mandible, or cleft palate; 70%, hearing loss; and 90%, joint problems, primarily early joint pain from degenerative joint disease. Treatment included cryotherapy and laser therapy for retinal detachment, repair of cleft palate, use of hearing and mobility aids, and joint replacements.

CONCLUSIONS

There are wide variations of symptoms and signs among affected persons, even within the same family. There are delays in diagnosis, lack of understanding among family members, denial about the risk of serious eye problems, and joint disease.

[Screening of myopic LASIK patients with increased epithelial wound healing]

BACKGROUND

Wound healing of the cornea is critical for the refractive outcome of myopic laser-assisted in situ keratomileusis (LASIK). As epidermal growth factor (EGF) is important for the origin of epithelial hyperplasia, this study examined preoperative EGF mRNA concentrations in the corneal epithelial cells to detect patients with increased epithelial wound healing response.

PATIENTS AND METHODS

The epithelium was biopsied before LASIK in 35 eyes with myopia of -10.0 D. The EGF mRNA concentration in the epithelial cells was quantified by polymerase chain reaction and enzyme-linked oligosorbent assay, and the correlation with postoperative refraction at 6 months was assessed.

RESULTS

All eyes were around emmetropia 3 weeks after the surgery. At 6 months postoperatively 27 eyes were within +/- 1.0 D of emmetropia while 8 showed regression of 2.0-4.0 D. Higher EGF mRNA levels were found in eyes with regression than in eyes with postoperative emmetropia.

CONCLUSIONS

Preoperative EGF mRNA concentration in the corneal epithelial cells may be an indicator of postoperative refractive outcome of myopic LASIK and offers a new possibility for pharmaceutical manipulation.

Genes and environment in refractive error: the twin eye study

PURPOSE

A classical twin study was performed to examine the relative importance of genes and environment in refractive error.

METHODS

Refractive error was examined in 226 monozygotic (MZ) and 280 dizygotic (DZ) twin pairs aged 49 to 79 years (mean age, 62.4 years). Using a Humphrey-670 automatic refractor, continuous measures of spherical equivalent, total astigmatism, and corneal astigmatism were recorded. Univariate and bivariate maximum likelihood model fitting was used to estimate genetic and environmental variance components using information from both eyes.

RESULTS

For the continuous spectrum of myopia/hyperopia, a model specifying additive genetic and unique environmental factors showed the best fit to the data, yielding a heritability of 84% to 86% (95% confidence interval [CI], 81%-89%). If myopia and hyperopia (< or = -0.5 D and > or = 0.5 D, respectively) were treated as binary traits, the heritability was 90% (95% CI, 81%-95%) for myopia and 89% (95% CI, 81%-94%) for hyperopia. For total and corneal astigmatism, modeling showed dominant genetic effects are important; dominant genetic effects accounted for 47% to 49% of the variance of total astigmatism (95% CI, 37%-55%) and 42% to 61% of corneal astigmatism variance (95% CI, 8%-71%), with additive genetic factors accounting for 1% to 4% and 4% to 18%, respectively (95% CIs, 0%-13% and 0%-60%, respectively).

CONCLUSIONS

Genetic effects are of major importance in myopia/hyperopia; astigmatism appears to be dominantly inherited.

Stickler syndrome and vitreoretinal degeneration: correlation between locus mutation and vitreous phenotype. Apropos of a case

BACKGROUND

Autosomal dominant vitreoretinopathies are characterized by genetic heterogeneity. Structural mutations in COL2A1 are the most frequent cause of Stickler syndrome with ocular involvement. The affected patients have a characteristic vitreous alteration, so-called membranous vitreous, or type 1 vitreous phenotype. Recently a novel mutation in the gene encoding the alpha 1 chain of type XI collagen (COL11A1) was reported in rare Stickler pedigrees, with a different, so-called beaded or type 2 vitreous phenotype.

METHODS

Five patients of an Italian family affected by high myopia, high frequency of retinal detachment, and other systemic stigmata evocative of Stickler syndrome (flat midface, depressed nasal bridge, short nose, spondyloepiphyseal dysplasia and osteoarthritis) were studied. Genetic investigations were also performed, considering three candidate loci for Stickler syndrome and Wagner syndrome (COL2A1, COL11A1, WGN1).

RESULTS

Segregation analysis was performed utilizing polymorphic markers. COL2A1 and WGN1 segregations were excluded; COL11A1 showed concordance with the disease. The vitreous phenotype of the family was a typical type 1 or "membranous" vitreous, although all the previously reported COL11A1-related Stickler syndromes had always shown the type 2 or "beaded" vitreous phenotype.

CONCLUSIONS

The clear presence of the type 1 or "membranous" vitreous phenotype in our family, despite the probable mutation in the COL11A1 gene, suggests greater phenotypical heterogeneity and a more extensive mutation spectrum, even of the COL11A1 gene, than previously thought, explaining the basis for the different vitreous phenotypes seen in Stickler syndrome.

Associations of high myopia in childhood

PURPOSE

High myopia in early childhood is a recognised association of ocular and systemic disease. The aim of this study was to describe the types, pattern and frequency of these associations.

METHODS

All children presenting to two ophthalmology units over 3 years who were found to have high myopia were recruited. High myopia was defined as one or both eyes demonstrating 6 dioptres spherical equivalent or more of myopic refractive error on retinoscopy. We limited the age to less than 10 years old. A retrospective case review was undertaken of the 112 consecutive children who fulfilled the criteria above. The demographic data, source and indication for referral were recorded along with the ocular and systemic findings and diagnosis.

RESULTS

Only 9 (8%) of the children had 'simple high myopia' with no associated ocular or systemic associations. In 54% there was an underlying systemic association with or without further ocular problems (e.g. developmental delay, prematurity, Marfan, Stickler, Noonan, Down syndrome) and in the remaining 38% there were further ocular problems associated with the high myopia (e.g. lens subluxation, coloboma, retinal dystrophy, anisometropic amblyopia). A family history of high myopia did not preclude associated abnormality: in 4 cases the diagnosis of a systemic condition in the child led to the identification of the disease in at least one myopic relative. Asian (p < 0.001) and male (p < 0.05) patients were overrepresented in the series.

CONCLUSION

High myopia is strongly associated with systemic and ocular problems; it may be the reason for the child's initial medical referral and an important clue to an underlying systemic or ocular condition. Referrals infrequently originated from community optometrists despite prior attendance. We suggest that all children under 10 years of age with high myopia are referred to a paediatric ophthalmology clinic for review and we propose a structured clinical evaluation in the hospital eye clinic.

Expression of Sonic hedgehog and retinal opsin genes in experimentally-induced myopic chick eyes

The purpose of this study was to evaluate changes in the expression of different genes in chick retinal tissues after induction of experimental myopia and to evaluate the roles of these genes in the regulation of postnatal eye growth and myopia. Form-deprivation using occlusive goggles and hyperopic defocus by negative spectacle lenses were used to induce myopia in hatched chicks. Expression levels of Sonic hedgehog, its receptor complex, and other retinal cell genes were evaluated by semi-quantitative reverse transcription-polymerase chain reaction. Levels of Sonic hedgehog protein were further evaluated by Western blot analysis. The induction of myopia caused significant increase in expression of Sonic hedgehog mRNA and protein and increased expression of blue and red opsin mRNA. In contrast, the expression of mRNA for Sonic hedgehog receptor complex (Patched-Smoothened), rhodopsin, vimentin, green opsin, violet opsin, and HPC-1 were unaffected by the induction of myopia. The increase in expression of Sonic hedgehog in chick retinas in experimentally-induced myopia suggests involvement in the retina control of postnatal eye growth. Furthermore, Sonic hedgehog may influence the expression of blue and red opsins under myopic conditions.

Variation in the vitreous phenotype of Stickler syndrome can be caused by different amino acid substitutions in the X position of the type II collagen Gly-X-Y triple helix

Stickler syndrome is a dominantly inherited disorder characterized by arthropathy, midline clefting, hearing loss, midfacial hypoplasia, myopia, and retinal detachment. These features are highly variable both between and within families. Mutations causing the disorder have been found in the COL2A1 and COL11A1 genes. Premature termination codons in COL2A1 that result in haploinsufficiency of type II collagen are a common finding. These produce a characteristic congenital "membranous" anomaly of the vitreous of all affected individuals. Experience has shown that vitreous slit-lamp biomicroscopy can distinguish between patients with COL2A1 mutations and those with dominant negative mutations in COL11A1, who produce a different "beaded" vitreous phenotype. Here we characterize novel dominant negative mutations in COL2A1 that result in Stickler syndrome. Both alter amino acids in the X position of the Gly-X-Y triple-helical region. A recurrent R365C mutation occurred in two unrelated sporadic cases and resulted in the membranous vitreous anomaly associated with haploinsufficiency. In a large family with linkage to COL2A1, with a LOD score of 2.8, a unique L467F mutation produced a novel "afibrillar" vitreous gel devoid of all normal lamella structure. These data extend the mutation spectrum of the COL2A1 gene and help explain the basis for the different vitreous phenotypes seen in Stickler syndrome.

Ophthalmologic findings in Cohen syndrome. A long-term follow-up

OBJECTIVE

To determine the nature and course of ophthalmologic abnormalities and their clinical significance in Cohen syndrome.

STUDY DESIGN

Observational case series.

PARTICIPANTS

Twenty-two Cohen syndrome patients aged 2 to 57 years were examined, and a retrospective review of ophthalmologic records was carried out for 14 of them. All but one were part of the Finnish study of refined mapping of the Cohen syndrome gene by linkage disequilibrium in chromosome 8.

MAIN OUTCOME MEASURES

Visual acuity (VA), cycloplegic refraction, biomicroscopy, lens opacitometry, ophthalmoscopy, and fundus photography.

RESULTS

With the exception of the two youngest patients, all had symptoms such as nyctalopia, impaired vision, and visual field loss. Progressive, often high-grade myopia, astigmatism, and retinochoroidal dystrophy resembling retinitis pigmentosa occurred in all, except for the youngest patients. The earliest fundus changes were pale disc and pale fundus with or without pigment granularity, followed by narrowed vessels, pigment clumps, and bone spiculelike pigment accumulations by 10 to 20 years of age. Pigment deposits increased and approached the posterior pole by 35 to 40 years of age. Patients more than 45 years of age had severe retinochoroidal atrophy. A bull's-eye macula was seen in most patients. Teenagers had peripheral lens opacities, and young adults had early nuclear sclerosis confirmed by lens opacitometry. Older patients also had posterior subcapsular cataracts, iris atrophy, and iridophacodonesis. Vision started to deteriorate at the age of 6 to 10 years, but remained relatively good (VA 0.5-0.1) in most patients until 30 and, in one case, 46 years of age. Older patients were severely visually handicapped (VA hand motion to light perception), but none were completely blind.

CONCLUSIONS

Progressive myopia and retinochoroidal dystrophy are essential features in Cohen syndrome and, together with early lens opacities, lead to deterioration of vision. Cohen syndrome patients need careful ophthalmologic follow-up at all ages. Nyctalopia and restricted visual fields should be considered when planning the patient's daily activities.

[Studies of the association of pathological myopia in Chinese patients with HLA alleles]

The second exons of the HLA-DQB1 genes in 55 patients with Pathological Myopia were amplified and then digested with ApaI, Bsp1286I, BsaHI, BssHII, HaeII, HaeIII, HpaII, RsaI to determinate the genotypes and the allele frequencies. Among the 16 alleles, HLA-DQB1*0201, *0301, *0303, *0401 alleles in PM patients differed significantly from that of the normal ones in the distribution of the alleles, and seemed to be the pathogenic genes (P < 0.05; AF = 0.1636, 0.1091, 0.1636, 0.1091 vs. 0.0400, 0.0300, 0.0400, 0.0200; RR = 4.2886, 3.5350, 4.2890, 5.0000); While the HLA-DQB1*0601, *0602 frequencies in PM patients were remarkably lower than that of the normal ones, which showed the property of protective genes (Pc = 0.0000, AF = 0.1182, 0.0818 vs. 0.4300, 0.3100). DQB1*05.32, *0504 and *0605 can not be detected. The association of PM with DQB1 was found for the first time in the world, which has great significance both to theoretical study and to clinical diagnosis.

Clinical variability among patients with incomplete X-linked congenital stationary night blindness and a founder mutation in CACNA1F

BACKGROUND

Incomplete X-linked congenital stationary night blindness (CSNB) is a clinically variable condition that has been shown to be caused by mutations in the calcium-channel CACNA1F gene. We assessed the clinical variability in the expression of the incomplete CSNB phenotype in a subgroup of patients of Mennonite ancestry with the same founder mutation.

METHODS

Sixty-six male patients from 15 families were identified with a common mutation in exon 27 of CACNA1F (L1056insC). Clinical variability in night blindness, reduced visual acuity, myopia, nystagmus and strabismus was examined.

RESULTS

At least one of the major features of CSNB (night blindness, myopia and nystagmus) was absent in 72% of the patients. All the examined features varied widely, both between and within families.

INTERPRETATION

Although the patients shared a common CACNA1F mutation, there was considerable variability in the clinical expression of the incomplete CSNB phenotype. These findings suggest the presence of other genetic factors modifying the phenotype of this disorder.

Genetic epidemiology study of pathological myopia

OBJECTIVE

To explore the genetic epidemiology of pathological myopia (PM), including hereditary and genetic model.

METHODS

The simple segregation analysis was done by SEGRANB. The values of segregation ratio p and the proportion of sporadic cases x were estimated. The complex segregation analysis was performed using SAGE-REGD. The genetic model and gene frequency were estimated. The 62 pedigrees with PM were random samples from hospital patients.

RESULTS

By simple segregation analysis, the genetic pattern of N*N is autosomal recessive and the frequency of sporadic cases is approximately 65.72%. The genetic pattern of A*N may be autosomal recessive (but autosomal dominant cannot be excluded), the frequency of sporadic cases is approximately 35.14%. By complex segregation analysis, the genetic model of PM is autosomal recessive and the gene frequency is 0.147385.

CONCLUSION

PM is compatible with autosomal recessive inheritance (autosomal dominant not excluded ), the sporadic cases are existent and the gene frequency is 0.147385.