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The genetics of vitiligo in Korean patients.

BACKGROUND: Vitiligo is a common disorder whose exact cause is unknown, but genetic factors are thought to be involved. We analyzed 120 Korean proband families to clarify which genetic factors are involved in the pathogenesis of vitiligo in Korean patients. METHODS: The genetics of vitiligo were analyzed in 120 Korean proband families out of 1030 vitiligo patients. Each family was analyzed through a proband afflicted with vitiligo. RESULTS: In 51 (42.5%) of 120 proband families, at least one first-degree relative of the proband had vitiligo. The incidence of those affected among 1755 relatives (first-, second-, and third-degree) was found to be 8.0+/-0.6%. There was a statistically significant departure for segregation analysis which was inconsistent with inheritance as an autosomal or X-linked locus model. On the basis of our results, the inheritance pattern of vitiligo is more likely to tend toward the model of multifactorial inheritance. The threshold trait among first-degree relatives (7.2%) appeared to tend more toward the square root of the frequency in the general population (10%) than towards those of dominant (50%) or recessive (25%) models. CONCLUSIONS: These results indicate that there are certain genetic factors involved in the etiology of vitiligo, and that vitiligo seems to have a polygenic nature.

Female↗

Enzyme heterogeneity in the porphyrias.

The use of immunological methods for measuring enzyme mass has identified several varieties of porphyria in which the reduction of porphyrin enzyme activity is not accompanied by a corresponding change in the enzyme mass. Currently, acute intermittent porphyria and hepatoerythropoietic porphyria have exhibited this phenomenon. In porphyria cutanea tarda, it has recently been shown that the pattern of enzyme deficiency in erythrocytic and nonerythrocytic tissues does not strictly follow the inheritance pattern (familial and sporadic) previously described. Also, contrary to previous dogma, some cases of type 1 porphyria cutanea tarda appear to be positive for cross reactive immunological material (CRIM).

Humans↗

Retinitis pigmentosa and progressive sensorineural hearing loss caused by a C12258A mutation in the mitochondrial MTTS2 gene.

Family ZMK is a large Irish kindred that segregates progressive sensorineural hearing loss and retinitis pigmentosa. The symptoms in the family are almost identical to those observed in Usher syndrome type III. Unlike that in Usher syndrome type III, the inheritance pattern in this family is compatible with dominant, X-linked dominant, or maternal inheritance. Prior linkage studies had resulted in exclusion of most candidate loci and >90% of the genome. A tentative location for a causative nuclear gene had been established on 9q; however, it is notable that no markers were found at zero recombination with respect to the disease gene. The marked variability in symptoms, together with the observation of subclinical muscle abnormalities in a single muscle biopsy, stimulated sequencing of the entire mtDNA in affected and unaffected individuals. This revealed a number of previously reported polymorphisms and/or silent substitutions. However, a C-->A transversion at position 12258 in the gene encoding the second mitochondrial serine tRNA, MTTS2, was heteroplasmic and was found in family members only. This sequence change was not present in 270 normal individuals from the same ethnic background. The consensus C at this position is highly conserved and is present in species as divergent from Homo sapiens as vulture and platypus. The mutation probably disrupts the amino acid-acceptor stem of the tRNA molecule, affecting aminoacylation of the tRNA and thereby reducing the efficiency and accuracy of mitochondrial translation. In summary, the data presented provide substantial evidence that the C12258A mtDNA mutation is causative of the disease phenotype in family ZMK.

Animals↗

A study of a myopathy presenting as idiopathic scoliosis. Multicore disease or mitochondrial myopathy?

Seven cases from a family with a myopathy categorized as "multicore disease" are presented. The clinical picture is unusual because of the predominant progressive involvement of the axial skeletal muscle, with scoliosis and disproportionate respiratory failure as the major clinical features. The propositus and his cousin have both suffered from scoliosis without limb weakness. There is a possibility that this myopathy may be responsible for some cases regarded as idiopathic scoliosis, especially idiopathic infantile scoliosis. The clinical picture is highly variable, and there are sub-clinical cases. The inheritance pattern is consistent with either autosomal dominant, sex-linked recessive or extra-chromosomally inherited disease. Electron microscopy revealed mitochondrial abnormalities, which may have resulted in the Z-disc pathology.

Adolescent↗

Mapping of the associated phenotype of an absent granular layer in ichthyosis vulgaris to the epidermal differentiation complex on chromosome 1.

Ichthyosis vulgaris (IV) is a mild to severe scaling disorder of uncertain etiology estimated to affect as many as 1 : 250 in the population. Family studies have shown that in many cases IV follows an autosomal dominant inheritance pattern, but gene mapping studies have not been reported. To investigate the genetic basis for inherited IV, we have performed gene linkage studies in two multigenerational families where affected individuals have clinical features of IV but distinct histological features. The epidermis in this disorder characteristically displays non-specific orthohyperkeratosis. Notably, a subset of IV patients with a reduced or absent granular epidermal layer (AGL) have been reported, and decreased filaggrin levels have been described in others. The prominent role of profilaggrin in human keratohyalin suggests that defects in the gene for profilaggrin (FLG), its processing of profillagrin to filaggrin, or a gene involved in profilaggrin regulation may underlie or modify the pathology in IV. Family 1 had seven individuals with IV, severe heat intolerance and epidermis with 1-3 granular layers (consistent with normal epidermal histology). Ichthyosis vulgaris in this family did not segregate with FLG or other genes in the epidermal differentiation complex. In contrast, five of the six IV patients in Family 2, all siblings, had epidermis with no granular layer. Significant evidence was obtained for linkage of IV with the associated AGL phenotype to the epidermal differentiation complex (which includes FLG) assuming either a recessive (max Lod 3.4) or dominant (max Lod 3.6) inheritance model. Sequence analysis of FLG did not reveal a mutation in the amino or carboxyl terminal portions of the coding sequence adjacent to filaggrin repeats. The AGL may represent an endophenotype for IV, and the presence of a modifier of IV pathology at this locus is discussed.

Adult↗

Digenic retinitis pigmentosa due to mutations at the unlinked peripherin/RDS and ROM1 loci.

In spite of recent advances in identifying genes causing monogenic human disease, very little is known about the genes involved in polygenic disease. Three families were identified with mutations in the unlinked photoreceptor-specific genes ROM1 and peripherin/RDS, in which only double heterozygotes develop retinitis pigmentosa (RP). These findings indicate that the allelic and nonallelic heterogeneity known to be a feature of monogenic RP is complicated further by interactions between unlinked mutations causing digenic RP. Recognition of the inheritance pattern exemplified by these three families might facilitate the identification of other examples of digenic inheritance in human disease.

Alleles↗

A family study of vitiligo patterns.

The anatomical distribution of vitiligo has been studied in families with evidence of organ-specific autoimmune disease. No examples of similar pattern inheritance were found in first degree relatives in contrast to published reports of similar vitiligo patterns in identical twins. The genetic predisposition to develop vitiligo apparently allows for a diversity of anatomical pattern. A similar mechanism may be responsible for the occurrence of different organ-specific autoimmune diseases in members of the same family.

Adolescent↗

A study of the inheritance of a bleeding disorder in Simmental cattle.

A study was designed to determine the inheritance pattern of a blood platelet aggregation disorder in Simmental cattle utilizing embryo transfer technology. A Simmental donor cow that had previously produced a calf with the platelet aggregation disorder was superovulated and mated to a bull that had also produced affected offspring. Twenty-seven calves were produced from the 63 (42.9%) embryos transferred. This somewhat lower than expected pregnancy rate is suggestive of an increased rate of embryo loss. Twenty-three of 25 (92%) calves had normal platelet aggregation patterns and 2 failed to show any evidence of platelet aggregation. Data are suggestive that inheritance is not simple Mendelian recessive. A more likely scenario is that the defect is the result of the inheritance of at least 2 genes, which is also consistent with the sporadic incidence reported in the population at large.

Animals↗

Genetic control of biological rhythms: independent expression of each rhythm parameter.

Biological rhythm whose pattern approaches a sinusoidal curve can be characterized by four parameters: Period, Mesor, Acrophase and Amplitude. Inheritance patterns of these parameters were assessed by monitoring White Blood Cell (WBC) count rhythms of C57BL/6J mice, BALB/c mice and the F1 progeny prior and after injection of Cisplatinum at either 0900, 1500, 2100, or 0300. All untreated mice exhibited similar WBC rhythms while a variety of rhythm phenotypes was revealed among the injected mice. Analyses of the variety in the parental strains and F1 progeny suggested that each of the rhythm parameters is independently controlled.

Analysis of Variance↗

Inheritance of spatial learning ability in inbred mice: a classical genetic analysis.

The inheritance of spatial learning ability in inbred mice was examined by performance of a classical genetic cross between the 2 inbred strains C57BL/6Ibg and DBA/2Ibg. The inbreds were crossed to produce the 1st filial generation (F1) hybrids. F1 mice were bred to each other and were backcrossed to the parental strains to produce 3 hybrid generations with recombinant genotypes. The animals were tested for spatial learning ability in the Morris water task. All hybrid generations showed greater spatial learning ability than the inbreds, with F1 hybrids showing the greatest degree of spatial learning. The inheritance pattern for spatial learning differed between male and female mice, with males showing a type of inheritance in which dominant genes made the major contribution to the expression of the behavior. Females showed equal contributions of dominance deviation and additive genetic effects. The results are discussed in terms of fitness value to the animals.

Animals↗

Myotonia and the muscle chloride channel: dominant mutations show variable penetrance and founder effect.

The delayed relaxation or sustained contraction of skeletal muscle-myotonia-is frequently seen in myotonic dystrophy and sodium channelopathies (hyperkalemic periodic paralysis, paramyotonia congenita). Many cases of congenital myotonia without other clinical symptoms have been associated with mutations in the muscle chloride channel gene. Most cases reported to date show a recessive inheritance pattern, with loss of function of the corresponding protein. Six families have been reported with dominantly inherited myotonia and mutations of the chloride channel gene. Here we report clinical and molecular data on 38 family members from four new families with dominantly inherited myotonia congenita. Three families show a previously characterized G230E mutation, and we show that these three share a common affected ancestor despite living in different regions of the United States (linkage disequilibrium). One Italian family is shown to have a novel dominant mutation-I290M. This is the sixth mutation identified in Thomsen's myotonia. Genotype/phenotype correlations in these four families showed that both of the dominant mutations resulted in a mild clinical picture in 90% of the patients, and no symptoms in 10% of mutation-positive patients. The EMG was the clinical feature that most closely correlated with mutation data; however, 3 of 16 (19%) mutation-positive patients tested negative by electromyography at least once, and 1 (6%) tested negative despite multiple tests. Only about half (55%) of the mutation-positive patients tested positive for percussion myotonia. Most of the clinically symptomatic individuals stated that cold temperatures and stress substantially worsened their myotonia. Our data show that dominantly inherited Thomsen's myotonia is most often a very mild disorder that shows considerable clinical heterogeneity.

Adult↗

Neurological progress. The neuronal ceroid lipofuscinoses: a review.

Neuronal ceroid lipofuscinosis is a common cause of neurodegenerative disease in children. The disease is characterized by visual failure, seizures and dementia. The presence of cortical atrophy by computerized axial tomography and distinctive ultrastructural findings by skin biopsy, together with a suggestive clinical course and neurophysiologic abnormalities, lead to a diagnosis. Presently four subtypes and rare atypical forms are recognized: the infantile, late infantile, juvenile and adult or Kufs variants and atypical early juvenile and protracted juvenile types. The inheritance pattern is autosomal recessive in all subtypes with some of the adult cases representing autosomal dominant inheritance. The biochemical characterization of this disorder is just beginning. There is some evidence to implicate overglycosylation of proteins as playing a role in pathogenesis. Further biochemical description coupled with linkage analysis techniques using DNA probes are needed to develop a better understanding of this group of disorders.

Humans↗

Congenital central hypoventilation syndrome: mutation analysis of the receptor tyrosine kinase RET.

Congenital central hypoventilation syndrome (CCHS) usually occurs as an isolated phenotype. However, 16% of the index cases are also affected with Hirschsprung disease (HSCR). Complex segregation analysis suggests that CCHS is familial and has the same inheritance pattern with or without HSCR. We postulate that alteration of normal function of the receptor tyrosine kinase, RET, may contribute to CCHS based on RET's expression pattern and the identification of RET mutations in HSCR patients. To further explore the nature of the inheritance of CCHS, we have undertaken two main routes of investigation: cytogenetic analysis and mutation detection. Cytogenetic analysis of metaphase chromosomes showed normal karyotypes in 13 of the 14 evaluated index cases; one index case carried a familial pericentric inversion on chromosome 2. Mutation analysis showed no sequence changes unique to index cases, as compared to control individuals, and as studied by single strand conformational polymorphism (SSCP) analysis of the coding region of RET. We conclude that point mutations in the RET coding region cannot account for a substantial fraction of CCHS in this patient population, and that other candidate genes involved in neural crest cell differentiation and development must be considered.

Child↗

Definition and properties of disequilibria within nuclear-mitochondrial-chloroplast and other nuclear-dicytoplasmic systems.

We define and determine the interrelationships among five sets of disequilibrium parameters that measure two- and three-locus nonrandom associations in nuclear-dicytoplasmic systems. These assume a diploid nuclear locus and two haploid cytoplasmic loci, with special reference to nuclear-mitochondrial-chloroplast systems. Three sets of two-locus disequilibria measure the association between haplotypes at the two cytoplasmic loci (DMC) and associations between each cytoplasmic locus and nuclear alleles or genotypes (DM, D1M, D2M, D3M; DC, D1C, D2C, D3C). In addition, we present two classes of higher-order disequilibria that measure nonrandom allelic or genotypic associations involving all three loci. The first class quantifies associations between the nuclear locus and the two cytoplasmic loci taken jointly (DA/MC, DAA/MC, DAa/MC, Daa/MC, etc.), whereas the second measures only those associations remaining after all two-locus associations have been taken into account (DA/M/C, DAA/M/C, DAa/M/C, Daa/M/C). Based on combinations of these five sets of measures, we suggest a variety of parameterizations of three-locus, nuclear-dicytoplasmic systems. The dynamics of these disequilibria are then investigated under models of random and mixed mating, either with both cytoplasmic genomes inherited through the same parent or through opposite parents. Except for associations between the cytoplasmic haplotypes, which are constant when the two cytoplasmic genomes are inherited through the same parent, all disequilibria ultimately decay to zero. These randomizations do not necessarily occur monotonically, however, and in some cases are preceded by an initial increase in magnitude or sign change. For both inheritance patterns, the asymptotic decay rates are steadily retarded by increasing levels of self-fertilization. This behavior contrasts with that in the extreme case of complete selfing, for which only the heterozygote disequilibria always decay to zero. For all models considered, the dynamics of the two-locus cytonuclear subsystems are solely a function of the mating system, whereas the dynamical behavior and sign patterns of the cytoplasmic and three-locus disequilibria also depend strongly on the mode of cytoplasmic inheritance.

Cell Nucleus↗

Molecular genetics of cataract.

Studies on hereditary congenital cataracts have led to the identification of genes involved in formation of these cataracts. Knowledge of the structure and function of a particular gene and the effect of disease-associated mutations on its function are providing insights into the mechanisms of cataract. Identification of the disease gene requires both the relevant clinical data as well as genetic data on the entire pedigree in which the disease is found to occur. Genes for hereditary cataract have been mapped by genetic linkage analysis, in which one examines the inheritance pattern of DNA markers throughout the genome in all individuals of the pedigree, and compares those with the inheritance of the disease. Cosegregation of a set of markers with disease implies that the disease gene is present at the same chromosomal location as those markers. The genes so far identified for hereditary cataracts in both humans and animal models encode structural lens proteins, gap junction proteins, membrane proteins and regulatory proteins involved in lens development. Understanding of the mechanisms of hereditary cataract may also help us understand the manner in which environmental and nutritional factors act on the lens to promote opacification.

Animals↗

Diaphragmatic hernia-exomphalos-hypertelorism syndrome: a new case and further evidence of autosomal recessive inheritance.

We describe a male patient with wide anterior fontanel and metopic suture, hypertelorism, down slanting palpebral fissures, bilateral iris coloboma, omphalocele, and bilateral absence of the diaphragm with herniation of abdominal organs causing pulmonary hypoplasia and death. Autopsy also showed intestinal malrotation. All findings in this case are consistent with those described as a newly recognized syndrome by Donnai and Barrow [1993]. Since the parents are first cousins, this case provides further evidence for the previously postulated autosomal recessive inheritance pattern. Follow-up on the patients and families reported by Donnai and Barrow [1993] also supports autosomal recessive inheritance.

Adult↗

A molecular perspective on corneal dystrophies.

Corneal dystrophies refer to a group of corneal diseases and that are genetically determined. These have been traditionally classified with respect to the layer of cornea involved. We now know that this does not reflect the underlying pathobiology. Most of the corneal dystrophies are of Mendelian inheritance with some phenotype diversity and a variable degree of penetrance. The dystrophies involving enzymatic processes tend to be of autosomal recessive inheritance. In some cases, such as keratoconus, the inheritance pattern is not always clear and is considered complex. The age of onset of the disease, as in most inherited eye disorders, is variable and does not reflect the underlying pathogenic defect. Few cases are congenital. Our understanding of corneal dystrophies is undergoing somewhat of a revolution as over 12 chromosomes have been associated with corneal dystrophies with mutations identified in at least 14 genes if one includes anterior segment dysgenesis in this group of conditions. Several dystrophies remain without a gene or a genetic location (locus) and more familial studies are required. The new molecular information is challenging the traditional thinking about these conditions that was usually guided by the histopathological findings. As this new knowledge becomes more refined, the classification of this group of disorders will eventually be revisited to have a molecular basis. The elucidation of the underlying biochemical pathways may allow us to envisage the possibility of modulating these phenotypes in the future.

Corneal Dystrophies, Hereditary↗

Familial müllerian agenesis.

Müllerian agenesis is characterized by the absence of the fallopian tubes, uterus and internal portion of the vagina. Patients have normal female phenotype and genotype, with normal secondary sex characteristics but with amenorrhea. We report a family in which müllerian agenesis was diagnosed in three siblings and their two paternal aunts. This family was ascertained when the proband was evaluated for primary amenorrhea. She had normal secondary sexual development. Her karyotype was 46, XX. Ultrasound examination and magnetic resonance imaging of the pelvis revealed absence of the uterus and vagina. The proband had three sisters and two of them showed similar physical and radiological findings. Two of the proband's paternal aunts had no uterus. Although the pathogenesis of müllerian agenesis is well understood, the etiology and genetics are still unknown. Various forms of inheritance patterns have been suggested by several authors. In conclusion, it would appear that müllerian agenesis is influenced by multifactorial inheritance and polygenic and familial factors.

Adolescent↗