X-linked Dominant Mode Of Inheritance Research Articles

A rare case of a male child with post-zygotic de novo mosaic variant c.538C\u2009>\u2009T in MECP2 gene: a case report of Rett syndrome

BackgroundRett syndrome (RTT) is characterized by a normal perinatal period with a normal head size at birth followed by normal development for the first 6 months of life followed by gradual deceleration of head growth, loss of acquired purposeful hand skills, severe expressive and receptive language impairment, severe intellectual disability and gait and truncal apraxia/ ataxia. It is caused due to mutations in the MECP2 gene and follows an X-linked dominant mode of inheritance. It was observed exclusively in females and was believed to be lethal in males. In contrast to this belief, several males were identified with RTT upon genetic analysis, however, most males expired by the age of 2 years due to neonatal encephalopathy. The ones that survived beyond the age of 2 years, were attributed to the presence of an extra X chromosome (co-occurrence of Klinefelter and RTT) or the ones having mosaic cell lines. Only 11 males with somatic mosaicism are known till date.Case presentationThis case reports an ultra-rare case of a male affected with RTT surviving beyond the age of 2 years due to post-zygotic de novo somatic mosaicism. He was identified with a known pathogenic variant c.538C > T (p.R180*), which to the best of our knowledge is exclusively seen in females and has never been reported in a male before.ConclusionThe present case is the first report of a mosaic male affected with RTT from India. The present report also carried out genotype-phenotype correlations across surviving mosaic males with RTT. We also postulate the effect of variant type, position along the gene and the variant allele fraction in different tissue types to be correlated with disease severity.

The molecular genetics of selective tooth agenesis.

Selective tooth agenesis is a congenital disorder divided into two types based on the number of missing teeth, i.e. hypodontia which is the absence of <6 teeth and oligodontia which is agenesis of >6 permanent teeth excluding the third molars. As the prevalence of tooth agenesis is higher in populations with Arab and Asian descent, it is intriguing to probe deeper into the molecular aspects of this disorder. Selective tooth agenesis inherits as autosomal dominant, autosomal recessive or X-linked dominant mode of inheritance. The 10 loci identified are selective tooth agenesis 1 through 9 and selective tooth agenesis X1. Genes for 8 of these loci have been characterised while the causative genes for selective tooth agenesis 2 and 5 still remain to be elucidated. The current broad-spectrum review was planned to discuss the molecular genetics of all 10 loci mapped with selective tooth agenesis, their mode of inheritance as well as the proteins encoded by these genes, their roles and their interactions.

Incontinentia Pigmenti: A Case Report

Incontinentia pigmenti (IP) is a genodermatosis with an X-linked dominant mode of inheritance, characterized by ectodermal, mesodermal, neurological, ocular, and dental manifestations. The purpose of this case study was to report the oral and dental manifestations of an IP case in a Venezuelan pediatric patient. A 9 year-old Venezuelan girl was evaluated. She showed macular pigmented lesions in her face, trunk, back, legs, and fingers as well as abnormal hair distribution, alopecia on the vertex, and hypoplasia of eyebrows. During the dental examination, conical shaped-teeth and delayed dental eruption was evidenced. The microanalytical examination showed dentin without significant alterations in the mineralization except for hypermineralization in focal areas. In addition, a decrease in the enamel mineralization was observed.

Focal dermal hypoplasia in a male

Focal dermal hypoplasia (FDH) is a rare mesoectodermal dysplasia syndrome characterized by cutaneous, skeletal, dental, ocular and soft-tissue defects. An X-linked dominant mode of inheritance with lethality in male subjects has been proposed. Only around 30 cases of FDH have been reported in male subjects. Live born affected males are mosaic for mutations in PORCN gene . We present the mosaic pattern of FDH in a young boy.

LAMP2 Microdeletions in Patients With Danon Disease

Danon disease is an X-linked dominant disorder characterized by the clinical triad of hypertrophic cardiomyopathy, skeletal myopathy, and variable mental retardation. Pathologically, autophagic vacuoles are noted in both skeletal and cardiac muscle. It exhibits an X-linked dominant mode of inheritance, and male carriers are severely affected, whereas female carriers develop milder and later-onset cardiac symptoms. Danon disease has been associated with mutations in the lysosome-associated membrane glycoprotein 2 (LAMP2) gene located at Xq24, typically resulting in splicing defects or protein truncation affecting the LAMP2. Because of its rarity, the full spectrum of genetic mutation resulting in Danon disease has not been elucidated. We analyzed 3 male cases with clinical and pathological findings consistent with Danon disease. Comprehensive mutational analysis failed to yield detectable products for selected LAMP2 exons, and genomic DNA deletion was suspected. Genomic junction fragment polymerase chain reaction analysis in case 1 identified a novel Alu-mediated 34-kb microdeletion encompassing the entire 5'-untranslated region and exon 1 of LAMP2. In case 2 and 3, junctional polymerase chain reaction and Southern blot analyses mapped the breakpoint to an MIRb and (TA)(n) simple repeats present in intron 3, which determined a 64-kb and a 58-kb deletion, respectively, thereby ablating exons 4 to 10. Western blot analysis confirmed the absence of LAMP2 in protein extract from lymphocytes of index case 2. This article is the first report of Danon disease caused by microdeletions at Xq24, which functionally ablate LAMP2. The microdeletion mechanism appears to involve 1 Alu-mediated unequal recombination and 2 chromosomal breakage points involving TA-rich repeat sequences.

A Whole-Genome Scan and Fine-Mapping Linkage Study of Auditory-Visual Synesthesia Reveals Evidence of Linkage to Chromosomes 2q24, 5q33, 6p12, and 12p12

Synesthesia, a neurological condition affecting between 0.05%-1% of the population, is characterized by anomalous sensory perception and associated alterations in cognitive function due to interference from synesthetic percepts. A stimulus in one sensory modality triggers an automatic, consistent response in either another modality or a different aspect of the same modality. Familiality studies show evidence of a strong genetic predisposition; whereas initial pedigree analyses supported a single-gene X-linked dominant mode of inheritance with a skewed F:M ratio and a notable absence of male-to-male transmission, subsequent analyses in larger samples indicated that the mode of inheritance was likely to be more complex. Here, we report the results of a whole-genome linkage scan for auditory-visual synesthesia with 410 microsatellite markers at 9.05 cM density in 43 multiplex families (n = 196) with potential candidate regions fine-mapped at 5 cM density. Using NPL and HLOD analysis, we identified four candidate regions. Significant linkage at the genome-wide level was detected to chromosome 2q24 (HLOD = 3.025, empirical genome-wide p = 0.047). Suggestive linkage was found to chromosomes 5q33, 6p12, and 12p12. No support was found for linkage to the X chromosome; furthermore, we have identified two confirmed cases of male-to-male transmission of synesthesia. Our results demonstrate that auditory-visual synesthesia is likely to be an oligogenic disorder subject to multiple modes of inheritance and locus heterogeneity. This study comprises a significant step toward identifying the genetic substrates underlying synesthesia, with important implications for our understanding of the role of genes in human cognition and perception.

Genomic deletions ofOFD1account for 23% of oral-facial-digital type 1 syndrome after negative DNA sequencing

Oral-facial-digital type I syndrome (OFDI) is characterised by an X-linked dominant mode of inheritance with lethality in males. Clinical features include facial dysmorphism with oral, dental and distal abnormalities, polycystic kidney disease and central nervous system malformations. Considerable allelic heterogeneity has been reported within the OFD1 gene, but DNA bi-directional sequencing of the exons and intron-exon boundaries of the OFD1 gene remains negative in more than 20% of cases. We hypothesized that genomic rearrangements could account for the majority of the remaining undiagnosed cases. Thus, we took advantage of two independent available series of patients with OFDI syndrome and negative DNA bi-directional sequencing of the exons and intron-exon boundaries of the OFD1 gene from two different European labs: 13/36 cases from the French lab; 13/95 from the Italian lab. All patients were screened by a semiquantitative fluorescent multiplex method (QFMPSF) and relative quantification by real-time PCR (qPCR). Six OFD1 genomic deletions (exon 5, exons 1-8, exons 1-14, exons 10-11, exons 13-23 and exon 17) were identified, accounting for 5% of OFDI patients and for 23% of patients with negative mutation screening by DNA sequencing. The association of DNA direct sequencing, QFMPSF and qPCR detects OFD1 alteration in up to 85% of patients with a phenotype suggestive of OFDI syndrome. Given the average percentage of large genomic rearrangements (5%), we suggest that dosage methods should be performed in addition to DNA direct sequencing analysis to exclude the involvement of the OFD1 transcript when there are genetic counselling issues.

Dominantly‐inherited lop ears

We describe a four-generation Chinese family that included five members who had an isolated bilateral lop ear anomaly. The presentation suggested a dominant mode of inheritance. The absence of male-to-male transmission does not exclude an X-linked dominant mode of inheritance. Since the phenotypic anomaly of the male proband was no more severe than the affected female members, an autosomal dominant mode of inheritance is most likely.

Lack of Association Between the Aggrecan Gene and Familial Idiopathic Scoliosis

A study was conducted to determine the potential association between a specific aggrecan gene polymorphism and familial idiopathic scoliosis (FIS). To determine the allelic distribution of the exon 12 polymorphism within a sample of families with FIS. FIS is a structural curvature of the spine where the underlying genetic etiology has not been established. The aggrecan locus has been linked to multiple skeletal disorders. A polymorphism, within the aggrecan gene, was previously reported to be associated with curve severity in individuals with scoliosis. Fifty-eight families with FIS were genotyped for the aggrecan exon 12 polymorphism using a polymerase chain reaction method. Model-independent sib-pair linkage analyses and tests of association were performed to analyze the genetic effects of the exon 12 polymorphism. Linkage analyses of a genomic screen performed on a subgroup of 48 families with a most likely to be X-linked dominant mode of inheritance of FIS showed marginally significant results on chromosome 15q25-26 (P < 0.05). The overall distribution of the alleles was consistent with previously reported literature; no evidence of association and marginal significance of linkage was found between the polymorphism and FIS or the degree of lateral curvature. Despite the negative association reported here, further investigation of the gene and its potential association to FIS is required.

Animal Models of Kennedy Disease

Since the identification of the polyglutamine repeat expansion responsible for Kennedy disease (KD) more than a decade ago, several laboratories have created animal models for KD. The slowly progressive nature of KD, its X-linked dominant mode of inheritance, and its recently elucidated hormone dependence have made the modeling of this lower motor neuron disease uniquely challenging. Several models have been generated in which variations in specificity, age of onset, and rate of progression have been achieved. Animal models that precisely reproduce the motor neuron specificity, delayed onset, and slow progression of disease may not support preclinical therapeutics testing, whereas models with rapidly progressing symptoms may preclude the ability to fully elucidate pathogenic pathways. Drosophila models of KD provide unique opportunities to use the power of genetics to identify pathogenic pathways at work in KD. This paper reviews the new wealth of transgenic mouse and Drosophila models for KD. Whereas differences, primarily in neuropathological findings, exist in these models, these differences may be exploited to begin to elucidate the most relevant pathological features of KD.

Is Synaesthesia an X-Linked Dominant Trait with Lethality in Males?

In previous research the inheritance patterns of synaesthesia (eg experiencing colours from graphemes) has been studied and it was concluded that synaesthesia is most likely to be the outcome of a single gene passed on the X chromosome in a dominant fashion. In addition, it has been reported that the female-male ratio of synaesthetes is as high as 6:1 and the families of synaesthetes contain more female than male members. This raises the possibility that the gene may be associated with lethality in males. In this study we replicate and extend previous research by investigating the female-male ratio and inheritance patterns in a large sample of synaesthetic families (N = 85). We were able to verify the authenticity of grapheme-colour associates in at least one proband from each family using internal consistency. As before, our results show a female-male bias and are broadly consistent with an X-linked dominant mode of inheritance. However, there was no evidence of male lethality (eg synaesthetes are just as likely to give birth to sons as to daughters). Moreover, our female-male ratio of synaesthetes within families was 2:1--considerably lower than previous estimates. We speculate that men may be more reluctant to disclose synaesthesia than women (indeed, our female-male ratio based on self-referral was 3.7: 1). Finally, we discuss how the genotype may give rise to the phenotype in terms of changes in synaptogenesis or plasticity extending into childhood, to be subsequently shaped by the environment.

Syndrome of short stature, widow's peak, ptosis, posteriorly angulated ears, and joint problems: exclusion of the Aarskog (FGD1) gene as a candidate gene.

A syndrome encompassing postnatal onset of short stature, widow's peak, ptosis, posteriorly angulated ears, and limitation of forearm supination is reported in a boy and his mother. The boy has not yet experienced dislocation of patella or other joint anomaly except for limitation of supination of the forearms. On the other hand, the mother has a milder limitation of supination only on the left arm and is devoid of ptosis. Their condition is reminiscent of that described in the family reported by Kapur et al. [1989: Am. J. Med. Genet. 33: 357-363.], which showed an X-linked dominant mode of inheritance. DNA study on our family using an intragenic polymorphism of the Aarskog syndrome (FGD1) gene and four other adjacent markers convincingly excludes the possibility that their condition could be caused by a mutation of the FGD1 gene. Our family and the family reported by Kapur et al. may suggest segregation of a novel X-linked dominant condition.

A family with X-linked dominant Charcot–Marie–Tooth caused by a connexin32 mutation

A family with a hereditary peripheral neuropathy is presented. Pedigree analysis suggested X-linked dominant mode of inheritance. The index patient became symptomatic at the age of 12 years. Clinical examination at 14 years revealed footdrop on the left, bilateral pes cavus, slight atrophy of thenar eminences, decreased muscle strength in both legs and brisk deep tendon reflexes. Electrophysiological studies were compatible with an axonal neuropathy. A novel point mutation located in codon 126 of the connexin32 gene, substituting a histidine for a tyrosine, was found in the index patient, in the mother, in two sisters and in a brother. The mother and the eldest sister had pes cavus bilaterally although they were asymptomatic. The younger brother and sister showed no signs of the disease.

Hereditary angioedema with normal C1-inhibitor activity in women

Hereditary angioedema (HAE) is a well defined autosomal dominant disease (Mendelian Inheritance in Man #106100) that results from an inherited deficiency of C1 (the activated first component of complement) inhibitor function. We report an unusual variant of HAE with normal biochemical C1-inhibitor function, occurring only in women. We screened 574 patients with recurrent angioedema of the skin for presence of HAE. 283 patients were selected, in whom angioedema was associated with abdominal pain attacks or recurrent life-threatening episodes of upper-airway obstruction, or both, rather than with urticaria. We measured C1-inhibitor concentration and functional activity as well as complement C4 concentration and took pedigrees to characterise patients. 94 HAE cases with C1-inhibitor deficiency, positive family history, or both were identified. Biochemical testing showed that 84 patients from 49 families had a functional C1-inhibitor deficiency. 11 of these patients had no affected family members (probably representing de-novo mutations). Ten women with HAE, from ten families, had normal C1-inhibitor protein concentrations and function, and normal C4 concentration. A more detailed study of these families identified another 26 affected members, who were also all women. Of those women, 14 could be studied and also had normal C1-inhibitor concentration and function. The disease was seen in successive generations, and in offspring of affected mothers, the sex ratio (M/F) was shifted to 1/1.5. HAE with normal C1-inhibitor concentration and function represents a unique genetic disease arising only in women. The formal genetics of this entity are suggestive of an X-linked dominant mode of inheritance. For this disorder we propose the term hereditary angioedema type 3 (HAE III).

The Bazex-Dupré-Christol Syndrome

The Bazex-Dupré-Christol syndrome is characterized by follicular atrophoderma, congenital hypotrichosis, and basal cell neoformations that include basal cell carcinomas and basal cell nevi. We describe a large family in which 20 persons across four generations present with typical features of the Bazex-Dupré-Christol syndrome. However, the clinical picture in this family differs with regard to gender and age. Male subjects have a uniformly severe disease, whereas female subjects exhibit a range of severity of the syndrome. The most striking difference between male and female subjects is provided by hypotrichosis. In male subjects, hypotrichosis is diffuse and affects all scalp hairs. On the other hand, female subjects do not have hypotrichosis, but normal hairs are intermingled with abnormal hairs. In infancy and childhood, multiple milia are present, whereas in adults only a few milia are observed. The family pedigree seems to be consistent with an X-linked inheritance, since male-to-male transmission does not occur. Moreover, further evidence of an X-linked dominant mode of inheritance could be derived from the observation of gender differences that can be attributed to the lyonization phenomenon in female subjects. From a clinical and morphologic point of view, the Bazex-Dupré-Christol syndrome seems to be a disorder of the hair follicle.

A critical analysis of data presented in eight studies favouring X-linkage of bipolar illness with special emphasis on formal genetic aspects.

High lod scores were obtained in several X-linkage studies of bipolar illness under the assumption that a subgroup of manic depression follows an X-linked dominant mode of inheritance. We have previously shown that the segregation patterns do not substantiate this assumption. We now statistically address the lack of evidence for X-linked inheritance by sex-dependently analyzing segregation ratios and clinical data presented in eight positive X-linkage studies. Accordingly, affected males have significantly fewer offspring, a lower mean age and a higher bipolar to unipolar ratio than affected females. There are two possible explanations for these findings: either the X-linked subgroup of bipolar illness has unique features that have not been accounted for clinically, or (more probably) the pedigree structures could also (and might be more likely to) result from ascertaining kindreds following autosomal or multifactorial inheritance only, with exclusion of kindreds encompassing male to male transmission.

A critical appraisal of X-linked bipolar illness. Evidence for the assumed mode of inheritance is lacking.

The major assumption underlying all X-linkage studies of bipolar disorder has been that a subgroup of manic-depressive illness follows an X-linked dominant mode of inheritance. An evaluation of the segregation patterns in the pedigrees that have been analysed for X-linkage over the past 20 years does not support this assumption, because the formal genetic criteria for an X-linked dominant mode of inheritance are virtually absent. Not a single pedigree has been ascertained in which the segregation pattern is suggestive of the assumed mode of inheritance. This is mainly because segregation ratios characteristic for X-linked dominant inheritance cannot be observed among the offspring of affected males.

Absence of Goodpasture's Antigen in Male Patients With Familial Nephritis

The presence of Goodpasture's (GP) antigen in the glomerular basement membrane (GBM) of the kidney was evaluated by indirect immunofluorescence in nine patients with familial nephritis from five kindreds. The GP antigen was not detected in seven males but was present in an affected sister and mother, an unaffected brother, and 13 normal controls. The specificity of this finding in affected males is supported by the persistence of other GBM antigens identified by monoclonal antibodies. The lack of GP antigen in affected males and its persistence in related females with the disease suggests a possible X-linked dominant mode of inheritance. We propose that the absence of GP antigen leads to severe disease in the male, whereas its presence in related females is associated with mild disease.

Orofaciodigital syndrome, Type I: A phenotypic and genetic analysis

An additional family with the orofaciodigital syndrome, Type I, is presented. On the basis of previously published pedigrees, as well as the present case, data are presented that conclusively support an X-linked dominant mode of inheritance. Segregation analysis demonstrated that not only is there lethality in the male but there is significant lethality in the female due to lyonization. In addition, a review of the familial cases will demonstrate a large degree of intra- and interfamilial variation.

An inherited X-linked serum system in man; the Xm system.

The detection of an inherited X-linked serum system in man, disclosed by a heteroantisenim made specific by absorption, is described. These studies suggest that the antigen, demonstrated by the specific antiserum, resides in the alpha(2)-macroglobulin fraction of serum. The system has been named the Xm system, where X refers to the localization of the gene on the X chromosome, and the m indicates that the antigen is part of the alpha(2)-macroglobulin fraction. The distribution of phenotypes in unrelated individuals from 4 populations, as well as studies performed in families are consistent with an X-linked dominant mode of inheritance. One Xm(a-) daughter was found in a family where the father was Xm(a+). This finding is discussed with particular reference to the possible influence of sex and age on the development of the phenotype. This common X-linked marker is likely to prove useful in mapping the human X chromosome.