Improved genetic mapping of X linked retinoschisis.

X linked retinoschisis (RS) causes poor vision in affected males owing to radial cystic changes at the macula. Genetic linkage analysis was carried out in 16 British families with X linked retinoschisis using markers from the Xp22 region. Linkage was confirmed between the RS locus and the markers DXS207 (lod score, Zmax = 17.9 at recombination fraction theta = 0.03; confidence interval for theta = 0.007-0.09), DXS1053 (Zmax = 18.0 at theta = 0.01, CI = 0.001-0.06), DXS43 (Zmax = 12.9 at theta = 0.03, CI = 0.004-0.09), DXS1195 (Zmax = 6.4 at theta = 0.00), DXS418 (Zmax = 8.2 at theta = 0.00), DXS999 (Zmax = 21.2 at theta = 0.01, CI = 0.001-0.05), DXS443 (Zmax = 14.2 at theta = 0.03, CI = 0.004-0.09), DXS365 (Zmax = 24.5 at theta = 0.008, CI = 0.001-0.04). Key recombinants placed RS between DXS43 distally and DXS999 proximally. Multipoint linkage analysis gave odds of 344:1 in favour of this location for RS and supported the map Xpter-(DXS207, DXS1053)-DXS43-1 cM-RS-1 cM-DXS999-DXS443-DXS365-DXS1052-Xcen.     

X染色体异常的临床与遗传学分析

目的探讨X染色体异常的临床特征并分析其产生的可能原因。方法对5268例生殖异常患者通过取外周血淋巴细胞培养,显带进行染色体核型分析。结果检出X染色体异常79例,占被检患者的1.49%。其中X染色体数目异常64例,占异常核型81.0%。X染色体数目异常嵌合体7例,占异常核型8.9%。X染色体结构异常5例,占异常核型的6.3%。X染色体结构异常及嵌合体3例,占异常核型的3.8%。结论 X染色体异常可导致性发育异常或生殖异常等遗传效应,在遗传咨询中应引起足够的重视,对临床诊治工作有重要意义。     

Extensive germinal mosaicism in a family with X linked myotubular myopathy simulates genetic heterogeneity.

A family with two male cousins affected with myotubular myopathy (MTM) was referred to us for genetic counselling. Linkage analysis appeared to exclude the Xq28 region. As a gene for X linked MTM was recently identified in Xq28, we screened the obligatory carrier mothers for mutation. We found a 4 bp deletion in exon 4 of the MTM1 gene, which originated from the grandfather of the affected children and which was transmitted to three daughters. This illustrates the importance of mutation detection to avoid pitfalls in linkage analysis that may be caused by such cases of germinal mosaicism.     

Characterisation and genetic mapping of a new X linked deafness syndrome

BACKGROUND—Hereditary forms of hearing loss are classified as syndromic, when deafness is associated with other clinical features, or non-syndromic, when deafness occurs without other clinical features. Many types of syndromic deafness have been described, some of which have been mapped to specific chromosomal regions.
METHODS—Here we describe a family with progressive sensorineural hearing loss, cognitive impairment, facial dysmorphism, and variable other features, transmitted by apparent X linked recessive inheritance. Haplotype analysis of PCR products spanning the X chromosome and direct sequencing of candidate genes were used to begin characterising the molecular basis of features transmitted in this family. Comparison to known syndromes involving deafness, mental retardation, facial dysmorphism, and other clinical features was performed by review of published reports and personal discussions.
RESULTS—Genetic mapping places the candidate locus for this syndrome within a 48 cM region on Xq1-21. Candidate genes including COL4A5, DIAPH, and POU3F4 were excluded by clinical and molecular analyses.
CONCLUSIONS—The constellation of clinical findings in this family (deafness, cognitive impairment, facial dysmorphism, variable renal and genitourinary abnormalities, and late onset pancytopenia), along with a shared haplotype on Xq1-21, suggests that this represents a new form of syndromic deafness. We discuss our findings in comparison to several other syndromic and non-syndromic deafness loci that have been mapped to the X chromosome.


     

X linked mental retardation: a clinical guide

Mental retardation is more common in males than females in the population, assumed to be due to mutations on the X chromosome. The prevalence of the 24 genes identified to date is low and less common than expansions in FMR1, which cause Fragile X syndrome. Systematic screening of all other X linked genes in X linked families with mental retardation is currently not feasible in a clinical setting. The phenotypes of genes causing syndromic and non‐syndromic mental retardation (NLGN3, NLGN4, RPS6KA3(RSK2), OPHN1, ATRX, SLC6A8, ARX, SYN1, AGTR2, MECP2, PQBP1, SMCX, and SLC16A2) are first discussed, as these may be the focus of more targeted mutation analysis. Secondly, the relative prevalence of genes causing only non‐syndromic mental retardation (IL1RAPL1, TM4SF2, ZNF41, FTSJ1, DLG3, FACL4, PAK3, ARHGEF6, FMR2, and GDI) is summarised. Thirdly, the problem of recurrence risk where a molecular genetics diagnosis has not been made and what proportion of the male excess of mental retardation is due to monogenic disorders of the X chromosome are discussed.     

Possible genetic heterogeneity in X linked hypohidrotic ectodermal dysplasia.

Hypohidrotic ectodermal dysplasia has been mapped to Xq11-q13 by linkage studies and by a translocation in a manifesting female. We report a family with hypohidrotic ectodermal dysplasia in which the disease did not segregate with this region of the X chromosome as expected. Ten DNA probes which are localised between Xp11 and Xq22 were used in the investigation. The difficulties in diagnosing the carrier state in this condition and the possibility of non-allelic heterogeneity are discussed.     

The X linked recessive form of XY gonadal dysgenesis with a high incidence of gonadal germ cell tumours: clinical and genetic studies.

Five phenotypic females in one family had the genotype 46,XY and all had gonadal germ cell tumours. Studies of the family pedigree suggest that this form of XY gonadal dysgenesis is inherited in an X linked recessive manner. G banding of elongated metaphase chromosomes from two subjects with XY gonadal dysgenesis and a female carrier showed no aberrations of the X chromosome. The titres of H-Y antigen in three girls with XY gonadal dysgenesis were in the male control range. Thus it appears that, in the X linked form, XY gonadal dysgenesis may be caused by a point deletion or mutation of a gene on the X chromosome, which controls the gonad specific receptor for the H-Y antigen. Studies of Xg blood groups were uninformative about linkage of Xg with the X borne gene causing the XY gonadal dysgenesis. Dermatoglyphic studies in the girls with XY gonadal dysgenesis and female carriers revealed high a-b palmar ridge counts and a tendency for the A mainline to terminate in the thenar area. Both of these features have been described in patients with Turner's syndrome.     

Contribution to carrier detection and genetic counselling in X linked retinoschisis.

X linked retinoschisis (RS) is a vitreoretinal disease resulting from microcystic degeneration of the macula associated with peripheral lesions. The disease gene has already been assigned to the distal short arm of the X chromosome (Xp22.2) by linkage studies. In order to contribute both to a better localisation of the RS locus and to genetic counselling in RS families, we have carried out a clinical and genetic analysis in seven pedigrees. We show, first, that in contrast with previous reports, heterozygote carriers frequently express the disease, and display peripheral retinal alterations similar to those found in affected males. Second, while distal markers DXS16, DXS207, and DXS43 are closely linked to the disease locus, a high level of recombination events was found with centromeric markers, namely DXS274, DXS41, and DXS164. These findings must be taken into account for both carrier detection and prenatal diagnosis in X linked RS.     

Clinical, immunologic and genetic analysis of 29 patients with autosomal recessive hyper-IgM syndrome due to Activation-Induced Cytidine Deaminase deficiency

Mutations of the Activation-Induced Cytidine Deaminase (AID) gene have been found in patients with autosomal recessive hyper-IgM (HIGM) syndrome type 2. We retrospectively analyzed clinical, immunologic and genetic characteristics of 29 patients from 22 families with AID deficiency. Patients' median age at diagnosis and at last evaluation was 4.9 years (range: 0 to 53) and 14.2 years (range: 2.7 to 63), respectively. Most patients had suffered from recurrent and severe infections, however, intravenous immunoglobulin (IVIG) replacement therapy resulted in a dramatic decrease in the number of infections. Lymphoid hyperplasia developed in 22 patients and persisted in 7 at last follow-up. It is striking to note that six patients developed autoimmune or inflammatory disorders including diabetes mellitus, polyarthritis, autoimmune hepatitis, hemolytic anemia, immune thrombocytopenia, Crohn's disease and chronic uveitis. Fifteen distinct AID mutations were found but there was no significant genotype-phenotype correlation. In conclusion, AID-deficient patients are prone to infections and lymphoid hyperplasia, which may be prevented by early-onset IVIG replacement, but also to autoimmune and inflammatory disorders.     

X linked muscular dystrophy with contractures.

Another family with X linked muscular dystrophy affecting particularly the humeral and tibial muscles is described. Cardiomyopathy in the eldest male necessitated the insertion of a pacemaker.     

Next generation sequencing analysis of consecutive Russian patients with clinical suspicion of inborn errors of immunity

Primary immune deficiencies are usually attributed to genetic defects and, therefore, frequently referred to as inborn errors of immunity (IEI). We subjected the genomic DNA of 333 patients with clinical signs of IEI to next generation sequencing (NGS) analysis of 344 immunity-related genes and, in some instances, additional genetic techniques. Genetic causes of the disease were identified in 69/333 (21%) of subjects, including 11/18 (61%) of children with syndrome-associated IEIs, 45/202 (22%) of nonsyndromic patients with Jeffrey Modell Foundation (JMF) warning signs, 9/56 (16%) of subjects with periodic fever, 3/30 (10%) of cases of autoimmune cytopenia, 1/21 (5%) of patients with unusually severe infections and 0/6 (0%) of individuals with isolated elevation of IgE level. There were unusual clinical observations: twins with severe immunodeficiency carried a de novo CHARGE syndrome-associated SEMA3E c.2108C>T (p.S703L) allele; however, they lacked clinical features of CHARGE syndrome. Additionally, there were genetically proven instances of Netherton syndrome, Х-linked agammaglobulinemia, severe combined immune deficiency (SCID), IPEX and APECED syndromes, among others. Some patients carried recurrent pathogenic alleles, such as AIRE c.769C>T (p.R257*), NBN c.657del5, DCLRE1C c.103C>G (p.H35D), NLRP12 c.1054C>T (p.R352C) and c.910C>T (p.H304Y). NGS is a powerful tool for high-throughput examination of patients with malfunction of immunity.     

X linked spondyloepiphyseal dysplasia: a clinical, radiological, and molecular study of a large kindred.

X linked spondyloepiphyseal dysplasia (SEDT) is a rare disorder characterised by disproportionate short stature and degenerative changes in the spine and hips. We report a large kindred with 11 affected males and 17 obligate carrier females. We examined clinically and radiographically the seven living affected males and obtained detailed historical information on the four dead. The natural history was characterised by normal growth until late childhood. Decreased growth velocity was the earliest detectable abnormality. In adulthood, four subjects required hip replacements but disability was minimal. Clinical examinations showed a characteristic habitus with short stature (> 2 SD below the mean) and a decreased upper segment to lower segment ratio (> 1 SD below the mean) in all affected subjects. Also noted were scoliosis (6/7), and decreased range of hip rotation (6/7), and decreased range of movement of the lumbar spine (4/7). Radiographic evaluations were available on nine subjects. Radiographic changes were evident in two patients in childhood; findings in adulthood included narrow disc spaces (8/9), platyspondyly (7/9), the characteristic central and posterior hump of the vertebral bodies (6/9), bony spurs (7/ 8), and pelvic abnormalities (7/9). We also systematically evaluated eight obligate carrier females. They could not be distinguished from the general population on clinical and radiographic findings. Linkage analysis showed significant linkage with markers on Xp22, as previously reported. A recombinant event between DXS43 and DXS207 places the locus distal to DXS43.     

Non-specific X linked mental retardation with aphasia exhibiting genetic linkage to chromosomal region Xp11.

A new type of non-specific X linked mental retardation is described in a three generation family. The three affected males had severe mental retardation (IQ 20 to 30), mutism, growth failure, frequent infections, seizures, and the following minor anomalies: brachycephaly, frontal hair whorl, square face, large mouth, thick lips, and prognathism. There was not a characteristic facies. Normal laboratory studies on the proband included a karyotype with fragile X screening, skeletal survey, blood amino acid, urine organic acid, and HGPRT levels. Linkage analysis was performed with 10 X chromosome DNA probes of which probe DXS255 at chromosomal region Xp11.22 gave a maximal two point lod score of 2.10 if phase was inferred and 1.20 if it was not. Crossovers were shown with probes mapping to regions Xp22, Xp21, and Xq28. Comparison of these patients with 80 X linked causes of mental retardation, including 41 which might be classified as 'non-specific', showed no other disorders compatible with the phenotypic and linkage data.     

Clinical and genetic analysis of patients with X‐linked hyper‐IgM syndrome

Congenital adrenal hyperplasia (CAH) due to 21‐hydroxylase deficiency (21‐OHD) is a common autosomal recessive disorder caused by mutations in the CYP21A2 gene. The carrier frequency of CYP21A2 mutations has been estimated to be 1:25 to 1:10 on the basis of newborn screening. The main objective of this study was to determine the carrier frequency in the Cypriot population of mutations in the CYP21A2 gene. Three hundred unrelated subjects (150 males and 150 females) from the general population of Cyprus were screened for mutations in the CYP21A2 gene and its promoter. The CYP21A2 genotype analysis identified six different mutants and revealed a carrier frequency of 9.83% with the mild p.Val281Leu being the most frequent (4.3%), followed by p.Qln318stop (2.5%), p.Pro453Ser (1.33%), p.Val304Met (0.83%), p.Pro482Ser (0.67%) and p.Met283Val (0.17%). The notable high CYP21A2 carrier frequency of the Cypriot population is one of the highest reported so far by genotype analysis. Knowledge of the mutational spectrum of CYP21A2 will enable to optimize mutation detection strategy for genetic diagnosis of 21‐OHD not only in Cyprus, but also the greater Mediterranean region.     

Mapping a new genetic locus for X linked retinitis pigmentosa to Xq28

We have defined a new genetic locus for an X linked form of retinitis pigmentosa (RP) on chromosome Xq28. We examined 15 members of a family in which RP appeared to be transmitted in an X linked manner. Ocular examinations were performed, and fundus photographs and electroretinograms were obtained for selected patients. Blood samples were obtained from all patients and an additional seven family members who were not given examinations. Visual acuity in four affected individuals ranged from 20/40 to 20/80+. Patients described the onset of night blindness and colour vision defects in the second decade of life, with the earliest at 13 years of age. Examined affected individuals had constricted visual fields and retinal findings compatible with RP. Based on full field electroretinography, cone function was more severely reduced than rod function. Female carriers had no ocular signs or symptoms and slightly reduced cone electroretinographic responses. Affected and non‐affected family members were genotyped for 20 polymorphic markers on the X‐chromosome spaced at 10 cM intervals. Genotyping data were analysed using GeneMapper software. Genotyping and linkage analyses identified significant linkage to markers DXS8061, DXS1073, and DXS1108 with two point LOD scores of 2.06, 2.17, and 2.20, respectively. Haplotype analysis revealed segregation of the disease phenotype with markers at Xq28.     

X linked hydrocephalus and MASA syndrome.

X linked hydrocephalus and MASA syndrome are clinically related, neurological disorders with an X linked recessive mode of inheritance. Although originally described as distinct entities, their similarity has become apparent as the number of reported families has increased and a high degree of intra- and interfamilial variation in clinical signs noted for both disorders. Consideration of this clinical overlap together with finding that genes for both diseases map to the same chromosomal band (Xq28) led to the hypothesis that they were caused by mutation at the same locus. This was confirmed by identification of mutations in patients with X linked hydrocephalus and MASA syndrome within the gene for neural cell adhesion molecule L1. Here we review the clinical and genetic characteristics of these disorders and the underlying molecular defects in the L1 gene.     

A linkage study of a large pedigree with X linked centronuclear myopathy.

Centronuclear myopathy (CNM) is a muscle wasting disorder that occurs in three distinct forms. Previous studies have shown linkage between the X linked form of the disease and the Xq28 probes ST14, DX13, and F8C. Our study on a previously unreported, three generation, X linked CNM family confirms linkage between these markers and the CNM locus (Z = 3.21, theta = 00). However, results from the laboratory of J-L Mandel (Samson and Hanover, personal communication) on a number of X linked CNM families exclude genetic linkage from the region Xq26-qter, suggesting genetic heterogeneity in this condition.     

Linkage analysis of X linked retinitis pigmentosa in the Irish population.

There is significant evidence for genetic and phenotypic heterogeneity in X linked retinitis pigmentosa (XLRP). We have studied the linkage of XLRP in four Irish families to a number of polymorphic DNA markers. We report linkage between the DXS7 (L1.28) locus and the XLRP locus (Z = 3.445, theta = 0.00). Combined with the previously published data on British and Danish families, the genetic distance between the DXS7 and XLRP loci is now estimated at 5 cM with a maximum lod score of 13.026 and a 1-lod confidence interval of 0.75 to 9.5 cM. Linkage was also observed between 754 and XLRP (Z = 3.41, theta = 0.00) and between pERT87 and XLRP (Z = 1.37, theta = 0.1). The heterogeneity of XLRP is discussed in relation to these observations.