Phenotype in 18 Danish subjects with genetically verified CHARGE syndrome.

CHARGE (coloboma of the eye, heart defects, choanal atresia, retarded growth and development, genital hypoplasia and ear anomalies and/or hearing loss) syndrome is a rare genetic, multiple-malformation syndrome. About 80% of patients with a clinical diagnose, have a mutation or a deletion in the gene encoding chromodomain helicase DNA-binding protein 7 (CHD7). Genotype-phenotype correlation is only partly known. In this nationwide study, phenotypic characteristics of 18 Danish CHD7 mutation positive CHARGE individuals (N = 18) are presented. We studied patient records, clinical photographs, computed tomography, and magnetic resonance imaging (MRI). Information was not available for all traits in all subjects. Therefore, the results are presented as fractions. The following prevalence of cardinal symptoms were found: coloboma, 16/17; heart defects, 14/18; choanal atresia, 7/17; retarded growth and development, 11/13; genital abnormalities, 5/18; ear anomalies, 15/17 and sensorineural hearing loss, 14/15. Vestibular dysfunction (10/13) and swallowing problems (12/15) were other frequent cranial nerve dysfunctions. Three-dimensional reconstructions of MRI scans showed temporal bone abnormalities in >85%. CHARGE syndrome present a broad phenotypic spectrum, although some clinical features are more frequently occurring than others. Here, we suggest that genetic testing for CHD7 mutation should be considered in neonates with a specific combination of several clinical symptoms.

A novel X-linked gene, DDP, shows mutations in families with deafness (DFN-1), dystonia, mental deficiency and blindness.

In 1960, progressive sensorineural deafness (McKusick 304,700, DFN-1) was shown to be X-linked based on a description of a large Norwegian pedigree. More recently, it was shown that this original DFN-1 family represented a new type of recessive neurodegenerative syndrome characterized by postlingual progressive sensorineural deafness as the first presenting symptom in early childhood, followed by progressive dystonia, spasticity, dysphagia, mental deterioration, paranoia and cortical blindness. This new disorder, termed Mohr-Tranebjaerg syndrome (referred to here as DFN-1/MTS) was mapped to the Xq21.3-Xq22 region2. Using positional information from a patient with a 21-kb deletion in chromosome Xq22 and sensorineural deafness along with dystonia, we characterized a novel transcript lying within the deletion as a candidate for this complex syndrome. We now report small deletions in this candidate gene in the original DFN-1/MTS family, and in a family with deafness, dystonia and mental deficiency but not blindness. This gene, named DDP (deafness/ dystonia peptide), shows high levels of expression in fetal and adult brain. The DDP protein demonstrates striking similarity to a predicted Schizosaccharomyces pombe protein of no known function. Thus, is it likely that the DDP gene encodes an evolutionarily conserved novel polypeptide necessary for normal human neurological development.

Myotonia congenita and myotonic dystrophy in the same family: coexistence of a CLCN1 mutation and expansion in the CNBP (ZNF9) gene.

Myotonia is characterized by hyperexcitability of the muscle cell membrane. Myotonic disorders are divided into two main categories: non-dystrophic and dystrophic myotonias. The non-dystrophic myotonias involve solely the muscle system, whereas the dystrophic myotonias are characterized by multisystem involvement and additional muscle weakness. Each category is further subdivided into different groups according to additional clinical features or/and underlying genetic defects. However, the phenotypes and the pathological mechanisms of these myotonic disorders are still not entirely understood. Currently, four genes are identified to be involved in myotonia: the muscle voltage-gated sodium and chloride channel genes SCN4A and CLCN1, the myotonic dystrophy protein kinase (DMPK) gene, and the CCHC-type zinc finger, nucleic acid binding protein gene CNBP. Additional gene(s) and/or modifying factor(s) remain to be identified. In this study, we investigated a large Norwegian family with clinically different presentations of myotonic disorders. Molecular analysis revealed CCTG repeat expansions in the CNBP gene in all affected members, confirming that they have myotonic dystrophy type 2. However, a CLCN1 mutation c.1238C>G, causing p.Phe413Cys, was also identified in several affected family members. Heterozygosity for p.Phe413Cys seems to exaggerate the severity of myotonia and thereby, to some degree, contributing to the pronounced variability in the myotonic phenotype in this family.

A novel mutation in the connexin 26 gene (GJB2) in a child with clinical and histological features of keratitis-ichthyosis-deafness (KID) syndrome.

BACKGROUND: Keratitis-ichthyosis-deafness (KID) syndrome is a rare congenital ectodermal disorder, caused by heterozygous missense mutation in GJB2, encoding the gap junction protein connexin 26. The commonest mutation is the p.Asp50Asn mutation, and only a few other mutations have been described to date. AIM: To report the fatal clinical course and characterize the genetic background of a premature male neonate with the clinical and histological features of KID syndrome. METHODS: Genomic DNA was extracted from peripheral blood and used for PCR amplification of the GJB2 gene. Direct sequencing was used for mutation analysis. RESULTS: The clinical features included hearing impairment, ichthyosiform erythroderma with hyperkeratotic plaques, palmoplantar keratoderma, alopecia of the scalp and eyelashes, and a thick vernix caseosa-like covering of the scalp. On histological analysis, features characteristic of KID syndrome, such as acanthosis and papillomatosis of the epidermis with basket-weave hyperkeratosis, were seen. The skin symptoms were treated successfully with acitretin 0.5 mg/kg. The boy developed intraventricular and intracerebral haemorrhage, leading to hydrocephalus. His condition was further complicated by septicaemia and meningitis caused by infection with extended-spectrum beta-lactamase-producing Klebsiella pneumoniae. Severe respiratory failure followed, and the child died at 46 weeks of gestational age (13 weeks postnatally). Sequencing of the GJB2 gene showed that the child was heterozygous for a novel nucleotide change, c.263C>T, in exon 2, leading to a substitution of alanine for valine at position 88 (p.Ala88Val). CONCLUSIONS: This study has identified a new heterozygous de novo mutation in the Cx26 gene (c.263C>T; p.Ala88Val) leading to KID syndrome.

Autosomal dominant optic atrophy associated with hearing impairment and impaired glucose regulation caused by a missense mutation in the WFS1 gene.

Autosomal dominant optic atrophy (ADOA) is genetically heterogeneous, with OPA1 on 3q28 being the most prevalently mutated gene. Additional loci are OPA3, OPA4, and OPA5, located at 19q13.2, 18q12.2, and 22q12.1-q13.1, respectively. Mutations in the WFS1 gene, at 4p16.3, are associated with either optic atrophy (OA) as part of the autosomal recessive Wolfram syndrome or with autosomal dominant progressive low frequency sensorineural hearing loss (LFSNHL) without any ophthalmological abnormalities. Linkage and sequence mutation analyses of the ADOA candidate genes OPA1, OPA3, OPA4, and OPA5, including the genes WFS1, GJB2, and GJB6 associated with recessive inherited OA or dominant LFSNHL, were performed. We identified one novel WFS1 missense mutation E864K, c.2590G-->A in exon 8 that co-segregates with ADOA combined with hearing impairment and impaired glucose regulation. This is the first example of autosomal dominant optic atrophy and hearing loss associated with a WFS1 mutation, supporting the notion that mutations in WFS1 as well as in OPA1 may lead to ADOA combined with impaired hearing.

A spectrum of functional effects for disease causing mutations in the Jervell and Lange-Nielsen syndrome.

OBJECTIVE: Jervell and Lange-Nielsen syndrome (JLNS) is a recessively inherited long QT syndrome (LQTS) characterised by profound sensorineural deafness and predisposition to syncope and sudden cardiac death. Mutation analysis has established the presence of mutations in affected individuals in the genes KCNQ1 and KCNE1: the potassium channel complex responsible for the cardiac I(Ks) current involved in repolarisation of the ventricular action potential. Our objective was to determine the functional effects of disease causing mutations in JLNS. METHODS: In this study we have investigated the electrophysiological effects of eight distinct JLNS mutations after expression of cRNA in Xenopus laevis oocytes. RESULTS: KCNE1 mutant T59P/L60P showed no dominant negative effect and was a pure loss of function mutation. KCNQ1 mutant E261D showed a strong dominant-negative effect. KCNQ1 mutant R243H produced a moderate dominant-negative effect, right shifted the steady-state activation curve and led to an increased deactivation rate. The behaviour of KCNQ1 mutants 572-576del, 1008delC, R518X, Q530X, R594Q depended on the relative quantities of mutant and wild-type proteins (with a weak dominant-negative effect present at 1:3 but not 1:1 injection ratios). These data indicate the presence of an additional assembly domain before S2-S3 and the importance of the S4-S5 region in channel function and gating. CONCLUSIONS: Our data suggest a spectrum of behaviour for disease causing mutations from simple loss of function through to prominent dominant negative behaviour.

Mutation analysis of the MEN1 gene in multiple endocrine neoplasia type 1, familial acromegaly and familial isolated hyperparathyroidism.

Multiple endocrine neoplasia type 1 (MEN 1) is an autosomal dominant disease characterized by neoplasia of the parathyroid glands, the endocrine pancreas, and the anterior pituitary gland. In addition, families with isolated endocrine neoplasia, notably familial isolated hyperparathyroidism (FIHP) and familial acromegaly, have also been reported. However, whether these families constitute MEN 1 variants or separate entities remains speculative as the genetic bases for these diseases are unclear. The gene for MEN 1 has recently been cloned and characterized. Using single strand conformation analysis (SSCA) and sequencing, we performed mutation analysis in: a) a total of 55 MEN 1 families from 7 countries, b) 13 isolated MEN 1 cases without family history of the disease, c) 8 acromegaly families, and d) 4 FIHP families. Mutations were identified in 27 MEN 1 families and 9 isolated cases. The 22 different mutations spread across most of the 9 translated exons and included frameshift (11), nonsense (6), splice (2), missense mutations (2), and in-frame deletions (1). Among the 19 Finnish MEN 1 probands, a 1466del12 mutation was identified in 6 families with identical 11q13 haplotypes and in 2 isolated cases indicating a common founder. One frameshift mutation caused by 359del4 (GTCT) was found in 1 isolated case and 4 kindreds of different origin and haplotypes; this mutation therefore represents a common "warm" spot in the MEN1 gene. By analyzing the DNA of the parents of an isolated case one mutation was confirmed to be de novo. No mutation was found in any of the acromegaly and small FIHP families, suggesting that genetic defects other than the MEN1 gene might be involved and that additional such families need to be analyzed.

Spectrum of CLCN1 mutations in patients with myotonia congenita in Northern Scandinavia.

Myotonia congenita is a non-dystrophic muscle disorder affecting the excitability of the skeletal muscle membrane. It can be inherited either as an autosomal dominant (Thomsen's myotonia) or an autosomal recessive (Becker's myotonia) trait. Both types are characterised by myotonia (muscle stiffness) and muscular hypertrophy, and are caused by mutations in the muscle chloride channel gene, CLCN1. At least 50 different CLCN1 mutations have been described worldwide, but in many studies only about half of the patients showed mutations in CLCN1. Limitations in the mutation detection methods and genetic heterogeneity might be explanations. In the current study, we sequenced the entire CLCN1 gene in 15 Northern Norwegian and three Northern Swedish MC families. Our data show a high prevalence of myotonia congenita in Northern Norway similar to Northern Finland, but with a much higher degree of mutation heterogeneity. In total, eight different mutations and three polymorphisms (T87T, D718D, and P727L) were detected. Three mutations (F287S, A331T, and 2284+5C>T) were novel while the others (IVS1+3A>T, 979G>A, F413C, A531V, and R894X) have been reported previously. The mutations F413C, A531V, and R894X predominated in our patient material. Compound heterozygosity for A531V/R894X was the predominant genotype. In two probands, three mutations cosegregated with myotonia. No CLCN1 mutations were identified in two families. Our data support the presence of genetic heterogeneity and additional modifying factors in myotonia congenita.

Identification of novel USH2A mutations: implications for the structure of USH2A protein.

Usher syndrome type II is an autosomal recessive disorder, characterised by stable hearing impairment from childhood and progressive retinitis pigmentosa from the late teens. Mutations in the USH2A gene, located on 1q41, were recently shown to be responsible for Usher syndrome type IIa. We have investigated the molecular pathology of Usher type II by screening the USH2A gene for mutations in 31 unrelated patients from Denmark and Norway. Besides the frequent 2299delG mutation, which accounted for 44% of the disease alleles, a heterogeneous spectrum of mutations was identified. Sixteen new, putative disease-causing mutations were detected, of which 12 were private and four were shared by unrelated patients. The disease-causing mutations were scattered throughout the gene and included six nonsense and seven missense mutations, two deletions and one small insertion. In addition, six non-pathogenic polymorphisms were identified. All missense mutations resulted in major amino acid side-chain alterations. Four missense mutations affected the N-terminal part of USH2A, whereas three missense mutations affected the laminin-type epidermal growth factor-like (LE) domain. The structural consequences of the mutations affecting the LE domain are discussed in relation to the three-dimensional structure of a LE-module of the mouse laminin gamma1 chain.

A de novo missense mutation in a critical domain of the X-linked DDP gene causes the typical deafness-dystonia-optic atrophy syndrome.

We report the first de novo mutation in the DDP gene in a Dutch 11-year-old boy with deafness and dystonia. Previously reported mutations in the DDP gene have all been frameshifts/nonsense mutations or deletion of the entire gene as part of a larger deletion encompassing the BTK gene. The clinical presentation was uniformly characterised by sensorineural hearing loss, dystonia, mental deterioration, paranoid psychotic features, and optic atrophy, indicating progressive neurodegeneration. Our report illustrates that de novo mutations occur and that a missense mutation, C66W, may cause an equally severe clinical picture. The diagnosis of sensorineural hearing impairment associated with neurologic and visual disability in a male, therefore, should encourage the search for mutations in the DDP gene, even in sporadic cases. The association of deafness-dystonia syndrome with a missense mutation provides valuable information for in vitro investigations of the functional properties of the deafness-dystonia peptide which was recently shown to be the human homolog of a yeast protein, Tim8p, belonging to a family of small Tim proteins involved in intermembrane protein transport in mitochondria.

Analysis of FMR1 (CGG)(n) alleles and DXS548-FRAXAC1 haplotypes in three European circumpolar populations: traces of genetic relationship with Asia.

Fragile X syndrome, the most common form of inherited mental retardation, is caused by expansion of a (CGG)(n) repeat located in the FMR1 gene. The molecular factors involved in the mutation process from stable (CGG)(n) alleles towards unstable alleles are largely unknown, although family transmission studies and population studies have suggested that loss of AGG interruptions in the (CGG)(n) repeat is essential. We have analysed the AGG interspersion pattern of the FMR1 (CGG)(n) repeat and the haplotype distribution of closely located microsatellite markers DXS548 and FRAXAC1, in three circumarctic populations: Norwegians, Nenets and Saami. The data confirm the conservation, reported in all human populations studied so far, of an AGG interruption for each 9-10 CGG and support the stabilising effect of AGG interruptions. The data also indicate the existence of chromosomes of Asian origin in the Saami and Nenets population, thereby confirming a genetic relationship between Northern Europe and Asia. DXS548-FRAXAC1 haplotype frequencies were compared between 24 Norwegian fragile X males and 119 normal males. Significant linkage disequilibrium were found between the fragile X mutation and haplotype 6-4 and between normal (CGG)(n) alleles and haplotype 7-3.

Founder effect in spinal and bulbar muscular atrophy (SBMA) in Scandinavia.

We haplotyped 13 Finnish, 10 Swedish, 12 Danish and 2 Norwegian SBMA (spinal and bulbar muscular atrophy, Kennedy disease) families with a total of 45 patients and 7 carriers for 17 microsatellite markers spanning a 25.2 cM region around the androgen receptor gene on chromosome Xq11-q12 in search of a genetic founder effect. In addition, the haplotypes of 50 Finnish, 20 Danish and 22 Swedish control males were examined. All the Scandinavian SBMA families shared the same 18 repeat allele for the intragenic GGC repeat, which was present in only 24% of the controls. Linkage disequilibrium was also seen for the closest microsatellite markers. In addition, extended haplotypes of the Finnish, Swedish and Danish SBMA families revealed country-specific common founder haplotypes, which over time became gradually shortened by recombinations. No common haplotype was found among the controls. The data suggest that the SBMA mutation was introduced into western Finland 20 generations ago. Haplotype analysis implies a common ancestor for the majority of Scandinavian SBMA patients.

Multiple founder effects in spinal and bulbar muscular atrophy (SBMA, Kennedy disease) around the world.

SBMA (spinal and bulbar muscular atrophy), also called Kennedy disease, is an X-chromosomal recessive adult-onset neurodegenerative disorder caused by death of the spinal and bulbar motor neurones and dorsal root ganglia. Patients may also show signs of partial androgen insensitivity. SBMA is caused by a CAG repeat expansion in the first exon of the androgen receptor (AR) gene on the X-chromosome. Our previous study suggested that all the Nordic patients with SBMA originated from an ancient Nordic founder mutation, but the new intragenic SNP marker ARd12 revealed that the Danish patients derive their disease chromosome from another ancestor. In search of relationships between patients from different countries, we haplotyped altogether 123 SBMA families from different parts of the world for two intragenic markers and 16 microsatellites spanning 25 cM around the AR gene. The fact that different SBMA founder haplotypes were found in patients from around the world implies that the CAG repeat expansion mutation has not been a unique event. No expansion-prone haplotype could be detected. Trinucleotide diseases often show correlation between the repeat length and the severity and earlier onset of the disease. The longer the repeat, the more severe the symptoms are and the onset of the disease is earlier. A negative correlation between the CAG repeat length and the age of onset was found in the 95 SBMA patients with defined ages at onset.

Mutation spectrum in patients with Wiskott-Aldrich syndrome and X-linked thrombocytopenia: identification of twelve different mutations in the WASP gene.

Twelve different mutations in the WASP gene were found in twelve unrelated families with Wiskott-Aldrich syndrome (WAS) or X-linked thrombocytopenia (XLT). Four frameshift, one splice, one nonsense mutation, and one 18-base-pair deletion were detected in seven patients with WAS. Only missense mutations were found in five patients diagnosed as having XLT. One of the nucleotide substitutions in exon 2 (codon 86) results in an Arg to Cys replacement. Two other nucleotide substitutions in this codon, R86L and R86H, have been reported previously, both giving rise to typical WAS symptoms, indicating a mutational hot spot in this codon. The finding of mutations in the WASP gene in both WAS and XLT gives further evidence of these syndromes being allelic. The relatively small size of the WASP gene facilitates the detection of mutations and a reliable diagnosis of both carriers and affected fetuses in families with WAS or XLT.

Prevalence of fra(X) and other specific diagnoses in autistic individuals in a Danish county.

In a Danish county (the island of Funen) cytogenetic screening for fragile X [fra(X)] of 32 autistic individuals aged 0-23 years showed a prevalence of 2/20 among boys and 0/12 among girls. In both cases additional fra(X) positive relatives were found. In 3 patients other chromosome aberrations were demonstrated and in one female Rett syndrome was diagnosed, initially suspected from observations of her behavior on videotapes. The presence of an underlying cause of autism in 6/32, of the patient group encourages an active search for a specific diagnosis among autistic males and females. Future screening of autistic individuals should include 1) fra(X) search also in females, 2) search for other chromosomal disorders, and 3) observation of behavior, in order to diagnose, i.e., Rett syndrome.

New X-linked syndrome with apraxia, ataxia, and mental deficiency: clinical, cytogenetic and neuropsychological studies in two Danish families.

In 2 unrelated families 9 males presented with ataxia, apraxia, and neuropsychological abnormalities or mental deficiency, inherited as an X-linked recessive syndrome with partial clinical expression in obligate female carriers. The symptoms were present in early childhood and were non-progressive. Additional findings in 2 males were congenital "club-feet" and generalized seizures. The affected males were 13-62 years old at the time of our examination. Chromosome abnormalities including fragile X fra(X) could not be demonstrated in any case. Results of metabolic screenings were also normal. The clinical picture with X-linked recessive inheritance distinguishes this syndrome from previously described inherited hereditary ataxias.

X-linked mental retardation associated with psoriasis: a new syndrome?

Four males, the sons of 2 sisters, apparently have a new syndrome of mental retardation, seizures and psoriasis. Due to the relationship between the affected males we propose the inheritance to be X-linked recessive although cosegregation of two separate disorders may be occurring. Psoriasis has never been reported as a monogenic disorder. Results of cytogenetic studies, including fra (X) and high-resolution prometaphase analysis, were negative. Steroid sulfatase activities of cultured fibroblasts from 2 surviving affected males were normal. The results of HLA typing of all available relatives did not indicate a strong association between the skin disorder and certain HLA antigens. A healthy sister, who may be heterozygous carrier of the mutant X chromosome, decided on termination of 3 successive pregnancies after prenatal male sex determinations. Her fourth pregnancy with a female fetus is ongoing.

Deletion mapping of a retinal cone-rod dystrophy: assignment to 18q211.

Deletion of 18q211 was observed in a mentally retarded young man with electrophysiologically demonstrated cone-rod dystrophy, present since childhood. He had hypogonadism and a central postsynaptic hearing impairment. This is the first case of a chromosome deletion in a patient with a cone-rod dystrophy. Three patients with more distal deletions on chromosome 18 did not present retinal dystrophies. We suggest that one of the loci for cone-rod dystrophy may be located on chromosome 18 at q211-213. Reports of similar findings will be necessary for confirmation of this assumption.

Interstitial deletion 13q: further delineation of the syndrome by clinical and high-resolution chromosome analysis of five patients.

Five patients with interstitial deletion 13q are reported. High-resolution chromosome banding established the diagnosis in two cases and stated the exact breakpoints in three remaining cases. All parents had normal chromosomes. An unequal and so far unexplained sex ratio of previously published and present cases was found: M:F = 1:2.75. Moderate to severe growth retardation was prominent in all patients. The patients were followed with psychological tests and growth data for 3-10 years. Mild to moderate mental retardation was present. Considerable phenotypic similarities were found in two patients with del(13)(q21.33 q31.3) and one with del(13)(q14.3q22.3). Repeat ophthalmological examinations showed no evidence of retinoblastoma in a male with del(13)(q13.1q21.1). In conclusion, the long-term study of five patients with interstitial deletion 13q, all evaluated with high-resolution banding, contributed to a more reliable mental and growth prognosis in such patients.