Facial dysmorphism is influenced by ethnic background of the patient and of the evaluator

The evaluation of facial dysmorphism is a critical step toward reaching a diagnostic. The aim of the present study was to evaluate the ability to interpret facial morphology in African children with intellectual disability (ID). First, 10 experienced clinicians (five from Africa and five from Europe) rated gestalt in 127 African non-Down Syndrome (non-DS) patients using either the score 2 for 'clearly dysmorphic', 0 for 'clearly non dysmorphic' or 1 for 'uncertain'. The inter-rater agreement was determined using kappa coefficient. There was only fair agreement between African and European raters (kappa-coefficient = 0.29). Second, we applied the FDNA Face2Gene solution to assess Down Syndrome (DS) faces. Initially, Face2Gene showed a better recognition rate for DS in Caucasian (80%) compared to African (36.8%). We trained the Face2Gene with a set of African DS and non-DS photographs. Interestingly, the recognition in African increased to 94.7%. Thus, training improved the sensitivity of Face2Gene. Our data suggest that human based evaluation is influenced by ethnic background of the evaluator. In addition, computer based evaluation indicates that the ethnic of the patient also influences the evaluation and that training may increase the detection specificity for a particular ethnic.

Dysmorphology services: a snapshot of current practices and a vision for the future

Dysmorphology concerns the recognition and management of rare, multiple anomaly syndromes. Genomic technologies and software for gestalt recognition will re-shape dysmorphology services. In order to reflect on a model of the service in the post-genomic era, we compared the utility of dysmorphology consultations in two Mediterranean cities, Athens, Greece and Afula, Israel (MDS), the Manchester Centre for Genomic Medicine, a UK service with dysmorphology expertise (UKDS) and the DYSCERNE, digital service (DDS). We show that it is more likely that chromosome microarray analysis will be performed if suggested in the UKDS rather than in the MDS; this, most probably reflects the difference of access to genetic testing following funding limitations in the MDS. We also show that in terms of achieved diagnosis, the first visit to a dysmorphology clinic is more significant than a follow-up. We show that a confirmed syndrome diagnosis significantly decreases the requests for other, non-genetic, laboratory investigations. Conversely, it increases the requests for reviews by other specialists and, most significantly (t-test: 8.244), it increases further requests for screening for possible associated complications. This is the first demonstration of the demands, on a health service, following the diagnosis of a dysmorphic condition.

Novel KDM6A (UTX) mutations and a clinical and molecular review of the X-linked Kabuki syndrome (KS2)

We describe seven patients with KDM6A (located on Xp11.3 and encodes UTX) mutations, a rare cause of Kabuki syndrome (KS2, MIM 300867) and report, for the first time, germ-line missense and splice-site mutations in the gene. We demonstrate that less than 5% cases of Kabuki syndrome are due to KDM6A mutations. Our work shows that similar to the commoner Type 1 Kabuki syndrome (KS1, MIM 147920) caused by KMT2D (previously called MLL2) mutations, KS2 patients are characterized by hypotonia and feeding difficulties during infancy and poor postnatal growth and short stature. Unlike KS1, developmental delay and learning disability are generally moderate-severe in boys but mild-moderate in girls with KS2. Some girls may have a normal developmental profile. Speech and cognition tend to be more severely affected than motor development. Increased susceptibility to infections, join laxity, heart, dental and ophthalmological anomalies are common. Hypoglycaemia is more common in KS2 than in KS1. Facial dysmorphism with KDM6A mutations is variable and diagnosis on facial gestalt alone may be difficult in some patients. Hypertrichosis, long halluces and large central incisors may be useful clues to an underlying KDM6A mutation in some patients.

A novel mutation of SOD-1 (Gly 108 Val) in familial amyotrophic lateral sclerosis

A novel mutation of the SOD-1 gene which encodes the enzyme copper-zinc superoxide dismutase was identified in a family manifesting amyotrophic lateral sclerosis (ALS) in three generations. The mutation is a heterozygote point mutation in exon 4, codon 108 (GGA to GTA), predicting the substitution of valine for glycine. The mutation creates a new restriction site for the endonuclease AccI. The mutation was demonstrated in two affected members of the family, who show features of autosomal dominant inheritance of ALS, but variable age at onset ranging from 48 to 72 years. Over 30 different mutations of SOD-1 have now been identified in families with ALS. The definition of the different mutations causing human disease may allow further investigation of their pathogenicity in transgenic animal models, and also offers insight into the variable phenotypic disease expression both within and between genotypes.

MLL2 mosaic mutations and intragenic deletion-duplications in patients with Kabuki syndrome

Kabuki syndrome (KS) is a rare multi-system disorder that can result in a variety of congenital malformations, typical dysmorphism and variable learning disability. It is caused by MLL2 point mutations in the majority of the cases and, rarely by deletions involving KDM6A. Nearly one third of cases remain unsolved. Here, we expand the known genetic basis of KS by presenting five typical patients with the condition, all of whom have novel MLL2 mutation types- two patients with mosaic small deletions, one with a mosaic whole-gene deletion, one with a multi-exon deletion and one with an intragenic multi-exon duplication. We recommend MLL2 dosage studies for all patients with typical KS, where traditional Sanger sequencing fails to identify mutations. The prevalence of such MLL2 mutations in KS may be comparable with deletions involving KDM6A. These findings may be helpful in understanding the mutational mechanism of MLL2 and the disease mechanism of KS.

Clinical spectrum of SIX3-associated mutations in holoprosencephaly: correlation between genotype, phenotype and function

BACKGROUND

Holoprosencephaly (HPE) is the most common structural malformation of the human forebrain. There are several important HPE mutational target genes, including the transcription factor SIX3, which encodes an early regulator of Shh, Wnt, Bmp and Nodal signalling expressed in the developing forebrain and eyes of all vertebrates.

OBJECTIVE

To characterise genetic and clinical findings in patients with SIX3 mutations.

METHODS

Patients with HPE and their family members were tested for mutations in HPE-associated genes and the genetic and clinical findings, including those for additional cases found in the literature, were analysed. The results were correlated with a mutation-specific functional assay in zebrafish.

RESULTS

In a cohort of patients (n = 800) with HPE, SIX3 mutations were found in 4.7% of probands and additional cases were found through testing of relatives. In total, 138 cases of HPE were identified, 59 of whom had not previously been clinically presented. Mutations in SIX3 result in more severe HPE than in other cases of non-chromosomal, non-syndromic HPE. An over-representation of severe HPE was found in patients whose mutations confer greater loss of function, as measured by the functional zebrafish assay. The gender ratio in this combined set of patients was 1.5:1 (F:M) and maternal inheritance was almost twice as common as paternal. About 14% of SIX3 mutations in probands occur de novo. There is a wide intrafamilial clinical range of features and classical penetrance is estimated to be at least 62%.

CONCLUSIONS

Our data suggest that SIX3 mutations result in relatively severe HPE and that there is a genotype-phenotype correlation, as shown by functional studies using animal models.

A clinical and genetic study of the Say/Barber/Biesecker/Young-Simpson type of Ohdo syndrome

We report a series of eight patients with the Say/Barber/Biesecker/Young-Simpson (SBBYS) type of Ohdo syndrome, which is the largest cohort described to date. We expand on the type, frequency and severity of the clinical characteristics in this condition; comment on the natural history of Ohdo syndrome and further refine previously published diagnostic criteria. Cytogenetic investigations and microarray CGH analysis undertaken in this cohort of patients failed to identify a chromosomal aetiology. It remains possible that this rare condition is heterogeneous and therefore caution must be undertaken during counselling until the underlying genetic mechanism(s) is (are) identified.

FISH mapping of de novo apparently balanced chromosome rearrangements identifies characteristics associated with phenotypic abnormality

We report fluorescence in situ hybridization (FISH) mapping of 152, mostly de novo, apparently balanced chromosomal rearrangement (ABCR) breakpoints in 76 individuals, 30 of whom had no obvious phenotypic abnormality (control group) and 46 of whom had an associated disease (case group). The aim of this study was to identify breakpoint characteristics that could discriminate between these groups and which might be of predictive value in de novo ABCR (DN-ABCR) cases detected antenatally. We found no difference in the proportion of breakpoints that interrupted a gene, although in three cases, direct interruption or deletion of known autosomal-dominant or X-linked recessive Mendelian disease genes was diagnostic. The only significant predictor of phenotypic abnormality in the group as a whole was the localization of one or both breakpoints to an R-positive (G-negative) band with estimated predictive values of 0.69 (95% CL 0.54-0.81) and 0.90 (95% CL 0.60-0.98), respectively. R-positive bands are known to contain more genes and have a higher guanine-cytosine (GC) content than do G-positive (R-negative) bands; however, whether a gene was interrupted by the breakpoint or the GC content in the 200 kB around the breakpoint had no discriminant ability. Our results suggest that the large-scale genomic context of the breakpoint has prognostic utility and that the pathological mechanism of mapping to an R-band cannot be accounted for by direct gene inactivation.

Genotype-phenotype correlation in Costello syndrome: HRAS mutation analysis in 43 cases

BACKGROUND

Costello syndrome (CS) is a rare multiple congenital abnormality syndrome, associated with failure to thrive and developmental delay. One of the more distinctive features in childhood is the development of facial warts, often nasolabial and in other moist body surfaces. Individuals with CS have an increased risk of malignancy, suggested to be about 17%. Recently, mutations in the HRAS gene on chromosome 11p13.3 have been found to cause CS.

METHODS

We report here the results of HRAS analysis in 43 individuals with a clinical diagnosis of CS.

RESULTS

Mutations were found in 37 (86%) of patients. Analysis of parental DNA samples was possible in 16 cases for both parents and in three cases for one parent, and confirmed the mutations as de novo in all of these cases. Three novel mutations (G12C, G12E, and K117R) were found in five cases.

CONCLUSIONS

These results confirm that CS is caused, in most cases, by heterozygous missense mutations in the proto-oncogene HRAS. Analysis of the major phenotypic features by mutation suggests a potential correlation between malignancy risk and genotype, which is highest for patients with an uncommon (G12A) substitution. These results confirm that mutation testing for HRAS is a reliable diagnostic test for CS.

CHARGE syndrome: the phenotypic spectrum of mutations in the CHD7 gene

BACKGROUND

CHARGE syndrome is a non-random clustering of congenital anomalies including coloboma, heart defects, choanal atresia, retarded growth and development, genital hypoplasia, ear anomalies, and deafness. A consistent feature in CHARGE syndrome is semicircular canal hypoplasia resulting in vestibular areflexia. Other commonly associated congenital anomalies are facial nerve palsy, cleft lip/palate, and tracheo-oesophageal fistula. Specific behavioural problems, including autistic-like behaviour, have been described. The CHD7 gene on chromosome 8q12.1 was recently discovered as a major gene involved in the aetiology of this syndrome.

METHODS

The coding regions of CHD7 were screened for mutations in 107 index patients with clinical features suggestive of CHARGE syndrome. Clinical data of the mutation positive patients were sampled to study the phenotypic spectrum of mutations in the CHD7 gene.

RESULTS

Mutations were identified in 69 patients. Here we describe the clinical features of 47 of these patients, including two sib pairs. Most mutations were unique and were scattered throughout the gene. All patients but one fulfilled the current diagnostic criteria for CHARGE syndrome. No genotype-phenotype correlations were apparent in this cohort, which is best demonstrated by the differences in clinical presentation in sib pairs with identical mutations. Somatic mosaicism was detected in the unaffected mother of a sib pair, supporting the existence of germline mosaicism.

CONCLUSIONS

CHD7 mutations account for the majority of the cases with CHARGE syndrome, with a broad clinical variability and without an obvious genotype-phenotype correlation. In one case evidence for germline mosaicism was provided.

Kohlschutter syndrome in siblings

Kohlschutter syndrome is a rare neurodegenerative disorder presenting with intractable seizures, developmental regression and characteristic hypoplastic dental enamel indicative of amelogenesis imperfecta. We report a new family with two affected siblings.

Filippi syndrome: two cases with ectodermal features, expanding the phenotype

We report two unrelated children with Filippi syndrome. Both show typical facial dysmorphism, syndactyly of fingers and toes, growth retardation, postnatal microcephaly and developmental delay, particularly involving speech. In addition both children have unusual teeth and hair. We review the literature and propose that neurological and ectodermal involvement may be under-recognised features of the syndrome.

Mutations in PAX1 may be associated with Klippel-Feil syndrome

Pax genes are a highly conserved family of developmental control genes that encode transcription factors. In vertebrates, Pax genes play a role in pattern formation during embryogenesis. Mutations in Pax genes have been associated with both spontaneous mouse mutants and congenital human diseases. The mouse Pax1 mutant phenotype undulated is characterised by vertebral segmentation defects reminiscent of the human disorder Klippel-Feil syndrome (KFS). To determine whether PAX1 haploinsufficiency plays a role in KFS, we have defined the gene structure of the human PAX1 gene and screened 63 KFS patients for mutations in this gene. Differences in the PAX1 sequence were detected in eight patients. Two patients had a silent change within the paired box that was also seen in 2/303 control chromosomes. The other variants were missense, silent or intronic changes not represented in the control panel tested. The significance of these results and the possible role of PAX1 in the pathogenesis of KFS are discussed.

Comparison of genetic services with and without genetic registers: knowledge, adjustment, and attitudes about genetic counselling among probands referred to three genetic clinics

Genetic register services incorporating long term follow up and a proactive approach to at risk subjects have been recommended as a way of improving access to genetic counselling for families with dominant or X linked genetic disorders and chromosome translocations. The aims of the present study were to evaluate the psychosocial benefits and drawbacks of long term family contact, and to evaluate the attitudes of probands and their general practitioners towards proactive genetic counselling. We interviewed 192 people referred to three regional genetic clinics because of a family history of Duchenne or Becker muscular dystrophy, myotonic dystrophy, or chromosome translocations, and 43 of the referring GPs. Probands attending the centre using a genetic register approach were compared with those from the two centres offering the standard clinical genetic service. A very high proportion of probands in both groups were well informed about the genetic risks to themselves and their children, were satisfied with the service they had received from their local genetic clinic, and felt adequately prepared to discuss the family illness with their children. The register probands expressed approval of the ongoing contact and open access provided by the register service. Asked whether previously unaware relatives should be informed of their at risk status, 98% (188/192) said it was acceptable for this information to be disclosed by a family member, while three quarters of the probands (149/192) and just over half the GPs (27/43) thought it acceptable for the genetic service to approach them; a similar proportion of both GPs and probands also found it acceptable for GPs to do so. More than half the probands (107/190) thought it was the family's responsibility to pass on genetic risk information, but 43% said that either the genetic service or the GP should be responsible for this. The findings show that the genetic register approach incorporating long term follow up and a proactive approach to genetic counselling is highly acceptable to the families concerned, and although the register and non-register probands did not differ significantly on any of the main outcome measures used in this relatively short term study, it may be that the continuing contact associated with the register approach offers long term benefits, especially for those genetic conditions where medical surveillance may have an impact on the prognosis.

Comparison of genetic services with and without genetic registers: access and attitudes to genetic counselling services among relatives of genetic clinic patients

The pedigrees of 192 subjects at risk of Duchenne or Becker muscular dystrophy, myotonic dystrophy, or balanced chromosome translocations attending three regional genetic clinics were inspected to identify relatives who were themselves at high risk of these disorders. Of the 342 relatives eligible for inclusion, 43% (63/147) of the register relatives and 26% (50/195) of the non-register relatives had had contact with the clinical genetic services, a significant difference (p<0.02). Relatives from families with muscular dystrophy were significantly more likely to have been in contact with genetic services than those from BT families. Fifty-two relatives were interviewed about their experience and attitudes regarding genetic counselling. Almost all regarded knowledge about the family genetic disorder as helpful, and only one thought it unacceptable for relatives to be informed that they are at risk; 94% thought it was acceptable for this information to come from family members, 92% from general practitioners, and 90% from the clinical genetic service. A majority of relatives (53%) thought it was the family's responsibility to pass on genetic risk information, but 22% said the genetic service should be responsible and 18% thought it should be the GP. These data, together with the findings from the study of probands attending genetic clinics for these disorders, indicate that the genetic register approach incorporating long term follow up and a proactive approach to genetic counselling is acceptable to the families concerned and improves access to genetic services for at risk relatives.

De novo GLI3 mutation in acrocallosal syndrome: broadening the phenotypic spectrum of GLI3 defects and overlap with murine models

Acrocallosal syndrome (ACS) is characterised by postaxial polydactyly, hallux duplication, macrocephaly, and absence of the corpus callosum, usually with severe developmental delay. The condition overlaps with Greig cephalopolysyndactyly syndrome (GCPS), an autosomal dominant disorder that results from mutations in the GLI3 gene. Here we report a child with agenesis of the corpus callosum and severe retardation, both cardinal features of ACS and rare in GCPS, who has a mutation in GLI3. Since others have excluded GLI3 in ACS, we suggest that ACS may represent a heterogeneous group of disorders that, in some cases, may result from a mutation in GLI3 and represent a severe, allelic form of GCPS. The finding is important for counselling families with suspected ACS.

Domain disruption and mutation of the bZIP transcription factor, MAF, associated with cataract, ocular anterior segment dysgenesis and coloboma

Human congenital cataract and ocular anterior segment dysgenesis both demonstrate extensive genetic and phenotypic heterogeneity. We identified a family where ocular developmental abnormalities (cataract, anterior segment dysgenesis and microphthalmia) co-segregated with a translocation, t(5;16)(p15.3;q23.2), in both balanced and unbalanced forms. We hypothesized that this altered the expression of a gene of developmental significance in the human lens and ocular anterior segment. Cloning the 16q23.2 breakpoint demonstrated that it transected the genomic-control domain of MAF, a basic region leucine zipper (bZIP) transcription factor, first identified as an oncogene, which is expressed in vertebrate lens development and regulates the expression of the eye lens crystallins. The homozygous null mutant Maf mouse embryo demonstrates defective lens formation and microphthalmia. Through mutation screening of a panel of patients with hereditary congenital cataract we identified a mutation in MAF in a three-generation family with cataract, microcornea and iris coloboma. The mutation results in the substitution of an evolutionarily highly conserved arginine with a proline at residue 288 (R288P) in the basic region of the DNA-binding domain of MAF. Our findings further implicate MAF/Maf in mammalian lens development and highlight the role of the lens in anterior segment development. The 16q23.2 breakpoint transects the common fragile site, FRA16D, providing a molecular demonstration of a germline break in a common fragile site.

Genetic services

This is a time of unprecedented increase in knowledge about the genetic basis of disease against a background of rapidly changing technology. Advances happen quickly, with the new knowledge rapidly becoming relevant to services for patients, and hence there is an increasing demand for, and expectation of, genetic services. This brings a challenge for health services worldwide to keep pace with the expectations of their populations. There is also a need for public and professional education and dialogue to dispel some of the hype and myths about what can be achieved. It should not be forgotten that any services must be provided and developed within a broad ethical framework. A statement from a WHO expert consultation (1) concluded that 'Genetic advances will only be acceptable if their application is carried out ethically, with due regard to autonomy, justice, education and the beliefs and resources of each nation and community'. That so many public bodies have commented on genetic services and their associated ethical, legal and social issues emphasizes not only the importance of this area in health care, but also that the wider issues are of great importance in democratic societies. The aim of this paper is to review the current situation in the provision of genetic services, to examine the drivers for change, to speculate on the likely need for future services and to suggest models for the development of such services. Pharmacogenetics and the determination of genetic factors indicating susceptibility to infection will not be discussed since these have been the subject of several recent excellent reviews (2, 3). Genetic services have been defined as health measures implemented to help people with a genetic disadvantage and their families to live and reproduce as normally as possible (4). Broadly they can be divided into those services which target whole populations with a view to identifying those at increased risk; and those which focus on the needs of families which are affected by a genetic disorder or who perceive themselves to be at increased risk.

A survey of TWIST for mutations in craniosynostosis reveals a variable length polyglycine tract in asymptomatic individuals

The human TWIST gene encodes a 202 amino acid transcription factor characterized by a highly conserved basic-helix-loop-helix motif in the C-terminal half, and a less conserved N-terminal half that has binding activity toward the histone acetyltransferase p300. Between these domains is a repeat region of unknown function that encodes the glycine-rich sequence (Gly)5Ala(Gly)5. Heterozygous mutations of TWIST were previously described in Saethre-Chotzen craniosynostosis syndrome [El Ghouzzi et al., 1997; Howard et al., 1997]. During a search for TWIST mutations in patients with craniosynostosis, we identified, in addition to 11 novel and one previously described bona fide mutations, several individuals with rearrangements of the glycine-rich region, involving either deletion of 18 nucleotides or insertion of three, 15, or 21 nucleotides. None of these rearrangements was consistently associated with clinical disease and we conclude that they are at most weakly pathogenic. The glycine stretch may serve as a flexible linker between the functional domains of the TWIST protein, and as such may be subject to reduced evolutionary constraint.

Abnormal corticospinal function but normal axonal guidance in human L1CAM mutations

L1 cell adhesion molecule (L1CAM) gene mutations are associated with X-linked 'recessive' neurological syndromes characterized by spasticity of the legs. L1CAM knock-out mice show hypoplasia of the corticospinal tract and failure of corticospinal axonal decussation and projection beyond the cervical spinal cord. The aim of this study was to determine if similar neuropathology underlies the spastic diplegia of males hemizygous for L1CAM mutations. Studies were performed on eight carrier females and 10 hemizygous males. Transcranial magnetic stimulation excited the corticospinal tract and responses were recorded in biceps brachii and quadriceps femoris. In contralateral biceps and quadriceps the responses had high thresholds and delayed onset compared with normal subjects. Ipsilateral responses in biceps were smaller, with higher thresholds and delayed onsets relative to contralateral responses. Subthreshold corticospinal conditioning of the stretch reflex of biceps and quadriceps was abnormal in both hemizygous males and carrier females suggesting there may also be a reduced projection to inhibitory interneurones. Histological examination of post-mortem material from a 2-week-old male with an L1CAM mutation revealed normal corticospinal decussation and axonal projections to lumbar spinal segments. These data support a role for L1CAM in corticospinal tract development in hemizygous males and 'carrier' females, but do not support a critical role for L1CAM in corticospinal axonal guidance.

Williams syndrome: from genotype through to the cognitive phenotype

Williams syndrome, due to a contiguous gene deletion at 7q11.23, is associated with a distinctive facial appearance, cardiac abnormalities, infantile hypercalcemia, and growth and developmental retardation. The deletion is approximately 1.5Mb and includes approximately 17 genes. Large repeats containing genes and pseudogenes flank the deletion breakpoints, and the mutation mechanism commonly appears to be unequal meiotic recombination. Elastin hemizygosity is associated with supravalvular aortic stenosis and other vascular stenoses. LIM Kinase 1 hemizygosity may contribute to the characteristic cognitive profile. The relationship of the other deleted genes to phenotypic features is not known. People with Williams syndrome tend to be over friendly-though anxious-and lack social judgement skills. They exhibit an uneven cognitive-linguistic profile together with mild to severe mental retardation. Analysis of the cognitive phenotype based on analyses of the mental processes underlying overt behavior demonstrates major differences between normal and WS subjects although for some areas, such as face processing, WS subjects can achieve near normal scores. Cognitive analysis of patients with small deletions in 7q11.23 which include elastin and LIM Kinase 1 have revealed varying results and it is premature to draw genotype-phenotype correlations.

Elastin: mutational spectrum in supravalvular aortic stenosis

Supravalvular aortic stenosis (SVAS) is a congenital narrowing of the ascending aorta which can occur sporadically, as an autosomal dominant condition, or as one component of Williams syndrome. SVAS is caused by translocations, gross deletions and point mutations that disrupt the elastin gene (ELN) on 7q11.23. Functional hemizygosity for elastin is known to be the cause of SVAS in patients with gross chromosomal abnormalities involving ELN. However, the pathogenic mechanisms of point mutations are less clear. One hundred patients with diagnosed SVAS and normal karyotypes were screened for mutations in the elastin gene to further elucidate the molecular pathology of the disorder. Mutations associated with the vascular disease were detected in 35 patients, and included nonsense, frameshift, translation initiation and splice site mutations. The four missense mutations identified are the first of this type to be associated with SVAS. Here we describe the spectrum of mutations occurring in familial and sporadic SVAS and attempt to define the mutational mechanisms involved in SVAS. SVAS shows variable penetrance within families but the progressive nature of the disorder in some cases, makes identification of the molecular lesions important for future preventative treatments.

The Conradi-Hünermann-Happle syndrome (CDPX2) and emopamil binding protein: novel mutations, and somatic and gonadal mosaicism

The Conradi-Hünermann-Happle (CHH) syndrome (X-chromosomal dominant chondrodysplasia punctata type II; MIM 302960) is an X-linked dominant disorder that is characterized by ichthyosis, chondrodysplasia punctata, cataracts and short stature. The disease occurs almost exclusively in females and shows increased disease expression in successive generations (anticipation). Recently, causative mutations in the emopamil binding protein (EBP) have been identified. To better appreciate the genetics of this syndrome we analyzed the EBP gene in seven independent families using PCR, conformation-sensitive gel electrophoresis, direct sequencing and restriction enzyme analysis. We found five novel mutations: three nonsense mutations in exon 2 and exon 3 and two frameshift mutations, one deletion in exon 4 and an insertion in exon 5. In two families, known mutations affecting exon 2 were identified. Surprisingly, we failed to detect the mutation in a grandmother exhibiting minor disease symptoms such as sectorial cataract and attribute this to gonadal and somatic mosaicism. Gonadal mosaicism appeared also to be involved in the case of healthy parents having two affected girls, one of whom died due to the disease. We conclude that gonadal mosaicism has to be considered when dealing with seemingly sporadic cases.

Nine novel L1 CAM mutations in families with X-linked hydrocephalus

Mutations in the gene for neural cell adhesion molecule L1 are responsible for the highly variable phenotype found in families with X-linked hydrocephalus, MASA syndrome, and spastic paraplegia type I. To date, 32 different mutations have been observed, the majority being unique to individual families. Here, we report nine novel mutations in L1 in 10 X-linked hydrocephalus families. Four mutations truncate the L1 protein and eliminate cell surface expression, and two would produce abnormal L1 through alteration of RNA processing. A further two of these mutations are small in-frame deletions that have occurred through a mechanism involving tandem repeated sequences. Together with a single missense mutation, these latter examples contribute to the growing number of existing mutations that affect short regions of the L1 protein that may have particular functional significance.

Genomic rearrangement in NEMO impairs NF-kappaB activation and is a cause of incontinentia pigmenti. The International Incontinentia Pigmenti (IP) Consortium

Familial incontinentia pigmenti (IP; MIM 308310) is a genodermatosis that segregates as an X-linked dominant disorder and is usually lethal prenatally in males. In affected females it causes highly variable abnormalities of the skin, hair, nails, teeth, eyes and central nervous system. The prominent skin signs occur in four classic cutaneous stages: perinatal inflammatory vesicles, verrucous patches, a distinctive pattern of hyperpigmentation and dermal scarring. Cells expressing the mutated X chromosome are eliminated selectively around the time of birth, so females with IP exhibit extremely skewed X-inactivation. The reasons for cell death in females and in utero lethality in males are unknown. The locus for IP has been linked genetically to the factor VIII gene in Xq28 (ref. 3). The gene for NEMO (NF-kappaB essential modulator)/IKKgamma (IkappaB kinase-gamma) has been mapped to a position 200 kilobases proximal to the factor VIII locus. NEMO is required for the activation of the transcription factor NF-kappaB and is therefore central to many immune, inflammatory and apoptotic pathways. Here we show that most cases of IP are due to mutations of this locus and that a new genomic rearrangement accounts for 80% of new mutations. As a consequence, NF-kappaB activation is defective in IP cells.

A novel hereditary developmental vitreoretinopathy with multiple ocular abnormalities localizing to a 5-cM region of chromosome 5q13-q14

BACKGROUND

To undertake a clinical and molecular analysis of a previously unpublished kindred with a phenotypically distinct vitreoretinopathy characterized by associated ocular developmental abnormalities.

DESIGN

Family genetic study.

PARTICIPANTS

A total of 23 members, both affected and unaffected, of 1 kindred with vitreoretinopathy.

METHOD

Individuals within the kindred were examined clinically and blood samples taken for DNA analysis. Genetic analysis was performed for the proximal region of chromosome 5q by means of polymerase chain reaction (PCR).

MAIN OUTCOME MEASURES

Detection of vitreoretinopathy and associated abnormalities.

RESULTS

This novel, hereditary vitreoretinopathy, showing the classic features of vitreous pathology and early-onset retinal detachments, was associated with a variety of ocular developmental abnormalities, including posterior embryotoxon, congenital glaucoma, iris hypoplasia, congenital cataract, ectopia lentis, microphthalmia, and persistent hyperplastic primary vitreous. There were no associated systemic features. Genetic mapping with markers from the proximal region of 5q13-q14 showed linkage to a 5-cM region between the markers D5S626 and D5S2103.

CONCLUSIONS

The 5-cM region is within that implicated in the etiology of both Wagner and erosive vitreoretinopathies. This suggests that this novel condition may be allelic, refines the genetic mapping for vitreoretinopathies that map to 5q13-q14, and implicates a gene important not only in vitreous production but also in early ocular development.

A transcription factor involved in skeletal muscle gene expression is deleted in patients with Williams syndrome

Williams-Beuren syndrome (WS) is a developmental disorder caused by a hemizygous microdeletion of approximately 1.4MB at chromosomal location 7q11.23. The transcription map of the WS critical region is not yet complete. We have isolated and characterised a 3.4 kb gene, GTF3, which occupies about 140 kb of the deleted region. Northern blot analysis showed that the gene is expressed in skeletal muscle and heart, and RT-PCR analysis showed expression in a range of adult tissues with stronger expression in foetal tissues. Part of the conceptual GTF3 protein sequence is almost identical to a recently reported slow muscle-fibre enhancer binding protein MusTRD1, and shows significant homology to the 90 amino-acid putative helix-loop-helix repeat (HLH) domains of the transcription factor TFII-I (encoded for by the gene GTF2I). These genes may be members of a new family of transcription factors containing this HLH-like repeated motif. Both GTF3 and GTF2I map within the WS deleted region, with GTF2I being positioned distal to GTF3. GTF3 is deleted in patients with classic WS, but not in patients we have studied with partial deletions of the WS critical region who have only supravalvular aortic stenosis. A feature of WS is abnormal muscle fatiguability, and we suggest that haploinsufficiency of the GTF3 gene may be the cause of this.

Disorganisation: a case with popliteal pterygia and placental-skin appendages

We report a girl with congenital anomalies which include amniotic rings and scars, cleft lip and palate, thumb abnormalities, hexadactyly of feet, severe flexion deformities of legs and unusual finger-like appendages which were attached to the placenta. We suggest this patient represents another example of human homologue for the mouse mutant disorganisation (Ds).

Duplications on human chromosome 22 reveal a novel Ret Finger Protein-like gene family with sense and endogenous antisense transcripts

Analysis of 600 kb of sequence encompassing the beta-prime adaptin (BAM22) gene on human chromosome 22 revealed intrachromosomal duplications within 22q12-13 resulting in three active RFPL genes, two RFPL pseudogenes, and two pseudogenes of BAM22. The genomic sequence of BAM22vartheta1 shows a remarkable similarity to that of BAM22. The cDNA sequence comparison of RFPL1, RFPL2, and RFPL3 showed 95%-96% identity between the genes, which were most similar to the Ret Finger Protein gene from human chromosome 6. The sense RFPL transcripts encode proteins with the tripartite structure, composed of RING finger, coiled-coil, and B30-2 domains, which are characteristic of the RING-B30 family. Each of these domains are thought to mediate protein-protein interactions by promoting homo- or heterodimerization. The MID1 gene on Xp22 is also a member of the RING-B30 family and is mutated in Opitz syndrome (OS). The autosomal dominant form of OS shows linkage to 22q11-q12. We detected a polymorphic protein-truncating allele of RFPL1 in 8% of the population, which was not associated with the OS phenotype. We identified 6-kb and 1.2-kb noncoding antisense mRNAs of RFPL1S and RFPL3S antisense genes, respectively. The RFPL1S and RFPL3S genes cover substantial portions of their sense counterparts, which suggests that the function of RFPL1S and RFPL3S is a post-transcriptional regulation of the sense RFPL genes. We illustrate the role of intrachromosomal duplications in the generation of RFPL genes, which were created by a series of duplications and share an ancestor with the RING-B30 domain containing genes from the major histocompatibility complex region on human chromosome 6.

Analysis of germline CDKN1C (p57KIP2) mutations in familial and sporadic Beckwith-Wiedemann syndrome (BWS) provides a novel genotype-phenotype correlation

Beckwith-Wiedemann syndrome (BWS) is a human imprinting disorder with a variable phenotype. The major features are anterior abdominal wall defects including exomphalos (omphalocele), pre- and postnatal overgrowth, and macroglossia. Additional less frequent complications include specific developmental defects and a predisposition to embryonal tumours. BWS is genetically heterogeneous and epigenetic changes in the IGF2/H19 genes resulting in overexpression of IGF2 have been implicated in many cases. Recently germline mutations in the cyclin dependent kinase inhibitor gene CDKN1C (p57KIP2) have been reported in a variable minority of BWS patients. We have investigated a large series of familial and sporadic BWS patients for evidence of CDKN1C mutations by direct gene sequencing. A total of 70 patients with classical BWS were investigated; 54 were sporadic with no evidence of UPD and 16 were familial from seven kindreds. Novel germline CDKN1C mutations were identified in five probands, 3/7 (43%) familial cases and 2/54 (4%) sporadic cases. There was no association between germline CDKN1C mutations and IGF2 or H19 epigenotype abnormalities. The clinical phenotype of 13 BWS patients with germline CDKN1C mutations was compared to that of BWS patients with other defined types of molecular pathology. This showed a significantly higher frequency of exomphalos in the CDKN1C mutation cases (11/13) than in patients with an imprinting centre defect (associated with biallelic IGF2 expression and H19 silencing) (0/5, p<0.005) or patients with uniparental disomy (0/9, p<0.005). However, there was no association between germline CDKN1C mutations and risk of embryonal tumours. No CDKN1C mutations were identified in six non-BWS patients with overgrowth and Wilms tumour. These findings (1) show that germline CDKN1C mutations are a frequent cause of familial but not sporadic BWS, (2) suggest that CDKN1C mutations probably cause BWS independently of changes in IGF2/H19 imprinting, (3) provide evidence that aspects of the BWS phenotype may be correlated with the involvement of specific imprinted genes, and (4) link genotype-phenotype relationships in BWS and the results of murine experimental models of BWS.

A complete physical contig and partial transcript map of the Williams syndrome critical region

Williams syndrome (WS) is a contiguous gene syndrome caused by hemizygosity for a chromosomal deletion at 7q11.23. The range of phenotypes includes mental retardation, dysmorphic facies, heart abnormalities, short stature, a specific cognitive profile, hyperacusis, and infantile hypercalcaemia. To identify all the deleted genes, we have constructed a detailed physical map and complete BAC/PAC contig of the critical region, extending a distance of approximately 2 Mb and delimited by the nondeleted markers D7S1816 and D7S489A. Somatic cell hybrids of WS patients were made and used to define the centromeric and telomeric deletion breakpoints, enabling the size of the WS deletion to be defined as approximately 1.4 Mb. Genes previously mapped to the region have been located on the contig, and we have isolated eight transcripts, two of which have been characterized as the genes CPETR1 and CPETR2. This contig and expressed sequence map will form the basis for the construction of a complete transcription map of the deleted region and will enable genotype-phenotype correlations to be attempted to identify the individual components of WS.

A mutation within exon 14 of the TGFBI (BIGH3) gene on chromosome 5q31 causes an asymmetric, late-onset form of lattice corneal dystrophy

PURPOSE

Two forms of autosomal-dominant lattice corneal dystrophy (LCD), types I and IIIA, have previously been shown to be caused by different mutations within the transforming growth factor, beta-induced (TGFBI) gene. A clinical and molecular analysis of three unrelated kindreds with a clinically distinct late-onset LCD was undertaken to determine whether this phenotype is also caused by mutations within the TGFBI gene.

DESIGN

Experimental study.

PARTICIPANTS

Thirty-two members of three kindreds with corneal dystrophy. DNA from 100 normal control subjects was used as a control population.

METHODS

Members of three kindreds with LCD were examined clinically, and blood samples were taken for DNA analysis. Mutation analysis was undertaken on all individuals for the coding region of the TGFBI gene by means of polymerase chain reaction (PCR) followed by single-stranded conformation polymorphism/heteroduplex analysis, subcloning, and sequencing.

MAIN OUTCOME MEASURES

Detection of mutations within the TGFBI gene.

RESULTS

Clinical examination revealed a form of LCD that was bilateral in all but one case, with onset around the fourth to fifth decade. The majority of cases showed significant asymmetry, and in one case there was evidence of onset directly after minor superficial corneal trauma. Molecular analysis in all families demonstrated sequence changes within exon 14 of the TGFBI gene on chromosome 5q31, at codon 622 in family 3, and at codon 626 in families 1 and 2, which are presumed to be responsible for the disease.

CONCLUSIONS

Previously, a late-onset form of LCD, termed IIIA, was shown to be caused by a P501T mutation in exon 11 of TGFBI. The authors present the first description of mutations in exon 14 of TGFBI causing an LCD, also of late onset. Although the condition presented is morphologically and histopathologically typical of an isolated lattice dystrophy, the age of onset and clinical course is not typical of type I, III, or IIIA lattice dystrophy. This, in conjunction with recent developments in our understanding of the molecular genetics of these disorders, calls into question the usefulness and validity of the current classification of the isolated lattice dystrophies.

Screening for submicroscopic chromosome rearrangements in children with idiopathic mental retardation using microsatellite markers for the chromosome telomeres

Recently much attention has been given to the detection of submicroscopic chromosome rearrangements in patients with idiopathic mental retardation. We have screened 27 subjects with mental retardation and dysmorphic features for such rearrangements using a genetic marker panel screening. The screening was a pilot project using markers from the subtelomeric regions of all 41 chromosome arms. The markers were informative for monosomy in both parents at 3661902 loci (40.6%, 95% confidence interval 37.0-44.2%) in the 22 families where DNA was available from both parents. In two of the 27 subjects, submicroscopic chromosomal aberrations were detected. The first patient had a 5-6 Mb deletion of chromosome 18q and the second patient had a 4 Mb deletion of chromosome 1p. The identification of two deletions in 27 cases gave an aberration frequency of 7.5% without adjustment for marker informativeness (95% confidence interval 1-24%) and an estimated frequency of 18% if marker informativeness for monosomy was taken into account. This frequency is higher than previous estimates of the number of subtelomeric chromosome abnormalities in children with idiopathic mental retardation (5-10%) although the confidence interval is overlapping. Our study suggests that in spite of the low informativeness of this pilot screening, submicroscopic chromosome aberrations may be a common cause of dysmorphic features and mental retardation.

A clinical study of type 1 neurofibromatosis in north west England

A clinical study of patients on the North West Regional Genetic Register with neurofibromatosis type 1 (NF1) identified 523 affected cases from 304 families. In those for whom relevant information was available, 86.7% (383 of 442) had more than six café au lait patches, 83.8% (310 of 370) had axillary freckling, 42.3% (151 of 357) had inguinal freckling, and 63% (157 of 249) had Lisch nodules. Cutaneous neurofibromas were present in 59.4% (217 of 365) and 45.5% (150 of 330) were noted to have subcutaneous tumours. Plexiform neurofibromas were present in 15.3% (80 of 523). A positive family history of NF1 was found in 71.2% (327 of 459) and 28.8% (132 of 459) of affected patients were considered to be the result of a new mutation. Learning difficulties of varying severity occurred in 62% (186 of 300). CNS tumours associated with NF1 were reported in 9.4% (49) of patients, optic gliomas occurring in 25 of these, 4.8% of patients. Some degree of scoliosis was reported for 11.7% (61), 1.9% (10) had pseudoarthrosis, 4.3% (23) had epilepsy, and 2.1% (11) had spinal neurofibromas. Actuarial analyses were carried out for both optic glioma and malignant nerve sheath tumours and the data are presented.

Williams syndrome: use of chromosomal microdeletions as a tool to dissect cognitive and physical phenotypes

In Williams syndrome (WS), a deletion of approximately 1.5 Mb on one copy of chromosome 7 causes specific physical, cognitive, and behavioral abnormalities. Molecular dissection of the phenotype may be a route to identification of genes important in human cognition and behavior. Among the genes known to be deleted in WS are ELN (which encodes elastin), LIMK1 (which encodes a protein tyrosine kinase expressed in the developing brain), STX1A (which encodes a component of the synaptic apparatus), and FZD3. Study of patients with deletions or mutations confined to ELN showed that hemizygosity for elastin is responsible for the cardiological features of WS. LIMK1 and STX1A are good candidates for cognitive or behavioral aspects of WS. Here we describe genetic and psychometric testing of patients who have small deletions within the WS critical region. Our results suggest that neither LIMK1 hemizygosity (contrary to a previous report) nor STX1A hemizygosity is likely to contribute to any part of the WS phenotype, and they emphasize the importance of such patients for dissecting subtle but highly penetrant phenotypes.

X-inactivation and marker studies in three families with incontinentia pigmenti: implications for counselling and gene localisation

Familial incontinentia pigmenti (IP) is an X-linked dominant disorder with an extremely variable clinical presentation. Ambiguous diagnosis can complicate genetic counselling and attempts to refine the gene location in Xq28. Marked skewing of X-inactivation patterns is a hallmark of IP and provides a means for investigating uncertain cases. We have conducted X-inactivation studies in three families where Xq28 marker studies were at odds with the original clinical assessment. The results indicate that no recombination between the disease locus and Xq28 loci has occurred and suggest that mosaicism is responsible for the discrepancy in one family.

EYA4, a novel vertebrate gene related to Drosophila eyes absent

We have isolated a family of four vertebrate genes homologous to eyes absent (eya), a key regulator of ocular development in Drosophila. Here we present the detailed characterization of the EYA4 gene in human and mouse. EYA4 encodes a 640 amino acid protein containing a highly conserved C-terminal domain of 271 amino acids which in Drosophila eya is known to mediate developmentally important protein-protein interactions. Human EYA4 maps to 6q23 and mouse Eya4 maps to the predicted homology region near the centromere of chromosome 10. In the developing mouse embryo, Eya4 is expressed primarily in the craniofacial mesenchyme, the dermamyotome and the limb. On the basis of map position and expression pattern, EYA4 is a candidate for oculo-dento-digital (ODD) syndrome, but no EYA4 mutations were found in a panel of ODD patients.

Costello syndrome: two cases with embryonal rhabdomyosarcoma

Costello syndrome is a well delineated mental retardation syndrome of unknown aetiology in which the occurrence of benign tumours, especially papillomata, is recognised. We report two children in whom the diagnosis of Costello syndrome was made in the first months of life, who both developed a retroperitoneal embryonal rhabdomyosarcoma. Although not previously reported, the occurrence of this relatively uncommon childhood tumour in two girls with Costello syndrome suggests that an increased risk of malignancy may be part of this condition. The genetic basis of this susceptibility requires further clarification.

Smith-Lemli-Opitz syndrome: a variable clinical and biochemical phenotype

We have reviewed all known UK cases of Smith-Lemli-Opitz syndrome. Among 49 cases with proven 7-dehydrocholesterol reductase deficiency, half had been terminated or had died in infancy. The minimum incidence is 1 in 60,000. The frequent occurrence of hypospadias may account for 71% of recognised cases being male. Important common features which emerged include short thumbs, severe photosensitivity, aggressive behaviour, and atrioventricular septal defect. The typical facial appearance becomes less obvious with age and 20% of cases did not have 2/3 toe syndactyly. Biochemical measurements of serum 7-dehydrocholesterol did not correlate with clinical severity.

An elastin gene mutation producing abnormal tropoelastin and abnormal elastic fibres in a patient with autosomal dominant cutis laxa

Elastin is the protein responsible for the characteristic elastic properties of many tissues including the skin, lungs and large blood vessels. Loss-of-function mutations in the elastin gene are known to cause the heart defect supravalvular aortic stenosis (SVAS). We and others have identified deletions, nonsense mutations and splice site mutations in SVAS patients that abolish the function of one elastin gene. We have now identified an elastin mutation in a patient with a completely different phenotype, the rare autosomal dominant condition cutis laxa. A frameshift mutation in exon 32 of the elastin gene is predicted to replace 37 amino acids at the C-terminus of elastin by a novel sequence of 62 amino acids. mRNA and immunoprecipitation studies show that the mutant allele is expressed. Electron microscopy of skin sections shows abnormal branching and fragmentation in the amorphous elastin component, and immunocytochemistry shows reduced elastin deposition in the elastic fibres and fewer microfibrils in the dermis. These findings suggest that the mutant tropoelastin protein is synthesized, secreted and incorporated into the elastic matrix, where it alters the architecture of elastic fibres. Interference with cross-linking would reduce elastic recoil in affected tissues and explain the cutis laxa phenotype.