A defect in the regional deposition of adipose tissue (partial lipodystrophy) is encoded by a gene at chromosome 1q

Partial lipodystrophy (PLD), also known as "Dunnigan-Kobberling syndrome," is transmitted as a highly penetrant autosomal dominant disorder that is characterized by a dramatic absence of adipose tissue in the limbs and trunk, more evident in females than in males. In contrast, fat is retained on the face, in retro-orbital space, and at periserous sites. Associated metabolic abnormalities, including insulin resistance, hyperinsulinemia, and dyslipidemia, are referred to as "metabolic syndrome X" (Reaven 1988). Despite the intense interest in the genetic determinants underlying fat deposition, the genes involved in the lipodystrophic syndromes have not been identified. We ascertained two multigeneration families, with a combined total of 18 individuals with PLD, and performed a genomewide search. We obtained conclusive evidence for linkage of the PLD locus to microsatellite markers on chromosome 1q21 (D1S498, maximum LOD score 6.89 at recombination fraction .00), with no evidence of heterogeneity. Haplotype and multipoint analysis support the location of the PLD locus within a 21.2-cM chromosomal region that is flanked by the markers D1S2881 and D1S484. These data represent an important step in the effort to isolate and characterize the PLD gene. The identification of the gene will have important implications for the understanding of both developmental and metabolic aspects of the adipocyte and may prove useful as a single-gene model for the common metabolic disorder known as "syndrome X."

Molecular analysis of the PDS gene in Pendred syndrome

Pendred syndrome is an autosomal recessive disorder characterized by the association between sensorineural hearing loss and thyroid swelling or goitre and is likely to be the most common form of syndromic deafness. Within the thyroid gland of affected individuals, iodide is incompletely organified with variable effects upon thyroid hormone biosynthesis, whilst the molecular basis of the hearing loss is unknown. The PDS gene has been identified by positional cloning of chromosome 7q31, within the Pendred syndrome critical linkage interval and encodes for a putative ion transporter called pendrin. We have investigated a cohort of 56 kindreds, all with features suggestive of a diagnosis of Pendred syndrome. Molecular analysis of the PDS gene identified 47 of the 60 (78%) mutant alleles in 31 families (includes three homozygous consanguineous kindreds and one extended family segregating three mutant alleles). Moreover, four recurrent mutations accounted for 35 (74%) of PDS disease chromosomes detected and haplotype analysis would favour common founders rather than mutational hotspots within the PDS gene. Whilst these findings demonstrate molecular heterogeneity for PDS mutations associated with Pendred syndrome, this study would support the use of molecular analysis of the PDS gene in the assessment of families with congenital hearing loss.

The diagnosis of Liddle syndrome by identification of a mutation in the beta subunit of the epithelial sodium channel

Hypertension is a common multifactorial disorder associated with considerable morbidity and mortality. The kidney plays a major role in the long term regulation of blood pressure. Liddle syndrome (pseudo-hyperaldosteronism) is one of a number of monogenic disorders of salt and water transport. In a kindred with at least four affected members suffering from Liddle syndrome, we confirmed by direct DNA sequencing the identity of a novel heterozygous mutation in h betaENaC, the gene encoding the beta subunit of the amiloride sensitive epithelial sodium channel which is expressed in the distal nephron. Single stranded conformational polymorphism analysis showed cosegregation of the mutant allele within the kindred with the Liddle phenotype. An insertion of an additional cytosine into a string of six located between codons 593 and 595 results in a sequence frameshift and is predicted to produce a protein truncated by 34 amino acids. The availability of a molecular diagnostic tool has implications for the management of hypertension and genetic counselling in families with Liddle syndrome.

Radiological malformations of the ear in Pendred syndrome

Pendred syndrome comprises the association of severe congenital sensorineural deafness with thyroid pathology. Although it is the commonest form of syndromic hearing loss, the primary genetic defect remains unknown. The variable clinical presentation allied to the difficulty in securing the diagnosis have resulted in relatively poor documentation of the radiological features of this syndrome. We now present data on 40 patients, all complying with strict diagnostic criteria for the disorder, and describe our experience of the prevalence of specific malformations of the inner ear as well as comparing the relative merits of computed tomography (CT) and magnetic resonance imaging (MRI) in the investigation of this inherited condition. Deficiency of the interscalar septum in the distal coils of the cochlea (Mondini deformity) was found to be a common but probably not a constant feature of Pendred syndrome. However, enlargement of the endolymphatic sac and duct in association with a large vestibular aqueduct was present in all 20 patients examined by MRI. We conclude that thin section high resolution MRI on a T2 protocol in the axial and sagittal planes is the imaging investigation of choice.

Association of atopic dermatitis to the beta subunit of the high affinity immunoglobulin E receptor

IgE dysregulation is a major pathogenic feature of atopic dermatitis and other IgE-mediated allergic diseases such as asthma and rhinitis. Allergen complexed to IgE binds to the high affinity receptor for IgE (Fc epsilon RI) on the surface of epidermal Langerhans cells, mast cells and basophils, triggering the release of inflammatory mediators. The beta subunit of Fc epsilon RI has been localized to human chromosome 11q12-13, and variants within this gene have been shown to associate with asthma and measures of atopy. We have tested several polymorphisms within Fc epsilon RI-beta for association to atopic dermatitis in a panel of 60 families (panel A), recruited through a proband with atopic dermatitis. The findings were tested in a second panel of families (panel B). Significant sharing of maternal alleles was seen for atopic dermatitis and allele 2 of RsaI intron 2 (RsaIvin2*2) (P = 0.0022) and allele 1 of RsaI exon 7 (RsaIvex7*1) (P = 0.0036) Fc epsilon RI-beta gene polymorphisms. These findings were replicated in Panel B, confirming the association of Fc epsilon RI-beta RsaI polymorphisms with atopic dermatitis. The combined significance of the association of atopic dermatitis to RsaI polymorphisms was P = 0.0002 (RsaIvin2*2) and P = 0.00034 (RsaIvex7*1). The polymorphisms also showed association with asthma: P = 0.0068 (RsaIvin2*2) and P = 0.018 (RsaIvex7*1). Polymorphisms within the Fc epsilon RI-beta gene are strongly associated with atopic dermatitis.

Identification of a major susceptibility locus on chromosome 6p and evidence for further disease loci revealed by a two stage genome-wide search in psoriasis

Psoriasis is a common chronic inflammatory disorder of the skin. To further understand the pathogenesis of psoriasis we have chosen to investigate the molecular genetic basis of the disorder. We have used a two-stage approach to search the human genome for the location of genes conferring susceptibility to psoriasis, using a total of 106 affected sibling pairs identified from 68 independent families. As over a third of the extended kindreds included affected relatives besides siblings, in addition to an analysis of allele sharing between affected sibling pairs, a novel linkage strategy was applied that extracts full non-parametric information. Four principal regions of possible linkage were identified on chromosomes 2, 8, 20 (p <0.005) and markers from the MHC region at 6p21 (p <0.0000006) for which significant evidence of linkage disequilibrium was also observed (p <0.00002). Whilst data from limited case control associations exist to implicate the MHC, the results of this genome wide analysis demonstrate that, at least in the population studied, a gene or genes located within the MHC and close to the class 1 HLA loci, represent the major determinant of the genetic basis of psoriasis.

Normal erythrocyte membrane Gs alpha bioactivity in two unrelated patients with acrodysostosis

Shortening of the tubular bones of the hands and feet with cone shaped epiphyses is known as peripheral dysostosis and is common to several syndromes including acrodysostosis and Albright's hereditary osteodystrophy (AHO). The underlying defect in AHO is known to be a reduction in bioactivity of the alpha subunit of the signal transducing protein, Gs, and heterozygous deactivating mutations have been shown in the Gs alpha gene. Because of additional overlapping clinical and radiological features it has been suggested that acrodysostosis and AHO represent poles of a single diagnostic spectrum. We have measured Gs alpha bioactivity in two unrelated patients with a clinical diagnosis of acrodysostosis and found both to be normal. Mutation analysis of the Gs alpha gene showed no sequence variation in 12 of the 13 exons examined. These results indicate that, at least in a proportion of patients with acrodysostosis, the condition is aetiologically distinct from AHO.

Dunnigan-Kobberling syndrome: an autosomal dominant form of partial lipodystrophy

Dunnigan-Kobberling syndrome is a form of partial lipodystrophy characterized by sparing of the face. Despite descriptions of six families since 1974, details of total body adipose tissue distribution and studies of carbohydrate and fat metabolism are lacking. The mode of inheritance also remains unclear, with most authors favouring an X-linked dominant transmission lethal in the hemizygous male. We examined 23 members of a family, of whom at least eight had partial lipodystrophy. Auxological evaluation and cross-sectional imaging showed absence of subcutaneous fat, presence of adipose tissue inside the body cavities, and skeletal muscle hypertrophy. Biochemical evaluation identified insulin resistance but revealed inadequate suppression of non-esterified fatty acids. In this family, male-to-male transmission supports an autosomal dominant mode of inheritance for Dunnigan-Kobberling syndrome.

Maternal uniparental disomy 7 in Silver-Russell syndrome

Silver-Russell syndrome (SRS) is characterised by intrauterine and postnatal growth failure accompanied by a variable number of dysmorphic features. It is usually sporadic although a few familial cases have been described. In a prospective study of 33 patients with sporadic SRS, we have studied the parent of origin of chromosome 7 using variable number tandem repeat (VNTR) or microsatellite repeat markers and have identified two patients with maternal uniparental disomy of chromosome 7 (mUPD7). In one family, inconsistent inheritance of paternal alleles of markers on chromosomes other than 7 led to their exclusion from further study. The probands were clinically mild and symmetrical, but showed no gross clinical differences from the 30 patients with chromosome 7 derived from both parents.

Genetic studies of atopy and atopic dermatitis

Atopy and the atopic disorders are likely to result from multifactorial inheritance, with interaction between genetic and environmental factors. It has been proposed that at least two major mechanisms, non-antigen specific (total IgE levels) and antigen specific (specific IgE antibodies and skin tests), regulate the immune response to allergens in humans: firstly, a gene/genes independent of the human leucocyte antigen system which is involved in the regulation of total IgE levels, and secondly, a specific immune response gene/genes associated with major histocompatibility complex class II genes which are involved in antigen-specific mechanisms. Candidate genes have been proposed for both mechanisms and linkage has been found between atopy and at least three different gene loci. This paper reviews the evidence supporting a genetic basis for atopy and atopic dermatitis and outlines recent advances in the molecular genetic mapping of genes associated with these disorders.

Familial infiltrative fibromatosis (desmoid tumours) (MIM135290) caused by a recurrent 3' APC gene mutation

Desmoid tumours are generally very rare but occur about 100 times more frequently in the colorectal cancer predisposition syndrome familial adenomatous polyposis (MIM 175100), being represented in about 10% of patients. In addition to desmoid disease occurring in familial adenomatous polyposis (FAP) there exist familial infiltrative fibromatosis (MIM 135290) kindreds where there is no evidence of FAP. Previously we have described a kindred with familial infiltrative fibromatosis (FIF) in which desmoid tumours were associated with nonpolyposis colorectal cancer. FAP is caused by mutations in the APC gene and various genotype-phenotype relationships have been defined including reports that colorectal polyposis is less severe with mutations 5' to codon 157 and that the risk of desmoid tumours is high in FAP patients with APC gene mutations between codons 1444 and 1598. There is relatively little information on the phenotype of APC gene mutations 3' to codon 1598; however, one large family has been reported with a mutation at codon 1987 which presents with a highly variable phenotype which includes desmoid disease. We screened our original FIF kindred and three further families with a similar phenotype for mutations in the APC gene. A 4 bp frameshift deletion in codon 1962 was identified in the original FIF kindred and two further apparently unrelated families. Haplotype analysis suggests a common origin for the APC mutation in all three families. Affected individuals had no evidence of congenital hypertrophy of the retinal pigment epithelium. Colorectal polyposis was variable, and most affected patients had either none or a few late onset polyps. These findings demonstrate (i) that FAP and FIF are allelic, and (ii) that APC gene mutations which truncate the APC protein distal to the beta-catenin binding domain are associated with desmoid tumours, absent CHRPE and variable but attenuated polyposis expression.

Pendred syndrome

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Isolated autosomal dominant type E brachydactyly: exclusion of linkage to candidate regions 2q37 and 20q13

Type E brachydactyly is a digital malformation which characteristically causes an asymmetrical shortening of one or more metacarpals or metatarsals or both. Although commonly seen as part of a syndrome, it can be inherited as an autosomal dominant characteristic, the gene acting with variable expressivity, but complete penetrance. As an Albright hereditary osteodystrophy (AHO)-like syndrome including brachydactyly type E and mental retardation may be caused by (micro) deletions at chromosome 2q37, this region together with the AHO locus at chromosome 20q13 were considered as candidate loci for brachydactyly type E. In this paper we described a family with isolated autosomal dominant type E brachydactyly in whom molecular analysis excludes linkage to these regions, providing support for further genetic heterogeneity of this trait.

Familial exudative vitreoretinopathy linked to D11S533 in a large Asian family with consanguinity

Familial exudative vitreoretinopathy (FEVR) is a disorder characterised by peripheral retinal vascularisation with subsequent traction of retinal vessels and detachment. Recently, autosomal dominant FEVR (ad FEVR) has been mapped to 11q13 by linkage in four northern European families. We describe a large consanguineous Asian family in which the severity of the proband's eye disease suggested homozygosity for a disease allele. Thirty family members were assessed by ophthalmological examination and fluorescein angiography. Thirteen had unequivocal features of FEVR. A further two were classified as unknown. Two point linkage analysis for DIIS533 and FEVR generated a lod score of 5.55 at a recombination fraction of 0.00. This supports autosomal dominant inheritance and demonstrates genetic homogeneity for the ad FEVR disease locus. The severely affected proband was heterozygous for alleles at this closely linked locus. Other causes, including non-genetic factors, should be considered to explain the extreme variability characteristic of ad FEVR.

Parental origin of Gs alpha gene mutations in Albright's hereditary osteodystrophy

Heterozygous mutations of the Gs alpha gene leading to reduced Gs alpha activity have been identified in patients with Albright's hereditary osteodystrophy (AHO). However, AHO may be associated with hormone resistance (pseudohypoparathyroidism type Ia, PHPIa) or a normal response (pseudo-pseudohypoparathyroidism, PPHP). As both disorders may occur within the same family, the relationship between Gs alpha genotype and phenotype remains unresolved. The AHO phenotype may be dependent upon the sex of the parent transmitting the Gs alpha mutation, perhaps through a gene imprinting mechanism. We have used an intragenic Gs alpha FokI polymorphism to determine the parental origin of Gs alpha gene mutations in sporadic and familial AHO. We now show that a de novo G-->A substitution at the exon 5 donor splice junction in a child with PPHP was paternally derived. Furthermore, in a female with PPHP, the Gs alpha abnormality was shown to be of paternal origin, while subsequent maternal processing and transmission resulted in PHPIa in two offspring. As transmission of PPHP has rarely been reported, determining parental origin of the disease allele in sporadic cases may provide insight into the mechanism of hormone resistance in AHO.

Albright's hereditary osteodystrophy

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Maternally inherited diabetes and deafness is a distinct subtype of diabetes and associates with a single point mutation in the mitochondrial tRNA(Leu(UUR)) gene

We have recently reported an A to G transition at nucleotide position 3243 in the mitochondrial DNA (mtDNA) tRNA(Leu(UUR)) gene in a large family with non-insulin-dependent diabetes mellitus (NIDDM). Characteristic was its maternal transmission and an associated sensorineural hearing loss. In a screening of a Dutch and French NIDDM population for the presence of the tRNA(Leu(UUR)) mutation we identified two new pedigrees in which NIDDM is present in combination with deafness. The mode of inheritance agrees with a maternal one. This result shows that patients with a phenotype of NIDDM and deafness can be identified within groups of NIDDM patients based on the tRNA(Leu(UUR)) mutation. The same mutation has also been linked to the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). How the same mutation can give rise to different clinical phenotypes is not clear. We obtained the complete mtDNA sequence from our initial pedigree and identified a number of additional mutations that could confer the phenotype of the tRNA(Leu(UUR)) mutation to diabetes. We examined the presence of these additional, potentially pathogenic mutations in the mtDNA from the two new pedigrees and from a previously described British pedigree. The absence of these mutations in all three pedigrees shows that the tRNA(Leu(UUR)) mutation alone associates with the phenotype of NIDDM and deafness. We conclude that maternally inherited diabetes and deafness is a distinct subtype of diabetes that is associated with a single mitochondrial tRNA(Leu(UUR)) mutation. We propose the abbreviation MIDD for this particular subtype.

An association between psoriasis and hereditary multiple exostoses. A clue for the mapping of a psoriasis susceptibility gene?

Chronic plaque psoriasis affects approximately 1.6% of the U.K. population. Population, family and twin studies all strongly suggest an important genetic component in the pathogenesis of the disease, although genetic linkage studies have, so far, failed to identify susceptibility genes. We describe a family in which psoriasis cosegregates through three generations with a known autosomal dominant disorder, hereditary multiple exostoses (HME). A major locus for HME has recently been mapped to chromosome 8q. Observations in this family may provide a mapping clue for a psoriasis susceptibility gene.

Genetic mechanisms and mental retardation

The past five years have witnessed rapid and apparently relentless progress in the delineation of the genetic basis of disorders associated with mental retardation. Each gene discovery has a new story to tell but inevitably generates further questions. For the clinical geneticist and, perhaps more importantly, for patients and their families, many of these recent discoveries have yielded information which has immediate implications for diagnostic testing, family and population screening and prenatal testing. Many of the ethical issues consequent upon the rapid progress are only now being addressed. This article highlights a number of disorders whose molecular genetic basis has recently been further characterised. Brain development and maintenance of neurological networks provide the unifying theme; the genetic defects are disparate and each of their mechanisms appears to be novel.

Erythromycin induces supranormal gall bladder contraction in diabetic autonomic neuropathy

Gall bladder motor function is impaired in some patients with diabetes. It has been suggested that the abnormalities of gall bladder motility are confined to those patients with autonomic neuropathy. Erythromycin, a motilin receptor agonist, causes gall bladder contraction in both normal subjects and patients with gall stones with impaired gall bladder emptying. The effect of erythromycin on gall bladder motility in seven patients with diabetes with an autonomic neuropathy, six patients with diabetes without autonomic neuropathy, and 17 normal subjects was studied using ultrasound. There was no significant difference in gall bladder fasting volume between the three groups, but the patients with diabetes with autonomic neuropathy had impaired postprandial gall bladder emptying compared with normal subjects (percentage emptied (SEM) 40 (10.3)% v 64 (2.8)%, p < 0.01) and those with autonomic neuropathy (48 (7.7)%, NS). Erythromycin produced a dramatic reduction in gall bladder fasting volume in patients with diabetes with an autonomic neuropathy, compared with either normal subjects or patients with diabetes without autonomic neuropathy (percentage reduction 62 (4.6)% in patients with autonomic neuropathy, v 37 (17.6)% in those without autonomic neuropathy, and 26 (7.3)% in the normal subjects, (p < 0.02) and returned gall bladder emptying to normal in all patients with impaired emptying. The pronounced effect of erythromycin in diabetic autonomic neuropathy suggests denervation supersensitivity and that the action of erythromycin on the gall bladder is neurally modulated.

Chromosome 11q13 and atopy underlying atopic eczema

Genetic linkage has been reported between atopic respiratory disease and chromosome site 11q13. We recruited 95 multiplex families through probands with active atopic eczema. Linkage analyses between atopy and markers on 11q13 excluded a major susceptibility locus for atopy in this region. Nor was there significant deviation from the expected proportions of alleles shared by affected sib-pairs. When we analysed families according to parental atopic phenotype, we observed a positive lod score (0.8) in 19 families with unaffected fathers, in contrast to markedly negative scores for other combinations of affected parental phenotype. The possibility of a maternal influence on the inheritance of atopy cannot, therefore, be excluded.

Effect of octreotide on gall stone prevalence and gall bladder motility in acromegaly

Octreotide therapy in acromegaly is associated with an increased prevalence of gall stones, which may be the result of an inhibition of gall bladder motility. Gall stone prevalence in untreated acromegalic patients relative to the general population is unknown, however, and the presence of gall stones and gall bladder motility in these patients and in acromegalic patients receiving octreotide was therefore examined. Thirty four percent of 39 patients who had taken octreotide for a mean of 20 months had gall stones compared with 16% of 38 patients who had not been treated with octreotide (p < 0.005). In a subgroup of 21 patients studied prospectively over 4 to 18 months, two patients developed stones. No patient had symptoms referrable to their gall stones. In 31 untreated acromegalic patients, the mean fasting gall bladder volume was similar to that in normal subjects. Maximal percentage emptying, however, was impaired (34 v 64%, p < 0.001) and the mean postprandial residual gall bladder volume increased (21.7 v 9.0 ml, p < 0.001). Treatment with octreotide increased the mean postprandial residual volume further to 36.8 ml (p < 0.001). Gall bladder emptying in untreated acromegalic subjects is impaired. Octreotide further increases postprandial residual gall bladder volume and this may be a factor in the increased gall stone prevalence seen in these patients.