Unusual presentation of a severe autosomal recessive anhydrotic ectodermal dysplasia with a novel mutation in the EDAR gene

We report on an 18-year-old woman, born to first-cousin parents, presenting with a severe form of anhydrotic ectodermal dysplasia (EDA/HED). She had sparse hair, absent limb hair, absent sweating, episodes of hyperpyrexia, important hypodontia, and hyperconvex nails. She also showed unusual clinical manifestations such as an absence of breasts, a rudimentary extranumerary areola and nipple on the left side, and marked palmo-plantar hyperkeratosis. Light microscopy of skin biopsies showed orthokeratotic hyperkeratosis and absence of sweat glands. A novel homozygous mutation (IVS9 + 1G > A) in the EDAR gene was identified. This mutation results in a total absence of EDAR transcripts and consequently of the EDAR protein, which likely results in abolition of all ectodysplasin-mediated NF-kappaB signaling. This is the first complete loss-of-function mutation in the EDAR gene reported to date, which may explain the unusual presentation of HED in this patient, enlarging the clinical spectrum linked to the dysfunction of the ectodysplasin mediated NF-kappaB signaling.

Re-assigning the DFNB33 locus to chromosome 10p11.23-q21.1

Homozygosity mapping is a powerful resource for mapping and identifying loci and genes responsible for autosomal recessive disorders. Nevertheless, it could result in the identification of several homozygous regions unrelated to the disease locus or non-informative regions. Previously, a genome-wide screen in a large consanguineous Jordanian family allowed us to assign the DFNB33 locus to chromosome 9q34.3. Sequencing of 23 candidate genes showed 11 SNPs in a heterozygous state in affected individuals. These results ruled out the candidate region on chromosome 9. Using additional markers, we were able to restrict the disease locus to an approximately 14 cM region at chromosome 10, located between markers D10S193 and D10S1784. A maximum LOD score of 3.99 was obtained with two markers, D10S199 and D10S220. The screening of two candidate genes, CX40.1 and FXYD4, failed to reveal any disease-causing mutations.

2-Methylbutyryl-coenzyme A dehydrogenase deficiency: functional and molecular studies on a defect in isoleucine catabolism

2-Methylbutyryl-CoA dehydrogenase (MBD; coded by the ACADSB gene) catalyzes the step in isoleucine metabolism that corresponds to the isovaleryl-CoA dehydrogenase reaction in the degradation of leucine. Deficiencies of both enzymes may be detected by expanded neonatal screening with tandem-mass spectrometry due to elevated pentanoylcarnitine (C5 acylcarnitine) in blood, but little information is available on the clinical relevance of MBD deficiency. We biochemically and genetically characterize six individuals with MBD deficiency from four families of different ethnic backgrounds. None of the six individuals showed clinical symptoms attributable to MBD deficiency although the defect in isoleucine catabolism was demonstrated both in vivo and in vitro. Several mutations in the ACADSB gene were identified, including a novel one. MBD deficiency may be a harmless metabolic variant although significant impairment of valproic acid metabolism cannot be excluded and further study is required to assess the long-term outcome of individuals with this condition. The relatively high prevalence of ACADSB gene mutations in control subjects suggests that MBD deficiency may be more common than previously thought but is not detected because of its usually benign nature.

Familial Mediterranean Fever in Lebanon: founder effects for different MEFV mutations

Haplotype analysis of 376 Familial Mediterranean Fever (FMF) patients and 100 controls from Lebanon was performed using 4 microsatellite loci to study founder effects for the five most frequent mutations within the MEFV gene (M694V, M694I, V726A, M680I and E148Q). Each of these mutations was associated with a particular haplotype that was less frequent among controls, confirming that they have probably arisen from unique mutation events and that the carrier chromosomes derived from a common ancestor. The estimated ages of the most recent common ancestor for each of the 5 mutations, using the ESTIAGE program, were 7000, 8500, 15000, 23000 and 30000 years for M694V, M694I, V726A, M680I and E148Q, respectively. Varying the mutation rate at one of the markers led to younger age estimates, but the mutation E148Q remained the oldest one. Comparison of haplotype distributions among the different Lebanese religious groups confirmed that Muslim sub-populations (Shiites and Sunnites) as well as Christian ones, including Armenians who were formerly settled in the South-Eastern part of Asia Minor (Cilicia), are all derived from an ancient common ancestral population in which most of the MEFV mutations were already present with their respective associated haplotypes.

Cytogenetic investigation of a child with a mosaic isochromosome 18q and ring 18q

We report on a baby girl from non-consanguineous Palestinian parents with intrauterine growth retardation, low birth weight, and developmental delay. She had a short stature, microcephaly, a prominent metopic suture, a glabellar haemangioma, exophthalmos, hypertelorism, upslanting palpebral fissures, horizontal nystagmus, flat nose, cleft lip and palate, a short neck, widely spaced nipples, umbilical hernia, flexion deformity of the wrist, ulnar deviation of fingers, and right club foot. Cortical atrophy, enlarged ventricles, a thin corpus callosum, thoracic hemivertebrae, and a ventricular septal defect were detected as well. High resolution chromosome analysis identified in 92% of cells an isochromosome 18 and in 8% of cells a ring 18. Molecular cytogenetic investigations confirmed that it was an i(18q) and a r(18q). The hypothesis to account for this anomaly and its corresponding phenotype are discussed.

Molecular study of six families originating from the Middle-East and presenting with autosomal recessive osteopetrosis

Autosomal recessive osteopetrosis is a severe hereditary bone disease whose cellular basis is in the osteoclast, but with heterogeneous molecular defects. We hereby report the clinical and the molecular study of seven patients affected by the recessive form of osteopetrosis (ARO) from six families originating from the Middle-East: four from Lebanon and two from Syria. Parental consanguinity was found in five families. The mean age of diagnosis was 3 months. Failure to thrive, prominent forehead, exophthalmia, optic atrophy, hepatosplenomegaly, neurological manifestations, anaemia, thrombocytopenia, hypocalcaemia, elevated hepatic enzymes and acid phosphatase, and an early fatal outcome were common. Macrocephaly, strabismus, and brain malformations were relatively less common. Mutations were identified in two genes: TCIRG1 and OSTM1. Phenotype-genotype correlation is discussed.

Osseous dysplasia with severe short stature, multiple dislocations, and delayed bone age: Report on a second Lebanese patient

We describe a young girl with severe pre- and postnatal short stature, bilateral dislocation of hips, knees and elbows, and right clubfoot. Skeletal investigations disclosed an anisospondyly, the absence of ossification of the odontoid apophysis and of fusion of the neural arches of the cervical vertebrae, abnormal L3 and L4 vertebrae, partial agenesis of the coccyx, abnormal and sub-luxated radial heads, bilateral dislocation of the hips, dysplastic acetabulae, pseudoacetabulae, hypoplasia of the femoral heads, short femoral necks, short long bones with thin diaphyses, widening of the medullary canal and thinning of the cortical one, slightly enlarged metaphyses, and diffuse osseous demineralization. Bone age was delayed. The girl's parents are first cousins. Differential diagnoses are discussed and the possibility is raised that this might be a second patient with clinical features indicating an entity recently described in a young Lebanese boy [Mégarbané and Ghanem (2004); Am J Med Genet Part A 130A: 107-109]. A clinical follow-up of the latter patient is also reported.

Familial Mediterranean fever in the Syrian population: gene mutation frequencies, carrier rates and phenotype–genotype correlation

BACKGROUND

Familial Mediterranean fever (FMF) is an autosomal recessive disease mainly affecting particularly Arabs, Non-Ashkenazi Jews, Armenians, and Turks. It is an autoinflammatory periodic disorder characterized by febrile and painful attacks due to inflammation involving the serosal membranes in the abdomen, chest or joints. Over 50 mutations have been identified in the MEFV gene responsible for FMF.

OBJECTIVE

To identify the distribution and the frequency of the MEFV gene mutations in Syrian FMF patients and population and perform a genotype/phenotype correlation in the patients' cohort.

PATIENTS AND METHODS

The study was carried out on 83 clinically diagnosed Syrian FMF patients and 242 healthy subjects. The tested individuals were screened for the most common five MEFV mutations (M694V, M694I, M680I, V726A and E148Q) by restriction fragment length polymorphism. Sequencing of exon 10 was performed only for the patients' DNA where just one or no mutation was detected.

RESULTS AND DISCUSSION

Of the 83 patients studied, 74 (89%) were positive either for one, two or three mutations and nine (11%) had no mutations detected. Of those positive for mutations, 25 were homozygous, 30 were compound heterozygotes, three had complex alleles, and 16 patients had only one mutation. The M694V, V726A, M694I, M680I and E148Q mutations accounted for 45.8%, 26%, 13.9%, 4.8% and 6% of the alleles, respectively. The carrier rate in the Syrian population for the tested mutations was 17.5%, E148Q being the most common mutation, followed by V726A and M694V. The severity of the disease and development of amyloidosis seem to have an association with M694V, the most common mutation in Syrian FMF patients.

A newly recognized autosomal recessive syndrome with short stature and oculo-skeletal involvement

This report describes a young girl and her cousin presenting with postnatal short stature, strabismus, photophobia, retinitis pigmentosa, short neck, rhizomelic shortening of the long bones, short and slightly bowed humeri with prominent deltoid tuberosities, short and wide ribs and clavicles, dorso-lumbar scoliosis, biconcave vertebral bodies of the thoraco-lumbar spine, and narrowed lumbar canal. In addition, in the girl there were amelogenesis imperfecta of the hypomaturation type, and the radiographs showed short distal ulnae, sloping epiphyses of the radii, short femoral necks, and slightly flat uncovered femoral heads. The children's parents are first cousins. Differential diagnoses are discussed and the possibility of a newly recognized oculo-skeletal syndrome is raised.

Pitfalls of homozygosity mapping: an extended consanguineous Bardet-Biedl syndrome family with two mutant genes (BBS2, BBS10), three mutations, but no triallelism

The extensive genetic heterogeneity of Bardet-Biedl syndrome (BBS) is documented by the identification, by classical linkage analysis complemented recently by comparative genomic approaches, of nine genes (BBS1-9) that account cumulatively for about 50% of patients. The BBS genes appear implicated in cilia and basal body assembly or function. In order to find new BBS genes, we performed SNP homozygosity mapping analysis in an extended consanguineous family living in a small Lebanese village. This uncovered an unexpectedly complex pattern of mutations, and led us to identify a novel BBS gene (BBS10). In one sibship of the pedigree, a BBS2 homozygous mutation was identified, while in three other sibships, a homozygous missense mutation was identified in a gene encoding a vertebrate-specific chaperonine-like protein (BBS10). The single patient in the last sibship was a compound heterozygote for the above BBS10 mutation and another one in the same gene. Although triallelism (three deleterious alleles in the same patient) has been described in some BBS families, we have to date no evidence that this is the case in the present family. The analysis of this family challenged linkage analysis based on the expectation of a single locus and mutation. The very high informativeness of SNP arrays was instrumental in elucidating this case, which illustrates possible pitfalls of homozygosity mapping in extended families, and that can be explained by the rather high prevalence of heterozygous carriers of BBS mutations (estimated at one in 50 in Europeans).

BBS10 encodes a vertebrate-specific chaperonin-like protein and is a major BBS locus

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous ciliopathy. Although nine BBS genes have been cloned, they explain only 40-50% of the total mutational load. Here we report a major new BBS locus, BBS10, that encodes a previously unknown, rapidly evolving vertebrate-specific chaperonin-like protein. We found BBS10 to be mutated in about 20% of an unselected cohort of families of various ethnic origins, including some families with mutations in other BBS genes, consistent with oligogenic inheritance. In zebrafish, mild suppression of bbs10 exacerbated the phenotypes of other bbs morphants.

Screening for subtelomeric rearrangements using automated fluorescent genotyping of microsatellite markers: a Lebanese study

A screening for submicroscopic rearrangements using specific polymorphic microsatellite markers from the subtelomeric regions of all chromosome arms was performed in 34 independent Lebanese families, including 45 patients with idiopathic mental retardation plus additional features. Five cryptic rearrangements were found in five different families, but subsequent FISH studies confirmed only three of those, showing a proportion of nearly 9% of subtelomeric rearrangements in our population. Two patients presented a de novo deletion from paternal origin, one involving telomere 3p, and another telomere 7p. An unbalanced paternally inherited translocation was detected in two patients from the same family resulting in both trisomy for telomere 5q and monosomy for telomere 6p.

[Pre-symptomatic diagnosis of severe hereditary diseases with late onset in Lebanon: a choice or a necessity?]

Progress achieved in the field of molecular genetics has opened the door to pre-symptomatic diagnosis tests of several severe hereditary disease, a majority of which are dominant and appear later in life. Given the importance of diagnosis in some of the cases where medical supervision and prevention are possible, there are a number of ethical dilemmas with regards to most of these diseases that, unfortunately, do not have a cure or any preventive treatment available. Above and beyond the capacity for medical care provision, there is a very high level of pressure and anxiety felt by every member of a family who has someone affected by one of these diseases in that they might be a carrier of a mutated gene which could be the cause or source of illness. They carry the burden of uncertainty that they may have already transmitted this gene or could give it to any of their children, and often there is also a significant level of guilt when one is the carrier but not to be affected by the disease itself. More and more frequently in these types of cases, there is a strong desire to know--in order to better organise and plan one's life and that of one's potential future family in the instance where one wishes to found one. This article discusses these problems based upon the consideration of four examples of such diseases with late onset: Huntington's disease, the common forms of thyroid cancer, the familiar forms of a predisposition to breast and ovarian cancer, and von Hippel-Lindau syndrome. However, regardless of the type of disease, the decision to take a genetic test is solely the choice of the individual in question, and the person should be accompanied and guided in his or her reflection by a multi-disciplinary team who can advise him or her and initiate useful deliberations on the various possibilities, their advantages and their disadvantages.

Mutations in a new cytochrome P450 gene in lamellar ichthyosis type 3

We report the identification of mutations in a non-syndromic autosomal recessive congenital ichthyosis (ARCI) in a new gene mapping within a previously identified locus on chromosome 19p12-q12, which has been defined as LI3 in the OMIM database (MIM 604777). The phenotype usually presents as lamellar ichthyosis and hyperlinearity of palms and soles. Seven homozygous mutations including five missense mutations and two deletions were identified in a new gene, FLJ39501, on chromosome 19p12 in 21 patients from 12 consanguineous families from Algeria, France, Italy and Lebanon. FLJ39501 encodes a protein which was found to be a cytochrome P450, family 4, subfamily F, polypeptide 2 homolog of the leukotriene B4-omega-hydroxylase (CYP4F2) and could catalyze the 20-hydroxylation of trioxilin A3 from the 12(R)-lipoxygenase pathway. Further oxidation of this substrate by the fatty alcohol:nicotinamide-adenine dinucleotide oxidoreductase (FAO) enzyme complex, in which one component, ALDH3A2, is known to be mutated in Sjögren-Larsson syndrome (characterized by ichthyosis and spastic paraplegia), would lead to 20-carboxy-(R)-trioxilin A3. This compound could be involved in skin hydration and would be the essential missing product in most forms of ARCI. Its chiral homolog, 20-carboxy-(S)-trioxilin A3, could be implicated in spastic paraplegia and in the maintenance of neuronal integrity.

BBS8 is rarely mutated in a cohort of 128 Bardet–Biedl syndrome families

BBS8 is one of the eight genes identified to date for Bardet-Biedl syndrome (BBS)-an autosomal recessive condition associated with retinitis pigmentosa, obesity, polydactyly, cognitive impairment and kidney failure. The identification of BBS8 gave the key to the pathogenesis of the condition as a primary ciliary disorder. To date, only three families mutated in the BBS8 gene have been reported. Here, we report on three additional families with BBS8 mutations from a series of 128 BBS families. Two of the three families have homozygous mutations and one has a heterozygous mutation. Mutations in BBS8 probably account for only a minority of BBS families (2%), underlining the difficulty of genotyping heterogeneous conditions.

Familial Mediterranean fever (FMF) in Lebanon and Jordan: a population genetics study and report of three novel mutations

Familial Mediterranean fever (FMF) is an autosomal recessive disease mostly frequent in Mediterranean populations. Over 50 mutations have been identified in the gene responsible for the disease, MEFV. The present study reports the frequencies of MEFV mutations in 558 Lebanese and 55 Jordanian FMF patients and points out the severity of the M694V frequently observed mutation among these patients. Three novel mutations, T177I, S108R and E474K were also identified in the Lebanese group. An excess of homozygotes and a deficit of heterozygotes were observed in both samples when compared to the expected number of observed genotypes under the Hardy-Weinberg hypothesis. Homozygotes for M694V and M694I were still in excess in the Lebanese group of patients, even after consanguinous homozygotes were removed, or population structure was considered. This excess is therefore neither due to consanguinity nor to subgroups in the Lebanese population, but rather to more remote consanguinity or to a selection bias favoring the census of these genotypes. The fact that FMF female patients were less censed than male patients may be due to the greater resistance of females to pain and to the possibility of confusing abdominal and gynecological pain. The phenotypic heterogeneity of the FMF could then originate both from genetic causes like allelic heterogeneity or modulating genes, and cultural background facing the physiological consequences of genotypes at risk.