Search for ReCQL4 mutations in 39 patients genotyped for suspected Rothmund-Thomson/Baller-Gerold syndromes

Three overlapping conditions, namely Rothmund-Thomson (RTS), Baller-Gerold (BGS) and RAPADILINO syndromes, have been attributed to RECQL4 mutations. Differential diagnoses depend on the clinical presentation, but the numbers of known genes remain low, leading to the widespread prescription of RECQL4 sequencing. The aim of our study was therefore to determine the best clinical indicators for the presence of RECQL4 mutations in a series of 39 patients referred for RECQL4 molecular analysis and belonging to the RTS (27 cases) and BGS (12 cases) spectrum. One or two deleterious RECQL4 mutations were found in 10/27 patients referred for RTS diagnosis. Clinical and molecular reevaluation led to a different diagnosis in 7/17 negative cases, including Clericuzio-type poikiloderma with neutropenia, hereditary sclerosing poikiloderma, and craniosynostosis/anal anomalies/porokeratosis. No RECQL4 mutations were found in the BGS group without poikiloderma, confirming that RECQL4 sequencing was not indicated in this phenotype. One chromosomal abnormality and one TWIST mutation was found in this cohort. This study highlights the search for differential diagnoses before the prescription of RECQL4 sequencing in this clinically heterogeneous group. The combination of clinically defined subgroups and next-generation sequencing will hopefully bring to light new molecular bases of syndromes with poikiloderma, as well as BGS without poikiloderma.

Loss of ALDH18A1 function is associated with a cellular lipid droplet phenotype suggesting a link between autosomal recessive cutis laxa type 3A and Warburg Micro syndrome

Autosomal recessive cutis laxa type 3A is caused by mutations in ALDH18A1, a gene encoding the mitochondrial enzyme Δ¹-pyrroline-5-carboxylate synthase (P5CS). It is a rare disorder with only six pathogenic mutations and 10 affected individuals from five families previously described in the literature. Here we report the identification of novel compound heterozygous missense mutations in two affected siblings from a Lebanese family by whole-exome sequencing. The mutations alter a conserved C-terminal domain of the encoded protein and reduce protein stability as determined through Western blot analysis of patient fibroblasts. Patient fibroblasts exhibit a lipid droplet phenotype similar to that recently reported in Warburg Micro syndrome, a disorder with similar features but hitherto unrelated cellular etiology.

A second family with autosomal recessive spondylometaphyseal dysplasia and early death

We report on a consanguineous Lebanese family in which two sibs had pre- and post-natal growth retardation, developmental delay, large anterior fontanel, prominent forehead, low-set ears, depressed nasal bridge, short nose, anteverted nares, increased nasal width, prominent abdomen, and short limbs. Radiographs disclosed the presence of wormian bones, platyspondyly, decreased interpedicular distance at the lumbar vertebrae, square iliac bones, horizontal acetabula, trident acetabula, hypoplastic ischia, partial agenesis of the sacrum, ribs with cupped ends, short long bones with abnormal modeling, slight widening of the distal femoral metaphyses, and delayed epiphyseal ossification. Both sibs had a severe cardiomegaly and died at around 24 months from a heart failure. Differential diagnosis suggests that this is a second family presenting a newly described early lethal chondrodysplasia first reported by [Mégarbané et al. (2008); Am J Med Genet Part A 146A:2916-2919].

The intellectual disability of trisomy 21: differences in gene expression in a case series of patients with lower and higher IQ

Trisomy 21 (T21), or Down syndrome (DS), is the most frequent and recognizable cause of intellectual disabilities. The level of disability, as evaluated by the intelligence quotient (IQ) test, varies considerably between patients independent of other factors. To determine the genetic or molecular basis of this difference, a high throughput transcriptomic analysis was performed on twenty T21 patients with high and low IQ, and 10 healthy controls using Digital Gene Expression. More than 90 millions of tags were sequenced in the three libraries. A total of 80 genes of potential interest were selected for the qPCR experiment validation, and three housekeeping genes were used for normalizing purposes. HLA DQA1 and HLA DRB1 were significantly downregulated among the patients with a low IQ, the values found in the healthy controls being intermediate between those noted in the IQ+ and IQ- T21 patients. Interestingly, the intergenic region between these genes contains a binding sequence for the CCCTC-binding factor, or CTCF, and cohesin (a multisubunit complex), both of which are essential for expression of HLA DQA1 and HLA DRB1 and numerous other genes. Our results might lead to the discovery of genes, or genetic markers, that are directly involved in several phenotypes of DS and, eventually, to the identification of potential targets for therapeutic interventions.

Oto-facial syndrome and esophageal atresia, intellectual disability and zygomatic anomalies - expanding the phenotypes associated with EFTUD2 mutations

Background

Mutations in EFTUD2 were proven to cause a very distinct mandibulofacial dysostosis type Guion-Almeida (MFDGA, OMIM #610536). Recently, gross deletions and mutations in EFTUD2 were determined to cause syndromic esophageal atresia (EA), as well. We set forth to find further conditions caused by mutations in the EFTUD2 gene (OMIM *603892).

Methods and results

We performed exome sequencing in two familial cases with clinical features overlapping with MFDGA and EA, but which were previously assumed to represent distinct entities, a syndrome with esophageal atresia, hypoplasia of zygomatic complex, microcephaly, cup-shaped ears, congenital heart defect, and intellectual disability in a mother and her two children [AJMG 143A(11):1135-1142, 2007] and a supposedly autosomal recessive oto-facial syndrome with midline malformations in two sisters [AJMG 132(4):398-401, 2005]. While the analysis of our exome data was in progress, a recent publication made EFTUD2 mutations highly likely in these families. This hypothesis could be confirmed with exome as well as with Sanger sequencing. Also, in three further sporadic patients, clinically overlapping to these two families, de novo mutations within EFTUD2 were identified by Sanger sequencing. Our clinical and molecular workup of the patients discloses a broad phenotypic spectrum, and describes for the first time an instance of germline mosaicism for an EFTUD2 mutation.

Conclusions

The clinical features of the eight patients described here further broaden the phenotypic spectrum caused by EFTUD2 mutations or deletions. We here show, that it not only includes mandibulofacial dysostosis type Guion-Almeida, which should be reclassified as an acrofacial dysostosis because of thumb anomalies (present in 12/35 or 34% of patients) and syndromic esophageal atresia [JMG 49(12). 737-746, 2012], but also the two new syndromes, namely oto-facial syndrome with midline malformations published by Mégarbané et al. [AJMG 132(4): 398-401, 2005] and the syndrome published by Wieczorek et al. [AJMG 143A(11): 1135-1142, 2007] The finding of mild phenotypic features in the mother of one family that could have been overlooked and the possibility of germline mosaicism in apparently healthy parents in the other family should be taken into account when counseling such families.

Genotype-phenotype correlations emerging from the identification of missense mutations in MBTPS2

Missense mutations affecting membrane-bound transcription factor protease site 2 (MBTPS2) have been associated with Ichthyosis Follicularis with Atrichia and Photophobia (IFAP) syndrome with or without BRESHECK syndrome, with keratosis follicularis spinulosa decalvans, and Olmsted syndrome. This metalloprotease activates, by intramembranous trimming in conjunction with the protease MBTPS1, regulatory factors involved in sterol control of transcription and in cellular stress response. In this study, 11 different MBTPS2 missense mutations detected in patients from 13 unrelated families were correlated with the clinical phenotype, with their effect on cellular growth in media without lipids, and their potential role for sterol control of transcription. Seven variants were novel [c.774C>G (p.I258M); c.758G>C (p.G253A); c.686T>C (p.F229S); c.1427T>C (p.L476S); c.1430A>T (p.D477V); c.1499G>A (p.G500D); c.1538T>C (p.L513P)], four had previously been reported in unrelated sibships [c.261G>A (p.M87I); c.1286G>A (p.R429H); c.1424T>C (p.F475S); c.1523A>G (p.N508S)]. In the enzyme, the mutations cluster in transmembrane domains. Amino-acid exchanges near the active site are more detrimental to functionality of the enzyme and, clinically, associated with more severe phenotypes. In male patients, a genotype-phenotype correlation begins to emerge, linking the site of the mutation in MBTPS2 with the clinical outcome described as IFAP syndrome with or without BRESHECK syndrome, keratosis follicularis spinulosa decalvans, X-linked, Olmsted syndrome, or possibly further X-linked traits with an oculocutaneous component.

Report of a novel mutation in CRB1 in a Lebanese family presenting retinal dystrophy

PURPOSE

To identify the genetic basis of a recessive inheritance form of retinal dystrophy (RD) in a Lebanese family.

MATERIALS AND METHODS

Clinical data were recorded for five patients of the 14 family members. Genetic linkage was carried out using Affymetrix 250 K Nspl SNP array followed by sequencing.

RESULTS

The patients showed variable phenotypes ranging from Leber Congenital Amaurosis (LCA) to progressive forms of Retinitis Pigmentosa (RP). A 46.1 Mb chromosomal region at chromosome 1q23.3-32.2 was identified by homozygosity mapping. This region contained the Crumbs homologue-1, CRB1, a gene responsible for recessive retinal dystrophies. CRB1 is required for photoreceptor morphogenesis, and it has been associated with RP and LCA. Sequencing of CRB1 revealed two mutations: a novel deletion in exon 6 (c.1772_1775delGCAT; p.C591Sfs*28) and a missense mutation in exon 7 (c.2234C > T; p.T745M).

CONCLUSION

We report a novel CRB1 mutation in inherited RD in a Lebanese family, and confirm the considerable phenotype heterogeneity that may exist between individuals sharing the same mutations.

Report on a patient with a 12q24.31 microdeletion inherited from an insulin-dependent diabetes mellitus father

We report a 2.3-year-old female patient with global developmental delay, infantile spasms, hypotonia, microcephaly, flat face, full cheeks, macroglossia, highly arched palate, retro-gnathia, narrow ear orifices, and café-au-lait spots. Molecular karyotyping revealed approximately a 1-Mb interstitial deletion of the long arm of one chromosome 12, del(12)(q24.31). The same deletion was identified in her father who presents insulin-dependent diabetes mellitus (IDDM) diagnosed at 14 years. Only one other patient with a similar de novo deletion has been reported previously [Mol Syndromol 2010;1:42-45]. A phenotype-genotype correlation is discussed, and the description of a novel rare microdeletion entity is raised.

Homozygous mutation of the IGF1 receptor gene in a patient with severe pre- and postnatal growth failure and congenital malformations

BACKGROUND

Heterozygous mutations in the IGF1 receptor (IGF1R) gene lead to partial resistance to IGF1 and contribute to intrauterine growth retardation (IUGR) with postnatal growth failure. To date, homozygous mutations of this receptor have not been described.

SUBJECT

A 13.5-year-old girl born from healthy first-cousin parents presented with severe IUGR and persistent short stature. Mild intellectual impairment, dysmorphic features, acanthosis nigricans, and cardiac malformations were also present.

METHODS

Auxological and endocrinological profiles were measured. All coding regions of the IGF1R gene including intron boundaries were amplified and directly sequenced. Functional characterization was performed by immunoblotting using patient's fibroblasts.

RESULTS

IGF1 level was elevated at 950NG/ML (+7 S.D.). Fasting glucose level was normal associated with high insulin levels at baseline and during an oral glucose tolerance test. Fasting triglyceride levels were elevated. sequencing of the IGF1R gene led to the identification of a homozygous variation in exon 2: c.119G>T (p.Arg10Leu). As a consequence, IGF1-dependent receptor autophosphorylation and downstream signaling were reduced in patient's fibroblasts. Both parents were heterozygous for the mutation.

CONCLUSION

The homozygous mutation of the IGF1R is associated with severe IUGR, dysmorphic features, and insulin resistance, while both parents were asymptomatic heterozygous carriers of the same mutation.

The neuronal endopeptidase ECEL1 is associated with a distinct form of recessive distal arthrogryposis

Distal arthrogryposis (DA) is a heterogeneous subgroup of arthrogryposis multiplex congenita (AMC), a large family of disorders characterized by multiple congenital joint limitations due to reduced fetal movements. DA is mainly characterized by contractures afflicting especially the distal extremities without overt muscular or neurological signs. Although a limited number of genes mostly implicated in the contractile apparatus have been identified in DA, most patients failed to show mutations in currently known genes. Using a pangenomic approach, we demonstrated linkage of DA to chromosome 2q37 in two consanguineous families and the endothelin-converting enzyme like 1 (ECEL1) gene present in this region was associated with DA. Screening of a panel of 20 families with non-specific DA identified seven homozygous or compound heterozygous mutations of ECEL1 in a total of six families. Mutations resulted mostly in the absence of protein. ECEL1 is a neuronal endopeptidase predominantly expressed in the central nervous system and brain structures during fetal life in mice and human. ECEL1 plays a major role in intramuscular axonal branching of motor neurons in skeletal muscle during embryogenesis. A detailed review of clinical findings of DA patients with ECEL1 mutations revealed a homogeneous and recognizable phenotype characterized by limited knee flexion, flexed third to fifth fingers and severe muscle atrophy predominant on lower limbs and tongue that suggested a common pathogenic mechanism. We described a new and homogenous phenotype of DA associated with ECEL1 that resulted in symptoms involving rather the peripheral than the central nervous system and suggesting a developmental dysfunction.

A novel deletion in ZBTB24 in a Lebanese family with immunodeficiency, centromeric instability, and facial anomalies syndrome type 2

The immunodeficiency, centromeric instability and facial anomalies (ICF) syndrome is a rare autosomal recessive disease characterized by targeted chromosome breakage, directly related to a genomic methylation defect. It manifests with phenotypic and clinical variability, with the most consistent features being developmental delay, facial anomalies, cytogenetic defects and immunodeficiency with a reduction in serum immunoglobulin levels. From the molecular point of view, ICF syndrome was always divided into ICF type I (ICF1) and ICF type 2 (ICF2). Mutations in DNMT3B gene are responsible for ICF1, while mutations in ZBTB24 have been reported to be responsible for ICF2. In this study, we describe a Lebanese family with three ICF2 affected brothers. Sanger sequencing of the coding sequence of ZBTB24 gene was conducted and revealed a novel deletion: c.396_397delTA (p.His132Glnfs*19), resulting in a loss-of-function of the corresponding protein. ZBTB24 belongs to a large family of transcriptional factors and may be involved in DNA methylation of juxtacentromeric DNA. Detailed molecular and functional studies of the ZBTB24 and DNMT3B genes are needed to understand the pathophysiology of ICF syndrome.

Homozygous stop mutation in the SNX10 gene in a consanguineous Iraqi boy with osteopetrosis and corpus callosum hypoplasia

Recently a mutation in the SNX10 gene that belongs to the sorting nexin family was identified as a cause of a new subset of human autosomal recessive osteopetrosis. Here, we identified a novel homozygous mutation (c.46C > T, p.Arg16X) in SNX10, in an Iraqi boy from a consanguineous family with a history of infantile osteopetrosis. The proband exhibited macrocephaly, prominent forehead, proptosis of the eyes, strabismus, splenomegaly and joint hyperlaxity. Bone X-rays showed increased bone density, metaphyseal under-modelling, transverse alternating bands of greater and lesser density in tubular bones, anteriorly notched vertebral bodies and bone-in-bone appearance. Brain atrophy, external hydrocephalus and thin corpus callosum were noted at the brain MRI and CT scan. Blood test results revealed the presence of anaemia and leukopenia. Our findings confirm the role of SNX10 in autosomal recessive osteopetrosis and help to better define the core set of manifestations associated with this new pathological entity.

DNA replication is altered in Immunodeficiency Centromeric instability Facial anomalies (ICF) cells carrying DNMT3B mutations

ICF syndrome is a rare autosomal recessive disorder that is characterized by Immunodeficiency, Centromeric instability, and Facial anomalies. In all, 60% of ICF patients have mutations in the DNMT3B (DNA methyltransferase 3B) gene, encoding a de novo DNA methyltransferase. In ICF cells, constitutive heterochromatin is hypomethylated and decondensed, metaphase chromosomes undergo rearrangements (mainly involving juxtacentromeric regions), and more than 700 genes are aberrantly expressed. This work shows that DNA replication is also altered in ICF cells: (i) heterochromatic genes replicate earlier in the S-phase; (ii) global replication fork speed is higher; and (iii) S-phase is shorter. These replication defects may result from chromatin changes that modify DNA accessibility to the replication machinery and/or from changes in the expression level of genes involved in DNA replication. This work highlights the interest of using ICF cells as a model to investigate how DNA methylation regulates DNA replication in humans.

Mutation-based growth charts for SEDC and other COL2A1 related dysplasias

From data collected via a large international collaborative study, we have constructed a growth chart for patients with molecularly confirmed congenital spondylo-epiphyseal dysplasia (SEDC) and other COL2A1 related dysplasias. The growth chart is based on longitudinal height measurements of 79 patients with glycine substitutions in the triple-helical domain of COL2A1. In addition, measurements of 27 patients with other molecular defects, such as arginine to cysteine substitutions, splice mutations, and mutations in the C-terminal propeptide have been plotted on the chart. Height of the patients progressively deviate from that of normal children: compared to normal WHO charts, the mean length/height is -2.6 SD at birth, -4.2 SD at 5 years, and -5.8 SD in adulthood. The mean adult height (male and female combined) of patients with glycine substitutions in the triple-helical region is 138.2 cm but there is a large variation. Patients with glycine to cysteine substitutions tend to cluster within the upper part of the chart, while patients with glycine to serine or valine substitutions are situated between +1 SD and -1 SD. Patients with carboxy-terminal glycine substitutions tend to be shorter than patients with amino-terminal substitutions, while patients with splice mutations are relatively tall. However, there are exceptions and specific mutations can have a strong or a relatively mild negative effect on growth. The observation of significant difference in adult height between affected members of the same family indicates that height remains a multifactorial trait even in the presence of a mutation with a strong dominant effect.

Prevalance of BRCA1 and BRCA2 mutations in familial breast cancer patients in Lebanon

Breast cancer is the most prevalent malignancy in women in Western countries, currently accounting for one third of all female cancers. Familial aggregation is thought to account for 5–10 % of all BC cases, and germline mutations in BRCA1 and BRCA2 account for less of the half of these inherited cases. In Lebanon, breast cancer represents the principal death-causing malignancy among women, with 50 % of the cases diagnosed before the age of 50 years.

In order to study BRCA1/2 mutation spectra in the Lebanese population, 72 unrelated patients with a reported family history of breast and/or ovarian cancers or with an early onset breast cancer were tested. Fluorescent direct sequencing of the entire coding region and intronic sequences flanking each exon was performed.

A total of 38 BRCA1 and 40 BRCA2 sequence variants were found. Seventeen of them were novel. Seven confirmed deleterious mutations were identified in 9 subjects providing a frequency of mutations of 12.5 %. Fifteen variants were considered of unknown clinical significance according to BIC and UMD-BRCA1/BRCA2 databases.

In conclusion, this study represents the first evaluation of the deleterious and unclassified genetic variants in the BRCA1/2 genes found in a Lebanese population with a relatively high risk of breast cancer.

Clinical and molecular findings in three Lebanese families with Bietti crystalline dystrophy: report on a novel mutation

PURPOSE

Bietti crystalline dystrophy (BCD) is a rare autosomal recessive disorder caused by mutation of the cytochrome P450, family 4, subfamily V, polypeptide 2 (CYP4V2) gene and characterized by retinal pigmentary abnormalities and scattered deposits of crystals in the retina and the marginal cornea. The aim of this study was to investigate the spectrum of mutations in CYP4V2 in Lebanese families, and to characterize the phenotype of patients affected with BCD.

METHODS

Nine patients from three unrelated Lebanese families were clinically and molecularly investigated. Detailed characterization of the patients' phenotype was performed with comprehensive ophthalmic examination, color vision study, fundus photography, visual field testing, retinal fluorescein angiography, electroretinography, and electrooculography. One family was followed for 12 years. The 11 exons of the CYP4V2 gene were sequenced.

RESULTS

Symptoms consisting of night blindness, loss of paracentral visual field, and disturbed color vision were apparent during the third decade of life. Ophthalmoscopy revealed posterior pole crystalline deposits and areas of retinal pigment epithelium atrophy. Fluorescein angiography disclosed geographic areas of the pigment epithelium layer and choriocapillaris atrophy in the posterior pole and fundus periphery. The most striking findings were those of normal electroretinographic responses in some patients and clinical heterogeneity. Two mutations in CYP4V2 were found: p.I111T (c.332T>C) in exon 3 in two families and the novel p.V458M (c.1372G>A) mutation in exon 9 in one family.

CONCLUSIONS

These patients are affected with Bietti crystalline dystrophy without corneal involvement. Variation in disease severity and electroretinographic responses suggests that environmental or additional genetic factors influence the course of the retinal disease. The CYP4V2 p.I111T (c.332T>C) mutant allele may be especially prevalent among patients with BCD in Lebanon, resulting from a single founder.

Marfanoid habitus, inguinal hernia, advanced bone age, and distinctive facial features: a new collagenopathy?

We report on two sibs, a girl, and a boy, with tall stature, long, and triangular faces, prominent foreheads with high frontal hairlines, telecanthus, downward slanting of the palpebral fissures, ptosis of the eyelids, everted lower eyelids, large ears, long noses, full, and everted vermilions, highly arched and narrow palates, tooth crowding, thin and long uvulae, coloboma of the alae, hyperextensible joints, long digits, positive thumb signs, flat feet, slightly diminished muscle strength, myopia, astigmatia, inguinal hernia, and vesical diverticula. Total body X-rays showed the presence of advanced bone age in both sibs and bilateral hallux valgus in the girl. Array-CGH did not reveal any pathological CNV. Molecular analysis of FBN1, FBN2, TGFBR1, TGFBR2, and CHST14 gene was normal, and SNP linkage analysis excluded more candidate genes. Differential diagnoses and the possibility that we might be reporting on a hitherto unreported syndrome are discussed.

Identification of a novel causative mutation in the ROR2 gene in a Lebanese family with a mild form of recessive Robinow syndrome

Autosomal recessive Robinow syndrome (OMIM 268310) is a condition caused by mutations in the ROR2 gene, the receptor tyrosine kinase-like orphan receptor 2. The main characteristic features are: a face resembling that of a fetus, cleft lip and palate, mesomelic limb shortening, a micropenis in males, hydronephrosis or urinary tract infections, and skeletal and vertebral anomalies. This study reports two sisters from a consanguineous Lebanese family with an autosomal recessive Robinow syndrome. Both presented with short stature, dysmorphic facial features, and mild bone abnormalities. One of the affected girls had a malformation of her right hand: a mesoaxial polydactyly combined with a syndactyly of the 3rd and 4th fingers, and a short right 3rd metacarpal bone. Molecular analysis of the ROR2 gene revealed the presence of a previously undescribed missense mutation: p.R272C (c.814C>T), in the cysteine-rich domain of the protein. These patients are compared with other cases, and a phenotype-genotype correlation is discussed.

A novel 5-bp deletion in Clarin 1 in a family with Usher syndrome

BACKGROUND

To identify the genetic defect in a Lebanese family with two sibs diagnosed with Usher Syndrome.

MATERIALS AND METHODS

Exome capture and sequencing were performed on DNA from one affected member using Agilent in solution bead capture, followed by Illumina sequencing.

RESULTS

This analysis revealed the presence of a novel homozygous 5-bp deletion, in Clarin 1 (CLRN1), a known gene responsible for Usher syndrome type III. The deletion is inherited from both parents and segregates with the disease phenotype in the family. The 5-bp deletion, c.301_305delGTCAT, p.Val101SerfsX27, is predicted to result in a frameshift and protein truncation after 27 amino acids. Sequencing all the coding regions of the CLRN1 gene in the proband did not reveal any other mutation or variant.

CONCLUSION

Here we describe a novel deletion in CLRN1. Our data support previously reported intra familial variability in the clinical features of Usher syndrome type I and III.

Ichthyosis follicularis, alopecia, and photophobia (IFAP) syndrome

The IFAP syndrome is a rare X-linked genetic disorder reported in nearly 40 patients. It is characterized by the triad of Ichthyosis Follicularis, Alopecia, and Photophobia from birth. Other features such as short stature, intellectual disability, and seizures may develop in the first few years of life. Skin histopathology is non-specific and consists of dilated hair follicles with keratin plugs extending above the surface of the skin, decreased or absent sebaceous glands, and decreased desmosomes in number and size. The disorder results from mutations in the MBTPS2 gene that impairs cholesterol homeostasis and the ability to cope with endoplasmic reticulum stress. Follicular hyperkeratosis can be treated using topical keratolytics, emollients and urea preparations. A moderate response to acitretin therapy has been noted in some patients. Intensive lubrication of the ocular surface is essential. Life expectancy in patients with IFAP syndrome can vary from death in the neonatal period to normal surviving. Cardiopulmonary complications remain the major cause of death.

Heterochromatic genes undergo epigenetic changes and escape silencing in immunodeficiency, centromeric instability, facial anomalies (ICF) syndrome

Immunodeficiency, Centromeric Instability, Facial Anomalies (ICF) syndrome is a rare autosomal recessive disorder that is characterized by a marked immunodeficiency, severe hypomethylation of the classical satellites 2 and 3 associated with disruption of constitutive heterochromatin, and facial anomalies. Sixty percent of ICF patients have mutations in the DNMT3B (DNA methyltransferase 3B) gene, encoding a de novo DNA methyltransferase. In the present study, we have shown that, in ICF lymphoblasts and peripheral blood, juxtacentromeric heterochromatic genes undergo dramatic changes in DNA methylation, indicating that they are bona fide targets of the DNMT3B protein. DNA methylation in heterochromatic genes dropped from about 80% in normal cells to approximately 30% in ICF cells. Hypomethylation was observed in five ICF patients and was associated with activation of these silent genes. Although DNA hypomethylation occurred in all the analyzed heterochromatic genes and in all the ICF patients, gene expression was restricted to some genes, every patient having his own group of activated genes. Histone modifications were preserved in ICF patients. Heterochromatic genes were associated with histone modifications that are typical of inactive chromatin: they had low acetylation on H3 and H4 histones and were slightly enriched in H3K9Me(3), both in ICF and controls. This was also the case for those heterochromatic genes that escaped silencing. This finding suggests that gene activation was not generalized to all the cells, but rather was restricted to a clonal cell population that may contribute to the phenotypic variability observed in ICF syndrome. A slight increase in H3K27 monomethylation was observed both in heterochromatin and active euchromatin in ICF patients; however, no correlation between this modification and activation of heterochromatic genes was found.

Ambiguous genitalia, microcephaly, seizures, bone malformations, and early death: a distinct MCA/MR syndrome

We report on two siblings with hypotonia, ambiguous genitalia, microcephaly, ptosis, microretrognathia, thin lips, seizures, absent ossification of pubic rami, and brain abnormalities at the MRI. The two siblings died at 5 and 8 months, respectively. Molecular analysis indicated that SOX9, ARX, and DHCR7 genes were normal. Comparative genomic hybridization (CGH)-array analysis performed on the younger boy indicated two notable deletions, one on paternally inherited chromosome 4, and one on maternally inherited chromosome 5. The same deletions were found in a normal sister. Differential diagnoses and the possibility of a hitherto unreported syndrome are discussed.