Activating Mutations Affecting the Dbl Homology Domain of SOS2 Cause Noonan Syndrome.

The RASopathies constitute a family of autosomal-dominant disorders whose major features include facial dysmorphism, cardiac defects, reduced postnatal growth, variable cognitive deficits, ectodermal and skeletal anomalies, and susceptibility to certain malignancies. Noonan syndrome (NS), the commonest RASopathy, is genetically heterogeneous and caused by functional dysregulation of signal transducers and regulatory proteins with roles in the RAS/extracellular signal-regulated kinase (ERK) signal transduction pathway. Mutations in known disease genes account for approximately 80% of affected individuals. Here, we report that missense mutations altering Son of Sevenless, Drosophila, homolog 2 (SOS2), which encodes a RAS guanine nucleotide exchange factor, occur in a small percentage of subjects with NS. Four missense mutations were identified in five unrelated sporadic cases and families transmitting NS. Disease-causing mutations affected three conserved residues located in the Dbl homology (DH) domain, of which two are directly involved in the intramolecular binding network maintaining SOS2 in its autoinhibited conformation. All mutations were found to promote enhanced signaling from RAS to ERK. Similar to NS-causing SOS1 mutations, the phenotype associated with SOS2 defects is characterized by normal development and growth, as well as marked ectodermal involvement. Unlike SOS1 mutations, however, those in SOS2 are restricted to the DH domain.

Long term follow-up in a patient with a de novo microdeletion of 14q11.2 involving CHD8.

We identified a de novo deletion of 14q11.2 in a Czech patient with developmental delay, mild autistic features, macrosomy, macrocephaly, orthognathic deformities, and dysmorphic facial features. The clinical follow-up of the patient lasting 14 years documented changes in the facial dysmorphism from infancy to adolescence. The deletion affects approximately 200 kb of DNA with five protein-coding genes and two snoRNA genes. Two of the protein-coding genes, SUPT16H and CHD8, have been proposed as candidate genes for a new microdeletion syndrome. Our patient further supports the existence of this syndrome and extends its phenotypic spectrum, especially points to the possibility that orthognathic deformities may be associated with microdeletions of 14q11.2. CHD8 mutations have been found in patients with neurodevelopmental disorders and macrocephaly. The HNRNPC gene, repeatedly deleted in patients with developmental delay, is another candidate as its 5́ end is adjacent to the deletion, and the expression of this gene may be affected by position effect.

Deletions in the 3' part of the NFIX gene including a recurrent Alu-mediated deletion of exon 6 and 7 account for previously unexplained cases of Marshall-Smith syndrome.

Marshall-Smith syndrome (MSS) is a very rare malformation syndrome characterized by typical craniofacial anomalies, abnormal osseous maturation, developmental delay, failure to thrive, and respiratory difficulties. Mutations in the nuclear factor 1/X gene (NFIX) were recently identified as the cause of MSS. In our study cohort of 17 patients with a clinical diagnosis of MSS, conventional sequencing of NFIX revealed frameshift and splice-site mutations in 10 individuals. Using multiplex ligation-dependent probe amplification analysis, we identified a recurrent deletion of NFIX exon 6 and 7 in five individuals. We demonstrate this recurrent deletion is the product of a recombination between AluY elements located in intron 5 and 7. Two other patients had smaller deletions affecting exon 6. These findings show that MSS is a genetically homogeneous Mendelian disorder. RT-PCR experiments with newly identified NFIX mutations including the recurrent exon 6 and 7 deletion confirmed previous findings indicating that MSS-associated mutant mRNAs are not cleared by nonsense-mediated mRNA decay. Predicted MSS-associated mutant NFIX proteins consistently have a preserved DNA binding and dimerization domain, whereas they grossly vary in their C-terminal portion. This is in line with the hypothesis that MSS-associated mutations encode dysfunctional proteins that act in a dominant negative manner.

[Mutagenic effect of advanced paternal age in neurocardiofaciocutaneous syndrome]. / Mutagenní vliv vyssího veku otcu u neurokardiofaciokutánního syndromu.

BACKGROUND: Increased frequency of chromosomal aberration in children of mothers aged 35 years and older is very well known and since 1973 it is an indication to investigate the foetal karyotype in cells obtained by invasive method (amniocentesis), because the genetic risk of severe affection is higher than the risk of necessary invasive method. Mutagenic effect of advanced paternal age is known only among geneticists (1-4). The reason is not only low absolute risk of new mutation but particularly a high number of involved genes and last not least the limited spectrum of autosomal dominant disorders without abiotrofic character. Therefore the preventive methods for elimination of this risk are very limited. Only a few of them could be recognized prenatally by noninvasive methods of prenatal diagnostics. METHODS: Genealogical, anamnestic and clinical data of 83 patients were studied with clinical suspection on neurocardiofaciocutaneous syndrome (NCFCs) (5-7). The diagnosis has not been confirmed in 29 patients, no mutation was detected in 8 investigated genes (PTPN11, SOS1, HRAS, BRAF, RAF1, MEK1, KRAS, NRAS). In 54 patients with autosomal dominant inherited Noonan syndrome, Costello syndrome and cardiofaciocutaneous syndrome the diagnosis was confirmed on DNA level and the biological fitness was estimated for each disorder. Paternal age at conception was compared in the group of patients with familial and sporadic occurrence of Noonan and NCFC syndromes. The clinical prognosis of this disorder is represented by biological fitness of patients. Coefficient of selection is 0,6 in Noonan and LEOPARD syndromes (29 from 48). All 6 patients with Costello and cardiofaciocutaneous syndromes developed due to a new mutation. CONCLUSION: Paternal age at birth was studied in 83 children patients with autosomal dominant Neurocardiofaciocutaneous syndrome (Noonan, LEOPARD, Costello, CFC) with a high population incidence and decreased biological fitness. Due to severe congenital heart defects, failure to thrive in infancy, increased risk for malignancy and further health problems the clinical prognosis of patients in the past was not good. Therefore high mutation rate is expected until now. Identification of genes responsible for manifestation of this disorder, enables to confirm the diagnosis and to recognize inherited and de novo mutations. Genealogy and DNA analysis of PTPN11, SOS1, HRAS, BRAF, RAF1, MEK1, KRAS and NRAS were obtained in cohort of 54 patients with NCFC syndromes and their parents. There were 48 patients with Noonan and LEOPARD syndromes, in 29 cases due to mutation de novo, 19 patients inherited the mutation from one of parents. All 6 patients with Costello syndrome and CFC syndrome were affected due to new mutation. DNA analysis revealed 32 mutations in PTPN11 gene, mutation in SOS1 gene was found in 10 patients, RAF1 mutation was present in 3 patients; mutation in MEK1, KRAS and NRAS genes was present in one patient each. In Costello syndrome and CFC syndrome mutations in HRAS (4 patients) and BRAF (2 patients) genes were detected. Genealogic data allow analysing parental age in the group of patients with new mutation and inherited mutation. Paternal age at conception of patients with Noonan syndrome due to new mutation was significantly increased in comparison to the group of fathers of Noonan patients with inherited mutation - 38,4 years and 29,6 years, resp., range 28 to 55 years and 25 to 35 years, resp. Maternal age was slightly increased too, -30,9 and 27,7, resp. and range 24 to 42 years and 21 to 36 years, resp. but not significantly. The results support the mutagenic effect of paternal age, espec. autosomal dominant mutations.

Mutation spectrum in RAB3GAP1, RAB3GAP2, and RAB18 and genotype-phenotype correlations in warburg micro syndrome and Martsolf syndrome.

Warburg Micro syndrome and Martsolf syndrome (MS) are heterogeneous autosomal-recessive developmental disorders characterized by brain, eye, and endocrine abnormalities. Causative biallelic germline mutations have been identified in RAB3GAP1, RAB3GAP2, or RAB18, each of which encode proteins involved in membrane trafficking. This report provides an up to date overview of all known disease variants identified in 29 previously published families and 52 new families. One-hundred and forty-four Micro and nine Martsolf families were investigated, identifying mutations in RAB3GAP1 in 41% of cases, mutations in RAB3GAP2 in 7% of cases, and mutations in RAB18 in 5% of cases. These are listed in Leiden Open source Variation Databases, which was created by us for all three genes. Genotype-phenotype correlations for these genes have now established that the clinical phenotypes in Micro syndrome and MS represent a phenotypic continuum related to the nature and severity of the mutations present in the disease genes, with more deleterious mutations causing Micro syndrome and milder mutations causing MS. RAB18 has not yet been linked to the RAB3 pathways, but mutations in all three genes cause an indistinguishable phenotype, making it likely that there is some overlap. There is considerable genetic heterogeneity for these disorders and further gene identification will help delineate these pathways.

The NBN founder mutation-Evidence for a country specific difference in age at cancer manifestation.

BACKGROUND: Nijmegen breakage syndrome (NBS) is an autosomal-recessive chromosome instability disorder characterized by, among others, hypersensitivity to X-irradiation and an exceptionally high risk for lymphoid malignancy. The vast majority of NBS patients is homozygous for a common Slavic founder mutation, c.657del5, of the NBN gene, which is involved in the repair of DNA double-strand breaks (DSBs). The founder mutation also predisposes heterozygous carriers to cancer, apparently however, with a higher risk in the Czech Republic/Slovakia (CS) than in Poland. AIM: To examine whether the age of cancer manifestation and cancer death of NBN homozygotes is different between probands from CS and Poland. METHODS: The study is restricted to probands born until 1989, before replacement of the communist regime by a democratic system in CS and Poland, and a substantial transition of the health care systems. Moreover, all patients were recruited without knowledge of their genetic status since the NBN gene was not identified until 1998. RESULTS: Here, we show that cancer manifestation of NBN homozygotes is at a significantly earlier age in probands from CS than from Poland. This is explained by the difference in natural and medical radiation exposure, though within the permissible dosage. CONCLUSION: It is reasonable to assume that this finding also sheds light on the higher cancer risk of NBN heterozygotes in CS than in Poland. This has implications for genetic counseling and individualized medicine also of probands with other DNA repair defects.

[Heterozygous carriers of Slavic mutation 657del5 of NBN gene in patients with colorectal cancer]. / Heterozygotie slovanské mutace 657del5 NBN genu u pacientu s kolorektálním karcinomem.

BACKGROUND: Nijmegen breakage syndrome (NBS) is one of the chromosomal instability syndromes due to DNA repair disorder. The syndrome is autosomal recessive determined, in homozygotes is characterized by many disorders including high predisposition to lymphoreticular malignancy in childhood and adolescence. METHODS: Laboratory findings represent low level of immunoglobulins, B and T lymphocytes, increased sensitivity to the mutagens, especially hyperradiosensitivity and increased chromosomal instability. Heterozygotes show also elevated radiosensitivity and have an increased cancer risk in adult age. There is no predilection of the malignancy. Colorectal cancer was found often among the relatives of patients with NBS. Majority of the NBS patients are of the Central and Eastern European origin and carry the common founder mutation 657del5 in the NBN gene. The formation of second malignancy both in homozygotes and heterozygotes can be prevented by excluding any radiation. The aim of study is estimation of frequency of 657del5 heterozygotes among patients with colorectal cancer. RESULTS AND CONCLUSIONS: Within a group of 161 patients with colorectal cancer 5 heterozygotes with 657del5 mutation were registered, e.g. 5-times higher incidence than expected. The elemental prevention in patients with proved positivity of Slavic mutation in NBN gene is to exclude any radiation.

Telomere attrition and dysfunction: a potential trigger of the progeroid phenotype in nijmegen breakage syndrome.

BACKGROUND: Nibrin, as part of the NBN/MRE11/RAD50 complex, is mutated in Nijmegen breakage syndrome (NBS), which leads to impaired DNA damage response and lymphoid malignancy. RESULTS: Telomere length (TL) was markedly reduced in homozygous patients (and comparably so in all chromosomes) by ~40% (qPCR) and was slightly reduced in NBS heterozygotes older than 30 years (~25% in qPCR), in accordance with the respective cancer rates. Humanized cancer-free NBS mice had normal TL. Telomere elongation was inducible by telomerase and/or alternative telomere lengthening but was associated with abnormal expression of telomeric genes involved in aging and/or cell growth. Lymphoblastoid cells from NBS patients with long survival times (>12 years) displayed the shortest telomeres and low caspase 7 activity. CONCLUSIONS: NBS is a secondary telomeropathy. The two-edged sword of telomere attrition enhances the cancer-prone situation in NBS but can also lead to a relatively stable cellular phenotype in tumor survivors. Results suggest a modular model for progeroid syndromes with abnormal expression of telomeric genes as a molecular basis. METHODS: We studied TL and function in 38 homozygous individuals, 27 heterozygotes, one homozygous fetus, six NBS lymphoblastoid cell lines, and humanized NBS mice, all with the same founder NBN mutation: c.657_661del5.

Polycystic kidney and hepatic disease with mental retardation and hand anomalies in three siblings.

A family with three children affected with congenital polycystic kidneys, hepatic fibrosis, mental retardation, minor anomalies of the hands, and dysmorphic facial features is reported. All children progressed to chronic renal failure. Linkage to the locus for autosomal recessive polycystic kidney disease was excluded by haplotype analysis. The family is endogamic, and the affected siblings are of both sexes, which is in agreement with an autosomal recessive determination of this syndrome. A similar syndrome was reported in 1990 by Labrune et al. [J Pediatr Gastroenterol Nutr (1990) 10:540-543]. Our report provides further evidence for the etiological heterogeneity of polycystic kidney with hepatic fibrosis. The syndrome reported here should be considered in the differential diagnosis of the early manifestation of polycystic kidneys. Mental retardation and hand anomalies are the hallmarks for the differential diagnosis of this syndrome.

Extreme variation in apoptosis capacity amongst lymphoid cells of Nijmegen breakage syndrome patients.

The human genetic disorder, Nijmegen breakage syndrome (NBS), is characterised by radiosensitivity, immunodeficiency and an increased risk for cancer, particularly lymphoma. The NBS1 gene codes for a protein, nibrin, involved in the processing/repair of DNA double strand breaks and in cell cycle checkpoints. The majority of patients (>90%) are homozygous for a founder mutation. Despite this genetic homogeneity, the syndrome shows considerable clinical variability, for example, in age at development of a malignancy. We hypothesised that one reason for such variation might be individual differences in the clearance of heavily damaged precancerous cells by apoptosis. To test this hypothesis we have examined a set of 30 lymphoblastoid B-cell lines from NBS patients for their capacity to enter into apoptosis after a DNA-damaging treatment. There was a substantial 40-fold variation in apoptosis between cell lines from different patients. NBS patient cell lines could be grouped into a large, apoptosis-deficient group and a smaller group with essentially normal apoptotic response to DNA damage. In both groups, cell lines were proficient in TP53 phosphorylation and stabilisation after the same DNA-damaging treatment. Thus the observed variation in apoptosis capacity is not due to failure to activate TP53. Despite the large variation in apoptosis, no statistically significant correlation between apoptotic capacity of patient cell lines and clinical course of the disease was apparent.

Radiation-induced DNA damage and repair in peripheral blood mononuclear cells from Nijmegen breakage syndrome patients and carriers assessed by the Comet assay.

Nijmegen breakage syndrome (NBS) patients and carriers are predisposed to malignancy and are often treated with X-irradiation. In the present study, the single-cell gel electrophoresis (Comet) assay was used to examine radiation-induced DNA damage and repair in peripheral blood mononuclear cells from NBS patients (n=13) and carriers (n=36) of six unrelated families. Cells from apparently healthy donors (n=10) and from breast cancer patients with normal clinical radiosensitivity (n=10) served as controls. Cells were irradiated with 5 Gy of X-rays and assayed for initial DNA damage and for residual DNA damage after 40 min of repair; the kinetics of DNA repair also was estimated. In addition, the nuclear area of unirradiated cells was extracted from the Comet data. The initial radiation-induced DNA fragmentation indicated that cells from members of two out of six NBS families were significantly more sensitive to X-irradiation than cells from the controls. Cells from four NBS families had longer DNA repair half-time values, while cells from five NBS families had significantly increased residual DNA damage following repair. The mean nuclear area of unirradiated cells processed in the Comet assay was 1.3-fold higher in cells from all NBS families than in the controls (P<0.05). Notably, the Comet assay parameters (initial and residual DNA damage and the repair kinetics) of irradiated NBS cells predicted the carrier status of the majority (86%) of blindly tested individuals. The prediction of NBS status was higher if the nuclear area of unirradiated cells was used as the endpoint. The results of this study suggest that the impaired radiation response of NBS cells should be taken into account if radiotherapy of NBS patients and carriers is required.

The Slavic NBN Founder Mutation: A Role for Reproductive Fitness?

The vast majority of patients with Nijmegen Breakage Syndrome (NBS) are of Slavic origin and carry a deleterious deletion (c.657del5; rs587776650) in the NBN gene on chromosome 8q21. This mutation is essentially confined to Slavic populations and may thus be considered a Slavic founder mutation. Notably, not a single parenthood of a homozygous c.657del5 carrier has been reported to date, while heterozygous carriers do reproduce but have an increased cancer risk. These observations seem to conflict with the considerable carrier frequency of c.657del5 of 0.5% to 1% as observed in different Slavic populations because deleterious mutations would be eliminated quite rapidly by purifying selection. Therefore, we propose that heterozygous c.657del5 carriers have increased reproductive success, i.e., that the mutation confers heterozygote advantage. In fact, in our cohort study of the reproductive history of 24 NBS pedigrees from the Czech Republic, we observed that female carriers gave birth to more children on average than female non-carriers, while no such reproductive differences were observed for males. We also estimate that c.657del5 likely occurred less than 300 generations ago, thus supporting the view that the original mutation predated the historic split and subsequent spread of the 'Slavic people'. We surmise that the higher fertility of female c.657del5 carriers reflects a lower miscarriage rate in these women, thereby reflecting the role of the NBN gene product, nibrin, in the repair of DNA double strand breaks and their processing in immune gene rearrangements, telomere maintenance, and meiotic recombination, akin to the previously described role of the DNA repair genes BRCA1 and BRCA2.

Childhood overgrowth in patients with common NF1 microdeletions.

While growth retardation and short stature are well-known features of patients with classical neurofibromatosis type 1 (NF1), we found advanced height growth and accelerated carpal bone age in patients with an NF1 microdeletion. Our analysis is based on growth data of 21 patients with common 1.4/1.2 Mb microdeletions, including three patients with a Weaver-like appearance. Overgrowth was most evident in preschool children (2-6 years, n=10, P=0.02). We conclude that childhood overgrowth is part of the phenotypic spectrum in patients with the common 1.4/1.2 Mb NF1 microdeletions and assume that the chromosomal region comprised by the microdeletions contains a gene whose haploinsufficiency causes overgrowth.

Prevalence of mutations in AGPAT2 among human lipodystrophies.

Berardinelli-Seip congenital lipodystrophy (BSCL) is a heterogeneous genetic disease characterized by near absence of adipose tissue and severe insulin resistance. We have previously identified mutations in the seipin gene in a subset of our patients' cohort. Recently, disease-causing mutations in AGPAT2 have been reported in BSCL patients. In this study, we have performed mutation screening in AGPAT2 and the related AGPAT1 in patients with BSCL or other forms of lipodystrophy who have no detectable mutation in the seipin gene. We found 38 BSCL patients from 30 families with mutations in AGPAT2. Three of the known mutations were frequently found in our families. Of the eight new alterations, six are null mutations and two are missense mutations (Glu172Lys and Ala238Gly). All the patients harboring AGPAT2 mutations presented with typical features of BSCL. We did not find mutations in patients with other forms of lipodystrophies, including the syndromes of Lawrence, Dunnigan, and Barraquer-Simons, or with type A insulin resistance. In conclusion, mutations in the seipin gene and AGPAT2 are confined to the BSCL phenotype. Because we found mutations in 92 of the 94 BSCL patients studied, the seipin gene and AGPAT2 are the two major genes involved in the etiology of BSCL.

An AP4B1 frameshift mutation in siblings with intellectual disability and spastic tetraplegia further delineates the AP-4 deficiency syndrome.

The recently proposed adaptor protein 4 (AP-4) deficiency syndrome comprises a group of congenital neurological disorders characterized by severe intellectual disability (ID), delayed or absent speech, hereditary spastic paraplegia, and growth retardation. AP-4 is a heterotetrameric protein complex with important functions in vesicle trafficking. Mutations in genes affecting different subunits of AP-4, including AP4B1, AP4E1, AP4S1, and AP4M1, have been reported in patients with the AP-4 deficiency phenotype. We describe two siblings from a non-consanguineous couple who presented with severe ID, absent speech, microcephaly, growth retardation, and progressive spastic tetraplegia. Whole-exome sequencing in the two patients identified the novel homozygous 2-bp deletion c.1160_1161delCA (p.(Thr387Argfs*30)) in AP4B1. Sanger sequencing confirmed the mutation in the siblings and revealed it in the heterozygous state in both parents. The AP4B1-associated phenotype has previously been assigned to spastic paraplegia-47. Identification of a novel AP4B1 alteration in two patients with clinical manifestations highly similar to other individuals with mutations affecting one of the four AP-4 subunits further supports the observation that loss of AP-4 assembly or functionality underlies the common clinical features in these patients and underscores the existence of the clinically recognizable AP-4 deficiency syndrome.

DYNC2LI1 mutations broaden the clinical spectrum of dynein-2 defects.

Skeletal ciliopathies are a heterogeneous group of autosomal recessive osteochondrodysplasias caused by defects in formation, maintenance and function of the primary cilium. Mutations in the underlying genes affect the molecular motors, intraflagellar transport complexes (IFT), or the basal body. The more severe phenotypes are caused by defects of genes of the dynein-2 complex, where mutations in DYNC2H1, WDR34 and WDR60 have been identified. In a patient with a Jeune-like phenotype we performed exome sequencing and identified compound heterozygous missense and nonsense mutations in DYNC2LI1 segregating with the phenotype. DYNC2LI1 is ubiquitously expressed and interacts with DYNC2H1 to form the dynein-2 complex important for retrograde IFT. Using DYNC2LI1 siRNA knockdown in fibroblasts we identified a significantly reduced cilia length proposed to affect cilia function. In addition, depletion of DYNC2LI1 induced altered cilia morphology with broadened ciliary tips and accumulation of IFT-B complex proteins in accordance with retrograde IFT defects. Our results expand the clinical spectrum of ciliopathies caused by defects of the dynein-2 complex.

Nijmegen breakage syndrome in 13% of age-matched Czech children with primary microcephaly.

The Nijmegen breakage syndrome is a rare autosomal recessive chromosomal instability disorder characterized by early growth retardation, congenital microcephaly, immunodeficiency, borderline mental development, and a high tendency to lymphoreticular malignancies. Most Nijmegen breakage syndrome patients are of Slavonic origin, and all of them known so far carry a founder homozygous 5 nucleotide deletion in the NBS1 gene. Microcephaly was present in 100% of Nijmegen breakage syndrome patients in a recent large international cooperative study. The frequency of Nijmegen breakage syndrome among children with primary microcephaly was not known. Early correct diagnosis of the syndrome is crucial for appropriate preventive care and therapy. We tested 67 Czech patients of different ages with simple microcephaly for the presence of the most common mutation in the NBS1 gene. Three new Nijmegen breakage syndrome cases were detected in this cohort, representing 4.5% of the cohort. All these newly diagnosed Nijmegen breakage syndrome patients were younger than 10 months at the time of diagnosis. They were all born within a 2.5-year period. Twenty-three of the 67 children in the cohort were born within this 2.5-year period, representing a 13% incidence of Nijmegen breakage syndrome. Frequency of Nijmegen breakage syndrome heterozygotes among infants in the Czech Republic is 1: 130-158 and the birth rate is 90,000 per year, therefore in the time span of 2.5 years, three new Nijmegen breakage syndrome homozygotes are expected to be born. Therefore we assume that by DNA testing of Czech primary microcephalic children it is possible to detect all Nijmegen breakage syndrome patients to be expected. The age at correct diagnosis was lowered from 7.1 years at the time before DNA testing, to well under 1 year of age. All new Nijmegen breakage syndrome patients could receive appropriate preventive care, which should significantly improve their life expectancy and prognosis.

A mutation in the c-fos gene associated with congenital generalized lipodystrophy.

BACKGROUND: Congenital generalized lipodystrophy (CGL) or Berardinelli-Seip congenital lipodystrophy (BSCL) is a rare genetic syndrome characterized by the absence of adipose tissue. As CGL is thought to be related to malfunctions in adipocyte development, genes involved in the mechanisms of adipocyte biology and maintenance or differentiation of adipocytes, especially transcription factors are candidates. Several genes (BSCL1-4) were found to be associated to the syndrome but not all CGL patients carry mutations in these genes. METHODS AND RESULTS: In a patient with CGL and insulin resistance we investigated the known candidate genes but the patient did not carry a relevant mutation. Analyses of the insulin activated signal transduction pathways in isolated fibroblasts of the patient revealed a postreceptor defect altering expression of the immediate early gene c-fos. Sequence analyses revealed a novel homozygous point mutation (c.-439, T→A) in the patients' c-fos promoter. The point mutation was located upstream of the well characterized promoter elements in a region with no homology to any known cis-elements. The identified mutation was not detected in a total of n=319 non lipodystrophic probands. In vitro analyses revealed that the mutation facilitates the formation of a novel and specific protein/DNA complex. Using mass spectrometry we identified the proteins of this novel complex. Cellular investigations demonstrate that the wild type c-fos promoter can reconstitute the signaling defect in the patient, excluding further upstream signaling alterations, and vice versa the investigations with the c-fos promoter containing the identified mutation generally reduce basal and inducible c-fos transcription activity. As a consequence of the identified point mutation gene expression including c-Fos targeted genes is significantly altered, shown exemplified in cells of the patient. CONCLUSION: The immediate-early gene c-fos is one essential transcription factor to initiate adipocyte differentiation. According to the role of c-fos in adipocyte differentiation our findings of a mutation that initiates a repression mechanism at c-fos promoter features the hypothesis that diminished c-fos expression might play a role in CGL by interfering with adipocyte development.