Zehra Oya Uyguner

Mild nasal malformations and parietal foramina caused by homozygous ALX4 mutations

We report on a boy born to consanguineous parents, who had hypertelorism, a broad nasal bridge, ridge and tip, bifid nasal tip, cleft alae nasi, broad columella, unilateral preauricular tag, shallow labiogingival sulcus, and bilateral large parietal foramina. Cranial MRI revealed a kinked corpus body and small cerebellar vermis. Molecular analysis uncovered a homozygous c.673C > G (p.Q225E) mutation in ALX4 gene. We compare the relatively mild phenotype in the patient to the more marked phenotype described in other patients with homozygous ALX4 mutations, and to the phenotypes in patients with mutations in other ALX genes.

Mutations in CDK5RAP2 cause Seckel syndrome

Seckel syndrome is a heterogeneous, autosomal recessive disorder marked by prenatal proportionate short stature, severe microcephaly, intellectual disability, and characteristic facial features. Here, we describe the novel homozygous splice‐site mutations c.383+1G>C and c.4005‐9A>G in CDK5RAP2 in two consanguineous families with Seckel syndrome. CDK5RAP2 (CEP215) encodes a centrosomal protein which is known to be essential for centrosomal cohesion and proper spindle formation and has been shown to be causally involved in autosomal recessive primary microcephaly. We establish CDK5RAP2 as a disease‐causing gene for Seckel syndrome and show that loss of functional CDK5RAP2 leads to severe defects in mitosis and spindle organization, resulting in cells with abnormal nuclei and centrosomal pattern, which underlines the important role of centrosomal and mitotic proteins in the pathogenesis of the disease. Additionally, we present an intriguing case of possible digenic inheritance in Seckel syndrome: A severely affected child of nonconsanguineous German parents was found to carry heterozygous mutations in CDK5RAP2 and CEP152. This finding points toward a potential additive genetic effect of mutations in CDK5RAP2 and CEP152.

The R110C mutation in Notch3 causes variable clinical features in two Turkish families with CADASIL syndrome

Mutations in Notch3 gene are responsible for the cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). It is a late onset neurological disorder recognized by recurrent strokes and dementia. We describe here the clinical and molecular findings of three unrelated Turkish families with CADASIL syndrome. Two of the families were identified to have the same mutation, p.R110C (c.C328T), located in exon 3 of the Notch3 gene. Interestingly, the phenotypic expression of the disease in these two families was markedly different in severity and age of onset implicating additional genetic and/or non-genetic modulating factors involved in the pathogenesis. In addition, we identified the novel p.C201R (c.T601C) mutation in exon 4 of the Notch3 gene in a proband of the third family with two consecutive stroke-like episodes and typical MRI findings. Mutations described here cause an odd number of cysteines in the N-terminal of the EGF domain of Notch3 protein, which seems to have an important functional effect in the pathophysiology of CADASIL. The phenotypic variability in families carrying the same molecular defect as presented here makes the prediction of prognosis inconceivable. Although DNA analysis is effective and valuable in diagnosing approximately 90% of the CADASIL patients, lack of genotype-phenotype correlation and prognostic parameters makes the presymptomatic genetic counseling very difficult.

Whole-Exome Sequencing Identifies Novel Variants for Tooth Agenesis

Tooth agenesis is a common craniofacial abnormality in humans and represents failure to develop 1 or more permanent teeth. Tooth agenesis is complex, and variations in about a dozen genes have been reported as contributing to the etiology. Here, we combined whole-exome sequencing, array-based genotyping, and linkage analysis to identify putative pathogenic variants in candidate disease genes for tooth agenesis in 10 multiplex Turkish families. Novel homozygous and heterozygous variants in LRP6, DKK1, LAMA3, and COL17A1 genes, as well as known variants in WNT10A, were identified as likely pathogenic in isolated tooth agenesis. Novel variants in KREMEN1 were identified as likely pathogenic in 2 families with suspected syndromic tooth agenesis. Variants in more than 1 gene were identified segregating with tooth agenesis in 2 families, suggesting oligogenic inheritance. Structural modeling of missense variants suggests deleterious effects to the encoded proteins. Functional analysis of an indel variant (c.3607+3_6del) in LRP6 suggested that the predicted resulting mRNA is subject to nonsense-mediated decay. Our results support a major role for WNT pathways genes in the etiology of tooth agenesis while revealing new candidate genes. Moreover, oligogenic cosegregation was suggestive for complex inheritance and potentially complex gene product interactions during development, contributing to improved understanding of the genetic etiology of familial tooth agenesis.

Skull defects, alopecia, hypertelorism, and notched alae nasi caused by homozygous ALX4 gene mutation

Skull Defects, Alopecia, Hypertelorism, and Notched Alae Nasi Caused by Homozygous ALX4 Gene Mutation Ariana Kariminejad,* Bita Bozorgmehr, Houman Alizadeh, Siavash Ghaderi-Sohi, Güven Toksoy, Zehra Oya Uyguner, and Hülya Kayserili Kariminejad-Najmabadi Pathology & Genetics Center, Tehran, Iran Tehran University of Medical Sciences, Children’s Medical Center Hospital, Tehran, Iran Medical Genetics Department, Istanbul Medical Faculty, Istanbul University, Istanbul, Turkey

The Turkish Hereditary Angioedema Pilot Study (TURHAPS): The First Turkish Series of Hereditary Angioedema

Background: No published data presently exist concerning hereditary angioedema (HAE) in Turkey. The aim of the study was to initiate a preliminary multicentric evaluation about HAE and to determine the genetic properties of Turkish patients. Methods: Based on records drawn from four medical centers we identified a total of 70 subjects, belonging to 60 unrelated families, fulfilling clinical and laboratory criteria for diagnosis of HAE with C1 inhibitor deficiency. Ten type I patients, and their first-degree relatives, underwent genetic analysis for HAE. Results: The majority of patients were female (60%), the mean age was 37.7 ± 14.1 years. The mean age at the time of first angioedema symptom was 12.5 ± 9.2 years. Mean time lag between first symptom and diagnosis was 26 ± 14.4 years. All but 3 subjects had HAE type I. Family history of angioedema was present in 75.7% of the cases. Cutaneous swelling was reported by 87.1% of the patients, facial edema by 65%, abdominal symptoms by 74.3% and approximately one half (55.7%) had experienced one or more laryngeal attack. Genetic analysis of 10 families demonstrated that 5 carried a mutation that had never been previously described. Conclusion: We found that the clinical features of Turkish HAE patients were consistent with previously described patterns of this rare disease. The most noteworthy feature identified in the study was a significantly long duration between the first symptom appearance and final diagnosis. Our detection of different mutations in 10 patients confirms the allelic heterogeneity of the disease.

A new hereditary congenital facial palsy case supports arg5 in HOX-DNA binding domain as possible hot spot for mutations

Moebius syndrome (MBS) is a rare congenital disorder characterized by rhombencephalic mal development, mainly presenting with facial palsy with limited gaze abduction. Most cases are sporadic, possibly caused by a combination of environmental and genetic factors; however, no proven specific associations have been yet established. Hereditary congenital facial palsy (HCFP) is an autosomal dominant congenital dysinnervation syndrome, recognizable by the isolated dysfunction of the seventh cranial nerve. Mutant mice for Hoxb1 were reported to present with facial weakness, resembling MBS. Recently a homozygous mutation altering arg5 residue of HOXB1 homeodomain into cys5 was identified in two families with HCFP. We screened 95 sporadic patients diagnosed as MBS or HCFP for mutations in HOXB1. A novel homozygous alteration was identified in one HCFP case, affecting the same residue, resulting to his5. In silico protein analysis predicted stronger HOXB1-DNA binding properties for his5 than cys5 that resulted to milder phenotype. It should be noted that, inclusive of the previous report, only two mutations revealed in HOXB1 associated with HCFP involved the same amino acid arg5 in HOXB1 residing in HOXB1-DNA-PBX1 ternary complex.

Twins with hereditary sensory and autonomic neuropathy type IV with preserved periodontal sensation.

Turkish twin brothers affected with hereditary sensory and autonomic neuropathy type IV (HSAN IV) are reported. Their clinical findings were generally typical for HSAN IV. Interestingly they both had preserved periodontal sensation. Mutation analysis of the NTRK1 gene showed a homozygous c.2001C>T substitution in exon 15 in both twins. This base substitution is predicted to change a polar, positively charged amino acid arginine to the highly active amino acid cystein at position 654 (p.Arg654Cys). The parents were heterozygous for the mutation. This mutation has been reported previously in one Japanese and one Arab patients. The preserved periodontal sensation has not previously been reported in patients affected with HSAN IV. This preserved sensation in our patients might have been through Ruffini endings, the periodontal mechanoreceptors which have been reported to be present in TrkA knockout mice. Here we report the first twins affected with HSAN IV and the observation that periodontal sensation is not affected by mutation in NTRK1.

RSPO2 inhibition of RNF43 and ZNRF3 governs limb development independently of LGR4/5/6

The four R-spondin secreted ligands (RSPO1–RSPO4) act via their cognate LGR4, LGR5 and LGR6 receptors to amplify WNT signalling1–3. Here we report an allelic series of recessive RSPO2 mutations in humans that cause tetra-amelia syndrome, which is characterized by lung aplasia and a total absence of the four limbs. Functional studies revealed impaired binding to the LGR4/5/6 receptors and the RNF43 and ZNRF3 transmembrane ligases, and reduced WNT potentiation, which correlated with allele severity. Unexpectedly, however, the triple and ubiquitous knockout of Lgr4, Lgr5 and Lgr6 in mice did not recapitulate the known Rspo2 or Rspo3 loss-of-function phenotypes. Moreover, endogenous depletion or addition of exogenous RSPO2 or RSPO3 in triple-knockout Lgr4/5/6 cells could still affect WNT responsiveness. Instead, we found that the concurrent deletion of rnf43 and znrf3 in Xenopus embryos was sufficient to trigger the outgrowth of supernumerary limbs. Our results establish that RSPO2, without the LGR4/5/6 receptors, serves as a direct antagonistic ligand to RNF43 and ZNRF3, which together constitute a master switch that governs limb specification. These findings have direct implications for regenerative medicine and WNT-associated cancers.Independently of the LGR4/5/6 receptors, RSPO2 acts as a direct antagonistic ligand to RNF43 and ZNRF3 during embryogenesis, and specifies the position and number of limbs that an embryo should form.

Newly described clinical features in two siblings with MACS syndrome and a novel mutation in RIN2

The disorder comprising Macrocephaly, Alopecia, Cutis laxa, and Scoliosis has been designated MACS syndrome. It is a rare condition, inherited in an autosomal recessive pattern. Three families from different ethnic origins have so far been reported and were all linked to homozygous mutations in RIN2, a gene encoding the Ras and Rab interactor 2 protein involved in cell trafficking. We describe herein the fourth family with MACS syndrome in two siblings carrying a novel homozygous mutation, c.1878_1879insC in exon 8 of the RIN2 gene, which predicts p.Ile627Hisfs*7. We also report on additional findings not previously described in MACS syndrome, including bronchiectasis and hypergonadotropic hypogonadism. Finally, our overall data support the argument that RIN2 syndrome is a more appropriate name for the disorder.