Griet Van Buggenhout

Heterozygous Germline Mutations in the p53 Homolog p63 Are the Cause of EEC Syndrome

EEC syndrome is an autosomal dominant disorder characterized by ectrodactyly, ectodermal dysplasia, and facial clefts. We have mapped the genetic defect in several EEC syndrome families to a region of chromosome 3q27 previously implicated in the EEC-like disorder, limb mammary syndrome (LMS). Analysis of the p63 gene, a homolog of p53 located in the critical LMS/EEC interval, revealed heterozygous mutations in nine unrelated EEC families. Eight mutations result in amino acid substitutions that are predicted to abolish the DNA binding capacity of p63. The ninth is a frameshift mutation that affects the p63alpha, but not p63beta and p63gamma isotypes. Transactivation studies with these mutant p63 isotypes provide a molecular explanation for the dominant character of p63 mutations in EEC syndrome.

Definition of a critical region on chromosome 18 for congenital aural atresia by arrayCGH

Deletions of the long arm of chromosome 18 occur in approximately 1 in 10,000 live births. Congenital aural atresia (CAA), or narrow external auditory canals, occurs in approximately 66% of all patients who have a terminal deletion 18q. The present report describes a series of 20 patients with CAA, of whom 18 had microscopically visible 18q deletions. The extent and nature of the chromosome-18 deletions were studied in detail by array-based comparative genomic hybridization (arrayCGH). High-resolution chromosome-18 profiles were obtained for all patients, and a critical region of 5 Mb that was deleted in all patients with CAA could be defined on 18q22.3-18q23. Therefore, this region can be considered as a candidate region for aural atresia. The array-based high-resolution copy-number screening enabled a refined cytogenetic diagnosis in 12 patients. Our approach appeared to be applicable to the detection of genetic mosaicisms and, in particular, to a detailed delineation of ring chromosomes. This study clearly demonstrates the power of the arrayCGH technology in high-resolution molecular karyotyping. Deletion and amplification mapping can now be performed at the submicroscopic level and will allow high-throughput definition of genomic regions harboring disease genes.

Structural chromosome rearrangements in couples with recurrent fetal wastage

OBJECTIVE A review of the cytogenetic data in 1743 couples (3486 patients) with recurrent fetal wastage (RFW) who were examined for RFW at the Leuven Centre for Human Genetics in the period 1986-1995. These results were compared with a previous study in the period 1970-1985. SUBJECTS Patients who had at least two first trimester miscarriages or patients who had a spontaneous first trimester abortion, preceded or followed by a second or third trimester fetal death. RESULTS Chromosomal rearrangements were found in 5.34%. Two-thirds of these chromosomal rearrangements were autosomal balanced translocations. This finding is a 30-fold increase compared to the general population. Other chromosomal abnormalities included Robertsonian translocations, inversions and sex-chromosomal abnormalities. DISCUSSION The Leuven experience was compared with several other studies. Mechanisms causing these chromosomal abnormalities are presented. CONCLUSIONS Chromosomal analyses are an important and necessary part of the etiological investigations in couples with RFW.

Angelman syndrome (AS, MIM 105830).

Angelman syndrome (AS) is a distinct neurogenetic syndrome, first described in 1965. The phenotype is well known in infancy and adulthood, but the clinical features may change with age. The main clinical characteristics include severe mental retardation, epileptic seizures and EEG abnormalilties, neurological problems and distinct facial dysmorphic features. Behavioural problems such as hyperactivity and sleeping problems are reported, although these patients present mostly a happy personality with periods of inappropriate laughter. Different underlying genetic mechanisms may cause AS, with deletion of chromosome 15 as the most frequent cause. Other genetic mechanisms such as paternal uniparental disomy, imprinting defect and mutation in the UBE3A gene are present in smaller groups of patients with AS. As the recurrence risk can be up to 50%, the clinical diagnosis of AS should be confirmed by laboratory tesing, and genetic counselling should be provided. Treatment of seizures, physical therapy or other intervention strategies are helpful to ameliorate the symptoms.

Tumor spectrum in children with Noonan syndrome and SOS1 or RAF1 mutations

Noonan syndrome (NS) is an autosomal dominant disorder caused by mutations in PTPN11, KRAS, SOS1, and RAF1. We performed SOS1, RAF1, BRAF, MEK1, and MEK2 mutation analysis in a cohort of 102 PTPN11‐ and KRAS‐negative NS patients and found pathogenic SOS1 mutations in 10, RAF1 mutations in 4, and BRAF mutations in 2 patients. Three novel SOS1 mutations were found. One was classified as a rare benign variant and the other remains unclassified. We confirm a high prevalence of pulmonic stenosis and ectodermal abnormalities in SOS1‐positive patients. Three patients with SOS1 mutations presented with tumors (embryonal rhabdomyosarcoma, Sertoli cell testis tumor, and granular cell tumors of the skin). One patient with a RAF1 mutation had a lesion suggestive for a giant cell tumor. This is the first report describing different tumor types in NS patients with germ line SOS1 mutations.

Lujan-Fryns syndrome (mental retardation, X-linked, marfanoid habitus)

The Lujan-Fryns syndrome or X-linked mental retardation with marfanoid habitus syndrome is a syndromal X-linked form of mental retardation, affecting predominantly males. The prevalence is not known for the general population. The syndrome is associated with mild to moderate mental retardation, distinct facial dysmorphism (long narrow face, maxillary hypoplasia, small mandible and prominent forehead), tall marfanoid stature and long slender extremities, and behavioural problems. The genetic defect is not known. The diagnosis is based on the presence of the clinical manifestations. Genetic counselling is according to X-linked recessive inheritance. Prenatal testing is not possible. There is no specific treatment for this condition. Patients need special education and psychological follow-up, and attention should be given to diagnose early psychiatric disorders.

A dysmorphic boy with 4qter deletion and 4q32.3-34.3 duplication: Clinical, cytogenetic, and molecular findings

An infant boy presented with trigonocephaly, mild craniofacial features, a small VSD, open ductus Botalli (ODB), bilateral hip dysplasia, psychomotor retardation, and hypotonia. The karyotype was 46,XY,del(4)(q34). Unexpectedly, fluorescence in situ hybridization (FISH) studies revealed not only a deletion but also a duplication. The deletion extends from 4qter to 4q34.3 and the duplication from 4q32.3 to q34.3. This is the first description of a deletion inverted duplication 4q. Possible mechanisms we can envision by which this deletion/duplication arose could be a U‐type exchange causing end‐to‐end fusion or a two step event with a paracentric inversion and subsequent cross‐over in the inverted segment. This observation suggests that the karyotype of patients with a 4q deletion should be confirmed by molecular cytogenetics.

THOC2 Mutations Implicate mRNA-Export Pathway in X-Linked Intellectual Disability

Export of mRNA from the cell nucleus to the cytoplasm is essential for protein synthesis, a process vital to all living eukaryotic cells. mRNA export is highly conserved and ubiquitous. Mutations affecting mRNA and mRNA processing or export factors, which cause aberrant retention of mRNAs in the nucleus, are thus emerging as contributors to an important class of human genetic disorders. Here, we report that variants in THOC2, which encodes a subunit of the highly conserved TREX mRNA-export complex, cause syndromic intellectual disability (ID). Affected individuals presented with variable degrees of ID and commonly observed features included speech delay, elevated BMI, short stature, seizure disorders, gait disturbance, and tremors. X chromosome exome sequencing revealed four missense variants in THOC2 in four families, including family MRX12, first ascertained in 1971. We show that two variants lead to decreased stability of THOC2 and its TREX-complex partners in cells derived from the affected individuals. Protein structural modeling showed that the altered amino acids are located in the RNA-binding domains of two complex THOC2 structures, potentially representing two different intermediate RNA-binding states of THOC2 during RNA transport. Our results show that disturbance of the canonical molecular pathway of mRNA export is compatible with life but results in altered neuronal development with other comorbidities.

Accuracy and clinical value of maternal incidental findings during noninvasive prenatal testing for fetal aneuploidies.

Purpose:Genome-wide sequencing of cell-free (cf)DNA of pregnant women aims to detect fetal chromosomal imbalances. Because the largest fraction of cfDNA consists of maternal rather than fetal DNA fragments, maternally derived copy-number variants (CNVs) are also measured. Despite their potential clinical relevance, current analyses do not interpret maternal CNVs. Here, we explore the accuracy and clinical value of maternal CNV analysis.Methods:Noninvasive prenatal testing was performed by whole-genome shotgun sequencing on plasma samples. Following mapping of the sequencing reads, the landscape of maternal CNVs was charted for 9,882 women using SeqCBS analysis. Recurrent CNVs were validated retrospectively by comparing their incidence with published reports. Nonrecurrent CNVs were prospectively confirmed by array comparative genomic hybridization or fluorescent in situ hybridization analysis on maternal lymphocytes.Results:Consistent with population estimates, 10% nonrecurrent and 0.4% susceptibility CNVs for low-penetrant genomic disorders were identified. Five clinically actionable variants were reported to the pregnant women, including haploinsufficiency of RUNX1, a mosaicism for segmental chromosome 13 deletion, an unbalanced translocation, and two interstitial chromosome X deletions.Conclusion:Shotgun sequencing of cfDNA not only enables the detection of fetal aneuploidies but also reveals the presence of maternal CNVs. Some of those variants are clinically actionable or could potentially be harmful for the fetus. Interrogating the maternal CNV landscape can improve overall pregnancy management, and we propose reporting those variants if clinically relevant. The identification and reporting of such CNVs pose novel counseling dilemmas that warrant further discussions and development of societal guidelines.Genet Med 19 3, 306–313.

Speech and language in Wolf-Hirschhorn syndrome: a case-study

UNLABELLED Wolf-Hirschhorn syndrome (WHS), a condition resulting from a distal deletion of the short arm of chromosome 4, is usually associated with a severe phenotypic expression including multiple malformations, delayed psychomotor development, and profound learning disabilities. As far as communicative development is concerned, speech is usually absent and comprehension is limited to simple orders or to a specific context. There is some suggestion, however, that the developmental outcome in WHS depends on deletion size. This paper reports on an individual with WHS illustrating that a smaller deletion may result in a milder phenotype with respect to communicative abilities. This 10-year-old girl developed speech and language to a considerable degree. Although most children with this syndrome are severely limited in communicative abilities, the school-based speech-language pathologist working with a special education caseload may encounter WHS children with smaller deletions (and thus less severe phenotypes) who may profit from speech language pathology services. LEARNING OUTCOMES The reader will learn about the genetics, incidence, and clinical characteristics of Wolf-Hirschhorn syndrome, and about the communicative abilities and genotype/phenotype correlations in children with this syndrome.