Contiguous deletion of the NDP, MAOA, MAOB, and EFHC2 genes in a patient with Norrie disease, severe psychomotor retardation and myoclonic epilepsy

Norrie disease (ND) is an X-linked disorder, inherited as a recessive trait that, therefore, mostly affects males. The gene responsible for ND, called NDP, maps to the short arm of chromosome X (Xp11.4-p11.3). We report here an atypical case of ND, consisting of a patient harboring a large submicroscopic deletion affecting not only the NDP gene but also the MAOA, MAOB, and EFHC2 genes. Microarray comparative genomic hybridization (CGH) analysis showed that 11 consecutive bacterial artificial chromosome (BAC) clones, mapping around the NDP gene, were deleted. These clones span a region of about 1 Mb on Xp11.3. The deletion was ascertained by fluorescent in situ hybridization (FISH) analysis with different BAC clones located within the region. Clinical features of the proband include bilateral retinal detachment, microcephaly, severe psychomotor retardation without verbal language skills acquired, and epilepsy. The identification and molecular characterization of this case reinforces the idea of a new contiguous gene syndrome that would explain the complex phenotype shared by atypical ND patients.     

WDR45B‐related intellectual disability,spastic quadriplegia,epilepsy, and cerebral hypoplasia: A consistent neurodevelopmental syndrome

The advancement in genomic sequencing has greatly improved the diagnostic yield for neurodevelopmental disorders and led to the discovery of large number of novel genes associated with these disorders. WDR45B has been identified as a potential intellectual disability gene through genomic sequencing of 2 large cohorts of affected individuals. In this report we present 6 individuals from 3 unrelated families with homozygous pathogenic variants in WDR45B: c.799C>T (p.Q267*) in 1 family and c.673C>T (p.R225*) in 2 families. These individuals shared a similar phenotype including profound development delay, early‐onset refractory epilepsy, progressive spastic quadriplegia and contractures, and brain malformations. Neuroimaging showed ventriculomegaly, reduced cerebral white matter volume, and thinning of cerebral gray matter. The consistency in the phenotype strongly supports that WDR45B is associated with this disease.     

Loss of the SHOX gene associated with Leri-Weill dyschondrosteosis in a 45,X male

A male patient is reported with a 45,X karyotype and Leri-Weill dyschondrosteosis (LWD). FISH analysis with SHOX and SRY gene probes was carried out. One copy of both SHOX and SRY was detected in interphase nuclei, clarifying the origin of LWD and the male phenotype. Molecular results suggested that the 45,X karyotype arose through two independent events. The first occurred at paternal meiosis leading to an unequal crossing over between the short arms of the X and Y chromosomes. As a consequence, the SRY gene was translocated onto Xp, thereby explaining the male phenotype of the patient. The second event probably occurred at maternal meiosis or at the early stages of the zygote resulting in the loss of the maternal X chromosome.     

Unknown diagnosis in two male cousins with facial abnormalities,optic atrophy,abnormal EEG,and severe psychomotor retardation

We report two male cousins with short stature, microcephaly, hypertelorism, optic atrophy, ptosis, absent ear lobes, high-arched palates, abnormal EEG, and severe mental retardation. Both cousins have consanguineous parents. Differential diagnoses are discussed and the possibility that we might be reporting on a new syndrome is raised.     

Spontaneous deletion of epilepsy gene orthologs in a mutant mouse with a low electroconvulsive threshold

The electroconvulsive threshold (ECT) test has been used extensively to determine the protection conferred by antiepileptic drug candidates against induced seizures in rodents. Despite its clinical relevance, the potential of ECT to identify mouse epilepsy models in genetic studies has not been thoroughly assessed. We adopted the ECT test to screen the progeny of ethylnitrosourea treated male C57BL/6J mice. In a small-scale screen, several mutant lines conferring a low threshold to ECT minimal clonic seizures were mapped to the telomeric region of mouse chromosome 2 in independent founder families. This high incidence was suggestive of a single spontaneous event that pre-existed in the founders of mutagenized stock. Genetic and physical mapping led to the discovery that several lines shared a single mutation, Szt1 (seizure threshold-1), consisting of a 300 kb deletion of genomic DNA involving three known genes. Two of these genes, Kcnq2 and Chrna4, are known to be mutated in human epilepsy families. Szt1 homozygotes and heterozygotes display similar phenotypes to those found in the respective Kcnq2 knockout mutant mice, suggesting that Kcnq2 haploinsufficiency is at the root of the Szt1 seizure sensitivity. Our results provide a novel genetic model for epilepsy research and demonstrate that the approach of using ECT to study seizures in mice has the potential to lead to the identification of human epilepsy susceptibility genes.     

Molecular cytogenetic characterization of an interstitial deletion of chromosome 21 (21q22.13q22.3) in a patient with dysmorphic features, intellectual disability and severe generalized epilepsy

We report on a de novo interstitial deletion of chromosome 21q in a patient presenting with characteristic facial features, intellectual disability, and epilepsy. The deletion extent was about 4.9 Mb from position 37713441 bp (21q22.13) to position 42665162 bp (21q22.3) (NCBI36/hg18 map).Patients with partial monosomy 21 are quite rare; this anomaly has been associated with a wide spectrum of clinical signs, ranging from very mild to quite severe phenotypes. This variability results from variability in the deleted regions, thus accurate molecular definition of the chromosomal breakpoints is necessary to make better genotype-phenotype correlations.We compared our patient's phenotype with the few other patients reported in the literature and found to have similar deletion when analyzed by array CGH. The minimal overlapping region contains only two genes, DYRK1A and KCNJ6, which may play a major role in these patients' phenotype.     

Interstitial 9q34.11-q34.13 deletion in a patient with severe intellectual disability, hydrocephalus, and cleft lip/palate

Interstitial deletions of chromosome bands 9q34.11-q34.13 are rare. We report on a 16-year-old female patient with severe intellectual disability, congenital hydrocephalus, cleft lip and palate, talipes equinovarus, epilepsy, kyphoscoliosis, convergent strabismus, severe short stature, dystrophy, and facial dysmorphic signs. Array analysis revealed a 3.7?Mb interstitial deletion in 9q34.11-q34.13. The deletion harbors more than 60 genes, including SPTAN1, DYT1/TOR1A, ABL1, ASS1, LAMC3, POMT1, DOLK, and GLE1, mutations in which have previously been associated with monogenic disorders. This is the first patient with a deletion of this size and position in 9q34.11-q34.13. Reports of additional patients with aberrations in this region will be needed to establish karyotype-phenotype correlations and to gain information on the contribution of individual genes for the clinical manifestations.     

Intragenic deletion as a novel type of mutation in Wolman disease

Two clinically distinct disorders, Wolman disease (WD) and cholesteryl ester storage disease (CESD), are allelic autosomal recessive disorders caused by different mutations in lysosomal acid lipase (LIPA) which encodes for an essential enzyme involved in the hydrolysis of intracellular cholesteryl esters and triglycerides. We describe a case of lysosomal acid lipase deficiency in an infant with WD and report on a novel mutation type, intragenic deletion.     

A HS6ST2 gene variant associated with X-linked intellectual disability and severe myopia in two male twins

X-linked intellectual disability (XLID) refers to a clinically and genetically heterogeneous neurodevelopmental disorder, in which males are more heavily affected than females. Among the syndromic forms of XLID, identified by additional clinical signs as part of the disease spectrum, the association between XLID and severe myopia has been poorly characterized. We used whole exome sequencing (WES) to study two Italian male twins presenting impaired intellectual function and adaptive behavior, in association with severe myopia and mild facial dysmorphisms. WES analysis detected the novel, maternally inherited, mutation c.916G > C (G306R) in the X-linked heparan sulfate 6-O-sulfotransferase 2 (HS6ST2) gene. HS6ST2 transfers sulfate from adenosine 3′-phosphate, 5′-phosphosulfate to the sixth position of the N-sulphoglucosamine residue in heparan sulfate (HS) proteoglycans. Low HS sulfation levels are associated with defective optic disc and stalk morphogenesis during mammalian visual system development. The c.916G>C variant affects the HS6ST2 substrate binding site, and its effect was considered “deleterious” by in-silico tools. An in-vitro enzymatic assay showed that the HS6ST2 mutant isoform had significantly reduced sulphotransferase activity. Taken together, the results suggest that mutant HS6ST2 is possibly involved in the development of myopia and cognitive impairment, characteristics of the probands reported here.     

Novel association of severe neonatal encephalopathy and Hirschsprung disease in a male with a duplication at the Xq28 region

Background  

Hirschsprung disease (HSCR) is a neurocristopathy characterized by the absence of parasympathetic intrinsic ganglion cells in the submucosal and myenteric plexuses along a variable portion of the intestinal tract. In approximately 18% of the cases HSCR also presents with multiple congenital anomalies including recognized syndromes.     

Mutations in PHD-like domain of the ATRX gene correlate with severe psychomotor impairment and severe urogenital abnormalities in patients with ATRX syndrome

Mutations in ATRX are associated with a wide and clinically heterogeneous spectrum of X-linked mental retardation syndromes. The ATRX protein, involved in chromatin remodelling, belongs to the family of SWI/SNF DNA helicases and contains a plant homeodomain (PHD)-like domain. To date, more than 60 different mutations have been reported in ATRX. One of them is recurrent and accounts for 20% of all the reported mutations, whereas all others are private. Most mutations are clustered in the two major functional domains, the helicase and the PHD-like domain. So far, no clear genotype-phenotype correlation has been established, with exception to the rare truncating mutations located at the C-terminal part of the protein, which are consistently associated with severe urogenital defects. In this study, we report the molecular analysis performed in 16 families positive for ATRX. Our findings indicate that, in addition to the previously described mutation 'hotspot' in the PHD-like domain, two other protein sections emerge as minor 'hotspots' in the helicase region encoded by exons 18-20 and 26-29, respectively, gathering 33% of all described mutations. Additionally, based on the clinical data collected for 22 patients from the 16 families, we observe that mutations in the PHD-like domain produce severe and permanent psychomotor deficiency, usually preventing patients from walking, as well as constant urogenital abnormalities, while mutations in the helicase domain lead to delayed but correct psychomotor acquisitions together with mild or absent urogenital abnormalities. In summary, mutations in the helicase domain are associated with milder phenotypes than mutations in the PHD-like domain.     

Sensorineural deafness and male infertility: a contiguous gene deletion syndrome

Background

Syndromic hearing loss that results from contiguous gene deletions is uncommon. Deafness‐infertility syndrome (DIS) is caused by large contiguous gene deletions at 15q15.3.

Methods

Three families with a novel syndrome characterised by deafness and infertility are described. These three families do not share a common ancestor and do not share identical deletions. Linkage was established by completing a genome‐wide scan and candidate genes in the linked region were screened by direct sequencing.

Results

The deleted region is about 100 kb long and involves four genes (KIAA0377, CKMT1B, STRC and CATSPER2), each of which has a telomeric duplicate. This genomic architecture underlies the mechanism by which these deletions occur. CATSPER2 and STRC are expressed in the sperm and inner ear, respectively, consistent with the phenotype in persons homozygous for this deletion. A deletion of this region has been reported in one other family segregating male infertility and sensorineural deafness, although congenital dyserythropoietic anaemia type I (CDAI) was also present, presumably due to a second deletion in another genomic region.

Conclusion

We have identified three families segregating an autosomal recessive contiguous gene deletion syndrome characterised by deafness and sperm dysmotility. This new syndrome is caused by the deletion of contiguous genes at 15q15.3.