Expanding the phenotype of the X-linked BCOR microphthalmia syndromes

Two distinct syndromes arise from pathogenic variants in the X-linked gene BCOR (BCL-6 corepressor): oculofaciocardiodental (OFCD) syndrome, which affects females, and a severe microphthalmia (‘Lenz’-type) syndrome affecting males. OFCD is an X-linked dominant syndrome caused by a variety of BCOR null mutations. As it manifests only in females, it is presumed to be lethal in males. The severe male X-linked recessive microphthalmia syndrome (‘Lenz’) usually includes developmental delay in addition to the eye findings and is caused by hypomorphic BCOR variants, mainly by a specific missense variant c.254C > T, p.(Pro85Leu). Here, we detail 16 new cases (11 females with 4 additional, genetically confirmed, affected female relatives; 5 male cases each with unaffected carrier mothers). We describe new variants and broaden the phenotypic description for OFCD to include neuropathy, muscle hypotonia, pituitary underdevelopment, brain atrophy, lipoma and the first description of childhood lymphoma in an OFCD case. Our male X-linked recessive cases show significant new phenotypes: developmental delay (without eye anomalies) in two affected half-brothers with a novel BCOR variant, and one male with high myopia, megalophthalmos, posterior embryotoxon, developmental delay, and heart and bony anomalies with a previously undescribed BCOR splice site variant. Our female OFCD cases and their affected female relatives showed variable features, but consistently had early onset cataracts. We show that a mosaic carrier mother manifested early cataract and dental anomalies. All female carriers of the male X-linked recessive cases for whom genetic confirmation was available showed skewed X-inactivation and were unaffected. In view of the extended phenotype, we suggest a new term of X-linked BCOR-related syndrome

De novo missense variants in FBXW11 cause diverse developmental phenotypes including brain, eye and digit anomalies

The identification of genetic variants implicated in human developmental disorders has been revolutionized by second-generation sequencing combined with international pooling of cases. Here, we describe seven individuals who have diverse yet overlapping developmental anomalies, and who all have de novo missense FBXW11 variants identified by whole exome or whole genome sequencing and not reported in the gnomAD database. Their phenotypes include striking neurodevelopmental, digital, jaw, and eye anomalies, and in one individual, features resembling Noonan syndrome, a condition caused by dysregulated RAS signaling. FBXW11 encodes an F-box protein, part of the Skp1-cullin-F-box (SCF) ubiquitin ligase complex, involved in ubiquitination and proteasomal degradation and thus fundamental to many protein regulatory processes. FBXW11 targets include b-catenin and GLI transcription factors, key mediators of Wnt and Hh signaling, respectively, critical to digital, neurological, and eye development. Structural analyses indicate affected residues cluster at the surface of the loops of the substrate-binding domain of FBXW11, and the variants are predicted to destabilize the protein and/or its interactions. In situ hybridization studies on human and zebrafish embryonic tissues demonstrate FBXW11 is expressed in the developing eye, brain, mandibular processes, and limb buds or pectoral fins. Knockdown of the zebrafish FBXW11 orthologs fbxw11a and fbxw11b resulted in embryos with smaller, misshapen, and underdeveloped eyes and abnormal jaw and pectoral fin development. Our findings support the role of FBXW11 in multiple developmental processes, including those involving the brain, eye, digits, and jaw

Identification of PITX3 mutations in individuals with various ocular developmental defects

International audienceBackground: Congenital cataract displays large phenotypic (syndromic and isolated cataracts) and genetic heterogeneity. Mutations in several transcription factors involved in eye development, like PITX3, have been associated with congenital cataracts and anterior segment mesenchymal disorders. Materials and methods: Targeted sequencing of 187 genes involved in ocular development was performed in 96 patients with mainly anophthalmia and microphthalmia. Additionally, Sanger sequencing analysis of PITX3 was performed on a second cohort of 32 index cases with congenital cataract and Peters anomaly and/or sclereocornea. Results: We described five families with four different PITX3 mutations, two of which were novel. In Family 1, the heterozygous recurrent c.640_656dup (p.Gly220Profs*95) mutation cosegregated with eye anomalies ranging from congenital cataract to Peters anomaly. In Family 2, the novel c.669del [p.(Leu225Trpfs*84)] mutation cosegregated with dominantly inherited eye anomalies ranging from posterior embryotoxon to congenital cataract in heterozygous carriers and congenital sclereocornea and cataract in a patient homozygous for this mutation. In Family 3, we identified the recurrent heterozygous c.640_656dup (p.Gly220Profs*95) mutation segregating with congenital cataract. In Family 4, the de novo c.582del [p.(Ile194Metfs*115)] mutation was identified in a patient with congenital cataract, microphthalmia, developmental delay and autism. In Family 5, the c.38G>A (p.Ser13Asn) mutation segregated dominantly in a family with Peters anomaly, which is a novel phenotype associated with the c.38G>A variant compared with the previously reported isolated congenital cataract. Conclusions: Our study unveils different phenotypes associated with known and novel mutations in PITX3, which will improve the genetic counselling of patients and their families

Identification of <i>PITX3</i> mutations in individuals with various ocular developmental defects

<p><b>Background</b>: Congenital cataract displays large phenotypic (syndromic and isolated cataracts) and genetic heterogeneity. Mutations in several transcription factors involved in eye development, like <i>PITX3</i>, have been associated with congenital cataracts and anterior segment mesenchymal disorders.</p> <p><b>Materials and methods</b>: Targeted sequencing of 187 genes involved in ocular development was performed in 96 patients with mainly anophthalmia and microphthalmia. Additionally, Sanger sequencing analysis of <i>PITX3</i> was performed on a second cohort of 32 index cases with congenital cataract and Peters anomaly and/or sclereocornea.</p> <p><b>Results</b>: We described five families with four different <i>PITX3</i> mutations, two of which were novel. In Family 1, the heterozygous recurrent c.640_656dup (p.Gly220Profs*95) mutation cosegregated with eye anomalies ranging from congenital cataract to Peters anomaly. In Family 2, the novel c.669del [p.(Leu225Trpfs*84)] mutation cosegregated with dominantly inherited eye anomalies ranging from posterior embryotoxon to congenital cataract in heterozygous carriers and congenital sclereocornea and cataract in a patient homozygous for this mutation. In Family 3, we identified the recurrent heterozygous c.640_656dup (p.Gly220Profs*95) mutation segregating with congenital cataract. In Family 4, the <i>de novo</i> c.582del [p.(Ile194Metfs*115)] mutation was identified in a patient with congenital cataract, microphthalmia, developmental delay and autism. In Family 5, the c.38G>A (p.Ser13Asn) mutation segregated dominantly in a family with Peters anomaly, which is a novel phenotype associated with the c.38G>A variant compared with the previously reported isolated congenital cataract.</p> <p><b>Conclusions</b>: Our study unveils different phenotypes associated with known and novel mutations in <i>PITX3</i>, which will improve the genetic counselling of patients and their families.</p

A mutation in CABP2, expressed in cochlear hair cells, causes autosomal-recessive hearing impairment

CaBPs are a family of Ca2+-binding proteins related to calmodulin and are localized in the brain and sensory organs, including the retina and cochlea. Although their physiological roles are not yet fully elucidated, CaBPs modulate Ca2+ signaling through effectors such as voltage-gated Ca-v Ca2+ channels. In this study, we identified a splice-site mutation (c.637+1G>T) in Ca2+-binding protein 2 (CABP2) in three consanguineous Iranian families affected by moderate-to-severe hearing loss. This mutation, most likely a founder mutation, probably leads to skipping of exon 6 and premature truncation of the protein (p.Phe164Serfs(star)4). Compared with wild-type CaBP2, the truncated CaBP2 showed altered Ca2+ binding in isothermal titration calorimetry and less potent regulation of Ca(v)1.3 Ca2+ channels. We show that genetic defects in CABP2 cause moderate-to-severe sensorineural hearing impairment. The mutation might cause a hypofunctional CaBP2 defective in Ca2+ sensing and effector regulation in the inner ear

Recurrent mutations in known autosomal recessive non-syndromic hearing loss (ARNSHL) genes in 6 Pakistani families.

<p>Acc. No., accession number of reference sequence; Chr, chromosome; Ex, exon; EVS, exome variant server; In, intron; SNPs, single nucleotide polymorphisms; Ref, references.</p

Novel mutations identified in known genes for autosomal recessive non-syndromic hearing loss (ARNSHL) in the current study.

<p>Acc. No., accession number of reference sequence; Chr, chromosome; Ex, exon; EVS, exome variant server; hg19, human genome assembly 19; In, intron; NA, not applicable; ND, not determined; SNPs, single nucleotide polymorphisms; PhyloP, phylogenetic P-values; Polyphen, polymorphism phenotyping; SIFT, sorting intolerance from tolerance.</p

Pedigrees and the segregation of novel mutations in known deafness genes.

<p>Unfilled circles indicate unaffected females, unfilled squares indicate unaffected males, filled circles indicate affected females, filled squares indicate affected males, double lines represent consanguineous marriages, slashed line across the symbols indicate deceased individual, + indicates wild type allele, M indicates mutant allele.</p