Blepharophimosis, ptosis, epicanthus inversus syndrome with translocation and deletion at chromosome 3q23 in a black African female

Long-Range Regulation of Key Sex Determination Genes

The development of sexually dimorphic gonads is a unique process that starts with the specification of the bipotential genital ridges and culminates with the development of fully differentiated ovaries and testes in females and males, respectively. Research on sex determination has been mostly focused on the identification of sex determination genes, the majority of which encode for proteins and specifically transcription factors such as SOX9 in the testes and FOXL2 in the ovaries. Our understanding of which factors may be critical for sex determination have benefited from the study of human disorders of sex development (DSD) and animal models, such as the mouse and the goat, as these often replicate the same phenotypes observed in humans when mutations or chromosomic rearrangements arise in protein-coding genes. Despite the advances made so far in explaining the role of key factors such as SRY, SOX9, and FOXL2 and the genes they control, what may regulate these factors upstream is not entirely understood, often resulting in the inability to correctly diagnose DSD patients. The role of non-coding DNA, which represents 98% of the human genome, in sex determination has only recently begun to be fully appreciated. In this review, we summarize the current knowledge on the long-range regulation of 2 important sex determination genes, SOX9 and FOXL2, and discuss the challenges that lie ahead and the many avenues of research yet to be explored in the sex determination field.

The Genetic and Clinical Features of FOXL2-Related Blepharophimosis, Ptosis and Epicanthus Inversus Syndrome

Blepharophimosis, ptosis, and epicanthus inversus syndrome (BPES) is a craniofacial disorder caused by heterozygous variants of the forkhead box L2 (FOXL2) gene. It shows autosomal dominant inheritance but can also occur sporadically. Depending on the mutation, two phenotypic subtypes have been described, both involving the same craniofacial features: type I, which is associated with premature ovarian failure (POF), and type II, which has no systemic features. The genotype-phenotype correlation is not fully understood, but it has been hypothesised that type I BPES involves more severe loss of function variants spanning the whole gene. Type II BPES has been linked to frameshift mutations that result in elongation of the protein rather than complete loss of function. A mutational hotspot has been identified within the poly-alanine domain, although the exact function of this region is still unknown. However, the BPES subtype cannot be determined genetically, necessitating informed genetic counselling and careful discussion of family planning advice in view of the associated POF particularly as the patient may still be a child. Following puberty, female patients should be referred for ovarian reserve and response assessment. Oculofacial features can be managed with surgical intervention and regular monitoring to prevent amblyopia.

De Novo 3q22.3q24 Microdeletion in a Patient With Blepharophimosis-Ptosis-Epicanthus Inversus Syndrome, Dandy-Walker Malformation, and Wisconsin Syndrome

Interstitial deletions affecting the long arm of chromosome 3 have been associated with a broad phenotype. This has included the features of blepharophimosis–ptosis–epicanthus inversus syndrome, Dandy-Walker malformation, and the rare Wisconsin syndrome. The authors report a young female patient presenting with features consistent with all 3 of these syndromes. This has occurred in the context of a de novo 3q22.3q24 microdeletion including FOXL2, ZIC1, and ZIC4. This patient provides further evidence for the role of ZIC1 and ZIC4 in Dandy-Walker malformation and is the third reported case of Dandy-Walker malformation to have associated corpus callosum thinning. This patient is also only the seventh to be reported with the rare Wisconsin syndrome phenotype.

Intragenic and extragenic disruptions of FOXL2 mapped by whole genome low-coverage sequencing in two BPES families with chromosome reciprocal translocation

Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is a rare autosomal dominant disorder that affects craniofacial development and ovarian function. FOXL2 is the only gene known to be responsible for BPES. The majority of BPES patients show intragenic mutations of FOXL2. Recently, a 7.4 kb sequence disruption, which was 283 kb upstream of FOXL2, was identified to independently contribute to the BPES phenotype. Several breakpoints nearing FOXL2 (0 Mb to 1.2 Mb, several of which were distant from the 7.4 kb sequence disruption) have been mapped or deduced through a traditional method in BPES patients with chromosome reciprocal translocation. In this study, two BPES families with chromosome reciprocal translocation were investigated. Intragenic mutations of FOXL2 or pathogenic copy number variations were excluded for the two BPES families. All of the four breakpoints were identified at a base-precise manner using Giemsa banding and whole genome low-coverage sequencing (WGLCS). In family 01, the breakpoints were found at chr1:95,609,998 and chr3:138,879, 114 (213,132 bp upstream of FOXL2). In family 02, the breakpoints were located at chr3:138,665,431 (intragenic disruptions of FOXL2) and chr20:56,924,609. Results indicate that the intragenic and extragenic interruptions of FOXL2 can be accurately and rapidly detected using WGLCS. In addition, both the 213 kb upstream and intragenic interruptions of FOXL2 can cause BPES phenotype.

Association between long non-coding RNA and human rare diseases (Review)

Long non-coding RNAs (lncRNAs) are untranslated transcripts with longer than 200 nucleotides (nt), which possess many of the structural characteristics of mRNAs, including a poly A tail, 5'-capping, and a promoter structure, but no conserved open reading frame. Moreover, lncRNA expression patterns change during differentiation and exhibit a variety of splicing patterns. Many lncRNAs are expressed at specific times and in specific tissues during development. It has been proposed that lncRNAs are involved in the epigenetic regulation of coding genes, and thus exert a powerful effect on a number of physiological and pathological processes, including the pathogenesis of many human rare diseases.

The CpG island in the murine foxl2 proximal promoter is differentially methylated in primary and immortalized cells

Forkhead box L2 (Foxl2), a member of the forkhead transcription factor family, plays important roles in pituitary follicle-stimulating hormone synthesis and in ovarian maintenance and function. Mutations in the human FOXL2 gene cause eyelid malformations and premature ovarian failure. FOXL2/Foxl2 is expressed in pituitary gonadotrope and thyrotrope cells, the perioptic mesenchyme of the developing eyelid, and ovarian granulosa cells. The mechanisms governing this cell-restricted expression have not been described. We mapped the Foxl2 transcriptional start site in immortalized murine gonadotrope-like cells, LβT2, by 5’ rapid amplification of cDNA ends and then PCR amplified approximately 1 kb of 5’ flanking sequence from murine genomic DNA. When ligated into a reporter plasmid, the proximal promoter conferred luciferase activity in both homologous (LβT2) and, unexpectedly, heterologous (NIH3T3) cells. In silico analyses identified a CpG island in the proximal promoter and 5’ untranslated region, suggesting that Foxl2 transcription might be regulated epigenetically. Indeed, pyrosequencing and quantitative analysis of DNA methylation using real-time PCR revealed Foxl2 proximal promoter hypomethylation in homologous compared to some, though not all, heterologous cell lines. The promoter was also hypomethylated in purified murine gonadotropes. In vitro promoter methylation completely silenced reporter activity in heterologous and homologous cells. Collectively, the data suggest that differential proximal promoter DNA methylation may contribute to cell-specific Foxl2 expression in some cellular contexts. However, gonadotrope-specific expression of the gene cannot be explained by promoter hypomethylation alone.