Alternative titles; symbols
HGNC Approved Gene Symbol: FOXL2
SNOMEDCT: 715391004;
Cytogenetic location: 3q22.3 Genomic coordinates (GRCh38): 3:138,944,224-138,947,137 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 3q22.3 | Blepharophimosis, epicanthus inversus, and ptosis, type 1 | 110100 | Autosomal dominant; Autosomal recessive | 3 |
| Blepharophimosis, epicanthus inversus, and ptosis, type 2 | 110100 | Autosomal dominant; Autosomal recessive | 3 | |
| Premature ovarian failure 3 | 608996 | Autosomal dominant | 3 |
Transcription factors belonging to the evolutionarily conserved forkhead box (FOX) superfamily contain a DNA-binding motif known as the forkhead box or winged-helix domain. The forkhead box domain is about 100 amino acids long and folds into a structure containing 3 N-terminal alpha helices, 3 beta strands, and 2 loop regions near the C-terminal end of the domain. In contrast with the highly conserved forkhead box domain, FOX proteins are highly divergent in other parts of their sequences. FOX proteins vary widely in their expression patterns, regulation, and physiologic functions, with roles in eye organogenesis, language acquisition, stress response, aging regulation, and tumor suppression. FOXL2 plays a crucial role in ovarian development and female fertility (summary by Benayoun et al., 2008).
Crisponi et al. (2001) positionally cloned a novel putative winged helix/forkhead transcription factor gene, FOXL2, in the blepharophimosis/ptosis/epicanthus inversus syndrome (BPES; 110100) critical region on chromosome 3q23. Consistent with an involvement in BPES, FOXL2 was selectively expressed in the mesenchyme of developing mouse eyelids and in adult ovarian follicles; in adult humans, it appeared predominantly in the ovary.
Cocquet et al. (2002) found that the FOXL2 coding region is highly conserved in human, goat, mouse, and pufferfish. They showed that the number of alanine residues is strictly conserved among the mammals studied, suggesting the existence of strong functional or structural constraints. They provided immunohistochemical evidence indicating that FOXL2 is a nuclear protein specifically expressed in eyelids and in fetal and adult ovarian follicular cells. It does not undergo any major posttranslational maturation. They pointed out that FOXL2 is the earliest known marker of ovarian differentiation in mammals and may play a role in ovarian somatic cell differentiation and in further follicle development and/or maintenance.
Udar et al. (2003) sequenced the mouse homolog for the FOXL2 gene and identified the Fugu rubripes (pufferfish) ortholog by screening the Joint Genome Institute database (Aparicio et al., 2002) with the mouse genomic sequence. By alignment of the human, mouse, and pufferfish sequences, they found an almost complete conservation of the forkhead domain in the 3 species. There is 95% and 61% conservation at the protein level between human-mouse and human-pufferfish, respectively. The polyalanine and polyproline tracts within the gene are absent in pufferfish.
Beysen et al. (2008) stated that the 376-amino acid FOXL2 protein has a DNA-binding forkhead domain (FHD) of about 110 amino acids and a polyalanine tract of 14 residues.
Crisponi et al. (2004) determined that mouse and human FOXL2 are single-exon genes.
By genomic sequence analysis, Crisponi et al. (2001) mapped the FOXL2 gene to chromosome 3q23.
More than 99% of ovarian germ cells undergo atresia. Lee et al. (2005) found that overexpression of human FOXL2 caused apoptosis in Chinese hamster ovary cells and in primed rat granulosa cells in a dose-dependent manner. Apoptosis was prevented by cotransfection of a baculoviral caspase inhibitor. Yeast 2-hybrid analysis revealed that FOXL2 interacted with the C-terminal domain of mouse Dp103 (DDX20; 606168), an ATP-dependent RNA helicase. The region of Dp103 that interacted with FOXL2 lacks the helicase domain, but it also interacts with SF1 (NR5A1; 184757), a nuclear factor involved in sex determination. Dp103 had no effect on cell viability alone, but cotransfection studies showed that Dp103 enhanced the apoptotic effect of FOXL2.
By PCR selection using a library of double-stranded DNA fragments and nuclear extracts of a mouse granulosa cell line, Benayoun et al. (2008) identified a Foxl2 response element (FLRE) that differed significantly from other FOX protein-binding sites. The common 7-bp FLRE was 5-prime-GT(C/G)AAGG-3-prime, or its reverse complement. By transfecting mouse and human granulosa-like cells with artificial promoter reporters, Benayoun et al. (2008) found that 4 tandem copies of FLRE resulted in higher reporter activity than 2, and that replacement of Gs with Ts in the FLRE core sequence resulted in an FLRE with lower FOXL2 affinity and weaker reporter activity. In addition, poly(A) expansion of FOXL2, notably expansion to 24 alanines (FOXL2-ala24), resulted in lower reporter activity when the reporter had fewer FLREs or when the FLRE had lower FOXL2 affinity. FOXL2-ala24 functioned in a dominant-negative fashion when coexpressed with wildtype FOXL2, but only with a reporter of low FOXL2 affinity. Benayoun et al. (2008) concluded that the impact of poly(A) expansion on expression of FOXL2-dependent genes depends on both the number and specific sequences of FLREs in FOXL2-responsive promoters.
Benayoun et al. (2009) showed that cell stress upregulated FOXL2 expression in an ovarian granulosa cell model. The response of FOXL2 to stress correlated with a dramatic remodeling of its posttranslational modification profile. Upon oxidative stress, there was increased recruitment of FOXL2 to several stress-response promoters, notably mitochondrial manganese superoxide dismutase, MnSOD (SOD2; 147460). FOXL2 activity was repressed by the SIRT1 (604479) deacetylase. SIRT1 transcription was, in turn, directly upregulated by FOXL2, which closed a negative-feedback loop. Treatment with the sirtuin inhibitor nicotinamide increased FOXL2 transcription. Eleven disease-causing mutations in the ORF of FOXL2 induced aberrant regulation of FOXL2 and/or the FOXL2 stress-response target gene MnSOD. Benayoun et al. (2009) concluded that FOXL2 is an actor of the stress response.
Blepharophimosis, Ptosis, and Epicanthus Inversus, Types I and II
There are 2 forms of the blepharophimosis/ptosis/epicanthus inversus syndrome (BPES; 110100). In type I, eyelid abnormalities are associated with ovarian failure. In type II, only the eyelid defects are found. Crisponi et al. (2001) identified mutations in the FOXL2 gene that produced truncated proteins in type I families and larger proteins in type II families. Because of the variable phenotypes produced by mutations in forkhead transcription factor genes, Crisponi et al. (2001) proposed that some mutations in the FOXL2 gene may be associated with other phenotypes, including nonsyndromic premature ovarian failure (POF; see 608996). FOXL2 was the third forkhead gene found to be involved in the pathogenesis of inherited developmental human disorders. A single-exon gene, FOXE1 (602617), is mutated in cases of thyroid agenesis, and FOXC1 (601090) is mutated in eye defects associated with congenital glaucoma.
In a study in Korean patients, Cha et al. (2003) identified FOXL2 mutations in 5 of 9 BPES families and 3 of 7 sporadic cases. No causal mutation was found in the other BPES families or sporadic cases, suggesting that the genetic defect in some BPES patients may reside in the noncoding region of the FOXL2 gene or in other genes.
Vincent et al. (2005) reported an 18-month-old girl with sporadic BPES and bilateral type 1 Duane syndrome (see 126800), in whom they identified a heterozygous duplication of 10 alanine residues in the FOXL2 gene (605597.0002).
In an Indian cohort comprising 6 familial and 2 sporadic cases of BPES type I or type II, Kaur et al. (2011) identified 6 heterozygous mutations in the FOXL2 gene, 3 of which were novel (see, e.g., 605597.0020). In 1 family, an affected female also had polycystic ovarian disease. Kaur et al. (2011) noted that mutations in the region downstream of the forkhead domain were predominantly responsible for BPES among Indian patients.
Premature Ovarian Failure 3
Harris et al. (2002) detected heterozygous FOXL2 mutations in 2 patients with isolated POF (POF3; 608996). One mutation removed 10 of the 14 alanines in the polyalanine tract downstream of the winged helix/forkhead domain (605597.0016). The other was a single-nucleotide substitution predicted to result in a tyr258-to-asn amino acid change (605597.0017).
In a 26-year-old Tunisian patient with nonsyndromic premature ovarian failure, Laissue et al. (2009) identified a heterozygous mutation in the FOXL2 gene (G187D; 605597.0019). Although the transactivation capacity of FOXL2-G187D was significantly lower than that of wildtype FOXL2, the mutant was able to strongly activate a reporter construct driven by the OSR2 (611297) promoter, believed to be a crucial target of FOXL2 in the craniofacial region. Laissue et al. (2009) noted that this is compatible with the absence of BPES in this patient.
Ovarian Granulosa-Cell Tumors
Shah et al. (2009) analyzed 4 adult-type ovarian granulosa-cell tumor (GCT) specimens for GCT-specific mutations and identified a somatic point mutation, 402C-G (C134W), in the FOXL2 gene in all 4 specimens. The C134W mutation was present in 86 (97%) of 89 additional adult-type GCTs, in 3 (21%) of 14 thecomas, and in 1 (10%) of 10 juvenile-type GCTs. The mutation was absent in 49 sex cord/stromal tumors of other types and in 329 unrelated ovarian or breast tumors. Shah et al. (2009) concluded that mutant FOXL2 is a potential driver in the pathogenesis of adult-type GCTs.
FOXL2 Mutation Database
Beysen et al. (2004) described a locus-specific human FOXL2 mutation database available on the Internet. The database contained approximately 135 intragenic mutations and variants of FOXL2, but did not include variants residing outside the coding region of FOXL2 or molecular cytogenetic rearrangements of the FOXL2 locus. Beysen et al. (2004) stated that at least 1 mutation in the FOXL2 gene with a putative pathogenic effect had been found in patients affected with isolated primary ovarian failure (Harris et al., 2002).
Pathogenic Effects of FOXL2 Mutations
Moumne et al. (2005) showed that premature stop codons in the FOXL2 gene (e.g., 605597.0008) may lead to the production of N-terminally truncated proteins by reinitiation of translation downstream of the stop codon. Truncated proteins strongly aggregated in the nucleus, partially localized in the cytoplasm, and retained a fraction of the wildtype protein. A complete deletion of the polyalanine tract of FOXL2 induced significant intranuclear aggregation.
Moumne et al. (2008) noted that polyalanine expansions of +10 residues (i.e., 24 alanines) in FOXL2 have been identified in approximately 30% of BPES patients and are mainly responsible for BPES type II. By transfecting COS-7 and KGN cells with a series of FOXL2 polyalanine variants, Moumne et al. (2008) found that the wildtype allele with 14 alanines was expressed exclusively in the nucleus. Cytoplasmic staining became statistically significant for FOXL2 containing 19 alanines, and it reached 100% for 37 alanines. FOXL2 proteins with 24 alanines or more showed aggregation in both nuclear and cytoplasmic compartments. FRAP analysis showed that wildtype FOXL2 was highly mobile within the nuclear compartment, while FOXL2 with 17 alanines showed reduced mobility, and FOXL2 with 19 alanines was virtually immobile. Reporter gene assays using the promoter regions of several FOXL2 target genes showed that alanine expansion had variable effects on promoter activity. Moumne et al. (2008) suggested that promoters with more FOXL2-binding sites or higher FOXL2 affinity would be less sensitive than other promoters to reduced FOXL2 availability due to protein aggregation or mislocalization.
By expression in COS-7 and KGN cells, Beysen et al. (2008) examined the consequences of 16 missense mutations within the DNA-binding FHD of FOXL2 and another mutation outside the FHD. The mutations had variable effects on subcellular localization, aggregation, and transactivation of a reporter gene.
Dipietromaria et al. (2009) dissected the molecular and functional effects of 10 FOXL2 mutants, known to induce BPES with or without premature ovarian failure (POF). There was a correlation between the transcriptional activity of FOXL2 variants on 2 different reporter promoter assays (4XFLRE-luc and SIRT1-luc) and the type of BPES. Application of this functional framework to 18 BPES missense mutations allowed classification as type I or II mutation based on transactivation abilities. They also found a loose correlation between intranuclear aggregation and cytoplasmic mislocalization of mutant FOXL2 and the type of BPES. Dipietromaria et al. (2009) suggested that a FOXL2 mutant completely lacking activity on the 2 reporter assays used in this study is likely to lead to BPES with POF.
De Baere et al. (2001) identified FOXL2 mutations in 21 of 34 patients with BPES types I and II. A genotype-phenotype correlation was evident, wherein mutations predicted to result in a truncated protein either lacking or containing the forkhead domain led to BPES type I. In contrast, duplications within or downstream of the forkhead domain and a frameshift downstream of them, all predicted to result in an extended protein, caused BPES type II. In 30 unrelated patients with isolated premature ovarian failure, no causal mutations were identified in FOXL2. The initial association of BPES type I and mutations in the FOXL2 gene raised the question of whether mutations in FOXL2 could lead to isolated POF (Prueitt and Zinn, 2001).
De Baere et al. (2003) described 21 FOXL2 mutations, 16 of which were novel, and stated that 53 mutations in the FOXL2 had been reported. Two mutation hotspots were identified: 30% of FOXL2 mutations led to polyalanine expansions, and 13% were novel out-of-frame duplications. They demonstrated intra- and interfamilial phenotypic variability, with both BPES types caused by the same mutation (see 605597.0006 and 605597.0009). They found exceptions to their previously constructed genotype-phenotype correlation, which required revision. They assumed that for predicted proteins with a truncation before the polyalanine tract, the risk for development of POF was high. For mutations leading to a truncated or extended protein containing an intact forkhead and polyalanine tract, no predictions were possible, because some of these mutations led to both types of BPES, even within the same family. Polyalanine expansions may lead to BPES type II (see 605597.0010). For missense mutations, no correlations could be made. Microdeletions were associated with mental retardation.
Boccone et al. (1994) described a de novo, apparently balanced, reciprocal translocation between the long arms of chromosomes 3 and 7 in a 2-year-old male with BPES; the breakpoints were 3q23 and 7q32. Crisponi et al. (2004) found that the chromosome 3 breakpoint in this patient was located about 170 kb upstream of the FOXL2 gene, within exon 6 of the MRPS22 gene (605810), which is transcribed in the opposite orientation. They identified regions within introns 6, 11, and 12 of the MRPS22 gene that may regulate FOXL2 expression, including a winged-helix transcription factor-binding site in intron 11. Crisponi et al. (2004) reviewed other examples of distant defects that alter gene function, including a translocation 120 kb from the FOXC2 (602402) gene that causes lymphedema-distichiasis syndrome (153400) and a translocation more than 150 kb from the PAX6 gene (607108) that causes aniridia (106210). They suggested several models for long-range regulation of FOXL2 gene expression, including higher order genome structures that bring distant regulatory sequences within proximity of gene transcription start sites.
In 2 sporadic patients and 2 families with BPES, Beysen et al. (2005) identified 4 overlapping extragenic microdeletions, ranging from 126 kb to 1.9 Mb in size, 230 kb upstream of the FOXL2 gene. The shortest region of deletion overlap contains several conserved nongenic sequences harboring putative transcription factor-binding sites and representing potential long-range cis-regulatory elements. In another family with BPES, Beysen et al. (2005) identified an approximately 188-kb microdeletion downstream of the FOXL2 gene. The father of the 2 affected half-sisters was unaffected, suggestive of germinal mosaicism; quantitative analysis using 3 SNPs located in the deletion showed that about 10% of paternal germ cells and 5% of somatic peripheral blood lymphocytes carried the mutation.
Crisponi et al. (2001) pointed out that polled/intersex syndrome (PIS) in the goat has been suggested to be an animal model of human BPES (Vaiman et al., 1999). It maps to 1q31 in the goat, a region homologous to human 3q23. Thus, the authors hypothesized that the goat FOXL2 gene may be the site of the mutation causing PIS.
Pailhoux et al. (2001) found by a positional cloning approach that the mutation underlying PIS in the goat is the deletion of a critical 11.7-kb DNA element containing mainly repetitive sequences. This deletion was shown to affect the transcription of at least 2 genes: PISRT1, encoding a 1.5-kb mRNA devoid of open reading frame, and FOXL2. These 2 genes are located 20 and 200 kb telomeric from the deletion, respectively.
Uda et al. (2004) reported that mice lacking Foxl2 recapitulated relevant features of human BPES: males and females were small and showed distinctive craniofacial morphology with absent upper eyelids. Furthermore, in mice as in humans, sterility was confined to females: all major somatic cell lineages failed to develop around growing oocytes from the time of primordial follicle formation.
Ottolenghi et al. (2005) found that mouse XX gonads lacking Foxl2 formed meiotic prophase oocytes, but then activated the genetic program for somatic testis determination. Pivotal Foxl2 action repressed the male gene pathway at several stages of female gonadal differentiation. The authors proposed a continued involvement of sex-determining genes in maintaining ovarian function throughout female reproductive life.
Ottolenghi et al. (2007) observed formation of testis-like tubules and spermatogonia in the ovaries of Wnt4/Foxl2 double-knockout XX mice, demonstrating that female sex-determining genes, the putative 'ovary organizer,' are required to suppress an alternative male fate in the ovary and act as a female equivalent of SRY (480000). Forced expression of Foxl2 impaired testis tubule differentiation in XY transgenic mice, and germ cell-depleted XX mice lacking Foxl2 and harboring a Kit (164920) mutation underwent partial female-to-male sex reversal. Ottolenghi et al. (2007) stated that the results were all consistent with an anti-testis role for FOXL2.
Uhlenhaut et al. (2009) found that Foxl2 was required to prevent transdifferentiation of an adult mouse ovary to a testis. Foxl2 repressed testis differentiation in vivo mainly through repression of the Sox9 (608160) cis-regulatory sequence TESCO. Foxl2 and estrogen receptor (ESR1; 133430) cooperated in Sox9 repression in vivo, thus providing a mechanism by which loss of estrogen signaling could lead to gonadal sex reversal.
Using piggyBac (PB) insertional mutagenesis, Shi et al. (2014) created a line of mice with a modest yet significant reduction in Foxl2 expression and a BPES-like phenotype. Homozygous PB/PB mice began to lose weight approximately 2 weeks after birth, and most died within the first month of life. At 3 weeks of age, they showed significant overgrowth of mandibular incisors with malocclusion, and some showed palpebral anomalies and periocular hair loss. Surviving female PB/PB mice were subfertile, with smaller than normal ovaries and uteri. Shi et al. (2014) mapped the PB insertion site to a region approximately 160 kb upstream of the Foxl2 transcription start site and approximately 10 kb upstream of an element, ECF1, that showed a high degree of conservation among goat, mouse, and human. ECF1 functioned as an enhancer in reporter gene assays and interacted directly with the Foxl2 promoter in chromosome conformation capture assays. Shi et al. (2014) noted that BPES patients with balanced translocations and chromosome breakpoints 130, 160, or 171 kb upstream of FOXL2 have been reported. The authors hypothesized that these translocations may isolate transcription regulatory elements, including the human ECF1 ortholog, leading to FOXL2 misregulation.
See Kaestner et al. (2000) for a unified nomenclature for winged helix/forkhead transcription factors.
In a family with type I BPES (110100), Crisponi et al. (2001) found that affected members had a C-to-T transition at position 892, resulting in a codon that predicted a truncated protein (gln219 to ter).
In affected members of 2 families with BPES type II (110100), and in a sporadic male BPES patient, Crisponi et al. (2001) identified a 30-bp duplication at position 909 to 938. Amino acids 224 to 234 were duplicated. In the 2 families with multiple cases, affected females transmitted the trait to the next generation.
Ramirez-Castro et al. (2002) identified this mutation in affected members of 2 families with BPES type II from a historically isolated population in northwest Colombia. The genotype/phenotype correlation in the families was consistent with a proposal that BPES type I is caused by truncating mutations leading to haploinsufficiency, while BPES type II is caused by mutations generating elongated protein products (see also 605597.0008). This duplication has also been described as recurrent in unrelated familial and sporadic BPES cases in Europe; its recurrence may be related to the secondary structure of the particular DNA region.
In both a family and sporadic case of BPES type II from Algeria, Dollfus et al. (2003) identified this mutation.
In an 18-month-old girl with sporadic BPES and bilateral type 1 Duane syndrome (see 126800), Vincent et al. (2005) identified heterozygosity for a 30-bp duplication, which they designated 672_701dup30 based on numbering from the ATG start codon, resulting in a duplication of 10 alanine residues at codon 224 in the FOXL2 gene.
In a family with BPES type I (110100), De Baere et al. (2001) found that affected members had a CA dinucleotide deletion from position 290 to 291, resulting in a frameshift generating 76 novel amino acids and terminating prematurely at codon 94. The entire forkhead domain was obliterated.
In a family with BPES type I (110100), De Baere et al. (2001) found that affected members had an 8-bp duplication at position 1149 to 1156, resulting in a frameshift generating 50 novel amino acids and terminating prematurely at codon 358. Neither the forkhead domain nor the polyalanine tract were disrupted.
In a family with BPES type II (110100), De Baere et al. (2001) found that affected members had a 15-bp duplication at position 415 to 429, resulting in duplication of amino acids 60 to 64 within the forkhead domain.
In 2 families with BPES II (110100), De Baere et al. (2001) found that affected members had a 1-bp cytosine insertion following position 1041, resulting in 264 novel amino acids beginning at codon 268 and extending the protein from 376 amino acids to 532 amino acids.
De Baere et al. (2003) found this mutation in a family with BPES I. They stated that this was the first mutation shown to lead to both BPES types in different families (interfamilial phenotypic variability).
In a Japanese family with BPES type II (110100), Yamada et al. (2001) found a heterozygous 17-bp deletion at nucleotide 1092 in the FOXL2 gene. BPES type II was suspected because the affected woman had 3 sons. Four individuals in 3 sibships in 3 generations were affected. There was 1 instance of male-to-male transmission.
A 17-bp duplication at nucleotide 1092 was described by Udar et al. (2003) in 3 unrelated pedigrees, indicating that nucleotide 1092 is a hotspot; see 605597.0014.
In a family from a historically isolated population in northwest Colombia with BPES type I (110100), Ramirez-Castro et al. (2002) demonstrated linkage to chromosome 3q23 and found a novel 394C-T mutation of the FOXL2 gene which deleted the forkhead DNA binding domain. This mutation resulted in the creation of a stop codon at position 53 (Q53X) of FOXL2.
Moumne et al. (2005) showed that the Q53X mutation could result in production of N-terminally truncated proteins by reinitiation of translation downstream of the stop codon. The Q53X fusion protein was detected by Western blot analysis as a band corresponding to initiation at codon 137 and localized to the nucleus.
De Baere et al. (2003) reported a family in which BPES (110100) was related to a 1059C-G transversion in the FOXL2 gene, predicted to result in a nonsense tyr274-to-ter (Y274X) mutation. The mother was affected by BPES type II and she transmitted the disease to her daughter, who was affected by BPES type I. The latter received ovum donation at age 33 years, resulting in 1 successful pregnancy. De Baere et al. (2003) stated that this was the first reported case in which both types of BPES caused by the same mutation were documented in the same family, indicating intrafamilial phenotypic variability.
In a family with BPES type II (110100), De Baere et al. (2003) found a novel in-frame 15-bp triplication of nucleotides 921-935 in the FOXL2 gene, leading to a polyalanine expansion of 5 alanine residues, 228-232. They stated that this was the first triplication observed in the polyalanine tract of FOXL2.
Dollfus et al. (2003) studied a family originating from Strasbourg, France, that was considered to be one of the largest reported BPES type I (110100) families. The first reported case in this family was born in 1841 from presumed unaffected parents, and thereafter 36 affected individuals were identified over 6 generations. The affected members of the family had typical BPES features. Only males, strikingly and exclusively, transmitted the disease, as affected females were known to be infertile. A 488T-G transversion (genomic sequence numbering) in the FOXL2 gene, resulting in an ile84-to-ser (I84S) mutation, segregated with the disorder in the family. On MRI studies, the superior levator palpebrae could not be seen in 4 patients and appeared to be very thin in a fifth patient, but the other oculomotor muscles appeared to be normal on the MRI images.
In a 24-month-old French girl with sporadic BPES type I (110100), Dollfus et al. (2003) identified a 532C-T transition (genomic sequence numbering) in the FOXL2 gene, resulting in a GLN98TER (Q98X) mutation. The mutation resulted in a truncated protein and was not found in her parents or 3 sibs.
As indicated in the report of Beysen et al. (2008), the amino acid at position 98 in FOXL2 is tryptophan. The correct nomenclature for the mutation reported by Dollfus et al. (2003) is gln99 to ter (Q99X), not GLN98TER.
In a male with BPES (110100), Udar et al. (2003) found a spontaneous 823C-T transition in the FOXL2 gene that resulted in a truncation (gln196 to ter; Q196X) of the putative protein downstream of the forkhead domain. The nucleotides and amino acid residues at this position are conserved in human, mouse, and pufferfish.
In 3 affected members of a family with BPES type I (110100), Crisponi et al. (2001) reported a duplication of 17 bp at position 1092-1108 (1092_1108dup17), causing a frameshift resulting in a shorter protein. In a mutation search by direct sequencing in 9 affected individuals representing familial or sporadic cases, Udar et al. (2003) found this mutation in 3 unrelated pedigrees. There is a proline tract at this position, and the mutation results in a His291fsTer361 frameshift. A deletion mutation involving the same 17 bases was reported in a Japanese BPES patient by Yamada et al. (2001); see (605597.0007).
In a 32-year-old woman with sporadic BPES type I (110100) and a history of menstrual irregularities and periods of secondary amenorrhea, Fokstuen et al. (2003) identified a heterozygous 1-bp insertion in the FOXL2 gene, 959insG, resulting in 212 novel amino acids at the carboxyl end of the protein beginning at codon 321 and extending the protein from 376 to 532 amino acids.
In 70 patients from New Zealand and Slovenia with premature ovarian failure (608996), Harris et al. (2002) screened the FOXL2 gene for causative mutations; in a Slovenian patient with POF3 (608996), they identified a heterozygous 30-bp deletion (898_927del) that removed 10 of the 14 alanines from a polyalanine tract downstream of the winged helix/forkhead domain of the protein (A221_A230del). Harris et al. (2002) stated that this was the first report of a deletion within a polyalanine tract being associated with a disease phenotype, although polyalanine expansions are known to be causative in several conditions; for example, in some families with BPES type II (110100), the polyalanine tract of FOXL2 has been shown to be expanded (605597.0010).
In a patient from New Zealand who underwent premature ovarian failure (POF3; 608996) at the age of 38 years, Harris et al. (2002) identified a heterozygous 1009T-A transversion in the FOXL2 gene, resulting in a tyr258-to-asn (Y258N) substitution.
In 3 affected males and 1 affected female of a consanguineous Indian family with BPES type I (110100), Nallathambi et al. (2007) identified a homozygous 15-bp duplication (684-698dup15), resulting in an in-frame polyalanine expansion from 14 to 19 residues (Ala19). Several unaffected relatives were heterozygous for the mutation, indicating autosomal recessive inheritance in this family. The affected 30-year-old woman had amenorrhea and impaired fertility, consistent with ovarian dysfunction. Transfection studies in COS-7 cells showed that the Ala19 mutant protein showed increased cytoplasmic retention compared to wildtype, but decreased retention compared to longer expansion mutations, consistent with Ala19 being a hypomorphic allele with residual activity. Nallathambi et al. (2007) noted that Ala19 is the shortest polyalanine expansion (+5) described in the FOXL2 gene.
In a 26-year-old Tunisian patient with nonsyndromic premature ovarian failure (POF3; 608996), Laissue et al. (2009) identified heterozygosity for a 560G-A transition in the FOXL2 gene, resulting in a gly187-to-asp (G187D) substitution in a highly conserved segment, C-terminal to the forkhead domain. The paternally inherited mutation was not found in 110 control chromosomes; it had been previously detected in an XX male (De Baere et al., 2002), but its link to that condition was unclear. Although transfection studies demonstrated normal subcellular localization of the mutant FOXL2, its transactivation capacity, which was tested on 2 reporter promoters including 1 that may be relevant to the ovary, was significantly lower than that of wildtype FOXL2. However, the G187D mutant was able to strongly activate a reporter construct driven by the OSR2 (611297) promoter, believed to be a crucial target of FOXL2 in the craniofacial region. Laissue et al. (2009) noted that this is compatible with the absence of BPES in this patient.
In a 4-generation Indian family segregating BPES type II (110100), Kaur et al. (2011) identified heterozygosity and homozygosity for a 205G-A transition in the FOXL2 gene, resulting in a glu69-to-lys (E69K) substitution. The proband and his brother were homozygous for the mutation; both parents were heterozygous for the mutation. Their mother and a paternal aunt had classic BPES and their father had telecanthus. The disease severity in the family was found to be directly linked to the allelic dosage.
Beysen et al. (2008) found that the E69K substitution resulted in massive nuclear aggregation of FOXL2 following expression in COS-7 cells. However, the mutation had no discernible effect on transactivation of a DK3-Luc reporter gene.
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