Construction and Identification of a Novel Mice Model of Microphthalmia.

Purpose: Microphthalmia is a rare developmental eye disease that affects 1 in 7000 births. Currently, there is no cure for this condition. This study aimed to construct a stable mouse model of microphthalmia, thus providing a new tool for the study of the etiology of microphthalmia. Methods: The Hedgehog signaling pathway plays a crucial role in eye development. One of the key mechanisms of the Sonic Hedgehog signaling is the strong transcriptional activation ability of GLI3, a major mediator of this pathway. This study used CRISPR/Cas9 system to construct a novel TgGli3Ki/Ki lens-specific over-expression mouse line. To identify the ocular characteristics of this line, quantitative PCR, Western blot, hematoxylin and eosin staining, immunofluorescent staining, and RNA-seq were performed on the ocular tissues of this line and normal mice. Results: The TgGli3Ki/Ki lens-specific over-expression mouse model exhibits the ocular phenotype of microphthalmia. In the TgGli3Ki/Ki mouse, Gli3 is over-expressed in the lens, and the size of the eyeball and lens is significantly smaller than the normal one. RNA-seq analysis using the lens and the retina samples from TgGli3Ki/Ki and normal mice indicates that the phototransduction pathway is ectopically activated in the lens. Immunofluorescent staining of the lens samples confirmed this activation. Conclusions: The TgGli3Ki/Ki mouse model consistently manifests the stereotypical microphthalmia phenotype across generations, making it an excellent tool for studying this severe eye disease. Translational Relevance: This study developed a novel animal model to facilitate clinical research on microphthalmia.

Evolutionary conservation of VSX2 super-enhancer modules in retinal development.

Super-enhancers (SEs) are expansive regions of genomic DNA that regulate the expression of genes involved in cell identity and cell fate. We recently identified developmental stage- and cell type-specific modules within the murine Vsx2 SE. Here, we show that the human VSX2 SE modules have similar developmental stage- and cell type-specific activity in reporter gene assays. By inserting the human sequence of one VSX2 SE module into a mouse with microphthalmia, eye size was rescued. To understand the function of these SE modules during human retinal development, we deleted individual modules in human embryonic stem cells and generated retinal organoids. Deleting one module results in small organoids, recapitulating the small-eyed phenotype of mice with microphthalmia, while deletion of the other module led to disruptions in bipolar neuron development. This prototypical SE serves as a model for understanding developmental stage- and cell type-specific effects of neurogenic transcription factors with complex expression patterns. Moreover, by elucidating the gene regulatory mechanisms, we can begin to examine how dysregulation of these mechanisms contributes to phenotypic diversity and disease.

Comprehensive genetic analysis uncovers the mutational spectrum of MFRP and its genotype-phenotype correlation in a large cohort of Chinese microphthalmia patients.

PURPOSE: Microphthalmia is a severe congenital ocular disease featured by abnormal ocular development. The aim of this study was to detail the genetic and clinical characteristics of a large cohort of Chinese patients with microphthalmia related to MFRP variants, focusing on uncovering genotype-phenotype correlations. METHODS: Fifty microphthalmia patients from 44 unrelated Chinese families were recruited. Whole-exome sequencing (WES) was conducted to analyze the coding regions and adjacent intronic regions of MFRP. Axial lengths (AL) were measured for all probands and available family members. Protein structures of mutations with high frequency in our cohort were predicted. The genotype-phenotype correlations were explored by statistical analysis. RESULTS: Sixteen MFRP variants were detected in 17 families, accounting for 38.64 % of all microphthalmia families. There were 9 novel mutations (c.427+1G>C, c.428-2A>C, c.561_575del:p.A188_E192del, c.836G>A:p.C279Y, c.1010_1021del:p.H337_E340del:p.Y479*, c.1516_1517del:p.S506Pfs*66, c.1561T>G:p.C521G, c.1616G>A:p.R539H, and c.1735C>T:p.P579S) and six previously reported variants in MFRP, with p.E496K and p.H337_E340del being highly frequent, found in eight (47.06 %) and two families (11.76 %), respectively. Seven variants (43.75 %) were located in the C-terminal cysteine-rich frizzled-related domain (CRD) (7/16, 43.75 %). Protein prediction implicated p.E496K and p.H337_E340del mutations might lead to a destabilization of the MFRP protein. The average AL of all 42 eyes was 16.02 ± 1.05 mm, and 78.36 % of eyes with AL < 16 mm harbored p.E496K variant. Twenty-six eyes with variant variant had shorter AL than that of the other 16 eyes without this variant (p = 0.006), highlighting a novel genotype-phenotype correlation. CONCLUSIONS: In this largest cohort of Chinese patients with microphthalmia, the 9 novel variants, high frequency of p.E496W, and mutation hotspots in CRD reveals unique insights into the MFRP mutation spectrum among Chinese patients, indicating ethnic variability. A new genotype-phenotype correlation that p.E496K variant associated with a shorter AL is unveiled. Our findings enhance the current knowledge of MFRP-associated microphthalmia and provide valuable information for prenatal diagnosis as well as future therapy.

Perfluorocarbon liquid-assisted subretinal fluid drainage via the choroid as a treatment for bullous central serous chorioretinopathy in a nanophthalmic eye.

PURPOSE: The report presents a modified surgical technique wherein the perfluorocarbon liquid (PFCL)-assisted drainage of subretinal fluid (SRF) through the choroid was combined with partial-thickness sclerectomy (PTS) and punch sclerostomy as a treatment for bullous central serous chorioretinopathy (bCSCR) in a nanophthalmic eye. METHODS: The developed surgical approach is herein discussed together with a corresponding surgical video. Briefly, two 5 × 4 mm half-thickness sclerectomies and a punch sclerostomy (diameter: 2 mm) to the choroid were performed in the inferior quadrants. Following vitrectomy, SRF was drained through the exposed choroid in the region where the punch sclerostomy was performed, whereafter PFCL was instilled into the vitreous cavity. RESULTS: The complete resolution of SRF accumulation was evident at one-week post-surgery, with no evidence of recurrence over an 18-month follow-up period. No abnormal fluorescent leakage or choroidal vasodilation were evident via fundus fluorescein angiography and indocyanine green angiography examination at the patient's final follow-up visit. CONCLUSION: PFCL-assisted SRF drainage through the choroid combined with PTS and punch sclerostomy may represent a viable approach to treating patients with bCSCR and nanophthalmic eyes, providing a rapid and long-lasting means of eliminating SRF accumulation.

Nanophthalmos-Associated MYRF gene mutation facilitates intraocular inflammation in mice.

PURPOSE: Patients with nanophthalmos might be prone to developing intraocular inflammation following an acute glaucoma attack. Here, we aimed to investigate the role of MYRF in intraocular inflammation by modeling the mutation in mice. METHODS: Nanophthalmos frameshift mutation of Myrf was introduced into the mouse genome with the CRISPR-Cas9 system. Signaling pathways in eye tissues were delineated using RNA sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Intraocular inflammation was induced by a lipopolysaccharide (LPS) intravitreal injection. Dexamethasone (DEX) was administered systemically and locally a week before the LPS injection. The anterior segment clinical scores of the mice were examined 24 h after the LPS injection. Infiltrating inflammatory cells were evaluated with histopathology and immunofluorescence. The mRNA levels of inflammatory cytokines were quantified with reverse transcription-quantitative PCR (RT-qPCR) and the corresponding protein concentrations using enzyme-linked immunosorbent assay (ELISA). RESULTS: Many inflammation-associated signaling pathways were enriched in Myrf mut/+ mice ocular tissues. Clinical scores of Myrf mut/+ mice were significantly higher than those of Myrf +/+ mice 24 h after LPS administration. Histological examination demonstrated high inflammatory cell infiltration in the anterior and vitreous chambers in Myrf mut/+ mice, with numerous CD45+ and CD11b+ inflammatory cells. Moreover, enhanced expression of inflammatory cytokines MCP-1, TGF-ß, and IL-1ß in eyes and aqueous humor of Myrf mut/+ mice was detected. Remarkably, pretreating Myrf mut/+ mice with DEX relieved the intraocular inflammation. CONCLUSION: Nanophthalmos-associated MYRF mutation renders mouse eyes more susceptible to inflammation. Dexamethasone treatment ameliorates the inflammatory response.

Disruption of common ocular developmental pathways in patient-derived optic vesicle models of microphthalmia.

Genetic perturbations influencing early eye development can result in microphthalmia, anophthalmia, and coloboma (MAC). Over 100 genes are associated with MAC, but little is known about common disease mechanisms. In this study, we generated induced pluripotent stem cell (iPSC)-derived optic vesicles (OVs) from two unrelated microphthalmia patients and healthy controls. At day 20, 35, and 50, microphthalmia patient OV diameters were significantly smaller, recapitulating the "small eye" phenotype. RNA sequencing (RNA-seq) analysis revealed upregulation of apoptosis-initiating and extracellular matrix (ECM) genes at day 20 and 35. Western blot and immunohistochemistry revealed increased expression of lumican, nidogen, and collagen type IV, suggesting ECM overproduction. Increased apoptosis was observed in microphthalmia OVs with reduced phospho-histone 3 (pH3+) cells confirming decreased cell proliferation at day 35. Pharmacological inhibition of caspase-8 activity with Z-IETD-FMK decreased apoptosis in one patient model, highlighting a potential therapeutic approach. These data reveal shared pathophysiological mechanisms contributing to a microphthalmia phenotype.

Identification of a pathogenic SMCHD1 variant in a Chinese patient with bosma arhinia microphthalmia syndrome: a case report.

BACKGROUND: Bosma arhinia microphthalmia syndrome (BAMS; MIM603457) is a rare genetic disorder, predominantly autosomal dominant. It is a multi-system developmental disorder characterized by severe hypoplasia of the nose and eyes, and reproductive system defects. BAMS is extremely rare in the world and no cases have been reported in Chinese population so far. Pathogenic variants in the SMCHD1 gene (MIM614982) cause BAMS, while the underlying molecular mechanisms requires further investigation. CASE PRESENTATION: In this study, a Chinese girl who has suffered from congenital absence of nose and microphthalmia was enrolled and subsequently submitted to a comprehensive clinical and genetic evaluation. Whole-exome sequencing (WES) was employed to identify the genetic entity of thisgirl. A heterozygous pathogenic variant, NM_015295, c.1025G > C; p. (Trp342Ser) of SMCHD1 was identified. By performing very detailed physical and genetic examinations, the patient was diagnosed as BAMS. CONCLUSION: This report is the first description of a variant in SMCHD1 in a Chinese patient affected with BAMS.Our study not only furnished valuable genetic data for counseling of BAMS, but also confirmed the diagnosis of BAMS, which may help the management and prognosis for this patient.

Posterior microphthalmos with retinal involvement related to MFRP gene: a report of 10 Brazilian patients.

BACKGROUND: To describe the phenotype and genotype of 10 Brazilian patients with variants in MFRP, posterior microphthalmos and retinal findings. METHODS: Complete ophthalmological evaluation was done at 4 different Brazilian centers. Genetic analysis was performed using commercial next generation sequencing panels for inherited retinal disorders. RESULTS: Ages of the patients ranged from 10 to 65 years and visual acuities from 0,05 to no perception of light. All were hyperopes (+4,25 to + 17,50) with a short axial length (14,4 mm to 18 mm). Common posterior segment features, though not present in all, were optic disc drusen (5/10), foveoschisis (5/10) and retinal pigmentary changes (8/10). Isolated patients presented with macular atrophy, serous retinal detachment, and chorioretinal folds. The most common variant in MFRP found in our patients was a deletion in exon 5 (c.498delC; p.Asn267Thrfs *25), present in all except 2 patients. Other variants found were c.523C>T (p.Gln175*), c.298delG (p.Ala100Argfs *37), c.666del (p.Thr223Argfs *83) and the novel variant c.257C>A (p.Ala86Asp). CONCLUSIONS: This is the first report of Brazilian patients with posterior microphthalmos and pathogenic variants in MFRP and the first describe of the variant p.Ala86Asp in literature. Our cases confirm the previously reported phenotype of high hyperopia, optic disc drusen, alterations in foveal architecture, retinal pigmentary changes with loss of photoreceptor function and visual field constriction. Report of such a rare condition is important to increase awareness to the phenotype of posterior microphthalmia with associated retinal conditions.

A naturally occurring canine model of syndromic congenital microphthalmia.

In humans, the prevalence of congenital microphthalmia is estimated to be 0.2-3.0 for every 10,000 individuals, with nonocular involvement reported in ∼80% of cases. Inherited eye diseases have been widely and descriptively characterized in dogs, and canine models of ocular diseases have played an essential role in unraveling the pathophysiology and development of new therapies. A naturally occurring canine model of a syndromic disorder characterized by microphthalmia was discovered in the Portuguese water dog. As nonocular findings included tooth enamel malformations, stunted growth, anemia, and thrombocytopenia, we hence termed this disorder Canine Congenital Microphthalmos with Hematopoietic Defects. Genome-wide association study and homozygosity mapping detected a 2 Mb candidate region on canine chromosome 4. Whole-genome sequencing and mapping against the Canfam4 reference revealed a Short interspersed element insertion in exon 2 of the DNAJC1 gene (g.74,274,883ins[T70]TGCTGCTTGGATT). Subsequent real-time PCR-based mass genotyping of a larger Portuguese water dog population found that the homozygous mutant genotype was perfectly associated with the Canine Congenital Microphthalmos with Hematopoietic Defects phenotype. Biallelic variants in DNAJC21 are mostly found to be associated with bone marrow failure syndrome type 3, with a phenotype that has a certain degree of overlap with Fanconi anemia, dyskeratosis congenita, Shwachman-Diamond syndrome, Diamond-Blackfan anemia, and reports of individuals showing thrombocytopenia, microdontia, and microphthalmia. We, therefore, propose Canine Congenital Microphthalmos with Hematopoietic Defects as a naturally occurring model for DNAJC21-associated syndromes.

Couching of cataractous lens in microphthalmic eyes with irido-fundal coloboma: revisiting the historical technique.

PURPOSE: Cataract surgery in microphthalmic eyes is challenging due to anatomical restraints, hard bulky nucleus. This series aims to evaluate the safety and efficacy of couching of intraocular lens in irido-fundal coloboma with microphthalmos. SETTING: Tertiary care centre in South India. DESIGN: Retrospective non-comparative study in eyes with irido-fundal coloboma, corneal diameter < 7 mm and brown cataract. Visual acuity less than 6/60 in other eye. METHODS: Anterior chamber entry made, zonules broken and lens dislocated into the vitreous cavity in a controlled manner. Baseline Clinico-demographic details, corrected distance visual acuity (CDVA), Intra-ocular pressure (IOP), corneal diameter, axial length, lens status and post-surgery CDVA, IOP and complications recorded and followed up for atleast 6 months. RESULTS: Fifteen eyes of 15 subjects were evaluated with a mean age 49.4 ± 10.9 years. At baseline, mean IOP 14.5 ± 3.8 mmHg, mean axial length 19.3 ± 0.5 mm, mean corneal diameter was 6.5 ± 0.34 mm and CDVA 2 logMAR which improved to 1.5 logMAR at 3 months (p value 0.002). Transient spike in IOP in 33.3% subjects was medically managed with no significant difference in IOP (p > 0.05) at baseline (14.5 ± 3.8 mmHg), 3 months post-surgery (16 ± 2.8 mmHg) and 6 months post-surgery (14.9 ± 2.5 mmHg). One patient underwent re-couching. No other major complications were noted. CONCLUSION: Couching of cataractous lens is an effective and safe method in microphthalmic eyes with irido-fundal coloboma as last resort procedure, where no other surgical procedure may work. It provides an ambulatory gain of visual acuity in previously non-ambulatory subjects. Corneal measurements help in determining the subset of patients where couching offers viable option.

Long term follow-up of axial length and orbital dimensions in congenital microphthalmia and anophthalmia.

PURPOSE: To evaluate axial length (AL), orbital width (OW) and height (OH) development in congenital microphthalmia and anophthalmia (MICA) using serial ultrasonography measurements. METHODS: A longitudinal prospective cohort (n = 74) of unilaterally and bilaterally affected MICA patients was followed from 2013 to 2022 at the university hospital in Amsterdam, the Netherlands. Clinical entity, age, severity category based on axial length, conformer treatment and intra-orbital cysts were registered. The main outcome measures were the absolute and relative growth of AL, OW and OH. Surgical and intra-orbital cyst cases were described separately. RESULTS: Absolute microphthalmic eye size increased in 27/49 (55%) unilateral MICA eyes, but growth arrest/decrease in the remaining could shift the case to a more severe category over time. A final affected/unaffected orbital symmetry ≥80% was seen in the large majority of unilateral cases (45/46 for OW, 43/46 for OH). Cases with AL < 10.5 mm had orbital symmetry <80% more often. Most orbital symmetry changes were seen in moderate and severe unilateral cases treated with 3D-printed conformer therapy starting at age <1 year, with 6/10 (60%) symmetry increase, 30% unchanged symmetry and 10% symmetry decrease. All cases older than 6.5 years (n = 6) did not show any change anymore, regardless of treatment. For bilateral and unilateral mild cases, orbital dimensions kept the same proportions during follow-up, with or without conformer treatment. CONCLUSIONS: Using severity categories in MICA based on relative AL may aid the decision to start conformer treatment, as most orbital symmetry changes were seen in moderate and severe unilateral cases receiving 3D-printed conformer therapy that started under age 1.

Dacryocystocele and Subsequent Dacryocystectomy in a Patient With Bosma Arhinia Microphthalmia Syndrome (BAMS): A Case Report and Review of Literature.

Bosma arhinia microphthalmia syndrome (BAMS) is a rare syndrome consisting of several craniofacial abnormalities, including congenital arhinia. In this case report, the authors present the first case of a patient with BAMS and dacryocystocele who successfully underwent dacryocystectomy. Dacryocystectomy may serve as a viable surgical approach for dacryocystocele in patients with abnormal nasal anatomy. [J Pediatr Ophthalmol Strabismus. 2024;61(3):e16-e18.].

Clinical report of Bosma arhinia microphthalmia syndrome with a new variant on SMCHD1 gene. A case report.

The Bosma syndrome (BAMS: Bosma arhinia microphthalmia syndrome) is a condition first described in 1972. Since then, several reviews have published the cases looking for diagnostic criteria and associated genetic alterations. The mutation in the SMCHD1 gene (Structural Maintenance of Chromosomes flexible Hinge Domain containing protein 1) seems to explain a part of the development of the phenotype. Not all cases show the same alterations or meet the classic diagnostic criteria, and few have undergone genetic analysis. We present a case with a new variant in this gene and an update of the literature on this syndrome with the aim of improving the diagnosis and follow-up of these patients.

Structural Variant Disrupting the Expression of the Remote FOXC1 Gene in a Patient with Syndromic Complex Microphthalmia.

Ocular malformations (OMs) arise from early defects during embryonic eye development. Despite the identification of over 100 genes linked to this heterogeneous group of disorders, the genetic cause remains unknown for half of the individuals following Whole-Exome Sequencing. Diagnosis procedures are further hampered by the difficulty of studying samples from clinically relevant tissue, which is one of the main obstacles in OMs. Whole-Genome Sequencing (WGS) to screen for non-coding regions and structural variants may unveil new diagnoses for OM individuals. In this study, we report a patient exhibiting a syndromic OM with a de novo 3.15 Mb inversion in the 6p25 region identified by WGS. This balanced structural variant was located 100 kb away from the FOXC1 gene, previously associated with ocular defects in the literature. We hypothesized that the inversion disrupts the topologically associating domain of FOXC1 and impairs the expression of the gene. Using a new type of samples to study transcripts, we were able to show that the patient presented monoallelic expression of FOXC1 in conjunctival cells, consistent with the abolition of the expression of the inverted allele. This report underscores the importance of investigating structural variants, even in non-coding regions, in individuals affected by ocular malformations.

High Clinical Exome Sequencing Diagnostic Rates and Novel Phenotypic Expansions for Nonisolated Microphthalmia, Anophthalmia, and Coloboma.

Purpose: A molecular diagnosis is only made in a subset of individuals with nonisolated microphthalmia, anophthalmia, and coloboma (MAC). This may be due to underutilization of clinical (whole) exome sequencing (cES) and an incomplete understanding of the genes that cause MAC. The purpose of this study is to determine the efficacy of cES in cases of nonisolated MAC and to identify new MAC phenotypic expansions. Methods: We determined the efficacy of cES in 189 individuals with nonisolated MAC. We then used cES data, a validated machine learning algorithm, and previously published expression data, case reports, and animal models to determine which candidate genes were most likely to contribute to the development of MAC. Results: We found the efficacy of cES in nonisolated MAC to be between 32.3% (61/189) and 48.1% (91/189). Most genes affected in our cohort were not among genes currently screened in clinically available ophthalmologic gene panels. A subset of the genes implicated in our cohort had not been clearly associated with MAC. Our analyses revealed sufficient evidence to support low-penetrance MAC phenotypic expansions involving nine of these human disease genes. Conclusions: We conclude that cES is an effective means of identifying a molecular diagnosis in individuals with nonisolated MAC and may identify putatively damaging variants that would be missed if only a clinically available ophthalmologic gene panel was obtained. Our data also suggest that deleterious variants in BRCA2, BRIP1, KAT6A, KAT6B, NSF, RAC1, SMARCA4, SMC1A, and TUBA1A can contribute to the development of MAC.

A founder variant expands the phenotype of WNT7B-related PDAC syndrome.

Pulmonary hypoplasia, Diaphragmatic anomalies, Anophthalmia/microphthalmia, and Cardiac defects (PDAC) syndrome is a genetically heterogeneous multiple congenital malformation syndrome. Although pathogenic variants in RARB and STRA6 are established causes of PDAC, many PDAC cases remain unsolved at the molecular level. Recently, we proposed biallelic WNT7B variants as a novel etiology based on several families with typical features of PDAC syndrome albeit with variable expressivity. Here, we report three patients from two families that share a novel founder variant in WNT7B (c.739C > T; Arg247Trp). The phenotypic expression of this variant ranges from typical PDAC features to isolated genitourinary anomalies. Similar to previously reported PDAC-associated WNT7B variants, this variant was found to significantly impair WNT7B signaling activity further corroborating its proposed pathogenicity. This report adds further evidence to WNT7B-related PDAC and expands its variable expressivity.

Microphthalmia and congenital cataract in two patients with Stickler syndrome type II: a case report.

BACKGROUND: Stickler syndrome (STL) is a collagenopathy caused by pathogenic variants in collagen-coding genes, mainly COL2A1 or COL11A1 associated with Stickler syndrome type 1 (STL1) or type 2 (STL2), respectively. Affected individuals manifest ocular, auditory, articular, and craniofacial findings in varying degrees. Previous literature and case reports describe high variability in clinical findings for patients with STL. With this case report, we broaden the clinical spectrum of the phenotype. MATERIALS AND METHODS: Case report on two members of a family (mother and son) including clinical examination and genetic testing using targeted trio whole exome sequencing (trio-WES). RESULTS: A boy and his mother presented with microphthalmia, congenital cataract, ptosis, and moderate-to-severe sensorineural hearing loss. Trio-WES found a novel heterozygote missense variant, c.4526A>G; p(Gln1509Arg) in COL11A1 in both affected individuals. CONCLUSIONS: We report a previously undescribed phenotype associated with a COL11A1-variant in a mother and son, expanding the spectrum for phenotype-genotype correlation in STL2, presenting with microphthalmia, congenital cataract, and ptosis not normally associated with Stickler syndrome.

Stepwise self-inflating hydrogel expansion for congenital anophthalmia and blind microphthalmia: Over 15 years' experience in China.

BACKGROUND: Self-inflating hydrogel expanders have been used to treat anophthalmia and blind microphthalmia. This study aimed to investigate the long-term outcomes of treatment with self-inflating hydrogel expanders for congenital anophthalmia and blind microphthalmia. METHODS: In this retrospective study, the medical records of 161 patients with anophthalmia and blind microphthalmia who underwent hydrogel expansion were reviewed. We measured the palpebral fissure height (PFH), palpebral fissure length (PFL), and distance between the inner canthal and mid-nasal line (ICMN) before and after surgery. Cox regression analysis was conducted to determine which variables were related to the implantation of spherical expanders following hemispherical expander implantation. RESULTS: After treatment, the PFH and PFL increased significantly (p < 0.001). Complications including expander migration and extrusion occurred in 15 cases. Five patients needed enucleation or further dermis fat graft implantation because of insufficient expansion. The necessity for further spherical expansion was substantially related to a relative axial length (rAL) <0.5 (p = 0.007). CONCLUSION: Self-inflating hydrogel expansion can significantly increase the lid fissure. The occurrence of complications is rare, and surgical intervention can effectively address them. Abnormal eyes with a rAL of less than 0.5 demonstrate a higher possibility of needing additional orbital expansion.