Unilateral buphthalmos, corneal staphyloma and corneal fistula caused by pathogenic variant in the PITX3 gene: a case report

Abstract

Introduction

PITX3 has been reported to be associated with congenital cataracts, anterior segment mesenchymal dysgenesis, Peters’ anomaly, and microphthalmia. In this case, an infant with unilateral buphthalmos, corneal staphyloma and corneal fistula carrying a variant in PITX3 was reported.

Case description

We describe a 4-month-old female infant who was referred to our Eye Clinic because of gradual enlargement of the eyeball in the right eye and whitish opacity in both eyes. Buphthalmos with long axial length (22.04 mm), macrocornea with diffuse corneal oedema and opacity (14.50 mm*14.50 mm) and high intraocular pressure (23.78 mmHg) were detected in the right eye. Microphthalmia with short axial length (16.23 mm), microcornea with diffuse corneal oedema and opacity (7.50 mm*6.50 mm) were detected in the left eye. A 360° trabeculotomy was performed for the right eye. However, corneal staphyloma and corneal fistula in the right eye were detected 6 months after the surgery. A variant in exon 4 of PITX3 (c.640_656dup (p. Gly220Profs*95)) was identified in the proband but was not detected in her healthy parents.

Conclusion

A novel phenotype characterized by unilateral buphthalmos, corneal staphyloma and corneal fistula in an infant were reported to be associated with PITX3 in our study. Our study expands the scope of the clinical heterogeneity of PITX3 variants. It also improves our understanding and increases the attention given to patients with PITX3 variants.

Introduction

Buphthalmos is derived from “ox-eyed” in Greek. It describes the visible enlargement of the eyeball at birth or soon after due to increased intraocular pressure (IOP ) [1]. Primary congenital glaucoma (onset at birth) and primary infantile glaucoma (onset after birth to 3 years) are the most frequent causes of buphthalmos [2, 3]. Corneal oedema, increased corneal diameter, and optic disc cupping are the classical manifestations in patients with buphthalmos [4]. PITX3 is the third PITX gene in the PITX/RIEG homeobox family and plays a critical role in normal lens development during vertebrate eye formation [5, 6]. PITX3 is responsible for various ocular defects, including congenital cataract, anterior segment dysgenesis (ASD), Peters’ anomaly, and microphthalmia [7, 8]. In this case, our aim is to report novel phenotype (unilateral buphthalmos and corneal opacity) of a 4-month-old female infant with variants in PITX3.

Case description

The proband in this study is a 4-month-old female infant. She was born after a full-term uneventful pregnancy and did not suffer a significant perinatal history. Physical examination after birth revealed a birth weight of 3015 g, a head circumference of 34 cm, and a body length of 47 cm. She had no systemic anomalies and no remarkable family history.

She was referred to our Eye Clinic because of an enlarged and cloudy right eye. Ophthalmologic examination (including B-scan and slit lamp examination) showed the following manifestations before surgery: right eye buphthalmos with long axial length (22.04 mm), macrocornea with diffuse corneal oedema and opacity (14.50 mm*14.50 mm), left eye microphthalmia (short axial length: 16.23 mm) and microcornea with diffuse corneal oedema and opacity (7.50 mm*6.50 mm) (Fig. 1). The IOP was 23.78 mmHg and 17.30 mmHg in the right and left eyes, respectively. Additionally, an inferiorly decentred excavation within the superficial optic disc tissue was revealed by the B-scan in the right eye (Fig. 1). A 360° trabeculotomy was immediately performed on the right eye. She did not return for routine follow-up. Six months after the trabeculotomy, corneal staphyloma and corneal fistula with iris plugging of the perforated ulcer were detected according to the telephone follow-up. Ophthalmectomy was performed for the right eye at the local hospital.

Fig. 1

The phenotype of the proband with variant in PITX3. Fig. A1 The photography of the right eye. Buphthalmos with macrocornea (14.50 mm*14.50 mm), corneal opacity and edema were detected. Fig. A2 B-scan of the right eye. Buphthalmos with axial length of 22.04 mm was present and an inferiorly decentred excavation within the superficial optic disc tissue revealed in the red box. Fig. B1 The photography of the left eye. Microcornea (7.50 mm*6.50 mm) and corneal opacity were detected. Fig. B2 Microphthalmia with axial length of 16.23 mm was detected

Informed consent was obtained from the parents of the proband according to the protocol approved by West China Hospital Sichuan University. Whole exome sequencing has been performed on the proband’s genomic DNA sample. S220 Focused-ultrasonicator (Covaris, Massachusetts, USA) was used to shear Genomic DNA (1-3μg) into an average size of 150-bp. The preparation of standard Illumina libraries was conducted by DNA Sample Prep Reagent Set (MyGenostics, Beijing, China).

To acquire the DNA library, genomic DNA (1–3 μg) and the probes were mixed and then PCR amplification was performed. A DNBSEQ-T7RS sequencer for paired reads of 150 bp (average sequencing depth: 1485.68; target area coverage: 10X: 99.93 20X: 99.87) was used for next-generation sequencing. Variants in genes responsible for glaucoma, microphthalmia and macrophthalmia (Table S1) were selected and analysed through multiple bioinformatic analytic steps. Variants with a minor allele frequency (MAF) smaller than 0.01 (based on the 1000 genome, ESP6500, dbSNP, EXAC) and sequencing quality with a coverage of more than 5 were included. Additionally, synonymous variants without a splice site change and benign variants predicted by online tools (SIFT, PolyPhen-2, MutationTaster, GERP++ and REVEL) were excluded.

Only one truncation in exon 4 (c.640_656dup (p. Gly220Profs*95)) of PITX3 was identified (Fig. 2). No pathogenic variants were identified in other genes. Sanger sequencing validation, including amplification, sequencing, and target sequence analysis, was performed following a previously described method [9]. Additionally, segregation analysis was conducted, and her healthy parents did not carry the same variant.

Fig. 2

The pedigree and Sanger sequence of the proband and her parents. A The pedigree of the family. Squares represent males and circles represent females. An arrow pointing towards the symbol indicates proband individuals. The shaded symbol indicates affected proband. +: wide type, Mu: mutation. B the Sanger sequencing of the pathogenic variant in PITX3. The arrow indicates the position of the variant in PITX3

Conclusions

PITX3 has been reported to be mapped close to aphakia on mouse chromosome 19. The lens develops normally in mice with Pitx3 knockdown until an arrest occurs around embryonic Days 10.5–11. This timing corresponds to the moment of initial expression of Pitx3 in the lens [10]. Microphthalmos or aphakia could be detected in mice with knockdown of Pitx3 [11]. Mutations of this gene have been reported to be associated with congenital cataract, anterior segment dysgenesis (ASD), Peters’ anomaly, and microphthalmia (Table 1 and Fig. 3).

Table 1 Summary of the reported variants in PITX3

Fig. 3

A summary of the phenotype and genotype of PITX3 with heterozygous variants in previous studies. A A summary of the phenotype of the heterozygous individuals in previous studies. Abbreviation: Cat, Cataract; Asd, Anterior segment dysgenesis; Co, Corneal opacity; Pa, Peters anomaly; Micc, Microcornea; Mico, Microphthalmia; Nys, Nystagmus; Ia, iridocorneal adhesions; Gla, Glaucoma. B The distribution of the phenotype of Asian and Caucasian with heterozygous variant in PITX3. C The distribution of the variants in the exons of PITX3. Abbreviation: HD: homeo domain; OAR: Otp/aristaless/rax domains

Presently, twelve variants have been reported in 32 families. These variants include two missense variants in two families and ten truncations in 32 families [6,7,8, 12,13,14,15,16,17,18,19,20,21,22,23,24]. Four homozygote individuals with more severe phenotypic abnormalities were reported because of consanguineous marriage in three families (Table 1). Six Asian families and 26 Caucasian families have been reported to have these variants in previous studies. Congenital cataracts without other abnormities were more common in Asians than Caucasians with variants in PITX3. The c.640_656dup (p.Gly220Profs*95) mutation hot spot was detected in 18 families. For these affected individuals with heterozygous variants, cataracts were the most common manifestations and were detected in 92.74% of patients with PITX3 variants. Anterior segment dysgenesis and corneal opacity could be found in 14.53 and 2.13% of patients harbouring PITX3 variants, respectively. Microphthalmia (0.43%), microcornea (1.28%), nystagmus (0.85%), iridocorneal adhesions (0.85%), and glaucoma (0.43%) could also be detected (Table 1 and Fig. 3). However, no studies have reported corneal staphyloma and corneal fistula in patients with PITX3 variants. Here, we report a 4-month-old female infant carrying a variant in PITX3. Unilateral buphthalmos, corneal staphyloma and corneal fistula were detected, and 360° trabeculotomy was conducted on the right eye. However, ophthalmectomy was performed for the right eye at the local hospital because of the protruding opaque cornea and corneal fistula that presented 6 months after the 360° trabeculotomy.

In summary, we report a novel phenotype characterized by unilateral buphthalmos, corneal staphyloma and corneal fistula this is associated with a PITX3 variant. Our study expands the scope of the clinical heterogeneity of PITX3 variants. It also improves our understanding and increases the attention given to patients with PITX3 variants.