We report two cases of 46,XY siblings with pontocerebellar hypoplasia type 7 (PCH7) and conduct a systematic literature review for genetically confirmed PCH7 cases, focusing on phenotypic characteristics, particularly gonadal parameters, and associated genotypic data. Two 46,XY siblings diagnosed with PCH7 were reviewed. Both exhibited hypoplastic male external genitalia, absent uterus, and cryptorchid testes, confirmed through histological assessments showing dysgenesis. A systematic literature search revealed an additional 26 cases of 46,XY PCH7, with neurological involvement noted in all cases except one. The external genitalia were described as abnormal (17/23); however, few of these were hypoplastic male type on pictorial review. Nonlocalized testes (5/5) and absent uterus (4/7) on ultrasonography, elevated FSH (7/7), and low testosterone (3/3) were observed. Besides a novel variant (p.Ile133Thr) in Indian siblings, a total of 25 variants in TOE1 were identified with no specific genotype-phenotype correlation. Testicular development was defective in all PCH7 patients but was variable, with the predominant phenotypic manifestation being testicular regression syndrome/partial gonadal dysgenesis with Müllerian duct regression (TRS/PGD-MDR).

The Target of EGR1 (TOE1) gene encodes the TOE1 deadenylase, which is essential for the maturation of Pol-II transcribed snRNAs in humans. Over a dozen missense mutations in the TOE1 gene have been linked to Pontocerebellar Hypoplasia Type 7 (PCH7), a rare but serious neurodevelopmental and neurodegenerative disease that leads to early mortality. The biochemical mechanisms for why these PCH7-linked mutations alter TOE1's biochemical characteristics remains vague. Here, we utilized AlphaFold predicted structures of TOE1 and biochemical characterizations to investigate the impact of TOE1 variants on TOE1's biochemical properties. We performed characterization of the thermal stability and activity of eleven PCH-linked TOE1 variants and found that eight variants have significant reduced protein thermal stability and only two variants impair TOE1's ribonuclease activity, particularly its exonuclease activity. Additionally, we found that the F148Y mutation impacts TOE1's oligomeric state in vitro and in vivo. Together, these results demonstrated that PCH-linked mutations of TOE1 impact many different aspects of TOE1 biochemistry, providing novel insights which may provide potential therapeutic strategies to treat PCH7 patients. In addition, these mutations provide a library of TOE1 variants that will be useful for future studies of TOE1 function and regulation.

Biallelic TOE1 variants can cause pontocerebellar hypoplasia type 7 (PCH7), a condition characterized by pontocerebellar hypoplasia with genital abnormality. TOE1 is a 3'-exonuclese for 3'-end maturation in small nuclear RNA. TOE1 pathogenic variants have been reported at the DEDD catalytic domain and zinc finger motif. Here, we describe a PCH7 patient with novel compound heterozygous TOE1 variants and a detailed clinical course. The patient was a 3-year-old female and showed developmental delay without cerebellar ataxic behavior. Head MRI revealed delayed myelination without pontocerebellar hypoplasia at 9 months of age. Progressive pontocerebellar atrophy was prominent at follow-up MRI. Cerebral abnormalities are characteristic features of PCH7 before pontocerebellar atrophy is observed. One variant, p.Arg331*, was located at the nuclear localization motif (NLM) and partially escaped from nonsense-mediated decay. This variant affected nuclear localization in mutant expressing cells, thus, the TOE1 variant at NLM leads to TOE1 dysfunction associated with nuclear mis-localization.

Pontocerebellar Hypoplasia (PCH) is a rare autosomal recessive hereditary neurological degenerative disease. To elaborate upon the clinical phenotypes of PCH and explore the correlation between TOE1 gene mutations and clinical phenotype, we analyze the clinical and genetic features of a Chinese infant afflicted with pontocerebellar dysplasia accompanied by gender reversal with bioinformatics methods. The main clinical features of this infant with TOE1 gene mutation included progressive lateral ventricle widening, hydrocephalus, severe postnatal growth retardation, and hypotonia, and simultaneously being accompanied by 46, XY female sex reversal. Whole exome sequencing revealed a compound heterozygous mutation in the TOE1 gene (c.299T > G, c.1414T > G), with the protein homology modeling-generated structure predicting a pathogenic variation, which is closely related to the clinical manifestations in the patient. The new mutation sites, c.299T > G and c.1414T > G, in the TOE1 gene are pathogenic variants of pontocerebellar hypoplasia type 7.