A novel PTRH2 missense mutation causing IMNEPD: a case report

Severe Respiratory and Swallowing Disorders in Infantile-Onset Multisystem Neurologic, Endocrine, and Pancreatic Disease Type 1: Two Cases

Objectives

The objective of this study was to expand the phenotypic spectrum of infantile-onset multisystem neurologic, endocrine, and pancreatic disease type 1 (IMNEPD1) and highlight the importance of analyzing the PTRH2 gene in patients with neuropathy presenting with pancreatic lipomatosis.

Methods

Two sisters, aged 73 and 71 years, respectively, presented a severe, length-dependent sensorimotor axonal neuropathy, associated with deafness and intellectual deficiency.

Results

They both needed a wheelchair from the fourth decade. They developed a severe respiratory dysfunction, requiring nocturnal noninvasive ventilation from around 50 years of age. The younger sister developed severe dysphagia complicated by aspiration pneumonia. A muscle biopsy of the younger sister was suggestive of mitochondrial myopathy. The youngest presented a complete pancreatic lipomatosis. A biallelic novel likely pathogenic variant within PTRH2, c.254A>G (p.Gln85Arg), was evidenced in both patients.

Discussion

IMNEPD1 is a rare autosomal recessive disorder caused by sequence variant in the PTRH2 gene and characterized by a peripheral neuropathy, cerebellar atrophy, intellectual disability, hearing loss, pancreatic insufficiency, hypothyroidism, and dysmorphic features. In addition to these classic manifestations of the disorder, severe dysphagia and respiratory insufficiency may develop over the course of the disease and should be systematically screened. PTRH2 gene should be considered in patients with pancreatic lipomatosis and neuropathy.

A Novel PTRH2 Gene Mutation Causing Infantile-onset Multisystem Neurologic, Endocrine, and Pancreatic Disease in a Bahraini Patient

Infantile-onset multisystem neurologic, endocrine, and pancreatic disease (IMNEPD) is a rare autosomal recessive multisystemic disease with a prevalence of < 1/1 000 000. The wide spectrum of symptoms and associated diseases makes the diagnosis of this disease particularly challenging. Here, we report a 12-year-old Bahraini male who presented with the core clinical features of IMNEPD including intellectual disability, global developmental delay, sensorineural hearing loss, endocrine dysfunction, and exocrine pancreatic insufficiency. The diagnosis was confirmed by genetic testing using whole exome sequencing. This is the first reported case of IMNEPD from Bahrain and was found to have a novel homozygous peptidyl-tRNA hydrolase 2 (PTRH2) gene mutation (NM_001015509.2: c.370del p.(Glu124Lysfs*4)). Moreover, we conducted an extensive literature review with an emphasis on the variable clinical spectrum and genotypes of previously reported patients in comparison to our case.

PTRH2 Gene Variants: Recent Review of the Phenotypic Features and Their Bioinformatics Analysis

Peptidyl-tRNA hydrolase 2 (PTRH2) is an evolutionarily highly conserved mitochondrial protein. The biallelic mutations in the PTRH2 gene have been suggested to cause a rare autosomal recessive disorder characterized by an infantile-onset multisystem neurologic endocrine and pancreatic disease (IMNEPD). Patients with IMNEPD present varying clinical manifestations, including global developmental delay associated with microcephaly, growth retardation, progressive ataxia, distal muscle weakness with ankle contractures, demyelinating sensorimotor neuropathy, sensorineural hearing loss, and abnormalities of thyroid, pancreas, and liver. In the current study, we conducted an extensive literature review with an emphasis on the variable clinical spectrum and genotypes in patients. Additionally, we reported on a new case with a previously documented mutation. A bioinformatics analysis of the various PTRH2 gene variants was also carried out from a structural perspective. It appears that the most common clinical characteristics among all patients include motor delay (92%), neuropathy (90%), distal weakness (86.4%), intellectual disability (84%), hearing impairment (80%), ataxia (79%), and deformity of head and face (~70%). The less common characteristics include hand deformity (64%), cerebellar atrophy/hypoplasia (47%), and pancreatic abnormality (35%), while the least common appear to be diabetes mellitus (~30%), liver abnormality (~22%), and hypothyroidism (16%). Three missense mutations were revealed in the PTRH2 gene, the most common one being Q85P, which was shared by four different Arab communities and was presented in our new case. Moreover, four different nonsense mutations in the PTRH2 gene were detected. It may be concluded that disease severity depends on the PTRH2 gene variant, as most of the clinical features are manifested by nonsense mutations, while only the common features are presented by missense mutations. A bioinformatics analysis of the various PTRH2 gene variants also suggested the mutations to be deleterious, as they seem to disrupt the structural confirmation of the enzyme, leading to loss of stability and functionality.