Craniofacial features of POLR3-related leukodystrophy caused by biallelic variants in POLR3A, POLR3B and POLR1C.

BACKGROUND: RNA polymerase III-related or 4H leukodystrophy (POLR3-HLD) is an autosomal recessive hypomyelinating leukodystrophy characterized by neurological dysfunction, hypodontia and hypogonadotropic hypogonadism. The disease is caused by biallelic pathogenic variants in POLR3A, POLR3B, POLR1C or POLR3K. Craniofacial abnormalities reminiscent of Treacher Collins syndrome have been originally described in patients with POLR3-HLD caused by biallelic pathogenic variants in POLR1C. To date, no published studies have appraised in detail the craniofacial features of patients with POLR3-HLD. In this work, the specific craniofacial characteristics of patients with POLR3-HLD associated with biallelic pathogenic variants in POLR3A, POLR3B and POLR1C are described. METHODS: The craniofacial features of 31 patients with POLR3-HLD were evaluated, and potential genotype-phenotype associations were evaluated. RESULTS: Various craniofacial abnormalities were recognized in this patient cohort, with each individual presenting at least one craniofacial abnormality. The most frequently identified features included a flat midface (61.3%), a smooth philtrum (58.0%) and a pointed chin (51.6%). In patients with POLR3B biallelic variants, a thin upper lip was frequent. Craniofacial anomalies involving the forehead were most commonly associated with biallelic variants in POLR3A and POLR3B while a higher proportion of patients with POLR1C biallelic variants demonstrated bitemporal narrowing. CONCLUSION: Through this study, we demonstrated that craniofacial abnormalities are common in patients with POLR3-HLD. This report describes in detail the dysmorphic features of POLR3-HLD associated with biallelic variants in POLR3A, POLR3B and POLR1C.

A Cockayne-like phenotype resulting from a de novo variant in MORC2: expanding the phenotype of MORC2-related disorders.

Cockayne syndrome is a rare inherited DNA repair multisystemic disorder. Here, we aim to raise awareness of the phenotypic resemblances between Cockayne syndrome and the neurodevelopmental disorder caused by pathogenic variants in MORC2, a gene also involved in DNA repair. Using exome sequencing, we identified a de novo pathogenic variant in MORC2 in our patient. Our patient's phenotype was characterized by multiple features evocative of Cockayne syndrome. Based on our patient's phenotype, in addition to the phenotypic description of patients with pathogenic variants in MORC2 reported in the literature, we suggest that pathogenic variants in this gene are associated with a Cockayne-like phenotype.

Longitudinal Characterization of the Clinical Course of Intermediate-Severe Salla Disease.

BACKGROUND: Biallelic pathogenic variants in SLC17A5 cause three forms of free sialic acid storage disease categorized based on severity from least to most severe: Salla disease, intermediate-severe Salla disease, and infantile free sialic acid storage disease. Intermediate-severe Salla disease is the most recently described form. Here, we report a longitudinal characterization of intermediate-severe Salla disease progression in two sisters carrying the following biallelic variants in SLC17A5: c.406A>G (p.Lys136Glu) and c.819+1G>A. METHODS: A retrospective review of medical records was performed. A developmental questionnaire was completed to obtain further clinical information. For functional characterization of the predicted splice site variant, RNA was extracted from patient blood samples and sequenced. RESULTS: Disease onset occurred within the first six months of life in both patients. Early childhood development was delayed with achievement of some milestones followed by a developmental plateau in late childhood. After this, both patients began a slow and progressive neurological regression in adolescence. Functional studies confirmed the pathogenicity of the c.819+1G>A variant, resulting in a frameshift and deletion of exon 6. CONCLUSIONS: We present a detailed study describing the clinical course of intermediate-severe Salla disease with over 15 to 20 years of evolution and demonstrate the pathogenicity of the c.819+1G>A splice site variant.

The Spectrum of MORC2-Related Disorders: A Potential Link to Cockayne Syndrome.

BACKGROUND: Cockayne syndrome (CS) is a DNA repair disorder primarily associated with pathogenic variants in ERCC6 and ERCC8. As in other Mendelian disorders, there are a number of genetically unsolved CS cases. METHODS: We ascertained five individuals with monoallelic pathogenic variants in MORC2, previously associated with three dominantly inherited phenotypes: an axonal form of Charcot-Marie-Tooth disease type 2Z; a syndrome of developmental delay, impaired growth, dysmorphic facies, and axonal neuropathy; and a rare form of spinal muscular atrophy. RESULTS: One of these individuals bore a strong phenotypic resemblance to CS. We then identified monoallelic pathogenic MORC2 variants in three of five genetically unsolved individuals with a clinical diagnosis of CS. In total, we identified eight individuals with MORC2-related disorder, four of whom had clinical features strongly suggestive of CS. CONCLUSIONS: Our findings indicate that some forms of MORC2-related disorder have phenotypic similarities to CS, including features of accelerated aging. Unlike classic DNA repair disorders, MORC2-related disorder does not appear to be associated with a defect in transcription-coupled nucleotide excision repair and follows a dominant pattern of inheritance with variants typically arising de novo. Such de novo pathogenic variants present particular challenges with regard to both initial gene discovery and diagnostic evaluations. MORC2 should be included in diagnostic genetic test panels targeting the evaluation of microcephaly and/or suspected DNA repair disorders. Future studies of MORC2 and its protein product, coupled with further phenotypic characterization, will help to optimize the diagnosis, understanding, and therapy of the associated disorders.

NTRK1-related Hereditary Sensory and Autonomic Neuropathy Type 4: The Role of the Histamine Challenge Test.

Hereditary sensory and autonomic neuropathies (HSAN) are rare, genetically inherited disorders characterized by impaired unmyelinated nerve fiber function. Here we report a patient with self-mutilation behavior and decreased response to pain, suggestive of an underlying small fiber neuropathy. Nerve conduction studies were normal but sympathetic skin response was absent at the left arm. Intradermal histamine challenge test was performed to evaluate the function of small unmyelinated nerve fibers and revealed absence of a flare response. Using whole genome sequencing, a novel variant in the neurotrophic tyrosine kinase type 1 gene was identified, expanding the known disease-causing variants associated with HSAN type 4. Through this case, we demonstrate the role of the histamine challenge test in patients suspected to have a small fiber neuropathy where electrophysiological testing may be normal and who may present with non-specific symptoms including hypotonia and failure to thrive. The information gained can guide genetic testing and contribute to interpretation of new variants identified.

A Novel De Novo Variant in DYNC1H1 Causes Spinal Muscular Atrophy Lower Extremity Predominant in Identical Twins: A Case Report.

Mutations in DYNC1H1 have been shown to cause spinal muscular atrophy lower extremity predominant type 1 (SMALED1), an autosomal dominant genetic neuromuscular disorder characterized by degeneration of spinal cord motor neurons resulting in muscle weakness. Here, we describe monozygotic twins, one with a more severe upper motor neuron phenotype as a result of a suspected perinatal hypoxic-ischemic event and the other presenting a typical lower motor neuron phenotype. Using exome sequencing, we identified the novel de novo variant c.752G>T; p.Arg251Leu in DYNC1H1. We thereby add this variant to the growing list of mutations in DYNC1H1 that cause SMALED1.

Endocrine and Growth Abnormalities in 4H Leukodystrophy Caused by Variants in POLR3A, POLR3B, and POLR1C.

CONTEXT: 4H or POLR3-related leukodystrophy is an autosomal recessive disorder typically characterized by hypomyelination, hypodontia, and hypogonadotropic hypogonadism, caused by biallelic pathogenic variants in POLR3A, POLR3B, POLR1C, and POLR3K. The endocrine and growth abnormalities associated with this disorder have not been thoroughly investigated to date. OBJECTIVE: To systematically characterize endocrine abnormalities of patients with 4H leukodystrophy. DESIGN: An international cross-sectional study was performed on 150 patients with genetically confirmed 4H leukodystrophy between 2015 and 2016. Endocrine and growth abnormalities were evaluated, and neurological and other non-neurological features were reviewed. Potential genotype/phenotype associations were also investigated. SETTING: This was a multicenter retrospective study using information collected from 3 predominant centers. PATIENTS: A total of 150 patients with 4H leukodystrophy and pathogenic variants in POLR3A, POLR3B, or POLR1C were included. MAIN OUTCOME MEASURES: Variables used to evaluate endocrine and growth abnormalities included pubertal history, hormone levels (estradiol, testosterone, stimulated LH and FSH, stimulated GH, IGF-I, prolactin, ACTH, cortisol, TSH, and T4), and height and head circumference charts. RESULTS: The most common endocrine abnormalities were delayed puberty (57/74; 77% overall, 64% in males, 89% in females) and short stature (57/93; 61%), when evaluated according to physician assessment. Abnormal thyroid function was reported in 22% (13/59) of patients. CONCLUSIONS: Our results confirm pubertal abnormalities and short stature are the most common endocrine features seen in 4H leukodystrophy. However, we noted that endocrine abnormalities are typically underinvestigated in this patient population. A prospective study is required to formulate evidence-based recommendations for management of the endocrine manifestations of this disorder.

Health-Related Quality of Life for Patients With Genetically Determined Leukoencephalopathy.

BACKGROUND: We attempted to characterize the health-related quality of life in patients with genetically determined leukoencephalopathies as it relates to the severity of clinical features and the presence or absence of a precise molecular diagnosis. METHODS: Health-related quality of life was assessed using the Pediatric Quality of Life Inventory model (Pediatric Quality of Life Inventory 4.0 Self- and Proxy-reports) on 59 patients diagnosed with genetically determined leukoencephalopathies. In total, 38 male and 21 female patients ranging from one to 32 years of age (mean nine years), as well as their parents, completed the Pediatric Quality of Life Inventory health-related quality of life measures. In addition, participants completed detailed standardized clinical assessments or questionnaires. The correlation between health-related quality of life results and the severity of the clinical features, as well as the presence or absence of a molecular diagnosis, were analyzed. RESULTS: Patients with more severe clinical features showed statistically significant lower total Pediatric Quality of Life Inventory scores. More specifically, lower health-related quality of life was noted in children with sialorrhea, gastrostomy, and dystonia and in children who use a wheelchair. CONCLUSIONS: Patients with more severe clinical features experience a lower quality of life. Our study further highlights the importance of addressing both physical and psychosocial issues and discussing perception of quality of life with both parents and children. A larger multicenter prospective study will be needed to further define the burden of these diseases and to identify modifiable factors.