Uniparental disomy of chromosome 16 unmasks recessive mutations of FA2H/SPG35 in 4 families

Objective: Identifying an intriguing mechanism for unmasking recessive hereditary spastic paraplegias. Method: Herein, we describe 4 novel homozygous FA2H mutations in 4 nonconsanguineous families detected by whole-exome sequencing or a targeted gene panel analysis providing high coverage of all known hereditary spastic paraplegia genes. Results: Segregation analysis revealed in all cases only one parent as a heterozygous mutation carrier whereas the other parent did not carry FA2H mutations. A macro deletion within FA2H, which could have caused a hemizygous genotype, was excluded by multiplex ligation-dependent probe amplification in all cases. Finally, a microsatellite array revealed uniparental disomy (UPD) in all 4 families leading to homozygous FA2H mutations. UPD was confirmed by microarray analyses and methylation profiling. Conclusion: UPD has rarely been described as causative mechanism in neurodegenerative diseases. Of note, we identified this mode of inheritance in 4 families with the rare diagnosis of spastic paraplegia type 35 (SPG35). Since UPD seems to be a relevant factor in SPG35 and probably additional autosomal recessive diseases, we recommend segregation analysis especially in nonconsanguineous homozygous index cases to unravel UPD as mutational mechanism. This finding may bear major repercussion for genetic counseling, given the markedly reduced risk of recurrence for affected families

Prospective evaluation of NGS-based sequencing in epilepsy patients: results of seven NASGE-associated diagnostic laboratories

BackgroundEpilepsy is one of the most common and disabling neurological disorders. It is highly prevalent in children with neurodevelopmental delay and syndromic diseases. However, epilepsy can also be the only disease-determining symptom. The exact molecular diagnosis is essential to determine prognosis, comorbidity, and probability of recurrence, and to inform therapeutic decisions.Methods and materialsHere, we describe a prospective cohort study of patients with epilepsy evaluated in seven diagnostic outpatient centers in Germany. Over a period of 2 months, 07/2022 through 08/2022, 304 patients (317 returned result) with seizure-related human phenotype ontology (HPO) were analyzed. Evaluated data included molecular results, phenotype (syndromic and non-syndromic), and sequencing methods.ResultsSingle exome sequencing (SE) was applied in half of all patients, followed by panel (P) testing (36%) and trio exome sequencing (TE) (14%). Overall, a pathogenic variant (PV) (ACMG cl. 4/5) was identified in 22%; furthermore, a significant number of patients (12%) carried a reported clinically meaningful variant of unknown significance (VUS). The average diagnostic yield in patients ≤ 12 y was higher compared to patients >12 y cf. Figure 2B vs. Figure 3B. This effect was more pronounced in cases, where TE was applied in patients ≤ 12 vs. >12 y [PV (PV + VUS): patients ≤ 12 y: 35% (47%), patients > 12 y: 20% (40%)]. The highest diagnostic yield was achieved by TE in syndromic patients within the age group ≤ 12 y (ACMG classes 4/5 40%). In addition, TE vs. SE had a tendency to result in less VUS in patients ≤ 12 y [SE: 19% (22/117) VUS; TE: 17% (6/36) VUS] but not in patients >12 y [SE: 19% (8/42) VUS; TE: 20% (2/10) VUS]. Finally, diagnostic findings in patients with syndromic vs. non-syndromic symptoms revealed a significant overlap of frequent causes of monogenic epilepsies, including SCN1A, CACNA1A, and SETD1B, confirming the heterogeneity of the associated conditions.ConclusionIn patients with seizures—regardless of the detailed phenotype—a monogenic cause can be frequently identified, often implying a possible change in therapeutic action (36.7% (37/109) of PV/VUS variants); this justifies early and broad application of genetic testing. Our data suggest that the diagnostic yield is highest in exome or trio-exome-based testing, resulting in a molecular diagnosis within 3 weeks, with profound implications for therapeutic strategies and for counseling families and patients regarding prognosis and recurrence risk

Monogenic Human Skin Disorders

Human genodermatoses represent a broad and partly confusing spectrum of countless rare diseases with confluent and overlapping phenotypes often impeding a precise diagnosis in an affected individual. High-throughput sequencing techniques have expedited the identification of novel genes and have dramatically simplified the establishment of genetic diagnoses in such heterogeneous disorders. The precise genetic diagnosis of a skin disorder is crucial for the appropriate counselling of patients and their relatives regarding the course of the disease, prognosis and recurrence risks. Understanding the underlying pathophysiology is a prerequisite to understanding the disease and developing specific, targeted or individualized therapeutic approaches. We aimed to create a comprehensive overview of human genodermatoses and their respective genetic aetiology known to date. We hope this may represent a useful tool in guiding dermatologists towards genetic diagnoses, providing patients with individual knowledge on the respective disorder and applying novel research findings to clinical practice

A Novel PKD1 Mutation Associated With Autosomal Dominant Kidney Disease and Cerebral Cavernous Malformation

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by the presence of renal cysts and specific extrarenal abnormalities. ADPKD is caused by mutations in either PKD1 or PKD2 genes that encode for integral membrane proteins Polycystin-1 (PC1) and Polycystin-2 (PC2), respectively. Extrarenal involvement includes noncystic manifestations such as dilatation of the aortic root, artery dissection and intracranial aneurysms. Cerebral cavernous malformation (CCM) is a rare vascular malformation disorder characterized by closely clustered and irregularly dilated capillaries that can be asymptomatic or cause variable neurological manifestations, such as seizures, non-specific headaches, progressive or transient focal neurologic deficits, and cerebral hemorrhages. Familial CCM is typically associated with mutations in KRIT1 (CCM1), CCM2, and PDCD10 (CCM3). The co-occurrence of ADPKD and CCM has been previously described in a single patient, although genetic analysis was not performed in this study. We report here a family with ADPKD associated with CCM in two sisters. Direct sequencing of the index patient revealed a single novel heterozygous frameshift mutation in PKD1, and lack of mutations in genes usually related to CCM. This suggests that CCM represents an additional phenotype of ADPKD

Familial Forms of Cushing Syndrome in Primary Pigmented Nodular Adrenocortical Disease Presenting with Short Stature and Insidious Symptoms: A Clinical Series.

Cushing syndrome (CS) is a rare disease in children, frequently associated with subtle or periodic symptoms that may delay its diagnosis. Weight gain and growth failure, the hallmarks of hypercortisolism in pediatrics, may be inconsistent, especially in ACTH-independent forms of CS. Primary pigmented nodular adrenocortical disease (PPNAD) is the rarest form of ACTH-independent CS, and can be associated with endocrine and nonendocrine tumors, forming the Carney complex (CNC). Recently, phenotype/genotype correlations have been described with particular forms of CNC where PPNAD is isolated or associated only with skin lesions. We present four familial series of CS due to isolated PPNAD, and compare them to available data from the literature. We discuss the clinical and molecular findings, and underline challenges in diagnosing PPNAD in childhood

Familial Forms of Cushing Syndrome in Primary Pigmented Nodular Adrenocortical Disease Presenting with Short Stature and Insidious Symptoms: A Clinical Series

Cushing syndrome (CS) is a rare disease in children, frequently associated with subtle or periodic symptoms that may delay its diagnosis. Weight gain and growth failure, the hallmarks of hypercortisolism in pediatrics, may be inconsistent, especially in ACTH-independent forms of CS. Primary pigmented nodular adrenocortical disease (PPNAD) is the rarest form of ACTH-independent CS, and can be associated with endocrine and nonendocrine tumors, forming the Carney complex (CNC). Recently, phenotype/genotype correlations have been described with particular forms of CNC where PPNAD is isolated or associated only with skin lesions. We present four familial series of CS due to isolated PPNAD, and compare them to available data from the literature. We discuss the clinical and molecular findings, and underline challenges in diagnosing PPNAD in childhood

A Novel Variant (Asn177Asp) in SPTLC2 Causing Hereditary Sensory Autonomic Neuropathy Type 1C

Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is a rare, autosomal dominantly inherited, slowly progressive and length-dependent axonal peripheral neuropathy. HSAN1 is associated with several mutations in serine-palmitoyltransferase (SPT), the first enzyme in the de novo sphingolipid biosynthetic pathway. HSAN1 mutations alter the substrate specificity of SPT, which leads to the formation of 1-deoxysphingolipids, an atypical and neurotoxic subclass of sphingolipids. This study describes the clinical and neurophysiological phenotype of a German family with a novel SPTCL2 mutation (c.529A > G; N177D) associated with HSAN1 and the biochemical characterization of this mutation.) The mutaion was identified in five family members that segregated with the diesease. Patients were characterized genetically and clinically for neurophysiological function. Their plasma sphingolipid profiles were analyzed by LC-MS. The biochemical properties of the mutation were characterized in a cell-based activity assay. Affected family members showed elevated 1-deoxysphingolipid plasma levels. HEK293 cells expressing the N177D SPTLC2 mutant showed increased de novo 1-deoxysphingolipid formation, but also displayed elevated canonical SPT activity and increased C20 sphingoid base production. This study identifies the SPTLC2 N177D variant as a novel disease-causing mutation with increased 1-deoxySL formation and its association with a typical HSAN1 phenotype