Delineating the molecular and phenotypic spectrum of the SETD1B-related syndrome.

PURPOSE: Pathogenic variants in SETD1B have been associated with a syndromic neurodevelopmental disorder including intellectual disability, language delay, and seizures. To date, clinical features have been described for 11 patients with (likely) pathogenic SETD1B sequence variants. This study aims to further delineate the spectrum of the SETD1B-related syndrome based on characterizing an expanded patient cohort. METHODS: We perform an in-depth clinical characterization of a cohort of 36 unpublished individuals with SETD1B sequence variants, describing their molecular and phenotypic spectrum. Selected variants were functionally tested using in vitro and genome-wide methylation assays. RESULTS: Our data present evidence for a loss-of-function mechanism of SETD1B variants, resulting in a core clinical phenotype of global developmental delay, language delay including regression, intellectual disability, autism and other behavioral issues, and variable epilepsy phenotypes. Developmental delay appeared to precede seizure onset, suggesting SETD1B dysfunction impacts physiological neurodevelopment even in the absence of epileptic activity. Males are significantly overrepresented and more severely affected, and we speculate that sex-linked traits could affect susceptibility to penetrance and the clinical spectrum of SETD1B variants. CONCLUSION: Insights from this extensive cohort will facilitate the counseling regarding the molecular and phenotypic landscape of newly diagnosed patients with the SETD1B-related syndrome.

Families with BAP1-Tumor Predisposition Syndrome in The Netherlands: Path to Identification and a Proposal for Genetic Screening Guidelines.

Germline pathogenic variants in the BRCA1-associated protein-1 (BAP1) gene cause the BAP1-tumor predisposition syndrome (BAP1-TPDS, OMIM 614327). BAP1-TPDS is associated with an increased risk of developing uveal melanoma (UM), cutaneous melanoma (CM), malignant mesothelioma (MMe), renal cell carcinoma (RCC), meningioma, cholangiocarcinoma, multiple non-melanoma skin cancers, and BAP1-inactivated nevi. Because of this increased risk, it is important to identify patients with BAP1-TPDS. The associated tumors are treated by different medical disciplines, emphasizing the need for generally applicable guidelines for initiating genetic analysis. In this study, we describe the path to identification of BAP1-TPDS in 21 probands found in the Netherlands and the family history at the time of presentation. We report two cases of de novo BAP1 germline mutations (2/21, 9.5%). Findings of this study combined with previously published literature, led to a proposal of guidelines for genetic referral. We recommend genetic analysis in patients with ≥2 BAP1-TPDS-associated tumors in their medical history and/or family history. We also propose to test germline BAP1 in patients diagnosed with UM <40 years, CM <18 years, MMe <50 years, or RCC <46 years. Furthermore, other candidate susceptibility genes for tumor types associated with BAP1-TPDS are discussed, which can be included in gene panels when testing patients.

Pseudodominant inheritance pattern in a family with CMT2 caused by GDAP1 mutations.

We report a family in which an autosomal dominantly inherited Charcot-Marie-Tooth (CMT) disease type 2 was suspected. The affected family members (proband, sister, father, and paternal aunt) showed intrafamilial clinical variability. The proband needed walking aids since adolescence because of generalized muscle weakness. The sister showed the same symptoms although to a lesser extent. The father and paternal aunt had foot deformity and atrophy of lower legs. A homozygous GDAP1 mutation was found in the proband and in the sister. Further testing showed compound heterozygous GDAP1 mutations in the father and paternal aunt. In this CMT2 family with a pseudodominant inheritance pattern DNA-diagnostics revealed the presence of both homozygous and compound heterozygous GDAP1 mutations. We recommend including multiple family members in genetic studies on CMT families.

PMP22 related neuropathies: Charcot-Marie-Tooth disease type 1A and Hereditary Neuropathy with liability to Pressure Palsies.

PMP22 related neuropathies comprise (1) PMP22 duplications leading to Charcot-Marie-Tooth disease type 1A (CMT1A), (2) PMP22 deletions, leading to Hereditary Neuropathy with liability to Pressure Palsies (HNPP), and (3) PMP22 point mutations, causing both phenotypes. Overall prevalence of CMT is usually reported as 1:2,500, epidemiological studies show that 20-64% of CMT patients carry the PMP22 duplication. The prevalence of HNPP is not well known. CMT1A usually presents in the first two decades with difficulty walking or running. Distal symmetrical muscle weakness and wasting and sensory loss is present, legs more frequently and more severely affected than arms. HNPP typically leads to episodic, painless, recurrent, focal motor and sensory peripheral neuropathy, preceded by minor compression on the affected nerve. Electrophysiological evaluation is needed to determine whether the polyneuropathy is demyelinating. Sonography of the nerves can be useful. Diagnosis is confirmed by finding respectively a PMP22 duplication, deletion or point mutation. Differential diagnosis includes other inherited neuropathies, and acquired polyneuropathies. The mode of inheritance is autosomal dominant and de novo mutations occur. Offspring of patients have a chance of 50% to inherit the mutation from their affected parent. Prenatal testing is possible; requests for prenatal testing are not common. Treatment is currently symptomatic and may include management by a rehabilitation physician, physiotherapist, occupational therapist and orthopaedic surgeon. Adult CMT1A patients show slow clinical progression of disease, which seems to reflect a process of normal ageing. Life expectancy is normal.

Severe fatigue and reduced quality of life in children with hereditary motor and sensory neuropathy 1A.

Severe fatigue and low quality of life are reported by a majority of adult patients with hereditary motor and sensory neuropathy 1A. In children with hereditary motor and sensory neuropathy 1A, the prevalence and impact of fatigue have not been studied yet. In this questionnaire survey, 55 Dutch children (response rate 77%) with genetically confirmed hereditary motor and sensory neuropathy 1A participated (mean age 15 years [standard deviation 2.1]). Prevalence of severe fatigue (based on a cut-off score of the Checklist Individual Strength) was 24%, in contrast to 14% in a Dutch school-based population (P < .05). Almost all quality-of-life scores (measured with the Child Health Questionnaire-Child Form 87) were significantly worse than population norms (P < .05). Fatigue severity was associated significantly (P < .01) with all quality-of-life scores (-0.4 < r < -0.7). In conclusion, severe fatigue and diminished quality of life are more frequent among children with hereditary motor and sensory neuropathy 1A compared to healthy peers. The strong association between fatigue severity and quality of life suggests a negative impact of fatigue on quality of life in these children.

The phenotype of the Gly94fsX222 PMP22 insertion.

Point mutations in PMP22 are relatively rare and the phenotype may vary from mild hereditary neuropathy with liability to pressure palsies (HNPP) to severe Charcot-Marie-Tooth type 1 (CMT1). We describe the phenotype of the Gly94fsX222 mutation in the PMP22 gene. Medical records of all patients were reviewed and 11 patients were re-examined. EMG was carried out in nine patients and nerve biopsy in one. Thirteen patients originating from seven families with a Gly94fsX222 mutation were included and consisted of 10 women and 3 men with a median age of 41 years (range 7-67). Five index patients were originally suspected of CMT1. Ten patients had abnormal motor skills during childhood. Nine patients had a history of pressure palsies. Involvement of the olfactory, trigeminal, facial, and pudendal nerves occurred in three patients. Twelve patients had pes cavus and one scoliosis. Distal anterior leg and distal arm weakness were found in 12 and 4 patients, respectively. Twelve patients had distal leg sensory abnormalities. Electrophysiological examination revealed a demyelinating sensorimotor neuropathy, both resembling CMT1 and HNPP. Sural nerve biopsy showed demyelinating neuropathy with presence of tomacula. More than three-fourths of the patients with Gly94fsX222 mutation demonstrated a CMT1 phenotype combined with transient deficits. Clinicians should test for this mutation in those patients exhibiting a generalised neuropathy combined with compressive like episodes.