Parkinson's disease (PD) is a neurodegenerative disorder that may sometimes be caused by deleterious genetic variants. Among them, RAB39B polymorphisms are known as rare causes of early-onset PD associated with intellectual disability (Waisman's syndrome). Here we describe a 45-year-old white male affected by developmental delay, childhood onset intellectual disability, epilepsy, and PD who was treated with subthalamic deep brain stimulation and subcutaneous L-DOPA infusion. Next Generation Sequencing analysis revealed a currently unknown pathogenic hemizygous sequence variant c.463C>T (NM_171998.4) in the RAB39B gene, confirmed also in the proband's mother, affected by late-onset PD. This report expands the number of described RAB39B mutations in individuals with early- and late-onset, X-linked PD.

Connector enhancer of kinase suppressor of Ras2 (CNKSR2) is critical in neuronal dendrite growth. Hemizygous pathogenic variants of CNKSR2, which is located at Xp22.12, are associated with intellectual disability, epilepsy, and developmental and epileptic encephalopathy with spike wave activation during sleep. As an X-linked recessive genetic disorder, neurological symptoms usually manifest in males, while female carriers are typically asymptomatic. Here, we report a girl (Patient 1) and boy (Patient 2) with a pathogenic truncated variant of CNKSR2. Patient 1 had intractable epilepsy and severe developmental regression; her electroencephalogram showed continuous spike-and-wave activity during sleep. Whole-genome sequencing (WGS) revealed a heterozygous CNKSR2 c.2134C>T, p.(Arg712Ter) variant (de novo, previously reported), and X-chromosome inactivation analysis of her white blood cell DNA showed marked skewing (85:15). Her clinical symptoms were more severe than those of previously reported female patients, but they improved with ethosuximide and sulthiame treatment. Patient 2 had epilepsy and Angelman syndrome-like symptoms. WGS revealed a Clinical Genetics hemizygous c.492C>A, p (Cys164Ter) CNKSR2 variant (maternal or novel). The strength of the X-chromosome inactivation skewing may be related to severity. These novel pathogenic CNKSR2 variants have expanded the phenotypic spectrum of this disease.

Background: Christianson syndrome is a rare X-linked disorder characterized by intellectual and developmental disability, epilepsy, and regressions, requiring lifelong care. This study explored family experiences and treatment priorities from the caregiver perspectives. Methods: Qualitative semistructured interviews were conducted with 18 caregivers of 20 patients (aged 4-29 years) to discuss symptom onset, diagnosis, progression, coping, and priorities. Transcripts were thematically analyzed. Results: Initial symptoms included seizures, delayed developmental milestones, and lack of speech. Caregivers described sadness, anger, and feeling overwhelmed after diagnosis. Concerns included seizures, communication challenges, and sleep disruptions. Only half reported robust support networks. Coping strategies included exercise, work, and partner support. Despite challenges, caregivers highlighted the happy, affectionate demeanors of the children. Caregivers emphasized connecting with other families and prioritized treatments for seizures, communication, and preventing regressions. Conclusions: These findings reflect caregiver experiences, enhance knowledge of Christianson syndrome impacts, and highlight common challenges for families managing disabilities.

USP9X gene variations have been associated with the rare syndrome female-restricted X-linked syndromic intellectual disability (MRXS99F). Loss-of-function mutations in USP9X gene is primarily characterized by development delay, speech and motor disorders, special facial features and multiple congenital malformations. We reported a newborn who presented with special facial features and developmental delay. We performed whole-genome sequencing and identified a rare novel heterozygous USP9X variant, c.4071-4077delCTTTACT (p.Thr1359Trpfs*19). To date, only seven USP9X variants in infants have been reported. Affected individuals typically exhibit a spectrum of congenital anomalies, including craniofacial dysmorphisms (such as hypertelorism, flat nasal bridge, and cleft palate), skeletal abnormalities (such as limb shortening, scoliosis, and rib anomalies), and neurological deficits (including severe intellectual disability, epilepsy, and motor delay). The radio logical tests revealed structural anomalies, such as corpus callosum agenesis and congenital hip dysplasia. This study expands the genotypic and clinical phenotypic spectrum of USP9X-related MRXS99F and reinforces the utility of whole-genome sequencing in early diagnosis and genetic counseling.

Mutations in the X-linked endosomal Na+/H+ exchanger 6 (NHE6) cause Christianson syndrome (CS). Here, in the largest study to date, we examine genetic diversity and clinical progression in CS into adulthood. Data were collected as part of the International Christianson Syndrome and NHE6 (SLC9A6) Gene Network Study. 44 individuals with 31 unique NHE6 mutations, age 2-32 years, were followed prospectively, herein reporting baseline, 1 year follow-up and retrospective natural history. We present data on the CS phenotype with regard to physical growth and adaptive and motor regression across the lifespan including information on mortality. Longitudinal data on body weight and height were examined using a linear mixed model. The rate of growth across development was slow and resulted in prominently decreased age-normed height and weight by adulthood. Adaptive functioning was longitudinally examined; a majority of adult participants (18+ years) lost gross and fine motor skills over a 1 year follow-up. Previously defined core diagnostic criteria for CS (present in>85%)-namely non-verbal status, intellectual disability, epilepsy, postnatal microcephaly, ataxia, hyperkinesia-were universally present in age 6-16; however, an additional core feature of high pain tolerance was added (present in 91%). While neurologic examinations were consistent with cerebellar dysfunction, importantly, a majority of individuals (>50% older than 10) also had corticospinal tract abnormalities. Three participants died during the period of the study. In this large and longitudinal study of CS, we begin to define the trajectory of symptoms and the adult phenotype thereby identifying critical targets for treatment.