Antibody deficiency may be primary, because of an underlying inborn error of immunity, or secondary, due to another disease process or medication, leading to decreased antibody production or increased antibody loss. Secondary antibody deficiency is much more common than primary. It can, however, be difficult to distinguish primary from secondary, and both should be considered when assessing patients with hypogammaglobulinaemia. The case presented highlights the importance of confirming the underlying pathophysiology in patients presenting with antibody deficiency, the contribution of genetic assessment to the care of patients with complex phenotypes, and the impact this can have on long-term patient management.

Mutations in the non-coding RNA gene RNU4ATAC are associated with growth restriction and complications related to antibody deficiency. Here, we report that innate immune dysfunction is a previously unrecognised feature of this disorder. In particular, painful chilblain-like lesions are common in RNU4ATAC patients and are linked to dysregulated type I interferon signalling.

Microcephalic osteodysplastic primordial dwarfism type I (MOPDI) is a very rare and severe autosomal recessive disorder characterized by marked intrauterine growth retardation, skeletal dysplasia, microcephaly and brain malformations. MOPDI is caused by biallelic mutations in RNU4ATAC, a non-coding gene involved in U12-type splicing of 1% of the introns in the genome, which are recognized by their specific splicing consensus sequences. Here, we describe a unique observation of immunodeficiency in twin sisters with mild MOPDI, who harbor a novel n.108_126del mutation, encompassing part of the U4atac snRNA 3' stem-loop and Sm protein binding site, and the previously reported n.111G>A mutation. Interestingly, both twin sisters show mild B-cell anomalies, including low naive B-cell counts and increased memory B-cell and plasmablasts counts, suggesting partial and transitory blockage of B-cell maturation and/or excessive activation of naive B-cells. Hence, the localization of a mutation in stem II of U4atac snRNA, as observed in another RNU4ATAC-opathy with immunodeficiency, that is, Roifman syndrome (RFMN), is not required for the occurrence of an immune deficiency. Finally, we emphasize the importance of considering immunodeficiency in MOPDI management to reduce the risk of serious infectious episodes.

Roifman syndrome is a rare congenital disorder characterized by growth retardation, cognitive delay, spondyloepiphyseal dysplasia, immunodeficiency, and retinal dystrophy. However, very rarely, with only one case reported to date, a patient with Roifman syndrome may develop cardiomyopathy in their lifetime. We reported a case with underdiagnosed Roifman syndrome confirmed by whole genome sequencing, manifested as non-ischaemic cardiomyopathy, which has broadened the association between non-ischaemic cardiomyopathy and the genetic disorder Roifman syndrome. We also underscored that cardiomyopathy might be part of the clinical manifestations of Roifman syndrome and the importance of whole genome sequencing for diagnosis, as RNU4ATAC is not targeted by many commercially available exome capture kits.

To characterize the retinal phenotype in RNU4ATAC-associated Roifman syndrome. Ten patients (including 8 males) with molecularly confirmed Roifman syndrome underwent detailed ophthalmologic evaluation including fundus imaging, fundus autofluorescence (FAF) imaging, spectral-domain optical coherence tomography (SD-OCT), and electroretinography (ERG). Six patients had follow-up eye exams. All patients also underwent comprehensive examination for features of extra-retinal Roifman syndrome. All patients had biallelic RNU4ATAC variants. Nyctalopia was common (7/10). Visual acuity at presentation ranged from 20/20 to 20/200 (Age Range: 5-41 years). Retinal exam revealed features of generalized retinopathy with mid-peripheral pigment epithelial changes. A para or peri-foveal ring of hyper-autofluorescence was the commonest FAF abnormality noted (6/8). The SD-OCT demonstrated relative preservation of the foveal ellipsoid zone in six cases; associated features included cystoid changes (5/10) and posterior staphyloma (3/10). The ERG was abnormal in all patients; nine showed generalized rod-cone dystrophy, whilst one patient with sectoral retinal involvement only had isolated rod dystrophy (20 years old). On follow-up examination (Mean duration: 8.16 years), progressive loss of visual acuity (2/6), mid-peripheral retinal atrophy (3/6) or shortening of ellipsoid zone width (1/6) were observed. This study has characterized the retinal phenotype in RNU4ATAC-associated Roifman syndrome. Retinal involvement is universal, early-onset, and overall, the retinal and FAF features are consistent with rod-cone degeneration that is slowly progressive over time. The sub-foveal retinal ultrastructure is relatively preserved in majority of patients. Phenotypic variability independent of age exists, and more study of allelic- and sex-based determinants of disease severity are necessary. RNU4atac-opathy encompasses the phenotypic spectrum of biallelic RNU4ATAC pathogenic variants, including the three historically designated clinical phenotypes microcephalic osteodysplastic primordial dwarfism type I/III (MOPDI), Roifman syndrome, and Lowry-Wood syndrome, as well as varying combinations of the disease features / system involvement that do not match specific defined phenotypes. Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment. Less common but variable findings include brain anomalies, seizures, strokes, immunodeficiency, and cardiac anomalies, as well as ophthalmologic, skin, renal, gastrointestinal, hearing, and endocrine involvement. The diagnosis of RNU4atac-opathy is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in RNU4ATAC identified by molecular genetic testing. Treatment of manifestations: Supportive care to improve quality of life, maximize function, and reduce complications is recommended. This ideally involves multidisciplinary care by specialists in relevant fields, including orthopedists to monitor the associated skeletal dysplasia and immunologists to manage antibiotic treatment of infections and use of immunoglobulin replacement therapy as indicated to avoid life-threatening infections. Surveillance: To monitor existing manifestations and response to supportive care (such as growth, developmental progress, and educational needs), and to detect new manifestations (particularly brain MRI for detection of stroke in children with MOPDI with neurologic deterioration). Agents/circumstances to avoid: Perform immunologic evaluation prior to administration of live vaccines. For those with MOPDI, minimize medically stressful situations as much as possible, including stress during anesthesia, due to energy-related strokes. RNU4atac-opathy is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an RNU4ATAC pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of inheriting neither of the familial pathogenic variants. Intrafamilial clinical variability has been reported between sibs who inherit the same biallelic RNU4ATAC pathogenic variants. Once the RNU4ATAC pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible.