Mutations in riboflavin transporter present with severe sensory loss and deafness in childhood

Riboflavin transporter deficiency in young adults unmasked by dietary changes

Riboflavin transporter deficiency (RTD) is a genetic disorder of reduced riboflavin (vitamin B2) uptake that causes progressive, multifocal neurological dysfunction. Most patients present in early childhood; if patients present later in life, symptoms usually develop more gradually. We report three previously healthy young adults, who developed rapidly progressive neurological symptoms after decreasing dietary intake of meat and dairy. After a diagnostic odyssey, the diagnosis of a riboflavin transporter deficiency was made. Treatment with high dose oral riboflavin (20-40 mg/kg/day) partially reversed symptoms. This case series highlights that reduced riboflavin intake as a result of dietary changes can unmask RTD at a later age. We emphasize the importance of early recognition of this progressive and potentially lethal disease and show that timely treatment with high dose riboflavin is highly effective.

Case Report: A rare treatable metabolic syndrome (Brown-Vialetto-Van Laere syndrome) masquerading as chronic inflammatory demyelinating polyneuropathy from Saudi Arabia

Background

Brown-Vialetto-Van Laere (BVVL) syndrome is an extremely rare autosomal recessive progressive motoneuron disease that is caused by a defect in the riboflavin transporter genes SLC52A2 and SLC52A3. BVVL syndrome has a variable age of presentation, and it is characterized by progressive auditory neuropathy, bulbar palsy, stridor, muscle weakness, and respiratory compromise secondary to diaphragmatic and vocal cord paralysis. BVVL syndrome has a poor prognosis in the absence of treatment, including morbidity with quadriparesis and sensorineural hearing loss, with mortality in the younger age group. Early administration of riboflavin is associated with prolonged survival, low morbidity, and reversal of some clinical manifestations.

Case presentation

We describe an 18-month-old male infant with progressive pontobulbar palsy, loss of developmental milestones, and a clinical picture suggestive of chronic inflammatory demyelinating neuropathy. A nerve conduction study revealed axonal neuropathy, while molecular analysis revealed a homozygous mutation in one of the riboflavin transporter genes, SLC52A3, confirming BVVL syndrome. The patient needed long-term respiratory support and a gastrostomy tube to support feeding. With high-dose riboflavin supplementation, he experienced moderate recovery of motor function.

Conclusion

This report highlights the importance of considering BVVL syndrome in any patient who presents with the clinical phenotype of pontobulbar palsy and peripheral axonal neuropathy, as early riboflavin treatment may improve or halt disease progression, thus reducing the associated mortality and morbidity.

Effects of Methylenetetrahydrofolate Reductase (MTHFR) Polymorphisms on Retinal Tissue Perfusion in Mild Diabetic Retinopathy Patients Receiving the Medical Food, Ocufolin®

Purpose

We evaluate the effects of methylenetetrahydrofolate reductase (MTHFR) polymorphisms on retinal tissue perfusion in patients with mild diabetic retinopathy (DR + PM) taking the medical food, Ocufolin^®, for 6 months.

Methods

Prospective, case-controlled study. Eight early diabetic retinopathy patients with common reduced function MTHFR polymorphisms (DR+PM) and 15 normal controls (NC) were recruited. MTHFR polymorphisms were subtyped as normal, C677T, or A1298C. Best corrected visual acuity (BCVA) was evaluated. Retinal blood flow velocity (BFV) was measured using Retinal Function Imager. Retinal tissue perfusion (RTP, blood flow rate per inner retinal volume) was calculated within a 2.5 mm diameter circle centered on the fovea. The medical food is intended to address ocular ischemia with high doses of vitamin B-complexes and antioxidants, including L-methylfolate, methylcobalamin, zinc, copper, lutein, vitamins C, D, E, and n-acetylcysteine. The subjects were provided with a medical food for a period of 6 months.

Results

BCVA and vascular indices of DR + PM patients at baseline were initially below those of NC and improved after medical food. Compared to baseline, DR + PM patients after the medical food had significantly improved BCVA during the follow-up period (P < 0.05). In comparison, overall RTP and arteriolar BFV were significantly increased at 6 months (P < 0.05). The changes varied with MTHFR subtypes. In patients with the C677T and the C677T/A1298C compound mutations, RTP was increased at 6 months as compared to that at baseline and 4 months (P < 0.05). In patients with only the A1298C mutation, all microcirculation metrics were increased from baseline at 4 and 6 months, but with less improvement at 6 months than at 4 months (P < 0.05).

Conclusion

Medical food was effective in improving both visual acuity and retinal tissue perfusion in DR + PM patients. The degree of improvement of retinal microcirculation varied among MTHFR subtypes.

First report of paternal uniparental disomy of chromosome 8 with SLC52A2 mutation in Brown-vialetto-van laere syndrome type 2 and an analysis of genotype-phenotype correlations

Purpose: This study reports the clinical and genetic features of Brown-Vialetto-Van Laere syndrome (BVVL) type 2 in a case of uniparental disomy of chromosome 8 in mainland China and analyzes the genotype-phenotype correlation through a review of the literature of BVVL type 2 cases.

Methods: The clinical characteristics, treatment, and follow-up data of the patient were summarized, and the etiology was identified by whole-exome sequencing and gene chip analysis. Correlations between the genotype and phenotype were analyzed by collecting clinical and genetic data of published cases and our patient.

Results: We identified a homozygous mutation in SLC52A2 (NM_001253815.2 c.1255G>A) by trio-WES. Sanger sequencing confirmed that his father was heterozygous and his mother was wild type. Subsequently, paternal uniparental disomy of chromosome 8 [UPD (8)pat] was confirmed by chromosomal microarray analysis.The patient received long-term oral riboflavin treatment (7 mg/kg.d) and was followed up for 40 months by which time the child’s bulbar palsy, ataxia, and motor function had improved. A review of the literature and statistical analysis found that the symptoms of BVVL type 2 appear at the earliest shortly after birth and at the latest at 10 years of age. The median age of onset was 2.5 years, but the overall delay in diagnosis was a median of 5.6 years. The most common symptoms were hearing loss (83.9%), followed by muscle weakness (80.6%), visual impairment (64.5%), and ataxia (61.3%). To date, a total of 32 mutations in the SLC52A2 gene have been reported, with the most common being a missense mutation. Mutations occur throughout the length of the gene apart from at the N-terminus. In patients with missense mutations, homozygous pattern was more likely to present with ataxia as the first symptom (p < 0.05), while compound heterozygous pattern was more likely to develop respiratory insufficiency during the course of disease (p < 0.001). Moreover, patients with one missense mutation located in inside the transmembrane domain were more likely to have respiratory insufficiency than those with mutations both inside and outside the domain (p < 0.05). Riboflavin supplementation was an important factor in determining prognosis (p < 0.001).

Conclusion: We report the first UPD(8)pat with SLC52A2 homozygous pathogenic mutation case in BVVL type 2, which expand the mutation spectrum of gene.

Recent advances in riboflavin transporter RFVT and its genetic disease

Riboflavin (vitamin B2) is essential for cellular growth and function. It is enzymatically converted to flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which participate in the metabolic oxidation-reduction reactions of carbohydrates, amino acids, and lipids. Human riboflavin transporters RFVT1, RFVT2, and RFVT3 have been identified and characterized since 2008. They are highly specific transporters of riboflavin. RFVT3 has functional characteristics different from those of RFVT1 and RFVT2. RFVT3 contributes to absorption in the small intestine, reabsorption in the kidney, and transport to the fetus in the placenta, while RFVT2 mediates the tissue distribution of riboflavin from the blood. Several mutations in the SLC52A2 gene encoding RFVT2 and the SLC52A3 gene encoding RFVT3 were found in patients with a rare neurological disorder known as Brown-Vialetto-Van Laere syndrome. These patients commonly present with bulbar palsy, hearing loss, muscle weakness, and respiratory symptoms in infancy or later in childhood. A decrease in plasma riboflavin levels has been observed in several cases. Recent studies on knockout mice and patient-derived cells have advanced the understanding of these mechanisms. Here, we summarize novel findings on RFVT1-3 and their genetic diseases and discuss their potential as therapeutic drugs.

Catalogue for Transmission Genetics in Arabs (CTGA) Database: Analysing Lebanese Data on Genetic Disorders

Lebanon has a high annual incidence of birth defects at 63 per 1000 live births, most of which are due to genetic factors. The Catalogue for Transmission Genetics in Arabs (CTGA) database, currently holds data on 642 genetic diseases and 676 related genes, described in Lebanese subjects. A subset of disorders (14/642) has exclusively been described in the Lebanese population, while 24 have only been reported in CTGA and not on OMIM. An analysis of all disorders highlights a preponderance of congenital malformations, deformations and chromosomal abnormalities and demonstrates that 65% of reported disorders follow an autosomal recessive inheritance pattern. In addition, our analysis reveals that at least 58 known genetic disorders were first mapped in Lebanese families. CTGA also hosts 1316 variant records described in Lebanese subjects, 150 of which were not reported on ClinVar or dbSNP. Most variants involved substitutions, followed by deletions, duplications, as well as in-del and insertion variants. This review of genetic data from the CTGA database highlights the need for screening programs, and is, to the best of our knowledge, the most comprehensive report on the status of genetic disorders in Lebanon to date.

A 20-year Clinical and Genetic Neuromuscular Cohort Analysis in Lebanon: An International Effort

BACKGROUND

Clinical and molecular data on the occurrence and frequency of inherited neuromuscular disorders (NMD) in the Lebanese population is scarce.

OBJECTIVE

This study aims to provide a retrospective overview of hereditary NMDs based on our clinical consultations in Lebanon.

METHODS

Clinical and molecular data of patients referred to a multi-disciplinary consultation for neuromuscular disorders over a 20-year period (1999-2019) was reviewed.

RESULTS

A total of 506 patients were diagnosed with 62 different disorders encompassing 10 classes of NMDs. 103 variants in 49 genes were identified. In this cohort, 81.4%of patients were diagnosed with motor neuron diseases and muscular dystrophies, with almost half of these described with spinal muscular atrophy (SMA) (40.3%of patients). We estimate a high SMA incidence of 1 in 7,500 births in Lebanon. Duchenne and Becker muscular dystrophy were the second most frequently diagnosed NMDs (17%of patients). The latter disorders were associated with the highest number of variants (39) identified in this study. A highly heterogeneous presentation of Limb Girdle Muscular Dystrophy and Charcot-Marie-Tooth disease was notably identified. The least common disorders (5.5%of patients) involved congenital, metabolic, and mitochondrial myopathies, congenital myasthenic syndromes, and myotonic dystrophies. A review of the literature for selected NMDs in Lebanon is provided.

CONCLUSIONS

Our study indicates a high prevalence and underreporting of heterogeneous forms of NMDs in Lebanon- a major challenge with many novel NMD treatments in the pipeline. This report calls for a regional NMD patient registry.

Hearing loss in inherited metabolic disorders: A systematic review

Inherited metabolic disorders (IMDs) have been observed in individuals with hearing loss (HL), but IMDs are rarely the cause of syndromic HL. With early diagnosis, management of HL is more effective and cortical reorganization is possible with hearing aids or cochlear implants. This review describes relationships between IMDs and HL in terms of incidence, etiology of HL, pathophysiology, and treatment. Forty types of IMDs are described in the literature, mainly in case reports. Management and prognosis are noted where existing. We also describe IMDs with HL given age of occurrence of HL. Reviewing the main IMDs that are associated with HL may provide an additional clinical tool with which to better diagnose syndromic HL.

Late-onset riboflavin transporter deficiency: a treatable mimic of various motor neuropathy aetiologies

OBJECTIVE

Riboflavin transporter deficiencies (RTDs), involving SLC52A3 and SLC52A2 genes, have recently been related to Brown-Vialetto-Van Laere (BVVL) syndrome, a hereditary paediatric condition associating motor neuropathy (MN) and deafness. BVVL/RTD has rarely been reported in adult patients, but is probably underdiagnosed due to poor knowledge and lack of awareness of this form of disease among neurologists. In this study, we aimed to investigate the phenotype and prognosis of RTD patients with late-onset MN.

METHODS

We retrospectively collected clinical, biological and electrophysiological data from all French RTD patients with MN onset after 10 years of age (n=6) and extracted data from 19 other similar RTD patients from the literature.

RESULTS

Adult RTD patients with MN had heterogeneous clinical presentations, potentially mimicking amyotrophic lateral sclerosis or distal hereditary motor neuropathy (56%), multinevritis with cranial nerve involvement (16%), Guillain-Barré syndrome (8%) and mixed motor and sensory neuronopathy syndromes (20%, only in SLC52A2 patients). Deafness was often diagnosed before MN (in 44%), but in some patients, onset began only with MN (16%). The pattern of weakness varied widely, and the classic pontobulbar palsy described in BVVL was not constant. Biochemical tests were often normal. The majority of patients improved under riboflavin supplementation (86%).

INTERPRETATION

Whereas late-onset RTD may mimic different acquired or genetic causes of motor neuropathies, it is a diagnosis not to be missed since high-dose riboflavin per oral supplementation is often highly efficient.

The Clinical Journey of Patients with Riboflavin Transporter Deficiency Type 2

PURPOSE

To identify symptoms and health care interactions with patients with riboflavin transporter deficiency (RTD) type 2 prior to diagnosis.

METHODS

Parents of children with riboflavin transporter deficiency type 2 (n = 10) were interviewed to collect data on the patient's clinical journey.

RESULTS

The average diagnostic delay was 27.6 months. Neurologists were the most commonly visited clinician (90%). Common symptoms during the first year of the patient's clinical journey included abnormal gait and/or ataxia (70%), nystagmus (50%), and upper body muscle weakness (40%). Prior to diagnosis, optic atrophy, sleep apnea, breath-holding spells, and dysphagia were commonly observed. Hearing loss was only reported in 40% of subjects prior to diagnosis. Riboflavin responsive megaloblastic anemia is reported for the first time. Mitochondrial disease was the most common suspected diagnosis (30%).

CONCLUSION

Despite clinical variability, common early symptoms of riboflavin transporter deficiency type 2 exist that can better allow clinicians to more rapidly identify riboflavin transporter deficiency type 2.

Effect of Malnutrition on Hearing Loss in Children

OBJECTIVE

To characterize the relation between protein-calorie malnutrition (PCM) and hearing loss (HL) in children.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral hospital.

PATIENTS

Children in the Audiological and Genetic Database with a diagnosis of protein-calorie malnutrition, marasmus, and/or kwashiorkor.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Prevalence, type, severity (4-tone pure-tone average, PTA), and progression of HL.

RESULTS

Of 770 children with PCM, 57.8% had HL, compared to 45.5% of children without PCM (p < 0.001). Severely malnourished children had significantly higher odds of moderate-profound HL (aOR 2.27, 95% CI 1.47-3.43), high-frequency HL (aOR 1.82, 95% CI 1.21-2.75), and sensorineural or mixed HL (aOR 1.60, 95% CI 1.05-2.41) compared to children without PCM. Severely malnourished children had significantly worse initial (35.0 dB vs 25.0 dB, p < 0.001), and final median PTA (31.3 dB vs 20.0 dB, p < 0.001) compared to children without PCM. Additionally, HL in children who were moderately and severely malnourished was significantly less likely to improve (aOR 0.47, 95% CI 0.25-0.82 and aOR 0.4, 95% CI 0.2-0.9) when compared to those without PCM.

CONCLUSIONS

Given the greater prevalence and severity of hearing loss, children with PCM should be considered an at-risk group for poor audiological outcomes, and clinical practice should focus on early treatment and intervention for malnourished children. Routine audiological evaluation should be considered in this population.

An update on the genetics, clinical presentation, and pathomechanisms of human riboflavin transporter deficiency

Riboflavin transporter deficiency (RTD) is a rare neurological condition that encompasses the Brown-Vialetto-Van Laere and Fazio-Londe syndromes since the discovery of pathogenic mutations in the SLC52A2 and SLC52A3 genes that encode human riboflavin transporters RFVT2 and RFVT3. Patients present with a deteriorating progression of peripheral and cranial neuropathy that causes muscle weakness, vision loss, deafness, sensory ataxia, and respiratory compromise which when left untreated can be fatal. Considerable progress in the clinical and genetic diagnosis of RTDs has been made in recent years and has permitted the successful lifesaving treatment of many patients with high dose riboflavin supplementation. In this review, we first outline the importance of riboflavin and its efficient transmembrane transport in human physiology. Reports on 109 patients with a genetically confirmed diagnosis of RTD are then summarized in order to highlight commonly presenting clinical features and possible differences between patients with pathogenic SLC52A2 (RTD2) or SLC52A3 (RTD3) mutations. Finally, we focus attention on recent work with different models of RTD that have revealed possible pathomechanisms contributing to neurodegeneration in patients.

Role of MicroRNA-423-5p in posttranscriptional regulation of the intestinal riboflavin transporter-3

Riboflavin (RF) is essential for normal cellular functions and health. Humans obtain RF from exogenous sources via intestinal absorption that involves a highly specific carrier-mediated process. We have recently established that the riboflavin transporter-3 (RFVT3) is vital for the normal intestinal RF uptake process and have characterized certain aspects of its transcriptional regulation. Little is known, however, about how this transporter is regulated at the posttranscriptional level. We address this issue by focusing on the role of microRNAs. Using bioinformatics, we identified two potential interacting miRNAs with the human (h) RFVT3-3'-UTR, and showed (using pmirGLO-hRFVT3-3'-UTR) that the hRFVT3-3'-UTR is, indeed, a target for miRNA effect. Of the two putative miRNAs identified, miR-423-5p was found to be highly expressed in intestinal epithelial cells and that its mimic affected luciferase reporter activity of the pmirGLO-hRFVT3-3'-UTR construct, and also led to inhibition in RF uptake by intestinal epithelial Caco-2 and HuTu-80 cells. Furthermore, cells transfected with mutated seed sequences for miR-423-5p showed an abrogation in inhibitory effect of the miR-423-5p mimic on luciferase activity. While miR-423-5p did not affect the level of expression of the hRFVT3 mRNA, it did lead to a significant inhibition in the level of expression of its protein. Similarly, miR-423-5p was found to affect the level of expression of the mouse RFVT3 in cultured intestinal enteroids. These findings demonstrate, for the first time, that the RFVT3 is a target for posttranscriptional regulation by miRNAs in intestinal epithelial cells and that this regulation has functional consequences on intestinal RF uptake.NEW & NOTEWORTHY Our findings show for the first time that RFVT3 is a target for posttranscriptional regulation by miR-423-5p in intestinal epithelial cells, and this regulation has functional consequences on intestinal riboflavin (RF) uptake process.

Brown-Vialetto-Van Laere Syndrome as a Mimic of Neuroimmune Disorders: 3 Cases From the Clinic and Review of the Literature

We present 3 patients identified at 2 different institutions with Brown-Vialetto-Van Laere syndrome. Each patient was initially diagnosed with a neuroimmune disorder for a period of a few weeks to a few months. In each case, genetic analysis revealed mutations in one of the riboflavin transporters, confirming Brown-Vialetto-Van Laere syndrome. It is likely that Brown-Vialetto-Van Laere syndrome is more common than previously reported, and because it mimics neuroimmune disorders, it may be misdiagnosed as such. It shares many features with diseases such as chronic inflammatory demyelinating neuropathy, may present with positive cerebrospinal fluid antibody titers, and may transiently respond to intravenous immunoglobulin. We review the literature on Brown-Vialetto-Van Laere syndrome and Fazio-Londe syndrome, 2 riboflavin transporter disorders, looking for clinical presentations that may lead to confusion with neuroimmune disorders. We emphasize the importance of correctly diagnosing the disease, as its treatment is relatively benign and will stop progression of the disease and may even reverse it.

Auditory neuropathy in Brown-Vialetto-Van Laere syndrome due to riboflavin transporter RFVT2 deficiency

AIM

Mutations in the genes encoding the riboflavin transporters RFVT2 and RFVT3 have been identified in Brown-Vialetto-Van Laere syndrome, a neurodegenerative disorder characterized by hearing loss and pontobulbar palsy. Treatment with riboflavin has been shown to benefit individuals with the phenotype of RFVT2 deficiency. Understanding the characteristics of hearing loss in riboflavin transporter deficiency would enable early diagnosis and therapy.

METHOD

We performed hearing assessments in seven children (from four families) with RFVT2 deficiency and reviewed results from previous assessments. Assessments were repeated after 12 months and 24 months of riboflavin therapy and after cochlear implantation in one individual.

RESULTS

Hearing loss in these individuals was due to auditory neuropathy spectrum disorder (ANSD). Hearing loss was identified between 3 years and 8 years of age and progressed rapidly. Hearing aids were not beneficial. Riboflavin therapy resulted in improvement of hearing thresholds during the first year of treatment in those with recent-onset hearing loss. Cochlear implantation resulted in a significant improvement in speech perception in one individual.

INTERPRETATION

Riboflavin transporter deficiency should be considered in all children presenting with an auditory neuropathy. Speech perception in children with ANSD due to RFVT2 deficiency may be significantly improved by cochlear implantation.

Clinical presentation and outcome of riboflavin transporter deficiency: mini review after five years of experience

INTRODUCTION

Riboflavin (vitamin B2) is absorbed in the small intestine by the human riboflavin transporters RFVT1 and RFVT3. A third riboflavin transporter (RFVT2) is expressed in the brain. In 2010 it was demonstrated that mutations in the riboflavin transporter genes SLC52A2 (coding for RFVT2) and SLC52A3 (coding for RFVT3) cause a neurodegenerative disorder formerly known as Brown-Vialetto-Van Laere (BVVL) syndrome, now renamed to riboflavin transporter deficiency. Five years after the diagnosis of the first patient we performed a review of the literature to study the presentation, treatment and outcome of patients with a molecularly confirmed diagnosis of a riboflavin transporter deficiency.

METHOD

A search was performed in Medline, Pubmed using the search terms 'Brown-Vialetto-Van Laere syndrome' and 'riboflavin transporter' and articles were screened for case reports of patients with a molecular diagnosis of a riboflavin transporter deficiency.

RESULTS

Reports on a total of 70 patients with a molecular diagnosis of a RFVT2 or RTVT3 deficiency were retrieved. The riboflavin transporter deficiencies present with weakness, cranial nerve deficits including hearing loss, sensory symptoms including sensory ataxia, feeding difficulties and respiratory difficulties which are caused by a sensorimotor axonal neuropathy and cranial neuropathy. Biochemical abnormalities may be absent and the diagnosis can only be made or rejected by molecular analysis of all genes. Treatment with oral supplementation of riboflavin is lifesaving. Therefore, if a riboflavin transporter deficiency is suspected, treatment must be started immediately without first awaiting the results of molecular diagnostics.

Remaining challenges in cellular flavin cofactor homeostasis and flavoprotein biogenesis

The primary role of the water-soluble vitamin B₂ (riboflavin) in cell biology is connected with its conversion into FMN and FAD, the cofactors of a large number of dehydrogenases, oxidases and reductases involved in a broad spectrum of biological activities, among which energetic metabolism and chromatin remodeling. Subcellular localisation of FAD synthase (EC 2.7.7.2, FADS), the second enzyme in the FAD forming pathway, is addressed here in HepG2 cells by confocal microscopy, in the frame of its relationships with kinetics of FAD synthesis and delivery to client apo-flavoproteins. FAD synthesis catalyzed by recombinant isoform 2 of FADS occurs via an ordered bi-bi mechanism in which ATP binds prior to FMN, and pyrophosphate is released before FAD. Spectrophotometric continuous assays of the reconstitution rate of apo-D-aminoacid oxidase with its cofactor, allowed us to propose that besides its FAD synthesizing activity, hFADS is able to operate as a FAD “chaperone.” The physical interaction between FAD forming enzyme and its clients was further confirmed by dot blot and immunoprecipitation experiments carried out testing as a client either a nuclear lysine-specific demethylase 1 (LSD1) or a mitochondrial dimethylglycine dehydrogenase (Me₂GlyDH, EC 1.5.8.4). Both enzymes carry out similar reactions of oxidative demethylation, in which tetrahydrofolate is converted into 5,10-methylene-tetrahydrofolate. A direct transfer of the cofactor from hFADS2 to apo-dimethyl glycine dehydrogenase was also demonstrated. Thus, FAD synthesis and delivery to these enzymes are crucial processes for bioenergetics and nutri-epigenetics of liver cells.

Mutations in LAMA1 cause cerebellar dysplasia and cysts with and without retinal dystrophy

Cerebellar dysplasia with cysts (CDC) is an imaging finding typically seen in combination with cobblestone cortex and congenital muscular dystrophy in individuals with dystroglycanopathies. More recently, CDC was reported in seven children without neuromuscular involvement (Poretti-Boltshauser syndrome). Using a combination of homozygosity mapping and whole-exome sequencing, we identified biallelic mutations in LAMA1 as the cause of CDC in seven affected individuals (from five families) independent from those included in the phenotypic description of Poretti-Boltshauser syndrome. Most of these individuals also have high myopia, and some have retinal dystrophy and patchy increased T2-weighted fluid-attenuated inversion recovery (T2/FLAIR) signal in cortical white matter. In one additional family, we identified two siblings who have truncating LAMA1 mutations in combination with retinal dystrophy and mild cerebellar dysplasia without cysts, indicating that cysts are not an obligate feature associated with loss of LAMA1 function. This work expands the phenotypic spectrum associated with the lamininopathy disorders and highlights the tissue-specific roles played by different laminin-encoding genes.