A variant form of mucolipidosis IV: report on 4 patients from the Indian subcontinent

The High Association of Ophthalmic Manifestations in Individuals With Mucolipidosis Type IV

PURPOSE

To present a case report of mucolipidosis type IV (ML4) and review the literature for all of the ophthalmic abnormalities associated with this disease.

METHODS

A systematic review of the literature using PubMed/Medline was conducted, and with the addition of the current case report, the eye and ocular adnexa findings of 93 patients with ML4 are summarized.

RESULTS

The most common ophthalmic findings reported among the 93 patients included corneal clouding (90.3%), strabismus (58.1%), optic nerve pallor (52.2%), retinal dystrophy/pigmentary changes (50.5%), and retinal vascular attenuation (38.9%). Other less commonly reported findings included nystagmus, photophobia, ocular pain, excessive lacrimation, ptosis, and cataracts.

CONCLUSIONS

The ophthalmic findings discussed in the current case report and literature review serve as indicators for ML4. Early diagnosis of ML4 is important in forming a multidisciplinary management plan, genetic counseling strategy, and maximizing the visual development of affected individuals. [J Pediatr Ophthalmol Strabimus. 2022;59(5):332-337.].

Mucolipidosis Type IV in Omani Families with a Novel MCOLN1 Mutation: Search for Evidence of Founder Effect

Mucolipidosis Type IV (MLIV) is caused by a deficiency of the mucolipin cation channel encoded by Mucolipin TRP Cation Channel 1 gene (MCOLN1). It is a slowly progressive neurodevelopmental and neurodegenerative disorder causing severe psychomotor developmental delay and progressive visual impairment, which is often misdiagnosed as cerebral palsy. We describe six patients with MLIV from two Omani families with a novel c.237+5G>A mutation in the MCOLN1 gene predicted to affect mRNA splicing. Mutation screening with a high-resolution melting (HRM) assay in a large population sample did not detect this mutation in control subjects. This report highlights the importance of considering MLIV in the differential diagnosis of patients in a pediatric age group with cerebral palsy-like presentation. Although the same rare mutation was seen in two apparently unrelated families, this was not seen in the sample screened from the general population. The HRM assay provides a cost-effective assay for population screening for the c.237+5G>A mutation.

Neuropathophysiology, Genetic Profile, and Clinical Manifestation of Mucolipidosis IV-A Review and Case Series

Mucolipidosis type IV (MLIV) is an ultra-rare lysosomal storage disorder caused by biallelic mutations in MCOLN1 gene encoding the transient receptor potential channel mucolipin-1. So far, 35 pathogenic or likely pathogenic MLIV-related variants have been described. Clinical manifestations include severe intellectual disability, speech deficit, progressive visual impairment leading to blindness, and myopathy. The severity of the condition may vary, including less severe psychomotor delay and/or ocular findings. As no striking recognizable facial dysmorphism, skeletal anomalies, organomegaly, or lysosomal enzyme abnormalities in serum are common features of MLIV, the clinical diagnosis may be significantly improved because of characteristic ophthalmological anomalies. This review aims to outline the pathophysiology and genetic defects of this condition with a focus on the genotype–phenotype correlation amongst cases published in the literature. The authors will present their own clinical observations and long-term outcomes in adult MLIV cases.

Genetics of the human face: Identification of large-effect single gene variants

To discover specific variants with relatively large effects on the human face, we have devised an approach to identifying facial features with high heritability. This is based on using twin data to estimate the additive genetic value of each point on a face, as provided by a 3D camera system. In addition, we have used the ethnic difference between East Asian and European faces as a further source of face genetic variation. We use principal components (PCs) analysis to provide a fine definition of the surface features of human faces around the eyes and of the profile, and chose upper and lower 10% extremes of the most heritable PCs for looking for genetic associations. Using this strategy for the analysis of 3D images of 1,832 unique volunteers from the well-characterized People of the British Isles study and 1,567 unique twin images from the TwinsUK cohort, together with genetic data for 500,000 SNPs, we have identified three specific genetic variants with notable effects on facial profiles and eyes.

Mucolipidosis type IV: an update

Mucolipidosis type IV (MLIV) is a neurodevelopmental as well as neurodegenerative disorder with severe psychomotor developmental delay, progressive visual impairment, and achlorydria. It is characterized by the presence of lysosomal inclusions in many cell types in patients. MLIV is an autosomal recessive disease caused by mutations in MCOLN1, which encodes for mucolipin-1, a member of the transient receptor potential (TRP) cation channel family. Although approximately 70-80% of patients identified are Ashkenazi Jewish, MLIV is a pan-ethnic disorder. Importantly, while MLIV is thought to be a rare disease, its frequency may be greater than currently appreciated, for its common presentation as a cerebral palsy-like encephalopathy can lead to misdiagnosis. Moreover, patients with milder variants are often not recognized as having MLIV. This review provides an update on the ethnic distribution, clinical manifestations, laboratory findings, methods of diagnosis, molecular genetics, differential diagnosis, and treatment of patients with MLIV. An enhanced awareness of the manifestations of this disorder may help to elucidate the true frequency and range of symptoms associated with MLIV, providing insight into the pathogenesis of this multi-system disease.

Mucolipidosis type IV: a subtle pediatric neurodegenerative disorder

The mucolipidoses are a heterogeneous group of autosomal recessive neurodegenerative lysosomal storage disorders. Mucolipidosis type IV is rare; it is seen predominantly in the Ashkenazi Jewish population and usually presents with global neurodevelopmental delays in infancy, subtle corneal opacifications or clouding, and very slowly progressive neurodegeneration over many years. Elevation of serum gastrin is reported; findings from x-rays of bone and joints and lysosomal studies are normal. Reported here are two cases of mucolipidosis type IV in children not of Ashkenazi Jewish origin who presented during infancy with nonspecific global psychomotor delays, generalized hypotonia, and mild corneal abnormalities, but remained undiagnosed for years. A rare gene mutation in MCOLN1 was confirmed in one of the two patients, in addition to abnormal serum gastrin levels. More striking was the length of time that these children eluded detection of their final diagnosis.