Does the clinical phenotype of mucolipidosis-IIIγ differ from its αβ counterpart?: supporting facts in a cohort of 18 patients

Paediatric diabetes subtypes in a consanguineous population: a single-centre cohort study from Kurdistan, Iraq

AIMS/HYPOTHESIS

Monogenic diabetes is estimated to account for 1-6% of paediatric diabetes cases in primarily non-consanguineous populations, while the incidence and genetic spectrum in consanguineous regions are insufficiently defined. In this single-centre study we aimed to evaluate diabetes subtypes, obtain the consanguinity rate and study the genetic background of individuals with syndromic and neonatal diabetes in a population with a high rate of consanguinity.

METHODS

Data collection was carried out cross-sectionally in November 2021 at the paediatric diabetic clinic, Dr Jamal Ahmad Rashed Hospital, in Sulaimani, Kurdistan, Iraq. At the time of data collection, 754 individuals with diabetes (381 boys) aged up to 16 years were registered. Relevant participant data was obtained from patient files. Consanguinity status was known in 735 (97.5%) participants. Furthermore, 12 families of children with neonatal diabetes and seven families of children with syndromic diabetes consented to genetic testing by next-generation sequencing. Prioritised variants were evaluated using the American College of Medical Genetics and Genomics guidelines and confirmed by Sanger sequencing.

RESULTS

A total of 269 of 735 participants (36.5%) with known consanguinity status were offspring of consanguineous families. An overwhelming majority of participants (714/754, 94.7%) had clinically defined type 1 diabetes (35% of them were born to consanguineous parents), whereas only eight (1.1%) had type 2 diabetes (38% consanguineous). Fourteen (1.9%) had neonatal diabetes (50% consanguineous), seven (0.9%) had syndromic diabetes (100% consanguineous) and 11 (1.5%) had clinically defined MODY (18% consanguineous). We found that consanguinity was significantly associated with syndromic diabetes (p=0.0023) but not with any other diabetes subtype. The genetic cause was elucidated in ten of 12 participants with neonatal diabetes who consented to genetic testing (homozygous variants in GLIS3 [sibling pair], PTF1A and ZNF808 and heterozygous variants in ABCC8 and INS) and four of seven participants with syndromic diabetes (homozygous variants in INSR, SLC29A3 and WFS1 [sibling pair]). In addition, a participant referred as syndromic diabetes was diagnosed with mucolipidosis gamma and probably has type 2 diabetes.

CONCLUSIONS/INTERPRETATION

This unique single-centre study confirms that, even in a highly consanguineous population, clinically defined type 1 diabetes is the prevailing paediatric diabetes subtype. Furthermore, a pathogenic cause of monogenic diabetes was identified in 83% of tested participants with neonatal diabetes and 57% of participants with syndromic diabetes, with most variants being homozygous. Causative genes in our consanguineous participants were markedly different from genes reported from non-consanguineous populations and also from those reported in other consanguineous populations. To correctly diagnose syndromic diabetes in consanguineous populations, it may be necessary to re-evaluate diagnostic criteria and include additional phenotypic features such as short stature and hepatosplenomegaly.

Unraveling mucolipidosis type III gamma through whole genome sequencing in late-onset retinitis pigmentosa: a case report

BACKGROUND

We describe the case of a 47-year-old man referred to a retinal clinic and diagnosed with late-onset retinitis pigmentosa. Surprisingly, genetic testing revealed compound heterozygous pathogenic variants in GNPTG, leading to the diagnosis of the autosomal recessive lysosomal storage disorder mucolipidosis type III gamma. Mucolipidosis type III gamma is typically diagnosed during childhood due to symptoms relating to skeletal dysplasia. Retinal dystrophy is not a common phenotypic feature.

CASE PRESENTATION

Ophthalmologic examination was consistent with a mild form of retinitis pigmentosa and included fundus photography, measurement of best-corrected visual acuity, optical coherence tomography, electroretinogram and visual field testing. Extraocular findings included joint restriction and pains from an early age leading to bilateral hip replacement by age 30, aortic insufficiency, and hypertension. Genetic analysis was performed by whole genome sequencing filtered for a gene panel of 325 genes associated with retinal disease. Two compound heterozygous pathogenic variants were identified in GNPTG, c.347_349del and c.607dup. The diagnosis of mucolipidosis type III gamma was confirmed biochemically by measurement of increased activities of specific lysosomal enzymes in plasma.

CONCLUSION

To our knowledge this is the first description of retinitis pigmentosa caused by compound heterozygous variants in GNPTG, providing further indications that late-onset retinal dystrophy is part of the phenotypic spectrum of mucolipidosis type III gamma.

Lysosomal storage disorders: from biology to the clinic with reference to India

Lysosomal storage disorders (LSDs) are a group of seventy different metabolic storage diseases due to accumulation of substrate mainly in the form of carbohydrate, lipids, proteins, and cellular debris. They occur due to variant in different genes that regulate lysosomal enzymes synthesis, transport, and secretion. In recent years, due to an increased availability of various therapies to treat these disorders, and increased diagnostic tools, there has been an escalated awareness of LSDs. Due to heterogeneous population and various social reasons, India is likely to have a high frequency of LSDs. Therefore, to understand the burden of various LSDs, its molecular spectrum, and understanding the phenotype-genotype correlation, Indian Council of Medical Research (ICMR) and Department of Health Research (DHR), Government of India had set up a task force in the year 2015. It has resulted in identifying common LSDs, and founder variant for some of the storage disorders and molecular spectrum of various LSDs across the country. This review describes in detail the spectrum of LSDs, its molecular epidemiology and prevention in context to Indian population.

Hip disease in Mucopolysaccharidoses and Mucolipidoses: A review of mechanisms, interventions and future perspectives

The hips are frequently involved in inheritable diseases which affect the bones. The clinical and radiological presentation of these diseases may be very similar to common hip disorders as developmental dysplasia of the hip, osteoarthritis and avascular necrosis, so the diagnosis may be easily overlooked and treatment may be suboptimal. Mucopolysaccharidosis (MPS) and Mucolipidosis (ML II and III) are lysosomal storage disorders with multisystemic involvement. Characteristic skeletal abnormalities, known as dysostosis multiplex, are common in MPS and ML and originate from intra-lysosomal storage of glycosaminoglycans in cells of the cartilage, bones and ligaments. The hip joint is severely affected in MPS and ML. Hip pathology results in limitations in mobility and pain from young age, and negatively affects quality of life. In order to better understand the underlying process that causes hip disease in MPS and ML, this review first describes the normal physiological (embryonic) hip joint development, including the interplay between the acetabulum and the femoral head. In the second part the factors contributing to altered hip morphology and function in MPS and ML are discussed, such as abnormal development of the pelvic- and femoral bones (which results in altered biomechanical forces) and inflammation. In the last part of this review therapeutic options and future perspectives are addressed.

Clinical, radiological and computational studies on two novel GNPTG variants causing mucolipidosis III gamma phenotypes with varying severity

Mucolipidosis III gamma (ML III γ) is a slowly progressive disorder that affects multiple parts of the body such as the skeleton, joints, and connective tissue structures. It is caused by pathogenic variants in the GNPTG gene that provides instructions for producing the γ subunit of GlcNAc-1-phosphotransferase. In this study we aim to characterize clinical findings and biological insights on two novel GNPTG variants causing ML III γ phenotypes with varying severity. We report on two siblings with ML III γ bearing the previously undescribed c.477C > G (p.Y159*) nonsense variant in a homozygous state as well as a patient with ML III γ bearing the novel c.110 + 19_111-17del variant in a homozygous state. These variants were revealed by whole-exome sequencing and Sanger sequencing, respectively. Their parents, who are heterozygotes for the same mutation, are healthy. The clinical and radiographic presentation of ML III γ in our patients who had c.477C > G (p.Y159*) variant is consistent with a relatively severe form of the disease, which is further supported by a working three-dimensional model of the GlcNAc-1-phosphotransferase γ subunit. On the other hand, it is seen that our patient who carries the c.110 + 19_111-17del variant has a milder phenotype. Our findings help broaden the spectrum of GNPTG variants causing ML III γ and offer structural and mechanistic insights into loss of GlcNAc-1-phosphotransferase γ subunit function.

Clinical Characterization of Mucolipidoses II and III: A Multicenter Study

Mucolipidoses (MLs) II and III are rare lysosomal diseases caused by deficiency of GlcNAc-1-phosphotransferase, and clinical manifestations are multisystemic. Clinical and demographic data from 1983 to 2013 were obtained retrospectively. Twenty-seven patients were included (ML II = 15, ML III α/beta = 9, ML III gamma = 3). The median age at diagnosis was 2.7 years. The predominant clinical presentations were skeletal symptoms. The ML II patients showed physical and cognitive impairment, while the ML III α/beta patients have more somatic abnormalities and usually were delayed in early development as compared with ML III gamma patients. This is the most comprehensive study exploring characteristics of Brazilian patients with MLs II and III.