Identification and characterisation of a rare MTTP variant underlying hereditary non-alcoholic fatty liver disease.

Background & Aims: Non-alcoholic fatty liver disease (NAFLD) is a complex trait with an estimated prevalence of 25% globally. We aimed to identify the genetic variant underlying a four-generation family with progressive NAFLD leading to cirrhosis, decompensation, and development of hepatocellular carcinoma in the absence of common risk factors such as obesity and type 2 diabetes. Methods: Exome sequencing and genome comparisons were used to identify the likely causal variant. We extensively characterised the clinical phenotype and post-prandial metabolic responses of family members with the identified novel variant in comparison with healthy non-carriers and wild-type patients with NAFLD. Variant-expressing hepatocyte-like cells (HLCs) were derived from human-induced pluripotent stem cells generated from homozygous donor skin fibroblasts and restored to wild-type using CRISPR-Cas9. The phenotype was assessed using imaging, targeted RNA analysis, and molecular expression arrays. Results: We identified a rare causal variant c.1691T>C p.I564T (rs745447480) in MTTP, encoding microsomal triglyceride transfer protein (MTP), associated with progressive NAFLD, unrelated to metabolic syndrome and without characteristic features of abetalipoproteinaemia. HLCs derived from a homozygote donor had significantly lower MTP activity and lower lipoprotein ApoB secretion than wild-type cells, while having similar levels of MTP mRNA and protein. Cytoplasmic triglyceride accumulation in HLCs triggered endoplasmic reticulum stress, secretion of pro-inflammatory mediators, and production of reactive oxygen species. Conclusions: We have identified and characterised a rare causal variant in MTTP, and homozygosity for MTTP p.I564T is associated with progressive NAFLD without any other manifestations of abetalipoproteinaemia. Our findings provide insights into mechanisms driving progressive NAFLD. Impact and Implications: A rare genetic variant in the gene MTTP has been identified as responsible for the development of severe non-alcoholic fatty liver disease in a four-generation family with no typical disease risk factors. A cell line culture created harbouring this variant gene was characterised to understand how this genetic variation leads to a defect in liver cells, which results in accumulation of fat and processes that promote disease. This is now a useful model for studying the disease pathways and to discover new ways to treat common types of fatty liver disease.

An approach to familial lymphoedema.

Lymphoedema is the build-up of lymphatic fluid leading to swelling in the tissues. Most commonly it affects the peripheries. Diagnosis is based on clinical assessment and imaging with lymphoscintigraphy. Treatment is supportive with compression garments, massage, good skin hygiene and prompt use of antibiotics to avoid the complication of cellulitis. Most commonly, lymphoedema occurs as a result of damage to the lymphatic system following surgery, trauma, radiation or infection. However, it can be primary, often associated with a genetic defect that causes disruption to the development of the lymphatic system. Common genetic conditions associated with lymphoedema include Turner syndrome and Noonan syndrome; however, there are numerous others that can be classified based on their clinical presentation and associated features. Herein we discuss how to diagnose and classify the known primary lymphoedema conditions and how best to investigate and manage this group of patients.

Microform holoprosencephaly with bilateral congenital elbow dislocation; increasing the phenotypic spectrum of Steinfeld syndrome.

Steinfeld syndrome (MIM #184705) was first reported in 1982. It is characterised by holoprosencephaly and limb defects, however other anomalies may also be present. Following the initial description, three further cases have been reported in the literature. We report on a 23-year-old girl, with features of microform holoprosencephaly and bilateral congenital elbow dislocation in association with hypoplastic radial heads. She was identified to have a variant in the CDON gene inherited from her father who had ocular hypotelorism, but no other clinical features. We discuss the clinical features of Steinfeld syndrome, and broaden the phenotypic spectrum of this condition. Structural analysis suggests that this variant could lead to destabilisation of binding of CDON with hedgehog proteins. Further work needs to be done to confirm whether mutations in the CDON gene are the cause of Steinfeld syndrome.

Should we offer prenatal testing for 17q12 microdeletion syndrome to all cases with prenatally diagnosed echogenic kidneys? Prenatal findings in two families with 17q12 microdeletion syndrome and review of the literature.

OBJECTIVE: The objective of this study is to report the prenatal ultrasound scan findings in four fetuses from two families postnatally diagnosed with 17q12 microdeletion syndrome on microarray CGH and review the literature. METHODS: We report two families presenting with prenatally detected hyperechogenic kidneys. In family 1, the mother had three pregnancies complicated by anhydramnios with bilateral hyperechogenic kidneys, hyperechogenic enlarged cystic kidneys, and bilateral hyperechogenic kidneys with polyhydramnios respectively. In family 2, prenatal ultrasound scans detected hyperechogenic kidneys. A pubmed search for all reported cases of 17q12 deletion between 2005 and 2015 was performed. All publications were reviewed, and findings summarised. RESULTS: Fourteen publications were deemed suitable for literature review; there was a diagnosis of 17q12 deletion with documented prenatal findings in 25 cases. Prenatal renal anomalies were reported in 88% of these cases. Anomalies were documented from 15 weeks, and most common presentation was hyperechogenic, muticystic, or enlarged kidneys. Both oligohydramnios and polyhydramnios were seen. Postnatal renal ultrasound scan findings were of muticystic or multicystic dysplastic kidney. There did not appear to be correlation of prenatal presentation and severity of renal disease. CONCLUSION: Prenatal testing should be offered to all cases of hyperechogenic kidneys, with unknown cause.