X-linked adrenoleukodystrophy: phenotype-genotype correlation in hemizygous males and heterozygous females with ABCD1 mutations.

OBJECTIVES: X-linked adrenoleukodystrophy (X-ALD) causes cerebral adrenoleukodystrophy (cALD), myelopathy and/or adrenal insufficiency in males, and myelopathy/peripheral neuropathy in females. These distinct phenotypes are scarcely linked to a specific mutations. The objective herein was to find a link between the phenotype with the genotype mutation, serum very long-chain fatty acids (VLCFA), and the diet with Lorenzo´s and GTO oils in hemizygous males and heterozygous females. METHODS: A retrospective study design with follow-up of 45 hemizygous males and 50 heterozygous females carrying mutations in ABCD1 from 35 unrelated families with X-ALD. Mutation analysis was performed by Sanger sequencing of PCR and/or RT-PCR and the severity of missense mutations was evaluated using GERP++ score and CADD score. RESULTS: Twenty-five described and eight novel ABCD1 mutations were identified. Fifteen males and 23 females had severe mutations while 30 males and 27 females had less detrimental ones. cALD developed in 25 males (56%) including nine boys with severe mutations, 10 boys with less detrimental mutations and 6 adults with adrenomyelopathy. Myelopathy and/or adrenal insufficiency developed in 14 males (31%), six were asymptomatic. Adrenal insufficiency developed in two of five boys treated with hematopoietic stem cell transplantation (HSCT). Myelopathy/peripheral neuropathy developed in 26% of females. No correlation was found between the disease severity and the genotype, GERP++ and CADD scores, presence/absence of aberrant ALDP protein or X-inactivation. VLCFA were higher in males than heterozygous females and decreased during Lorenzo´s and GTO oils diet without a clear clinical impact on the disease. CONCLUSION: The prognosis was unfavourable in most males and significant part of females. Therapy with early HSCT is effective. Thus, the need for early diagnosis with the neonatal screening is crucial.

Novel allelic variants and evidence for a prevalent mutation in URAT1 causing renal hypouricemia: biochemical, genetics and functional analysis.

Renal hypouricemia (RHUC) is a heterogeneous inherited disorder characterized by impaired tubular uric acid (UA) transport with severe complications, such as acute kidney injury (AKI). Type 1 is caused by a loss-of-function mutation in the SLC22A12 gene (URAT1), type 2 in the SLC2A9 gene (GLUT9). This article describes three Czech families with RHUC type 1. The serum UA in the probands was 0.9, 1.1 and 0.5 mg/dl and expressed as an increase in the fractional excretion of UA (48, 43 and 39%). The sequencing analysis of SLC22A12 revealed three novel variants: p.G366R, p.T467M and a deletion p.L415_G417del. A detailed metabolic investigation in proband C for progressive visual failure supported suspicion of neuronal ceroid lipofuscinosis type 7 conditioned by the mutation in the MFSD8 gene. Functional studies showed significantly decreased urate uptake and a mis-localized URAT1 signal in p.G366R, p.L415_G417del and p.T467M. Furthermore, colocalization studies showed accumulation of URAT1 protein in the endoplasmic reticulum. The findings suggest that loss-of-function mutations cause RHUC via loss of UA absorption partly by protein misfolding. However, they do not necessarily lead to AKI and a possible genotype-phenotype correlation was not proposed. Furthermore, results confirm an uneven geographical and ethnic distribution of SLC22A12 variants; the p.L415_G417del mutation predominates in the Roma ethnic group in the Czech Republic.

Mutations in DNAJC5, encoding cysteine-string protein alpha, cause autosomal-dominant adult-onset neuronal ceroid lipofuscinosis.

Autosomal-dominant adult-onset neuronal ceroid lipofuscinosis (ANCL) is characterized by accumulation of autofluorescent storage material in neural tissues and neurodegeneration and has an age of onset in the third decade of life or later. The genetic and molecular basis of the disease has remained unknown for many years. We carried out linkage mapping, gene-expression analysis, exome sequencing, and candidate-gene sequencing in affected individuals from 20 families and/or individuals with simplex cases; we identified in five individuals one of two disease-causing mutations, c.346_348delCTC and c.344T>G, in DNAJC5 encoding cysteine-string protein alpha (CSPα). These mutations-causing a deletion, p.Leu116del, and an amino acid exchange, p.Leu115Arg, respectively-are located within the cysteine-string domain of the protein and affect both palmitoylation-dependent sorting and the amount of CSPα in neuronal cells. The resulting depletion of functional CSPα might cause in parallel the presynaptic dysfunction and the progressive neurodegeneration observed in affected individuals and lysosomal accumulation of misfolded and proteolysis-resistant proteins in the form of characteristic ceroid deposits in neurons. Our work represents an important step in the genetic dissection of a genetically heterogeneous group of ANCLs. It also confirms a neuroprotective role for CSPα in humans and demonstrates the need for detailed investigation of CSPα in the neuronal ceroid lipofuscinoses and other neurodegenerative diseases presenting with neuronal protein aggregation.