Marble brain disease: a rare cause of renal tubular acidosis
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NEPHROLOGY PICTURE
Marble brain disease: a rare cause of renal tubular acidosis Aghilès Hamroun1,2 · Mehdi Maanaoui1,3 · Rémi Lenain1 · Arnaud Lionet1 Received: 26 August 2020 / Accepted: 3 September 2020 © Italian Society of Nephrology 2020
Keywords Renal tubular acidosis · Osteopetrosis · Marble brain disease · Calcifications A 28-year-old man from North Africa was referred to our nephrology department for chronic metabolic acidosis. This patient, out of follow-up for several years, had been affected since childhood by metabolic acidosis of unknown etiology, associated with short stature, multiple fractures of the extremities, facial dysmorphism, impaired hearing and mental retardation. Biochemical evaluations revealed hyperchloremic acidosis (pH 7.25 [7.38–7.42], serum bicarbonate and chloride levels of 15 mEq/L [22–28] and 115 mEq/L [98–106], respectively), high urinary anion gap and inappropriately high urine pH (7.5 [4.5–6.5]), all consistent with renal tubular acidosis. Skull X-ray showed diffuse bone thickening (A), corpus callosum calcifications (B), mandibular prognathism and multiple dental abnormalities (C), while brain CT scan also revealed multiple intracerebral calcifications of the basal ganglia (arrows indicating respectively the caudate, lentiform and dentate nuclei) (Fig. 1). Genetic analysis confirmed the presence of a homozygous mutation in the CA2 gene (chromosome 8 q22 G > A c231 + 1, intron 2) responsible for constitutional type II carbonic anhydrase deficiency. The patient had had this condition since childhood but did not comply with treatment and was lost to follow-up for several years. This rare autosomal recessive The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.
mutation is responsible for a syndrome associating renal tubular acidosis, osteopetrosis and diffuse calcifications of the basal ganglia, otherwise called ‘marble brain disease’ or ‘Guibaud-Vainsel syndrome’ [1]. Osteopetrosis is a clinical condition characterized by failure of osteoclasts to resorb bone, leading to impaired remodeling and enhanced risk of fractures. Intracranial calcifications of the basal ganglia (also called Fahr Syndrome) are related to an alteration of cerebrospinal fluid acidification in the choroid plexus. Renal tubular acidosis is often mixed, including both proximal and distal components. However, the distal component is in most cases prominently impaired, as illustrated by the inappropriately high urine pH presented by our patient. To date, less than a hundred cases have been described in the literature, mostly involving families from North Africa and the Middle East [2]. However, recent cases have also been documented worldwide. In the most severe form of the disease (called ‘malignant’) with hematological involvement, early bone marrow transplantation may be proposed. Given the absence of any other specific treatment, our patient is currently receiving potassium citrate supplementation and is being close
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