Pathological alterations in haem synthesis

Table 3.8 Sideroblastic anaemias.

Hereditary X-linked Mitochondrial Autosomal

Acquired Primary Secondary

Mutations of erythroid-specific ALAS2 (Xp11.21), associated with spinocerebellar ataxia - ABC7 mutations (Xq13.3) DNA deletions (e.g. Pearson and Kearns-Sayre syndromes) Thiamine responsive, mutations in THTR-1 (DIDMOAD), other

Refractory anaemia with ring sideroblasts in FAB classification of myelodysplasia

Abnormal pyridoxine metabolism: pyridoxine antagonists (isoniazid, penicillamine), alcohol, pyridoxine deficiency

Mitochondrial toxicity: chloramphenicol, lead poisoning

Other diseases: e.g. rheumatoid arthritis, myxoedema, carcinomatosis

DIDMOAD, diabetes insipidus, diabetes mellitus, optic atrophy and deafness.

There is a marked increase in porphyrins in liver, plasma, urine and faeces. In the urine, uroporphyrin and heptacarboxyl porphyrin predominate with lesser amounts of coproporphyrin and penta- and hexacarboxylporphyrin. The disease is characterized by photosensitivity and dermatitis. It is precipitated in middle or later life, more often in men than women, by factors such as liver disease, alcohol excess or oestrogen therapy. A modest increase in liver iron is a common feature.

Either the homozygous or heterozygous presence of the HFE C282Y and H63D mutations may predispose to the development of PCT. Prevalence of the C282Y mutation is increased in both sporadic (type I) and familial (type II) PCT. In the UK, only homozygosity for C282Y (found in about 25% of patients) is significantly more common than in the general population (0.7%). In southern Europe, where C282Y is much less common, the H63D mutation is associated with PCT. Iron is known to inhibit uroporphyrinogen decarboxylase. Removal of the iron by repeated phlebotomy is standard treatment, usually leading to remission.

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