14 and left 0.14), full visual fields and pink optic nerves. Growth is poor at 8.5 years even though partially improved post-BMT (height from 0.3 cm below the 0.4th centile before BMT to 0.1 cm below the 0.4th centile). Hematological parameters are now within normal range. Patient 2 was born from consanguineous Pakistani parents (first cousins). She presented with the complaint of progressive pallor for one month at 12 years of age. On examination she showed severe anemia (Hb 6.3 g/dl) and splenomegaly, raising the suspicion of hemolytic anemia; however, work up turned out to be negative.

The presence of growth retardation (height < 2nd centile, weight 9th centile) and complete skeletal survey led to the diagnosis of osteopetrosis (see Fig. 1a upper panel, for the most recent radiological cranial evaluation). DNA Damage inhibitor She was initially treated with steroids and calcitriol and then received blood transfusion from the age of 15; at present (17 years old) she is on calcitriol only. She presents proptosis, malar prominence and short stature. Patient 3 was born from consanguineous Bangladeshi parents. He was diagnosed with mild osteopetrosis at 9 months due to a generalized increase in bone density on X-ray and visual impairment requiring optic nerve decompression (at 9 years of age), while the hematological compartment was normal. He has had also recurrent mal-uniting fractures

of the femur. At present he is alive and clinically stable at 19 years of age. Patient 4 was born from Black Caribbean unrelated parents. She was accidentally diagnosed at GSK-3 inhibition 3 years of age, during a routine X-ray performed after swallowing a screw. She also displayed moderate anemia (Hb 10.4 g/dl) and mild visual impairment with a slight nystagmus, while on a CT scan

foramen magnum narrowing and a syrinx were present. At the age of 7 she underwent a foramen magnum decompression for cerebellar tonsil ectopia and developed hydrocephalus in the postoperative period requiring placement of ventriculo-peritoneal shunt. She is alive at 10 years of age with stable hematological conditions, an important syrinx in the spinal cord, and obstructive sleep apnea requiring nocturnal continuous positive airway pressure. The available X-rays also Calpain show scaphocephaly (Fig. 1a central panel), which is rarely seen in osteopetrosis while it has been reported in Pycnodysostosis; distal phalangeal tufts are small, but no overt signs of acroosteolysis are apparent (Fig. 1b left panel). Patient 5 was born from Pakistani, reportedly unrelated parents. Since the age of 3, he was followed due to growth retardation (height < 3rd centile at 5 years of age) and anemia (Hb 8.8 g/dl). Recently, skeletal survey showed the presence of osteopetrotic radiological signs including generalized increase in bone density (Fig. 1b right panel), cranial sclerosis particularly at the skull base (Fig.