Griscelli syndrome type 2: a novel mutation in RAB27A gene with different clinical features in 2 siblings: a diagnostic conundrum
A 5-year-old boy, born out of nonconsanguineous marriage, second in birth order, presented with high grade intermittent fever and a rash over the lower limbs, for 3 months. His elder brother had expired 6 months back at 7 years of age due to an undiagnosed medical condition. On examination, the patient, of average built and nutrition, was febrile, with a heart rate of 142/min, respiratory rate of 22/min, blood pressure of 102/64 mmHg, severe pallor, hepatosplenomegaly (liver 2 cm below right costal margin and spleen 3.5 cm below left costal margin) and a soft ejection systolic murmur. He had a generalized hypopigmented skin with golden-brown hair (). Both lower limbs showed multiple, well-defined, tender, erythematous to hyperpigmented, nodular lesions, extending from midthighs to feet, some having scab formation (). The parents revealed that their deceased elder son had similar hypopigmented skin, though no other family member was affected.\nInvestigations at admission showed hemoglobin, 4.1 g/dL; total leucocyte count, 2,500/mm3; lymphocyte, 73.7%; neutrophils, 18.6%; platelet, 33,000/mm3; erythrocyte sedimentation rate, 11 mm (1st hour); C-reactive protein, 21 mg/L. The peripheral blood smear showed normocytic, normochromic red blood cells with mild anisocytosis, with a corrected reticulocyte count of 3.2%. The bone marrow aspiration smears showed erythroid hyperplasia, predominantly normoblastic, with normal maturation of myeloid series, no megakaryocytes and no abnormal cells or parasite. Neither the peripheral blood smear nor the bone marrow aspiration smears showed large granules in neutrophils, ruling out the possibility of Chediak Higashi syndrome. The results of kidney and liver function tests, serum electrolytes, uric acid, chest skiagram and Mantoux test were within normal limits. The blood and urine cultures were sterile. Investigations to rule out common infections like Widal test, rapid malaria antigen test, rK 39 antigen, Dengue serology, and Weil Felix test did not reveal any abnormalities. Also, hepatitis B surface antigen and human immunodeficiency virus serology were negative and his immunoglobin levels were within normal range. Serum ferritin was 1,334 ng/mL. The antinuclear antibody (ANA) showed speckled positivity (1+), anti-dsDNA was borderline positive at 50 IU/mL, RA factor being negative. Ultrasound of the abdomen was normal except for enlarged spleen (13.5 cm) and enlarged liver (15 cm). Skin biopsy taken from the lower limb lesions was suggestive of erythema nodosum (EN) ().\nThe patient was treated with antipyretics, blood product transfusions and intravenous ceftriaxone. However, the patient's condition deteriorated with worsening pancytopenia, increasing size of liver and spleen and aggravation of the rash. Considering the weakly positive ANA and presence of EN, a possibility of a connective tissue disorder was considered and an empirical trial of oral prednisolone at 2 mg/kg/day was started.\nWhile investigations for this patient were in progress, efforts were made to trace the medical records regarding the illness of his elder sibling. This child had presented with fever with raised intracranial tension, rapidly progressive spastic quadriparesis, and papilledema. He had no organomegaly and his blood counts were normal. An initial computed tomography (CT) scan of the brain showed obstructive hydrocephalus. The cerebrospinal fluid (CSF) examination showed 25 cells, (100% lymphocytes) with protein 112 mg/dL and glucose 80 mg/dL. Based on the CT and CSF findings, he was started on antitubercular treatment with steroids. However he continued to worsen and a magnetic resonance imaging (MRI) of the brain was obtained which showed extensive signal abnormalities in the cerebellar white matter and cortex, with inhomogeneous signal abnormalities in the thalamus, basal nuclei, internal capsule, and cerebral white matter. There was evidence of obstructive hydrocephalus with impending tonsillar herniation. There was a dot-like contrast enhancement in the cerebellum. After an expert review of the MRI, a possibility of vascular-perivascular disorders like malignancies or hemophagocytic lymphohistiocytosis (HLH) was considered. Bone marrow examination was normal. The patient underwent a ventriculoperitoneal shunt surgery along with a brain biopsy from the right parietal region. However, a very small volume of material was available from the brain biopsy which showed nonspecific lymphocytic proliferation. The patient could not be investigated further, as he continued to deteriorate, and died two weeks later.\nAfter obtaining information about the elder sibling's illness, it was inferred that both the siblings were suffering from a common disorder of hypopigmentation with potentially fatal phases with two varied manifestations. A possibility of GS2 in accelerated phase was considered. Subsequently, a hair shaft examination of the younger sibling was done, which revealed large sized melanin granules, distributed irregularly along the length of the hair shaft mainly near the medulla. (). Under polarized light microscopy, the hair appeared monotonously white (). A genetic analysis was done to detect mutation in RAB27A gene. Genomic DNA was extracted from peripheral blood sample and sequencing of RAB27A gene was done. The sequence of the pairs of primers used to amplify these regions is shown in . Mutation analysis of RAB27A gene revealed a novel homozygous mutation in RAB27A gene on chromosome 15 (exon 3) showing a single-base substitution (c.136T>A p.F46I), leading to an amino acid change from phenylalanine (TTC) to isoleucine (ATC). This mutation is damaging by Polyphen. Parents were found to be heterozygous for the same mutation ().\nHence the patient was diagnosed as a case of GS2 with HLH; his elder sibling was retrospectively diagnosed to have GS2 with cerebral lymphohistiocytic infiltration. The patient achieved normalization of blood counts on oral prednisolone. The parents were counseled about the disease, and possible need for bone marrow transplantation.