Biallelic hypomorphic variants in CAD cause uridine-responsive macrocytic anaemia with elevated haemoglobin-A2.

Biallelic pathogenic variants in CAD, that encode the multienzymatic protein required for de-novo pyrimidine biosynthesis, cause early infantile epileptic encephalopathy-50. This rare disease, characterized by developmental delay, intractable seizures and anaemia, is amenable to treatment with uridine. We present a patient with macrocytic anaemia, elevated haemoglobin-A2 levels, anisocytosis, poikilocytosis and target cells in the blood smear, and mild developmental delay. A next-generation sequencing panel revealed biallelic variants in CAD. Functional studies did not support complete abrogation of protein function; however, the patient responded to uridine supplement. We conclude that biallelic hypomorphic CAD variants may cause a primarily haematological phenotype.

Genetic backgrounds and clinical characteristics of congenital neutropenias in Israel.

BACKGROUND: Congenital neutropenias are characterized by severe infections and a high risk of myeloid transformation; the causative genes vary across ethnicities. The Israeli population is characterized by an ethnically diverse population with a high rate of consanguinity. OBJECTIVE: To evaluate the clinical and genetic spectrum of congenital neutropenias in Israel. METHODS: We included individuals with congenital neutropenias listed in the Israeli Inherited Bone Marrow Failure Registry. Sanger sequencing was performed for ELANE or G6PC3, and patients with wild-type ELANE/G6PC3 were referred for next-generation sequencing. RESULTS: Sixty-five patients with neutropenia were included. Of 51 patients with severe congenital neutropenia, 34 were genetically diagnosed, most commonly with variants in ELANE (15 patients). Nine patients had biallelic variants in G6PC3, all of consanguineous Muslim Arab origin. Other genes involved were SRP54, JAGN1, TAZ, and SLC37A4. Seven patients had cyclic neutropenia, all with pathogenic variants in ELANE, and seven had Shwachman-Diamond syndrome caused by biallelic SBDS variants. Eight patients (12%) developed myeloid transformation, including six patients with an unknown underlying genetic cause. Nineteen (29%) patients underwent hematopoietic stem cell transplantation, mostly due to insufficient response to treatment with granulocyte-colony stimulating factor or due to myeloid transformation. CONCLUSIONS: The genetic spectrum of congenital neutropenias in Israel is characterized by a high prevalence of G6PC3 variants and an absence of HAX1 mutations. Similar to other registries, for 26% of the patients, a molecular diagnosis was not achieved. However, myeloid transformation was common in this group, emphasizing the need for close follow-up.

[GENETIC PANELS FOR THE DIAGNOSIS OF RARE CONGENITAL HEMATOLOGICAL DISORDERS].

INTRODUCTION: Genetic diagnosis of congenital hematological disorders is complicated by the overlap of the clinical and laboratory presentation across different diseases and the large number of genes involved in each syndrome. Nonetheless, an accurate genetic diagnosis is essential for directing the follow-up and treatment program of the patients, as well as for identifying asymptomatic family members, choosing a non-affected related donor for hematopoietic stem cell transplantation and for offering a prenatal diagnosis. In recent years, a novel method of targeted next generation sequencing using gene panels was developed. In our laboratory, gene panels were incorporated for the diagnosis of congenital hematological disorders, including inherited bone marrow failure syndromes and rare anemias, and for the detection of somatic variant in the bone marrow. It is of utmost importance that an in-depth analysis will include a correlation of the genetic variants with the clinical and laboratory presentation and with the family history. Here, we demonstrate the importance of performing a timely genetic diagnosis in patients with congenital hematological disorders.

Syndromes predisposing to leukemia are a major cause of inherited cytopenias in children.

Prolonged cytopenias are a non-specific sign with a wide differential diagnosis. Among inherited disorders, cytopenias predisposing to leukemia require a timely and accurate diagnosis to ensure appropriate medical management, including adequate monitoring and stem cell transplantation prior to the development of leukemia. We aimed to define the types and prevalences of the genetic causes leading to persistent cytopenias in children. The study comprises children with persistent cytopenias, myelodysplastic syndrome, aplastic anemia, or suspected inherited bone marrow failure syndromes, who were referred for genetic evaluation from all pediatric hematology centers in Israel during 2016-2019. For variant detection, we used Sanger sequencing of commonly mutated genes and a custom-made targeted next-generation sequencing panel covering 226 genes known to be mutated in inherited cytopenias; the minority subsequently underwent whole exome sequencing. In total, 189 children with persistent cytopenias underwent a genetic evaluation. Pathogenic and likely pathogenic variants were identified in 59 patients (31.2%), including 47 with leukemia predisposing syndromes. Most of the latter (32, 68.1%) had inherited bone marrow failure syndromes, nine (19.1%) had inherited thrombocytopenia predisposing to leukemia, and three each (6.4%) had predisposition to myelodysplastic syndrome or congenital neutropenia. Twelve patients had cytopenias with no known leukemia predisposition, including nine children with inherited thrombocytopenia and three with congenital neutropenia. In summary, almost one third of 189 children referred with persistent cytopenias had an underlying inherited disorder; 79.7% of whom had a germline predisposition to leukemia. Precise diagnosis of children with cytopenias should direct follow-up and management programs and may positively impact disease outcome.

Congenital thrombocytopenia associated with a heterozygous variant in the MEIS1 gene encoding a transcription factor essential for megakaryopoiesis.

The transcription factor MEIS1 (myeloid ectotrophic insertion site 1) is crucial for the maintenance of hematopoietic stem cells and for megakaryopoiesis. Germline variants in MEIS1 are associated with restless-leg syndrome, but were not previously shown to cause cytopenias. This is the first report of a patient with congenital thrombocytopenia associated with a sequence variant in MEIS1, presenting with early onset severe thrombocytopenia and mild signs of bone marrow stress. Whole exome sequencing revealed a de novo monoallelic splice site variant in MEIS1, NM_002398.3:exon4:c.432 + 5 G > C, leading to a premature stop codon. We propose that heterozygous mutations in MEIS1 may cause congenital thrombocytopenia.

Inherited thrombocytopenia associated with mutation of UDP-galactose-4-epimerase (GALE).

Severe thrombocytopenia, characterized by dysplastic megakaryocytes and intracranial bleeding, was diagnosed in six individuals from a consanguineous kindred. Three of the individuals were successfully treated by bone marrow transplant. Whole-exome sequencing and homozygosity mapping of multiple family members, coupled with whole-genome sequencing to reveal shared non-coding variants, revealed one potentially functional variant segregating with thrombocytopenia under a recessive model: GALE p.R51W (c.C151T, NM_001127621). The mutation is extremely rare (allele frequency = 2.5 × 10-05), and the likelihood of the observed co-segregation occurring by chance is 1.2 × 10-06. GALE encodes UDP-galactose-4-epimerase, an enzyme of galactose metabolism and glycosylation responsible for two reversible reactions: interconversion of UDP-galactose with UDP-glucose and interconversion of UDP-N-acetylgalactosamine with UDP-N-acetylglucosamine. The mutation alters an amino acid residue that is conserved from yeast to humans. The variant protein has both significantly lower enzymatic activity for both interconversion reactions and highly significant thermal instability. Proper glycosylation is critical to normal hematopoiesis, in particular to megakaryocyte and platelet development, as reflected in the presence of thrombocytopenia in the context of congenital disorders of glycosylation. Mutations in GALE have not previously been associated with thrombocytopenia. Our results suggest that GALE p.R51W is inadequate for normal glycosylation and thereby may impair megakaryocyte and platelet development. If other mutations in GALE are shown to have similar consequences, this gene may be proven to play a critical role in hematopoiesis.

Incorporation of somatic panels for the detection of haematopoietic transformation in children and young adults with leukaemia predisposition syndromes and with acquired cytopenias.

Detection of somatic mutations may help verify the diagnosis of myelodysplastic syndrome (MDS) in patients with persistent cytopenias or with MDS-predisposition syndromes, prior to the development of overt leukemia. However, the spectrum and consequences of acquired changes in paediatric patients have not been fully evaluated, and especially not in the context of an underlying syndrome. We incorporated a targeted next-generation-sequencing panel of 54 genes for the detection of somatic mutations in paediatric and young adult patients with inherited or acquired cytopenias. Sixty-five patients were included in this study, of whom 17 (26%) had somatic mutations. We detected somatic mutations in 20% of individuals with inherited MDS-predisposition syndromes, including in patients with severe congenital neutropenia and Fanconi anaemia, and with germline mutations in SAMD9L. Thirty-eight per cent of children with acquired cytopenias and suspected MDS had somatic changes, most commonly in genes related to signal transduction and transcription. Molecularly abnormal clones often preceded cytogenetic changes. Thus, routine performance of somatic panels can establish the diagnosis of MDS and determine the optimal timing of haematopoietic stem cell transplantation, prior to the development of leukaemia. In addition, performing somatic panels in patients with inherited MDS-predisposition syndromes may reveal their unique spectrum of acquired mutations.

Pediatric myelodysplastic syndrome with inflammatory manifestations: Diagnosis, genetics, treatment, and outcome.

BACKGROUND: Inflammatory manifestations (IM) are well described in adult patients with myelodysplastic syndrome (MDS), but the presentation is highly variable and no standardized treatment exists. This phenomenon is rarely reported in children. As more pediatric patients are hematopoietic stem cell transplantation (HSCT) candidates, the role of anti-inflammatory treatment in relation to HSCT should be defined. PROCEDURE: Here, we report a series of five children from a tertiary center. We describe the clinical presentation, molecular findings, and treatment options. RESULTS: All patients presented with advanced MDS with blast percentages ranging 10-30%, all had severe IM. One patient had MDS secondary to severe congenital neutropenia, the other four patients had presumably primary MDS. All four were found to harbor a PTPN11 gene driver mutation, which is found in 35% of cases of juvenile myelomonocytic leukemia (JMML). The mutation was present in the myeloid lineage but not in T lymphocytes. Three had symptoms of Behcet's-like disease with trisomy 8 in their bone marrow. All patients were treated with anti-inflammatory medications (mainly systemic steroids) in an attempt to bring them to allogeneic HSCT in a better clinical condition. All demonstrated clinical improvement as well as regression in their MDS status post anti-inflammatory treatment. All have recovered from both MDS and their inflammatory symptoms post HSCT. CONCLUSION: Primary pediatric MDS with IM is driven in some cases by PTPN11 mutations, and might be on the clinical spectrum of JMML. Anti-inflammatory treatment may reverse MDS progression and improve the outcome of subsequent HSCT.

Characterization and genotype-phenotype correlation of patients with Fanconi anemia in a multi-ethnic population.

Fanconi anemia (FA), an inherited bone marrow failure (BMF) syndrome, caused by mutations in DNA repair genes, is characterized by congenital anomalies, aplastic anemia, high risk of malignancies and extreme sensitivity to alkylating agents. We aimed to study the clinical presentation, molecular diagnosis and genotype-phenotype correlation among patients with FA from the Israeli inherited BMF registry. Overall, 111 patients of Arab (57%) and Jewish (43%) descent were followed for a median of 15 years (range: 0.1-49); 63% were offspring of consanguineous parents. One-hundred patients (90%) had at least one congenital anomaly; over 80% of the patients developed bone marrow failure; 53% underwent hematopoietic stem-cell transplantation; 33% of the patients developed cancer; no significant association was found between hematopoietic stem-cell transplant and solid tumor development. Nearly 95% of the patients tested had confirmed mutations in the Fanconi genes FANCA (67%), FANCC (13%), FANCG (14%), FANCJ (3%) and FANCD1 (2%), including twenty novel mutations. Patients with FANCA mutations developed cancer at a significantly older age compared to patients with mutations in other Fanconi genes (mean 18.5 and 5.2 years, respectively, P=0.001); however, the overall survival did not depend on the causative gene. We hereby describe a large national cohort of patients with FA, the vast majority genetically diagnosed. Our results suggest an older age for cancer development in patients with FANCA mutations and no increased incidence of solid tumors following hematopoietic stem-cell transplant. Further studies are needed to guide individual treatment and follow-up programs.

Alpha-Thalassemia Carrier due to -α3.7 Deletion: Not So Silent.

BACKGROUND/OBJECTIVE: Alpha-thalassemia is one of the most prevalent genetic diseases, with the -α3.7 deletion being the most common mutation. Molecular studies have suggested mechanisms to explain the mild phenotype of "silent carrier" heterozygotes. However, the correlation between the clinical laboratory picture and the -α3.7 heterozygous state remains unclear, thus we chose to investigate. METHODS: We analyzed the medical files of 192 children evaluated for microcytosis at our tertiary center between 2007 and 2017 and diagnosed as heterozygotes for the -α3.7 deletion. Additional α-thalassemia mutations, iron deficiency anemia, and ß-thalassemia were ruled out. Laboratory parameters were compared to age- and sex-matched reference values. RESULTS: The -α3.7 carriers had significantly lower Hb and mean corpuscular volume (MCV) than the reference population, and significantly higher red blood cell counts across all age groups. The greatest reduction in Hb level appeared among male adolescents, while MCV was consistently 2 SDs lower than normal in most patients older than 2 years. CONCLUSION: Heterozygosity for the -α3.7 deletion was associated with clinically significant microcytosis and mild anemia in our pediatric population. In the absence of iron deficiency and ß-thalassemia, this finding provides a diagnosis for mild microcytic anemia, making additional investigations of microcytosis unnecessary.

Bone marrow failure unresponsive to bone marrow transplant is caused by mutations in thrombopoietin.

We report 5 individuals in 3 unrelated families with severe thrombocytopenia progressing to trilineage bone marrow failure (BMF). Four of the children received hematopoietic stem cell transplants and all showed poor graft function with persistent severe cytopenias even after repeated transplants with different donors. Exome and targeted sequencing identified mutations in the gene encoding thrombopoietin (THPO): THPO R99W, homozygous in affected children in 2 families, and THPO R157X, homozygous in the affected child in the third family. Both mutations result in a lack of THPO in the patients' serum. For the 2 surviving patients, improvement in trilineage hematopoiesis was achieved following treatment with a THPO receptor agonist. These studies demonstrate that biallelic loss-of-function mutations in THPO cause BMF, which is unresponsive to transplant due to a hematopoietic cell-extrinsic mechanism. These studies provide further support for the critical role of the MPL-THPO pathway in hematopoiesis and highlight the importance of accurate genetic diagnosis to inform treatment decisions for BMF.

Targeted next generation sequencing for the diagnosis of patients with rare congenital anemias.

BACKGROUND: Most patients with anemia are diagnosed through clinical phenotype and basic laboratory testing. Nonetheless, in cases of rare congenital anemias, some patients remain undiagnosed despite undergoing an exhaustive workup. Genetic testing is complicated by the large number of genes involved in rare anemias and the similarities in the clinical presentation of the different syndromes. OBJECTIVE: We aimed to enhance the diagnosis of patients with congenital anemias by using targeted next-generation sequencing. METHODS: Genetic diagnosis was performed by gene capture followed by next-generation sequencing of 76 genes known to cause anemia syndromes. RESULTS: Genetic diagnosis was achieved in 13 out of 21 patients (62%). Six patients were diagnosed with pyruvate kinase deficiency, 4 with dehydrated hereditary stomatocytosis, 2 with sideroblastic anemia, and 1 with CDA type IV. Eight novel mutations were found. In 7 patients, the genetic diagnosis differed from the pretest presumed diagnosis. The mean lag time from presentation to diagnosis was over 13 years. CONCLUSIONS: Targeted next-generation sequencing led to an accurate diagnosis in over 60% of patients with rare anemias. These patients do not need further diagnostic workup. Earlier incorporation of this method into the workup of patients with congenital anemia may improve patients' care and enable genetic counseling.

Morphological features of congenital dyserythropoietic anemia type I: The role of electron microscopy in diagnosis.

INTRODUCTION: Congenital dyserythropoietic anemias are rare blood disorders characterized by congenital anemia and a wide range of morphological and functional abnormalities of erythroid precursors. OBJECTIVES: To analyze the relative frequency of both light microscopic (LM) and electron microscopic (EM) morphological features of erythroblasts in a large group of patients with molecular proven congenital dyserythropoietic anemia type I (CDAI). METHODS: We retrospectively evaluated the LM and EM of bone marrow (BM) erythroblasts in 35 patients with CDAI. Thirty-four patients carried the CDAN1 Arg1042Trp founder mutation and one the p.Pro1130Leu mutation. BM slides of 24 patients were available for LM examination. EM studies were performed in all 35 patients. RESULTS: On LM, marked erythroid hyperplasia, binuclear erythroblasts, and various non-specific dyserythropoietic features were documented in every case; internuclear chromatin bridges were detected in 19 patients (79%). In all, EM of erythroblasts revealed a spongy appearance of heterochromatin, a widening of nuclear pores, and invagination of cytoplasm into the nuclear region. CONCLUSIONS: EM studies revealed high morphological frequency of specific ultrastructural changes in erythroblasts which facilitate prompt diagnosis of CDAI. Due to low specificity of BM LM findings, when BM EM is unavailable diagnostic approach should also include other inherited anemias.

Molecular diagnosis of α-thalassemia in a multiethnic population.

OBJECTIVE: α-Thalassemia, one of the most common genetic diseases, is caused by deletions or point mutations affecting one to four α-globin genes. Molecular diagnosis is important to prevent the most severe forms of the disease. However, the diagnosis of α-thalassemia is complex due to a high variability of the genetic defects involved, with over 250 described mutations. We summarize herein the findings of genetic analyses of DNA samples referred to our laboratory for the molecular diagnosis of α-thalassemia, along with a detailed clinical description. METHODS: We utilized a diagnostic algorithm including Gap-PCR, to detect known deletions, followed by sequencing of the α-globin gene, to identify known and novel point mutations, and multiplex ligation-dependent probe amplification (MLPA) for the diagnosis of rare or novel deletions. RESULTS: α-Thalassemia was diagnosed in 662 of 975 samples referred to our laboratory. Most commonly found were deletions (75.3%, including two novel deletions previously described by us); point mutations comprised 25.4% of the cases, including five novel mutations. Our population included mostly Jews (of Ashkenazi and Sephardic origin) and Muslim Arabs, who presented with a higher rate of point mutations and hemoglobin H disease. Overall, we detected 53 different genotype combinations causing a spectrum of clinical phenotypes, from asymptomatic to severe anemia. CONCLUSION: Our work constitutes the largest group of patients with α-thalassemia originating in the Mediterranean whose clinical characteristics and molecular basis have been determined. We suggest a diagnostic algorithm that leads to an accurate molecular diagnosis in multiethnic populations.

Diamond Blackfan Anemia: A Nonclassical Patient With Diagnosis Assisted by Genomic Analysis.

Diamond Blackfan anemia (DBA) is an inherited syndrome usually presenting with severe macrocytic anemia in infancy, paucity of erythroid precursors in the bone marrow, and congenital anomalies. We describe a child with mild, transfusion independent normocytic anemia whose diagnosis of DBA was established by identification of a novel de novo mutation disrupting normal splicing of the ribosomal protein RPL5. The diagnosis of DBA was confirmed by elevated erythrocyte adenosine deaminase levels and an abnormal ribosomal RNA profile. This case demonstrates the usefulness of genomic analysis in establishing the diagnosis of DBA in patients with a nonclassical presentation of the disease.

Genetic analysis and clinical picture of severe congenital neutropenia in Israel.

BACKGROUND: The relative frequency of mutated genes among patients with severe congenital neutropenia (SCN) may differ between various ethnic groups. To date, few population-based genetic studies have been reported. This study describes the genetic analysis of 32 Israeli patients with SCN. PROCEDURES: Clinical data were retrieved from the prospective Israeli Inherited Bone Marrow Failure Registry. Recruitment included living and deceased patients who were diagnosed between 1982 and 2012, for whom molecular diagnosis was performed. ELANE, HAX1 and G6PC3 genes were sequenced in all patients, and GFI-1 and WAS genes were sequenced if other genes were wildtype. RESULTS: Eleven patients (34%) had heterozygous mutations in ELANE (10 kindreds), eight (25%) had homozygous mutations in G6PC3 (5 kindreds) and 13 (41%) had no detected mutations. No patients had mutations in HAX1 or WAS. Four of the eight patients with G6PC3 mutations had congenital anomalies. The probability of survival for all patients was 50% at age of 18. Deaths were mainly due to sepsis (5 patients, 4/5 not responding to G-CSF, none with G6PC3 mutation). Two patients developed acute myelogenous leukemia (AML) and one myelodysplastic syndrome (MDS), none with G6PC3 mutation. CONCLUSIONS: We found a unique pattern of SCN mutations in Israel with homozygous G6PC3 mutations in eight (25%) patients, the highest frequency described so far. HAX1 mutations, reported mainly in Sweden and Iran, were absent. Patients with G6PC3 mutations had congenital anomalies, appeared to have a better response to G-CSF, and so far have not developed AML or MDS.

Characterization of two unique α-globin gene cluster deletions causing α-thalassemia in Israeli Arabs.

The molecular basis of α-thalassemia (α-thal) is complex. The use of multiplex ligation-dependent probe amplification (MLPA) has offered the possibility of identifying more gene deletions causing α-thal. Our objective was to determine the molecular basis of two patients with Hb H (ß4) disease. By using MLPA in combination with comparative genomic hybridization (CGH) we identified two novel α-globin gene cluster deletions: a 30 kb deletion (patient 1) we refer to as - -(JAL) and a large 216 kb deletion (patient 2) we refer to as - -(LOD). Patient 1 was a compound heterozygote for - -(JAL) and -α(3.7) (rightward deletion). Twelve family members of patient 1 carrying the - -(JAL) deletion were available for evaluation: five with - -(JAL)/-α(3.7), four with - -(JAL)/α(Hph I)α and three with - -(JAL)/αα. Their clinical picture of compound heterozygosity was compatible with moderate Hb H disease. In patient 2 (- -(LOD)/-α(3.7)), no additional symptoms were present despite the heterozygous deletion of seven known genes, three non coding RNAs (ncRNAs), four unknown genes and two pseudo genes. Further analysis of more patients with α-thal deletions will have implications for genetic counseling and appropriate therapy.

A novel epsilon gamma delta beta thalassemia presenting with pregnancy complications and severe neonatal anemia.

OBJECTIVE: The epsilon gamma delta beta (εγδß)-thalassemias are rare sporadic disorders caused by deletion of the ß-globin gene cluster. The main clinical feature is marked prenatal and neonatal anemia that resolves spontaneously within a few months. Reports originating mainly from Europe have so far identified 30 such deletions The aim of the present work was to describe a novel 1.78-Mb deletion, the longest ever reported, and to detail the clinical features in 12 members of an extended Bedouin family. METHODS: The deletion was identified by globin gene multiplex ligation-dependent probe amplification (MLPA) of the ß-globin cluster and further characterized by comparative genomic hybridization. Past and present clinical and laboratory data of ten symptomatic and two asymptomatic patients were collected. RESULTS: A 1.78-Mb εγδß-deletion, the largest ever described, was identified in all patients. Although other genes were included in the deletion, no other symptoms were observed. Of the ten symptomatic fetuses and neonates, three died of the disease. The remainder required packed cell transfusions during the first months of life. Pregnancy complications included intrauterine growth restriction and oligohydramnios, as well as additional neonatal complications including prematurity and persistent pulmonary hypertension of the neonate. CONCLUSIONS: We suggest that εγδß-thalassemia be added to the list of hemoglobinopathies that can cause neonatal anemia and that MLPA of the ß-globin cluster be used to confirm its diagnosis. Careful surveillance during pregnancy is important to reduce neonatal mortality and morbidity, especially given the dramatic improvement that occurs later.

MPL Baltimore mutation and thrombocytosis: case report and literature review.

Thrombocytosis is a common finding and is a frequent cause of referral for further investigation. The MPL Baltimore (Lys39Asn) mutation has been reported as a cause of thrombocytosis in 7% of African Americans. We describe an 11-month-old Ethiopian Jewish boy referred for evaluation of thrombocytosis who was found to be homozygous for MPL Baltimore. So far, there is no indication whether patients with thrombocytosis who have this mutation, particularly homozygotes, are at increased risk of thrombotic or hemorrhagic complications. Nevertheless, this entity should be considered in the differential diagnosis of every patient with thrombocytosis, particularly those of African origin.

From blood smear to lipid disorder: a case report.

Neutral lipid storage disease (Chanarin-Dorfman syndrome) is a rare autosomal recessive disorder of lipid metabolism, characterized by systemic accumulation of neutral lipids in multiple tissues. We report a case of a 14-year-old girl with generalized ichthyosis, liver cirrhosis, and a hearing impairment. A peripheral blood smear demonstrated marked cytoplasmatic vacuoles in most polymorphonuclear cells (Jordan's anomaly). Bone marrow examination revealed vacuoles in myeloid precursors. Genetic analysis showed that the patient was homozygous for the p.Arg312Ter mutation in the CGI-58 gene, a key enzyme in lipid metabolism. The peripheral blood smear is diagnostic, and should be performed in any patient with ichthyosis.