D-Bifunctional Protein Deficiency Diagnosis-A Challenge in Low Resource Settings: Case Report and Review of the Literature

Abstract

D-bifunctional protein deficiency (D-BPD) is a rare, autosomal recessive peroxisomal disorder that affects the breakdown of long-chain fatty acids. Patients with D-BPD typically present during the neonatal period with hypotonia, seizures, and facial dysmorphism, followed by severe developmental delay and early mortality. While some patients have survived past two years of age, the detectable enzyme activity in these rare cases was likely a contributing factor. We report a D-BPD case and comment on challenges faced in diagnosis based on a narrative literature review. An overview of Romania's first patient diagnosed with D-BPD is provided, including clinical presentation, imaging, biochemical, molecular data, and clinical course. Establishing a diagnosis can be challenging, as the clinical picture is often incomplete or similar to many other conditions. Our patient was diagnosed with type I D-BPD based on whole-exome sequencing (WES) results revealing a pathogenic frameshift variant of the HSD17B4 gene, c788del, p(Pro263GInfs*2), previously identified in another D-BPD patient. WES also identified a variant of the SUOX gene with unclear significance. We advocate for using molecular diagnosis in critically ill newborns and infants to improve care, reduce healthcare costs, and allow for familial counseling.

Keywords: D-bifunctional protein deficiency; neonatal hypotonia; neonatal seizures; peroxisomal disorders; whole-exome sequencing.

Figure 1

Magnetic resonance imaging: 1. enlarged ventricles; 2. bilateral temporal subarachnoid cyst, mega cisterna magna; 3. delayed partial myelination of the posterior limb of the internal capsule; 4. bilateral perisylvian polymicrogyria; 5. cerebellar atrophy (central lobule, culmen), dysgenesis of the corpus callosum.

Figure 2

Clinical course, investigations, and follow-up of the proband. Legend: m—months; d.—days; R—outpatient re-evaluation; DOL—day of life; HUS—head ultrasonography; US—ultrasonography; MLPA—multiplex ligation-dependent probe amplification; SMA—spinal muscular atrophy; MRI—magnetic resonance imaging; WES—whole exome sequencing; CT—computer tomography.

Figure 3

D-bifunctional protein peroxisomal enzymatic activity. Very-long-chain fatty acids (VLCFAs), pristanic acid (PRIS), dihydroxycholestanoic acid (DHCA), and trihydroxycholestanoic (THCA) are activated by free unesterified coenzyme A (CoA); acyl-CoA oxidase 1 (palmitoyl-CoA-oxidase) (ACOX1), and acyl-CoA oxidase 2 (branched-chain acyl-CoA oxidase) (ACOX2) are involved in the first step of peroxisomal β-oxidation, while D-bifunctional protein (D-BP) is involved in the next two steps—hydratation and dehydrogenation; straight-chain 3 oxoacyl-CoA thiolase (Th1) and sterol carrier protein-2/3-oxoacylCoA thiolase (sterol carrier protein X) (Th2) are involved in thiolysis [36,37].

Figure 4

D-bifunctional protein domains, HSD17B4 gene schematic structure, and classification of D-BP deficiency; red—location of the described patient defect. Legend: SCP-2 like—steroid carrier protein-2 like.

Figure 5

Diagnostic approach pathways in D-bifunctional protein deficit (D-BPD) during neonatal period. Legend: 1—hypotonia is present at birth in 98% of cases; 2—seizures occur at birth in 93% of cases and are refractory to anticonvulsants; 3—suggestive facial dysmorphism includes high forehead, hypertelorism, epicanthus, upslanted palpebral fissure, long philtrum, depressed nasal bridge, high arched palate, large fontanelle, retrognatism, macrocephaly, and low-set ears (most aspects are similar to Zellweger syndrome); 4—in severe forms of D-BPD, infants do not acquire any developmental skills; in mild forms, with some residual protein activity, infants may reach very early developmental milestones but gradual developmental regression is noted within a few months, and hyperreflexia and hypertonia develop with D-BPD progression; 5—routine biochemical tests, blood gases analysis, neonatal imaging (X-rays, ultrasound brain, heart, and abdomen), amplitude and conventional integrate electroencephalography, auditory and visual tests, DNA analysis that may exclude perinatal hypoxic–ischemic encephalopathy, neonatal sepsis and meningitis, chronic infections (TORCH syndrome), congenital brain abnormalities, and congenital neurological or muscular diseases; 6—D-BPD cases were reported in association with abnormal prenatal development (fetal ascites, polyhydramnios), other metabolic or homeostasis abnormalities (such as increased transaminases), digestive tract abnormalities (bile duct proliferation, cholestasis, hepatomegaly, hepatic steatosis, feeding difficulties), endocrine problems (primary adrenal insufficiency), renal cysts, splenomegaly, ocular abnormalities (nistagmus, strabismus, visual loss), osseous and muscular abnormalities (frontal bossing, dolichocephaly, clubfoot, hammertoe, split hand, clacific stippling, delayed skeletal maturation, osteopenia, decrease muscle mass), hearing impairments, central nervous system abnormalities (cerebral dysmyelination or hypoplasia, gliosis, cortical dysplasia, cerebellar atrophy, callosal hypoplasia or atrophy, ventriculomegaly), and failure to thrive; 7—consanguineous parents or siblings with neurodevelopmental delay (alive or dead) are suggestive of rare hereditary conditions; *—biochemical markers may be normal during neonatal period; 8—VLCFA—very-long-chain fatty acid levels are increased; 9—phytanic acid and pristanic acid (the final product of phytanic acid α-oxidation) are increased secondary to impaired peroxisomal β-oxidation due to D-BPD; 10—dihydroxycholestanoic acid (DHCA); 11—trihydroxycholestanoic acid (THCA); DHCA and THCA plasmatic levels are increased due to D-BPD; 12—normal plasmalogen levels in red blood cells excludes generalized peroxisomal disorders; 13—genetic testing may help exclude epileptic syndromes with neonatal/infantile onset; 14—cultures’ skin fibroblasts help in diagnosis in infants with normal biochemical markers during neonatal period and differential diagnosis from Zellweger syndrome, and allow for quantification of the enzyme activity, which is of further help in predicting D-BPD course; 15—magnetic resonance imaging may show congenital brain defects (see above; Legend 6), abnormal/delayed myelination, white substance demyelination, neuronal migration disorders, focal heterotopia, and germinolytic cysts; MRI may show normal aspects during the neonatal period, followed, in time, by a suggestive model of cerebral and cerebellar leukoencephalopathy; 16—WES—whole-exome sequencing; 17—WGS—whole-genome sequencing; 18—HSD17B4 gene—17β-hydroxystroid dehydrogenase type 4 sequencing identifies the defect and its location and helps in predicting the patient’s outcome [2,3,4,5,6,7,8,9,10,12,15,16,18,19,20,28,34].