biotindase deficiency in Kuwait newborn screening

1. Introduction:
Biotinidase deficiency (BTD) (OMIM #253260) is a rare
autosomal recessive disorder of biotin metabolism. The
biotinidase gene (BTD: OMIM 609019) is located on the Q-arm
of chromosome 3. The encoded enzyme, biotinidase, is required
to separate the essential vitamin biotin from either the ingested
protein-bound form or biotin-dependent enzymes in the body.
Biotin (vitamin H or B8) is important for fatty-acid synthesis,
amino-acid catabolism and gluconeogenesis. Its function is to
act as a co-factor for the carboxylase enzymes involved in these
three processes.
Clinical presentation of Biotinidase deficiency
Can cause insufficient biotin to be made available for the
maintenance of these processes; this can lead to acidosis or
lactic acidosis, abnormal catabolism and/or hypoglycemia.
These metabolic abnormalities can in turn lead to neurological
symptoms such as seizures, hearing loss, developmental delay
and/or cutaneous symptoms such as rash and alopecia. Different
mutations in BTD may result in varying levels of biotinidase
activity. Patients with the lowest enzyme activities usually
present with the severest symptoms. Once cerebral damage,
developmental delay and/or hearing loss have occurred in
patients with biotinidase deficiency; they are usually
irreversible. Only patients with a profound biotinidase
deficiency appear to be at risk of developing severe and
irreversible symptoms, and should therefore be the main target
of screening. Although screening has also been advocated for
partial deficiency, few individuals with a partial deficiency have
been known to develop symptoms. Not only were the symptoms
in these cases, such as skin-lesions and hair loss, generally mild
and easily treated.
Management of Biotinidase deficiency:
To prevent these symptoms, timely initiation of treatment with
oral free biotin is essential, which explains why various
countries have included biotinidase deficiency in their neonatal
screening programs. Also preimplantation genetic diagnosis
(PGT) is a good option to prevent the condition.
Laboratory method
Using DELFIA® (dissociation-enhanced lanthanide
fluorescence immunoassay) is a time-resolved fluorescence
(TRF) intensity technology. Our cut-off calculates as (15-60 U)
for partial and (<15 U) for profound.
Implications for screening cutoff level 60 U for partial and 15 U
for profound. biotinidase, produces a large number of false
positives and partially deficient cases. Our results indicate that,
at a cutoff level of (<15 U), all the profound cases would be
identified, our protocol including some partially deficient
patients who have consequently been labelled as ‘diseased’ and
treated with biotin.
View on results of Kuwait Newborn Screening program:
Biotinidase deficiency was included in the Kuwait newborn
screening program to prevent severe clinical presentations, since
then the number of cases detected has been high. This poster
describes the incidence of the disease and the type of mutations
found in the Kuwait medical genetic center, as 225,605 neonates
were screened between 2015 and 2018; and were identified for
further testing. Confirmatory testing done in Al-Sabah metabolic
lab revealed 10 (3%) with a profound biotinidase deficiency,
209 (64%) with a partial deficiency and 109 (33%) with normal
activity. All ten patients whose profound deficiency was
confirmed had enzyme activities very low in neonatal screening.
Mutation analysis was performed to all patients in 2017 and
2018 as the protocol was changed to include molecular study
ordered by metabolic specialist also in 2015 and 2016 many
cases was referred to molecular study sporadically, so we will
show in this poster the most common mutations found in
patients in 2017 and 2018 which were analyzed after official
induction of molecular study in biotindase deficiency algorithm
(figure2,3).
Result:
Total No of
Screened
newborns
(2015-2018)
No of
samples
showing
positive
screen
No of confirmed
cases
Detection
rate
225,605 328 Profound 10 1:22,560
Partial 209 1:1,079
The frequency and types of mutation:
DNA was extracted from peripheral blood cells according to
phenol extraction procedures. PCR and Sanger sequence
analysis were used to screen all coding BTD gene exons and
exon/intron boundaries, the most common mutation detected
was c.[1330G>C] (p.(Asp444His); 80%), which is considered
to be mild form of BTD, the following (figure.3) all discovered
mutation in the molecular lab (2017 and 2018).
Conclusion:
In Kuwait 1 in 1,030 neonates had partial or profound
biotinidase deficiency during our study period (2015-2018).
Only 3% of those referred had a profound deficiency. The
inclusion of biotinidase deficiency in the Kuwait Newborn
screening program led to the detection of a large number of false
positives and a large number of partially deficient cases.
The Program must be aiming to detect all neonates with a
profound deficiency who are at risk of developing severe
symptoms.
Newborn screening for biotinidase deficiency in the Kuwait: consequences and considerations
Amir.A.Ahmed , Mohmed Al-Ali , Iqbal Sarkhouh, May.R.AlRushood, Laila A.Bastaki
 Wolf B: Biotinidase deficiency. In Pagon RA, Adam MP, Ardinger HH et al: (eds), GeneReviews [Internet]. Seattle, WA, USA: University of Washington, (updated 5 December 2013).
 Li H, Spencer L, Nahhas F et al: Novel mutations causing biotinidase deficiency identified by newborn screening in Michigan the biotinidase gene. Mol Genet Metab 2014; 112: 242–246.
 Wolf B: Biotinidase deficiency: "if you have to have an inherited metabolic disease, this is the one to have". Genet Med 2012; 14: 565–575.
 Procter M, Wolf B, Crockett DK, Mao R: The Biotinidase Gene Variants Registry: a Paradigm Public Database. G3 2013; 3: 727–731.
 Jay AM, Conway ,etal, : Outcomes of individuals with profound and partial biotinidase deficiency ascertained by newborn screening in Michigan ,Genet Med 2015; 17: 205–209.
 Wolf B: Why screen newborns for profound and partial biotinidase deficiency? Mol Genet Metab 2015; 114: 382–387.
 Swango KL, Demirkol M, Huner G et al: Partial biotinidase deficiency is usually due to the D444H mutation in the biotinidase gene. Hum Genet 1998; 102: 571–575. amiral6666@gmail.com